The precise role of 5′AMP-activated kinase (AMPK) in cancer and its potential as a therapeutic target is controversial. Although it is well established that activation of this energy sensor inhibits the main anabolic processes that sustain cancer cell proliferation and growth, AMPK activation can confer on cancer cells the plasticity to survive under metabolic stress such as hypoxia and glucose deprivation, which are commonly observed in fast growing tumors. Thus, AMPK is referred to as both a “conditional” tumor suppressor and “contextual” oncogene. To add a further layer of complexity, AMPK activation in human cancer tissues and its correlation with tumor aggressiveness and progression appears to vary in different contexts. The current review discusses the different faces of this metabolic regulator, the therapeutic implications of its modulation, and provides an overview of the most relevant data available on AMPK activation and AMPK-activating drugs in human studies. Mol Cancer Res; 13(7); 1059–72. ©2015 AACR.

5′ AMP-activated kinase (AMPK) is a central metabolic sensor that stands at the crossroad between metabolic and signaling networks. In 2003, the discovery of the tumor suppressor liver kinase B1 (LKB1) as the major upstream kinase of AMPK established a link between an energy regulator and cancer pathogenesis, suggesting that the tumor suppressor functions of LKB1 could be mediated by AMPK (1–3). Since then, in vitro and in vivo studies have been conducted to dissect the role of AMPK in cancer initiation and progression, using AMPK-modulating drugs. The functional consequences of AMPK activation in cancer appear to be much more complex than initially thought, and AMPK can behave as both cancer “friend” or “foe” in a context-specific manner.

Drug-induced supraphysiological activation of AMPK reduces tumor growth in vitro and in preclinical models through the suppression of key biosynthetic pathways (reviewed in refs. 4, 5). However, physiological activation of AMPK in response to a broad range of stresses (e.g., hypoxia, glucose deprivation, and matrix detachment) provides cancer cells with the flexibility to adapt and survive metabolic stress (metabolic adaptation; reviewed in ref. 6). IHC evaluation of AMPK status in human tissues has revealed that the levels of AMPK activation are heterogeneous in different tumor types, while discordant data have been reported on the correlation between AMPK activation and tumor prognosis.

Here, we discuss the “two faces” of AMPK, the therapeutic benefit of AMPK modulators and we review the current data available on AMPK activation and AMPK-activating drugs in human studies. Throughout the review, we associate AMPK with both the terms “tumor promoter” and “tumor suppressor.” However, we do not intend to define AMPK as a classic bona fide tumor suppressor gene such as LKB1, which is mutated or deleted in several cancers, rather to emphasize the fact that AMPK activation may result in tumor growth inhibition, cell-cycle arrest, and apoptosis of cancer cells in some tumor types/contexts. Interrogating the cBioPortal data, the frequency of mutation/deletion in the genes codifying for AMPK catalytic subunits α1 (PRKAA1) and α2 (PRKAA2) ranges from 0.2% to 3.4% and from 0.2% to 10.3%, respectively (7).

AMPK is a heterotrimeric Ser/Thr kinase complex characterized by a catalytic α subunit and two regulatory subunits (β, γ), which exist in different isoforms, making up to 12 different heterotrimers. The different subunits show tissue specificity and may contribute to tumor cell growth and proliferation independently (8–10). The γ subunit contains four-tandem sequence repeats known as CBS repeats, which functions as four adenine nucleotide-binding domains. Site 2 is always unoccupied, site 4 is permanently bound by AMP, whereas sites 1 and 3 can be competitively bound by either AMP, or ADP, or ATP (11, 12).

AMPK functions as an energy sensor to restore energy homeostasis at cell and organismal levels in conditions of metabolic stress that reduce ATP levels either by inhibiting its production (e.g., hypoxia, glucose deprivation, and treatment with biguanides drugs or xenobiotics) or by accelerating its consumption (e.g., muscle contraction), resulting in increased ADP and AMP levels. For a detailed description of AMPK regulation, we refer readers to other excellent reviews (13, 14). However, a brief description of the biochemical circuits regulating AMPK follows. The binding of ADP and/or AMP to the γ subunit both promotes phosphorylation by upstream kinases and inhibits dephosphorylation of the residue Thr172 within the activation loop of the catalytic domain, which is required for the full activity of the kinase. Furthermore, the binding of AMP (but not ADP) causes a further allosteric activation of the phosphorylated kinase. The two major upstream kinases responsible for AMPK activation are the tumor suppressor LKB1 and Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2). An activating role, still not well characterized, for the transforming growth factor β-activated kinase 1 (TAK1) has also been described. LKB1 activates AMPK during energy stress, whereas CaMKK2 activity is induced by increased intracellular Ca2+ levels, regardless of the energy status of the cells (reviewed in ref. 13). However, CaMKK2 can compensate for the absence of LKB1 in mediating AMPK phosphorylation (15). In addition to AMP, ADP, and Ca2+, recent studies have also identified reactive oxygen species (ROS) as additional upstream activators of AMPK, acting in an LKB1-independent manner (Fig. 1; ref. 16). Once activated, AMPK maintains energy balance by switching off anabolic pathways that consume ATP and NADPH, while switching on catabolic pathways that generate ATP both by direct phosphorylation of metabolic enzymes, and through longer-term effects mediated by phosphorylation of transcription factors and coactivators (14). Thus, AMPK can restrain cell growth by (i) inhibiting protein synthesis [through direct phosphorylation of mammalian target of rapamycin complex 1 (mTORC1) signaling members tuberous sclerosis complex 2 (TSC2) and Raptor], (ii) blocking fatty acid (FA) and cholesterol biosynthesis [through direct phosphorylation of the enzymes acetyl-CoA carboxylase 1 (ACC1) and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and inhibition of the lipogenic transcription factors sterol regulatory element-binding proteins (SREBP) and carbohydrate-responsive element-binding protein (ChREBP)], required for new membrane formation in proliferating cells, (iii) inducing cell-cycle arrest and apoptosis [through several mechanisms, including stabilization of p53, regulation of the cyclin-dependent kinase inhibitors p21Waf1 and p27Cip1, phosphorylation of the hippo signaling member angiomotin-like 1 (AMOTL1), an upstream inhibitor of Yes-associated protein (YAP); refs. 13, 17, 18], while promoting cell survival mechanisms during metabolic stress (19), as discussed below (Fig. 2).

Figure 1.

Mechanisms of AMPK activation. AMPK functions as a metabolic sensor that is activated by metabolic stress induced by hypoxia, nutrient deprivation, and drugs/compounds [e.g., biguanides, 2-deoxyglucose (2-DG)], AMP mimetic, direct AMPK activators, or ROS. For the full activity of the kinase, a phosphorylation at the residue Thr172 in the catalytic loop is required. The main upstream kinases are LKB1, CaMKK2, and TAK1. Uncharacterized protein phosphates (PPs) can reverse this phosphorylation.

Figure 1.

Mechanisms of AMPK activation. AMPK functions as a metabolic sensor that is activated by metabolic stress induced by hypoxia, nutrient deprivation, and drugs/compounds [e.g., biguanides, 2-deoxyglucose (2-DG)], AMP mimetic, direct AMPK activators, or ROS. For the full activity of the kinase, a phosphorylation at the residue Thr172 in the catalytic loop is required. The main upstream kinases are LKB1, CaMKK2, and TAK1. Uncharacterized protein phosphates (PPs) can reverse this phosphorylation.

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Figure 2.

AMPK-mediated metabolic and signaling reprogramming. Once activated, AMPK switches off anabolic pathways while turning on catabolic pathways to restore energy homeostasis. Thus, AMPK controls pathways involved in metabolism, cell growth, and survival. Red lines indicate direct activation, whereas inhibition is depicted in blue. A question mark indicates that it is not yet certain that the protein is directly phosphorylated. GLUT1/4, glucose transporter 1, 4; PFKFB2/3,6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatases 2 and 3; TBC1D1, TBC1 domain protein-1; SIRT1, sirtuin 1; PGC-1α, PPARγ-coactivator-1α.

Figure 2.

AMPK-mediated metabolic and signaling reprogramming. Once activated, AMPK switches off anabolic pathways while turning on catabolic pathways to restore energy homeostasis. Thus, AMPK controls pathways involved in metabolism, cell growth, and survival. Red lines indicate direct activation, whereas inhibition is depicted in blue. A question mark indicates that it is not yet certain that the protein is directly phosphorylated. GLUT1/4, glucose transporter 1, 4; PFKFB2/3,6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatases 2 and 3; TBC1D1, TBC1 domain protein-1; SIRT1, sirtuin 1; PGC-1α, PPARγ-coactivator-1α.

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AMPK as a tumor suppressor

Because the role of LKB1 as tumor suppressor was well established, AMPK was primarily considered as a component of the LKB1-mediated tumor suppressor cascade and much less was known regarding its own independent role in cancer. This was due to the fact that most of the data were generated utilizing the AMPK activators AICAR and metformin, which also display AMPK-independent mechanisms or by experimental evidence in models of LKB1 inactivation, which affect an additional 12 AMPK-related downstream kinases, beyond AMPK. The role of the AMPK-related kinases is still not very well characterized, although they might themselves contribute to the tumor suppressive functions of LKB1, as well as have independent functions (20). Experiments of genetic ablation of AMPK, the use of direct AMPK activators, and detailed phosphorylation studies in different cancer models have recently helped to address this issue. Faubert and colleagues have reported that the ubiquitous knockout (KO) of AMPKα1, the only catalytic subunit expressed in B cells, accelerates the development of lymphomas in transgenic mice overexpressing c-Myc, suggesting that AMPK loss can cooperate with oncogenic drivers to promote tumorigenesis in a tissue-specific manner. The underpinning mechanism for AMPK tumor suppressor activity is the ability of the kinase to exert an “anti-Warburg” effect by downregulating hypoxia-inducible factor 1-alpha (HIF1α) and its downstream glycolytic genes, which, conversely, are upregulated in AMPKα1 KO mice (21).

Aside from antagonizing the Warburg effect, AMPK has also been shown to exert its “metabolic” tumor-suppressor role by inhibiting unchecked mTORC1 activity and de novo lipogenesis, required both during G1–S and G2–M phases. We have recently observed increased de novo FA synthesis concomitant to reduced AMPK activation and phosphorylation of its major target ACC1 (the rate-limiting enzyme for FA synthesis), prior to cytokinesis initiation. In this view, by inhibiting de novo FA synthesis and FA incorporation into membranes, activation of AMPK would prevent cells from completing mitosis, arresting them at a “lipogenic” G2–M checkpoint. This was indeed observed under direct supraphysiological activation of AMPK (22). Cell-cycle arrest (via decreased fraction of cells in the S phase) and/or apoptosis was previously confirmed using ACC1 and fatty acid synthase (FASN) siRNA to directly inhibit FA synthesis (23, 24).

AMPK also plays a direct metabolic-independent role in cell-cycle regulation (25–27). A fine-tuned biphasic activation of AMPK has been shown to be required for proper mitotic progression (28). However, alteration of the dynamic spatial and temporal regulation of AMPK by either its sustained activation or depletion can result in microtubule misalignment, spindle misorientation, abnormal chromosome segregation followed by mitotic catastrophe and polyploidy (e.g., observed under metformin treatment) or mitotic delay (e.g., observed in AMPK-silenced cells; refs. 27, 29). Thus, cell-cycle arrest induced by persistent supraphysiological activation of AMPK could be ascribed to both the inhibition of de novo FA synthesis (metabolic role) as well as mitotic spindle assembly/chromosome segregation abnormalities (nonmetabolic role). Recently, a role for the subunit AMPK α1 in the direct regulation of cell cycle, independently of energy balance, has also emerged (30).

A third mechanism in favor of AMPK's behavior as a “tumor suppressor” has been described by Shen and colleagues, showing AMPK-dependent phosphorylation of the oncogene BRAF at Ser729. This phosphorylation prevents BRAF interaction with the scaffolding protein kinase suppressor of Ras 1 (KSR1), leading to the suppression of the oncogenic MEK–ERK signaling and consequent impairment of cell proliferation and cell-cycle progression (31).

Furthermore, additional mechanisms of action to suppress tumor growth have been proposed. Chou and colleagues showed that AMPK knockdown promotes epithelial-to-mesenchymal transition (EMT) in breast and prostate cancer cell lines by reducing the expression of forkhead box O3 (Foxo3a) and E-cadherin in conjunction with increased expression of vimentin, Y-box-binding protein-1 (YB-1), Snail, and the formation of F-actin stress fibers (32). These results suggested that AMPK activation counteracts EMT, the process through which epithelial cells are thought to acquire cancer stem cell–like properties and gain the ability to breach basement membranes and metastasize to distant sites. DeRan and colleagues showed that AMPK activation induces phosphorylation of the hippo signaling component AMOTL1, which results in the cytoplasmic sequestration and inhibition of YAP and its targeted genes, involved in proliferation and survival. This mechanism was abolished when AMPK expression was silenced, suggesting that loss of AMPK activity may contribute to tumorigenesis through AMOTL1 destabilization, leading to hyperactivation of YAP (18). Finally, AMPK may be inactivated by its ubiquitination and degradation by the cancer-specific MAGE-A3/6-TRIM28 ubiquitin ligase. MAGE-A3 and MAGE-A6 proteins, normally expressed only in the male germline, are frequently re-activated in human cancers, they are necessary for cancer cell viability, and sufficient to induce cell transformation. Screening for targets of the MAGE-A3/6–TRIM28 complex revealed that it ubiquitinates and degrades AMPKα1, leading to inhibition of autophagy, activation of mTORC1 signaling, and hypersensitization to AMPK agonists, such as metformin. These findings elucidated a germline mechanism commonly hijacked in cancer to suppress AMPK (33).

Further evidence also supports the tumor suppressor role of AMPK in some tumor types and genetic contexts. First, protein kinase B (Akt) has been reported to induce AMPK phosphorylation at Ser485, reducing its activation by LKB1 (34). This might occur in tumors in which Akt is hyperactivated due to phosphatase and tensin homolog (PTEN) loss-of-function mutations, or activating mutations in phosphoinositide-3-kinase (PI3K). Second, AMPK activation is suppressed in melanoma cells carrying the most common BRAF mutation V600E, which induces a constitutively active downstream ERK. The lack of AMPK activity is due to ERK and ribosomal S6 kinase (RSK)-mediated phosphorylation of LKB1, which prevents its binding/activation of AMPK. These data suggested that suppression of the LKB1/AMPK pathway might play an important role in BRAFV600E-driven tumorigenesis (35). Third, inhibition of AMPK has been observed in a PTEN-deficient model of thyroid cancer and in non–small cell lung cancer (NSCLC) cells expressing the mitochondrial heat-shock protein 90 chaperone TRAP-1 (36). Fourth, in fumarate hydratase-deficient kidney tumors and cell lines from patients with hereditary leiomyomatosis renal cell cancer (HLRCC), which are characterized by a metabolic shift to aerobic glycolysis, AMPK levels are decreased. AMPK reduction leads to diminished expression of the DMT1 iron transporter, cytosolic iron deficiency, and activation of the iron regulatory proteins IRP1 and IRP2, resulting in increased expression of HIF1α. Silencing of HIF1α or activation of AMPK diminishes invasive activities of the HLRCC cell line UOK262, indicating that overexpression of HIF1α and downregulation of AMPK contribute to the oncogenic growth of fumarate hydratase-deficient cells (37). Recently, a study from Rodriguez and colleagues showed that cytochrome P450-1A1, constitutively expressed in the majority of breast cancer tumors, promotes breast cancer proliferation and survival, at least in part, through suppression of AMPK signaling (38). Finally, reduced expression of the catalytic α2 subunit has been reported in some cases of hepatocellular carcinomas, and it is associated with enhanced tumor cell growth in mouse xenografts (10).

Taken together, these results suggest that in specific genetic, metabolic, and signaling contexts, AMPK can exert a tumor suppressor role (Fig. 3).

Figure 3.

Main mechanisms through which AMPK can exert its double-faced role in cancer. AMPK activation triggers cellular processes that can both suppress and promote tumor development/progression by activating different downstream pathways in a context-specific manner. NADPH, reduced form of nicotinamide adenine dinucleotide phosphate.

Figure 3.

Main mechanisms through which AMPK can exert its double-faced role in cancer. AMPK activation triggers cellular processes that can both suppress and promote tumor development/progression by activating different downstream pathways in a context-specific manner. NADPH, reduced form of nicotinamide adenine dinucleotide phosphate.

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AMPK as contextual tumor promoter

The ability to survive in conditions of metabolic stress, such as hypoxia/nutrient deprivation, or matrix detachment is fundamental to cancer cells. Several mechanisms by which the AMPK pathway supports this plasticity have been described. These include: (i) the induction of autophagy by AMPK-dependent phosphorylation of the unc-51-like kinases (ULK; ref. 39), (ii) the promotion of FA oxidation (FAO) to generate ATP (40, 41), (iii) transcriptional changes induced by phosphorylation of the core histone H2B (42), and (iv) the increase of intracellular NADPH levels through the activation of FAO/inhibition of FA synthesis to neutralize cytotoxic ROS (Fig. 3; 43). Intriguingly, while in nutrient-replete conditions, the AMPK energy-sensing pathway and the PI3K/Akt cascade converge on mTOR with opposing regulatory effects, under glucose depletion, both AMPK and Akt are activated and coordinately support cell survival (44). Thus, whereas the LKB1/AMPK pathway can act as a tumor suppressor through its ability to restrain tumor growth, it can also behave as “tumor promoter,” allowing tumor cells to be more resistant to metabolic stress, such as when tumor growth exceeds the capacity of its blood supply to deliver oxygen and nutrients (Fig. 4). Recent experimental evidence in vitro, using the direct AMPK activator A-769662, indeed supports this notion (45). AMPK activation can also promote tumor growth in specific tumor types and genetic contexts, even in nutrient-replete conditions.

Figure 4.

AMPK functions as “conditional” tumor suppressor and “contextual” tumor promoter. The outcome of AMPK activation in cancer is affected by the genetic context, metabolic dependency of cancer cells, and the surrounding microenvironment. Differences in the intensity/duration of AMPK activation (e.g., physiological activation vs. drug-induced supraphysiological activation) as well as in the expression/activation of specific subunits of the heterotrimer contribute to the antitumorigenic vs. protumorigenic role of AMPK in different cancer types.

Figure 4.

AMPK functions as “conditional” tumor suppressor and “contextual” tumor promoter. The outcome of AMPK activation in cancer is affected by the genetic context, metabolic dependency of cancer cells, and the surrounding microenvironment. Differences in the intensity/duration of AMPK activation (e.g., physiological activation vs. drug-induced supraphysiological activation) as well as in the expression/activation of specific subunits of the heterotrimer contribute to the antitumorigenic vs. protumorigenic role of AMPK in different cancer types.

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Recent evidence showed the key role of AMPK in supporting tumor growth in aggressive breast and astrocytic tumors (46–49). Moreover, in contrast to the results obtained by Faubert and colleagues in a lymphoma model (21), MYC has been shown to establish a dependence on AMPK-related kinase 5 (ARK5) to maintain metabolic homeostasis and cell survival. Depletion of ARK5 prolongs survival in MYC-driven mouse models of hepatocellular carcinoma, suggesting that targeting cellular energy homeostasis is a valid therapeutic strategy to eliminate tumor cells that express deregulated MYC (50).

The therapeutic benefit of AMPK modulators: the metformin paradox

The better understanding of the dichotomous role of AMPK in cancer has also brought about the careful reevaluation of the use of AMPK modulators in cancer therapy. In this regard, the case of metformin is emblematic.

The interest in using AMPK activators began as evidence was accumulating for the antitumorigenic role of the LKB1/AMPK axis. The antiproliferative and growth-suppressing effects of supraphysiological activation of AMPK have been shown in vitro and in preclinical models. Activation was achieved with natural compounds, the AMP mimetic drug AICAR as well as the biguanides metformin and phenformin, which inhibit complex I of the mitochondrial electron transport chain, leading to increased levels of intracellular ADP, AMP, and energy stress (reviewed in refs. 4, 14, 51). Metformin has received particular attention, because it is a safe medication, used as first choice in the treatment of type II diabetes, and has been associated with reduced cancer incidence in diabetic patients (52). Thus, it is currently being tested for cancer treatment/prevention in several clinical trials, as discussed below. However, ascribing metformin's antitumor properties in vivo to AMPK activation has been criticized because the major effect of the drug is the inhibition of hepatic gluconeogenesis, resulting in reduced circulating levels of glucose and insulin, two well-known promoters of tumor cell proliferation. This is also valid for metformin's antitumor effects in vitro, where several AMPK-independent mechanisms have been described (45, 53–56). Moreover, the discovery of the so-called “biguanide paradox” has recently suggested that, in specific contexts, metformin-mediated suppression of tumor growth does not depend on AMPK activation but, rather, on its downregulation. Because cells with a defective LKB1/AMPK pathway are less able to restore ATP levels in response to metabolic stress induced by metformin treatment, LKB1/AMPK-deficient cancer cells are more susceptible to cell death than their counterparts with a functional LKB1/AMPK axis (Fig. 5). Several in vitro and in vivo studies using metformin, phenformin, or other compounds that cause metabolic stress (AICAR, salicylate, and 2-deoxyglucose) have supported this mechanism (discussed in ref. 57, 58). In light of this, the use of biguanides may be most effective in combination with agents that inhibit, rather than activate, AMPK and, overall, these data suggest that the use of AMPK inhibitors rather than activators would preferentially trigger cancer cell death in the context of metabolic stress. Interestingly, the chemotherapeutic agent sunitinib has been shown to inhibit AMPK, suggesting that combinatorial treatment of sunitinib and metformin could be clinically relevant (59).

Figure 5.

Mechanisms by which biguanides are therapeutically beneficial in LKB1-positive and -negative tumors. A, metformin or phenformin activates AMPK in preneoplastic cells with the functional LKB1/AMPK pathway, restraining their growth and proliferation and thus delaying the onset of tumorigenesis; B, cancer cells, in which the LKB1–AMPK pathway is not functional, cannot restore biguanides-induced energy stress and they are more sensitive to cell death (biguanide paradox).

Figure 5.

Mechanisms by which biguanides are therapeutically beneficial in LKB1-positive and -negative tumors. A, metformin or phenformin activates AMPK in preneoplastic cells with the functional LKB1/AMPK pathway, restraining their growth and proliferation and thus delaying the onset of tumorigenesis; B, cancer cells, in which the LKB1–AMPK pathway is not functional, cannot restore biguanides-induced energy stress and they are more sensitive to cell death (biguanide paradox).

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Novel direct AMPK activators have been developed to overcome the off-target effects of metformin and AICAR treatment. The direct activator A-769662 (which binds the β1 subunit) delays tumor formation in PTEN-null/LKB1 hypomorphic mice (60). The same compound has been shown to suppress the proliferation of breast, colon, and prostate cancer cells (61–63). A-769662 was, however, ineffective in models of glioma (56). OSU-53, a direct activator that binds the autoinhibitory domain of AMPK, displays tumor growth inhibition in vitro and in vivo in triple-negative breast cancer models (64). The same group reported that AMPK activation by OSU-53 blocks “EMT” in breast and prostate cancer cells by activating Foxo3a, which results in the inhibition of invasive phenotypes in vitro and metastatic properties in vivo (32). Direct supraphysiological activation of AMPK in nutrient-replete conditions has also been shown to suppress prostate cancer cells growth, in association with mitotic arrest and apoptosis, and to potentiate the effect of antiandrogens in vitro (65). The inhibitory effect of AMPK activation on the androgen receptor (AR) axis at both transcriptional and posttranslational levels was previously observed when a supraphysiological activation of AMPK was achieved by treatment with metformin or AICAR (66, 67). Finally, Compound 1, a novel AMPK activator, induces a significant antitumor activity in vitro and tumor growth delay in a mouse xenograft model of colorectal cancer (68). The mechanism through which Compound 1 activates AMPK is, however, still uncharacterized.

Taken together, the induction of a persistent, supraphysiological activation of AMPK results in tumor suppression in some cancer types (Fig. 3).

Salicylate, the active metabolite of aspirin following absorption from the gut, was recently identified as a direct AMPK activator, which binds to the same site on the β1 subunit as A-769662 (69). This suggests that AMPK activation might be involved in mediating aspirin's protective effects against cancer. Future preclinical studies in genetically engineered AMPK models are however required to validate this hypothesis.

Overall, these apparently conflicting data suggest that both AMPK activators and inhibitors can provide therapeutic benefit in different tumor types, different genetic/metabolic contexts, and different microenvironment conditions. Thus, the choice of AMPK modulators may be different at various phases of tumorigenesis/tumor progression.

AMPK activation in human cancers

Evaluation of AMPK activation in human tissues is not trivial. Early studies have demonstrated that when tissues and organs are removed by dissection at ambient temperature rather than by freeze clamping, ACC phosphorylation occurred as a postmortem artifact. Dissection at ambient temperature leads to elevation of AMP and depletion of ATP, presumably due to hypoxia following interruption of the blood supply, resulting in AMPK activation. Moreover, ACC phosphorylation in tissues such as liver has also been shown to follow a diurnal rhythm and to be influenced by dietary behavior (70). Therefore, analysis of AMPK activity and ACC phosphorylation in human tissues should be interpreted with caution.

AMPK activation has been investigated in fresh frozen and archival tumor tissue from numerous cancer sites, including prostate (63, 71, 72), breast (73, 74), head and neck (75), colorectal (76, 77), gastric (78, 79), liver (80), lung (81–83), ovary (84), and kidney (85, 86). Table 1 summarizes the population-based studies of AMPK activation, measured by protein expression of phosphorylated AMPKα1 (p-AMPKα1, n = 16 studies) or its phosphorylated substrate ACC (p-ACC, n = 6 studies), with cancer prognosis and clinicopathologic features. Of the 13 studies reporting on p-AMPKα1 at Thr172 and overall, cancer-specific, or progression-free survival (PFS), 8 studies found that AMPK activation was associated with improved prognosis among head and neck (75), colorectal (76, 77), gastric (79), liver (80), lung (81), and kidney (85, 86) cancer patients either within the entire study population or within subgroups. Consistent with the findings for p-AMPKα1 at Thr172, one additional study of lung cancer found that higher expression of p-AMPKα1 at Ser485, which inhibits AMPK signaling (14), was associated with shorter survival (82). Conversely, two studies in gastric cancer (78) and in prostate cancer (72) reported associations between higher p-AMPKα1 and disease recurrence; however, the gastric cancer study population was substantially smaller than that of Kim and colleagues (79). Three additional studies in lung (83) and breast cancer patients (73, 74) found no association between p-AMPKα1 expression and overall survival (OS). In cross-sectional analyses, higher p-AMPKα1 expression was associated with lower tumor grade and/or stage in breast (73), head and neck (75), colorectal (76), gastric (79), liver (80), and ovarian (84) cancer, while 4 additional studies in prostate (72), breast (74), gastric (78), and lung (81) cancer found no associations with clinicopathologic features. In contrast, Choudhury and colleagues found increasing p-AMPKα1 expression with higher tumor grade in prostate cancer specimens (63). Overall, these human studies support the hypothesis that AMPK activation may delay disease progression in several cancer types.

Table 1.

Population-based studies of AMPK activation in tumor tissue, clinicopathologic features, and prognosis

Population-based studies of AMPK activation in tumor tissue, clinicopathologic features, and prognosis
Population-based studies of AMPK activation in tumor tissue, clinicopathologic features, and prognosis

Of the 6 studies that used protein expression of p-ACC at Ser79 to characterize AMPK activation, higher p-ACC was associated with worse OS (82) and disease recurrence (83) among lung cancer patients, and with worse OS among head and neck cancer (75) and kidney cancer (86) patients. In contrast, higher p-ACC was associated with improved OS and PFS in colorectal cancer patients (77). Lastly, no correlation was observed between p-ACC expression and Gleason grade in prostate tumors (71). A better understanding of the effects of ACC inactivation and its downstream targets in different tumor tissues will help elucidate the complex role of AMPK activation in carcinogenesis.

Tumor expression of specific AMPK α, β, and γ subunits in relation to cancer outcomes has been explored in patients with melanoma (87), kidney cancer (85, 86), breast cancer (74), cervical cancer (88), lymphoma (89), ovarian cancer (84, 90, 91), lung cancer (82), and colorectal cancer (92). Total AMPKα1 protein expression, which captures both phosphorylated and nonphosphorylated AMPKα1, was associated with improved overall and disease-specific survival among 128 melanoma patients (87). Total AMPKα1/α2 protein expression was associated with improved PFS (P = 0.04) and borderline associated with OS (P = 0.06) in 37 renal cell carcinoma patients (85). Using publicly available data from The Cancer Genome Atlas (TCGA), overexpression of the genes encoding for AMPKα1, α2, β1, β2, and γ1 subunits was also associated with improved OS (P ≤ 0.05) in 417 clear-cell renal cell carcinoma patients (86). In a discovery (n = 166) and validation (n = 609) cohort of breast cancer patients, total AMPKα expression was associated with longer relapse-free (P = 0.016 and P = 0.06, respectively) and breast cancer-specific (P < 0.001 and P = 0.005, respectively) survival (74). Using fluorescence in situ hybridization, amplification of the gene encoding AMPKα1 was not significantly associated with lymph node positivity (P = 0.085) in pretreatment cervical biopsies among 31 cervical cancer patients (88). Using the Oncomine database, Hoffman and colleagues reported an association between higher expression of the genes encoding the regulatory AMPKβ1 and β2 subunits and increased 5-year survival (P = 0.001 and 0.021, respectively) among diffuse large B-cell lymphoma patients; marginal associations were found for higher expression of the gene encoding AMPKα1 and improved survival (P = 0.0751), and higher expression of the gene encoding AMPKγ3 and worse survival (P = 0.0646; ref. 89). Similarly, in a series of 70 ovarian cancer patients, higher protein expression of p-AMPKβ1 at Ser182 was associated with lower tumor grade (n = 70, P = 0.009) and improved OS in the subgroup of patients with serous subtype (n = 46, P = 0.037) and advanced-stage disease (n = 54, P = 0.0016; ref. 90). Phosphorylation of AMPKβ1 at Ser182 has not been shown to affect the kinase activity, but is associated with nuclear localization (93). Another study of total AMPKβ1 in ovarian cancer also found that higher protein expression was associated with early tumor stage (P = 0.008), lower tumor grade (P = 0.013), and absence of metastasis (P = 0.008; ref. 84). This same research group previously demonstrated that higher expression of the gene encoding AMPKα2, measured by quantitative PCR, was associated with improved overall (P = 0.030) and disease-free (P = 0.014) survival in a hospital-based series of 76 ovarian cancer patients, although gene expression of the α1, β1, β2, γ1, and γ2 subunits was not associated with outcomes (91). Zupa and colleagues, in addition to the findings for p-AMPKα1 and p-ACC listed in Table 1, reported an association between higher protein expression of p-AMPKβ1 at Ser108, indicative of AMPK activation (93), and short-term versus long-term survival (P = 0.0286) among 28 pathologic stage N0 NSCLC patients (82). Lastly, Vetvik and colleagues found that tumor expression of the gene encoding AMPKβ1 was positively correlated with advanced tumor stage, but not with the number of affected lymph nodes, in specimens from 60 colorectal cancer patients (92).

With the exception of Zupa and colleagues and Vetvik and colleagues, these studies suggest that higher tumor expression of specific AMPK subunits may be related to favorable clinicopathologic features and improved outcomes among cancer patients. Additional studies are warranted to confirm these findings in larger study populations and across cancer sites.

Differential expression of AMPK/ACC in tumor versus normal tissue has been reported in a few neoplasms, including liver (80), ovarian (90, 91), thyroid (94), cervical (95), brain (47), skin (87), prostate (63, 71, 72, 96), and colorectal cancer (92). In hepatocellular carcinoma, protein expression of p-AMPKα1 at Thr172 was downregulated in 62% of tumor versus distant normal liver tissue (80). In ovarian specimens, protein expression of p-AMPKβ1 at Ser182 was significantly higher (P = 0.038) in carcinoma compared with borderline tumors and normal ovaries (90). Li and colleagues also found higher expression of the genes encoding AMPKα2, β1, β2, γ1, and γ2 (P ≤ 0.001), but not AMPKα1 (P = 0.320), in primary cancer versus normal ovarian tissue (91). In papillary thyroid carcinoma patients, protein expression of total AMPKα, p-AMPKα1 at Thr172, and p-ACC at Ser79 was elevated (P < 0.001) in carcinoma versus paired nonneoplastic tissue (94). Similarly, protein expression of AMPKα1 was significantly higher (P < 0.001) in tumor versus normal epithelium in cervical cancer patients (95). In a small study of brain cancer, high protein expression of p-ACC at Ser79 was seen in all glioblastoma specimens compared with the absence of expression in normal brain (47). In melanoma patients, total AMPKα1 protein expression was increased in primary melanoma versus dysplastic nevi (P < 0.005), but slightly decreased in metastatic versus primary melanoma specimens (P < 0.05) (87). In prostate cancer patients, both p-AMPKα1 at Thr172 and p-ACC at Ser79 were expressed in tumor tissue, compared with no detectable expression in nonpaired benign prostatic hyperplasia samples (63). Two additional prostate studies reported elevated expression of p-AMPKα1 at Thr172 and p-ACC at Ser79 (P < 0.001) in prostate tumor versus nonneoplastic tissue (71, 72). Utilizing the Oncomine database, the gene encoding AMPKβ1 was expressed at greater levels in metastatic versus primary prostate cancer in publicly available data from 4 studies (96). Lastly, expression of the gene encoding AMPKβ1 was significantly higher in colorectal cancer versus adjacent mucosa (92). Taken together, these studies support that AMPK dysregulation contributes to neoplastic transformation.

In summary, AMPK expression/activation varies by tumor stage and histology, clinical outcomes, and tissue type (normal, tumor, and metastatic). Most of the studies in tumor tissue support a role of AMPK activation, measured by phosphorylation at Thr172, in delaying tumor progression. However, comparing tumor with nonneoplastic tissue suggests that AMPK may be involved in tumor initiation. Thus, evidence from human studies also underscores the dual role of AMPK in carcinogenesis.

AMPK-activating drugs in humans: metformin, phenformin, and aspirin

Several review articles and meta-analyses on metformin and cancer risk have been published in recent years. A 2012 meta-analysis of randomized controlled trials among participants with or at risk of type 2 diabetes did not find reduced cancer incidence for treatment with metformin versus placebo/usual care or active comparators [n = 9 studies; summary relative risk (RR), 1.02; 95% confidence interval (CI), 0.82–1.26; ref. 97]. Meta-analyses of observational studies among diabetics have shown a reduced risk of cancer associated with metformin use: the fixed-effect summary RRs (95% CI) were 0.70 (0.67–0.73) for 9 cohort studies (98), 0.90 (0.84–0.98) for 13 case–control studies (98), and 0.73 (0.61–0.88) for 21 cohort and case–control studies combined (99). However, both meta-analyses exhibited significant between-study heterogeneity, with Thakkar and colleagues reporting random-effects model estimates that were attenuated (summary RR, 0.85; 95% CI, 0.65–1.11) among cohort studies, but retained significance (summary RR, 0.71; 95% CI, 0.57–0.88) among case–control studies (98). Inconsistent results may be due to variations in metformin dose, duration of metformin use, length of follow-up, type of comparison group (diabetics taking nonmetformin antidiabetic medications, diabetics on alternative therapy, or nondiabetics), outcome assessed (incident cancer or cancer mortality as a surrogate), variation by cancer site, systematic biases, or confounding. Of particular concern are potential time-related biases that may arise when evaluating metformin and cancer risk (100). A recent meta-analysis of observational and randomized studies attempted to account for major biases and confounders, still finding a significant, though attenuated, reduction in cancer incidence among studies without time-related biases (n = 8 studies; summary RR, 0.90; 95% CI, 0.89–0.91) and among studies adjusted for body mass index (n = 11 studies; summary RR, 0.82; 95% CI, 0.70–0.96; ref. 101). Observational studies published after these meta-analyses have been either consistent with reduced cancer risk (102, 103) or null (104–106). Overall, the literature suggests that metformin either reduces or has no effect on cancer risk, though very few studies have addressed metformin use in the nondiabetic population. Future clinical trials of metformin therapy in the general population should provide vital data on the potential use of metformin as a chemopreventive agent.

Metformin use may also influence disease progression after a cancer diagnosis. In observational studies, metformin has been associated with a decreased risk of disease recurrence, overall mortality, or cancer-specific mortality in patient cohorts of prostate cancer (107, 108), multiple myeloma (109), liver cancer (110), ovarian/endometrial cancer (110–112), bladder cancer (113, 114), and breast cancer (115, 116). Two additional studies of prostate cancer patients who underwent radical prostatectomy found no significant associations between metformin use and time to biochemical recurrence or longer-term outcomes (117, 118). Two additional studies of breast cancer patients were null for metformin use and overall or cancer-specific survival (119, 120). Numerous clinical trials of metformin as an adjuvant therapy to cancer treatment are under way, as indicated on ClinicalTrials.gov. Combined with the observational data, these new clinical trials will shed light on the potential therapeutic role of metformin in cancer survivors.

In addition, a limited number of “window-of-opportunity” (i.e., phase 0) trials have been conducted to evaluate metformin administration in the time window between cancer diagnosis and surgery. These studies show mixed results for tumor p-AMPKα at Thr172 expression before and after metformin use (range, 850–2250 mg/day): p-AMPKα protein expression was increased in 1 study of endometrial cancer patients (121), decreased in another study of endometrial cancer patients (122), and unchanged in 2 studies of endometrial (123) and prostate (124) cancer patients. Thus, a direct link between short-term metformin use and AMPK activation in targeted tissue is unclear. Larger studies of longer duration and varying dosage of metformin use across various cancer types are needed to determine whether metformin acts through the AMPK pathway to influence tumor growth and progression.

Phenformin, a metformin analogue, is also a potent indirect activator of AMPK and was administered as antidiabetic medication starting in the mid-1900s. However, increased risk of lactic acidosis, often fatal, led to the withdrawal of phenformin by the FDA in 1977 (125). Phenformin has a longer half-life and displays more potent antineoplastic activity compared with metformin in in vitro and in vivo preclinical studies (126). In vitro studies of the antitumorigenic effects of metformin are often at supraphysiological concentrations that may be unattainable in humans; thus, phenformin may offer an alternative for chemoprevention or adjuvant therapy for cancer patients. Phenformin continues to be available in some parts of the world. In a recent cohort study of biguanide use and colorectal cancer risk in Denmark, phenformin comprised 0.5% of biguanide prescriptions (127). The investigators analyzed all biguanides as a group and found an increased risk of colorectal cancer among biguanide users compared with nondiabetics, and risk estimates were inconsistent when biguanide users were compared with diabetics on other oral antidiabetic drugs. These results conflict with the much of the current literature suggesting a reduced risk or null association for biguanide treatment and colorectal cancer incidence (99).

More recently, salicylate, the metabolic derivative of aspirin, has been shown to directly activate AMPK (69). Aspirin has long been known to exhibit antineoplastic properties, though whether these properties are mediated by AMPK is unknown. Algra and colleagues summarized the results for any aspirin use and long-term cancer incidence, reporting summary RRs (95% CI) of 0.88 (0.84–0.92) among 150 case–control studies and 0.87 (0.83–0.91) among 45 cohort studies for risk of all cancer types, with the most consistent findings for reduced risk of colorectal cancer (128). Rothwell and colleagues summarized the results for regular aspirin use and cancer incidence and mortality among randomized controlled trials for the primary prevention of cardiovascular disease, reporting summary RRs (95% CI) of 0.88 (0.80–0.98) for cancer risk among 6 trials and 0.85 (0.76–0.96) for cancer deaths among 34 trials (129). This group also found that aspirin use among patients with nonmetastatic adenocarcinoma at diagnosis was associated with a reduced risk of subsequent metastasis (summary RR, 0.45; 95% CI, 0.28–0.72) and cancer death (summary RR, 0.50; 95% CI, 0.34–0.74) among 5 randomized trials of daily aspirin for the prevention of vascular events (130). Additional observational studies support an association between regular aspirin use after diagnosis and improved survival outcomes among breast (131, 132), colorectal (refs. 133–137; reviewed in ref. 138), and prostate cancer (139, 140) patients, while other studies do not (141–144). Overall, the current evidence from long-term observational and randomized studies is strongly suggestive of a potential role for aspirin in the primary and secondary prevention of cancer.

In summary, observational and randomized studies suggest a potential benefit of AMPK-activating drugs for chemoprevention and/or improving cancer survival. These findings are in agreement with associations between AMPK activation levels in tumor tissue and more favorable clinicopathologic features and survival outcomes observed in several cancer types (Table 1). In future studies, it will be important to understand to what extent AMPK activation mediates the ability of these drugs to reduce cancer risk, and to define their action in the context of the metabolic status of the individual, concurrent medication use, and the natural history of cancer.

The duplicitous role of AMPK activation in cancer cells is context-specific and affects the outcome of AMPK modulation. More sophisticated genetic manipulation of AMPK is necessary to understand its biochemical and cell biology function in the different contexts. In addition, knowledge of long-term outcomes in healthy individuals and cancer patients in relation to AMPK status is necessary to inform the potential use of AMPK modulators in the clinical setting. Thus, the road toward a deeper understanding of AMPK's role in cancer and its therapeutic exploitation is still under construction.

No potential conflicts of interest were disclosed.

This work was supported by the NIH/NCI grant 2R01CA131945, the DF/HCC SPORE in Prostate Cancer (NIH/NCI P50 CA90381), the Prostate Cancer Foundation, the DOD synergist idea development award (PC130716) to M. Loda. J.L. Batista is supported, in part, by the Department of Defense Prostate Cancer Research Program (W81XWH-12-1-0072) and the Dana-Farber Cancer Institute Mazzone Awards Program.

1.
Hawley
SA
,
Boudeau
J
,
Reid
JL
,
Mustard
KJ
,
Udd
L
,
Makela
TP
, et al
Complexes between the LKB1 tumor suppressor, STRAD alpha/beta and MO25 alpha/beta are upstream kinases in the AMP-activated protein kinase cascade
.
J Biol
2003
;
2
:
28
.
2.
Woods
A
,
Johnstone
SR
,
Dickerson
K
,
Leiper
FC
,
Fryer
LG
,
Neumann
D
, et al
LKB1 is the upstream kinase in the AMP-activated protein kinase cascade
.
Curr Biol
2003
;
13
:
2004
8
.
3.
Shaw
RJ
,
Kosmatka
M
,
Bardeesy
N
,
Hurley
RL
,
Witters
LA
,
DePinho
RA
, et al
The tumor suppressor LKB1 kinase directly activates AMP-activated kinase and regulates apoptosis in response to energy stress
.
Proc Natl Acad Sci U S A
2004
;
101
:
3329
35
.
4.
Fogarty
S
,
Hardie
DG
. 
Development of protein kinase activators: AMPK as a target in metabolic disorders and cancer
.
Biochim Biophys Acta
2010
;
1804
:
581
91
.
5.
Mihaylova
MM
,
Shaw
RJ
. 
The AMPK signalling pathway coordinates cell growth, autophagy and metabolism
.
Nat Cell Biol
2011
;
13
:
1016
23
.
6.
Liang
J
,
Mills
GB
. 
AMPK: a contextual oncogene or tumor suppressor?
Cancer Res
2013
;
73
:
2929
35
.
7.
Gao
J
,
Aksoy
BA
,
Dogrusoz
U
,
Dresdner
G
,
Gross
B
,
Sumer
SO
, et al
Integrative analysis of complex cancer genomics and clinical profiles using the cBioPortal
.
Sci Signal
2013
;
6
:
pl1
.
8.
Li
J
,
Jiang
P
,
Robinson
M
,
Lawrence
TS
,
Sun
Y
. 
AMPK-beta1 subunit is a p53-independent stress responsive protein that inhibits tumor cell growth upon forced expression
.
Carcinogenesis
2003
;
24
:
827
34
.
9.
Fox
MM
,
Phoenix
KN
,
Kopsiaftis
SG
,
Claffey
KP
. 
AMP-activated protein kinase alpha 2 isoform suppression in primary breast cancer alters AMPK growth control and apoptotic signaling
.
Genes Cancer
2013
;
4
:
3
14
.
10.
Lee
CW
,
Wong
LL
,
Tse
EY
,
Liu
HF
,
Leong
VY
,
Lee
JM
, et al
AMPK promotes p53 acetylation via phosphorylation and inactivation of SIRT1 in liver cancer cells
.
Cancer Res
2012
;
72
:
4394
404
.
11.
Xiao
B
,
Heath
R
,
Saiu
P
,
Leiper
FC
,
Leone
P
,
Jing
C
, et al
Structural basis for AMP binding to mammalian AMP-activated protein kinase
.
Nature
2007
;
449
:
496
500
.
12.
Xiao
B
,
Sanders
MJ
,
Underwood
E
,
Heath
R
,
Mayer
FV
,
Carmena
D
, et al
Structure of mammalian AMPK and its regulation by ADP
.
Nature
2011
;
472
:
230
3
.
13.
Hardie
DG
,
Ross
FA
,
Hawley
SA
. 
AMPK: a nutrient and energy sensor that maintains energy homeostasis
.
Nat Rev Mol Cell Biol
2012
;
13
:
251
62
.
14.
Steinberg
GR
,
Kemp
BE
. 
AMPK in health and disease
.
Physiol Rev
2009
;
89
:
1025
78
.
15.
Goransson
O
,
McBride
A
,
Hawley
SA
,
Ross
FA
,
Shpiro
N
,
Foretz
M
, et al
Mechanism of action of A-769662, a valuable tool for activation of AMP-activated protein kinase
.
J Biol Chem
2007
;
282
:
32549
60
.
16.
Emerling
BM
,
Weinberg
F
,
Snyder
C
,
Burgess
Z
,
Mutlu
GM
,
Viollet
B
, et al
Hypoxic activation of AMPK is dependent on mitochondrial ROS but independent of an increase in AMP/ATP ratio
.
Free Radic Biol Med
2009
;
46
:
1386
91
.
17.
Luo
Z
,
Zang
M
,
Guo
W
. 
AMPK as a metabolic tumor suppressor: control of metabolism and cell growth
.
Future Oncol
2010
;
6
:
457
70
.
18.
DeRan
M
,
Yang
J
,
Shen
CH
,
Peters
EC
,
Fitamant
J
,
Chan
P
, et al
Energy stress regulates hippo-YAP signaling involving AMPK-mediated regulation of angiomotin-like 1 protein
.
Cell Rep
2014
;
9
:
495
503
.
19.
Jeon
SM
,
Hay
N
. 
The dark face of AMPK as an essential tumor promoter
.
Cell Logist
2012
;
2
:
197
202
.
20.
Bon
H
,
Wadhwa
K
,
Schreiner
A
,
Osborne
M
,
Carroll
T
,
Ramos-Montoya
A
, et al
Salt-inducible kinase 2 regulates mitotic progression and transcription in prostate cancer
.
Mol Cancer Res
2014
;
13
:
620
35
.
21.
Faubert
B
,
Boily
G
,
Izreig
S
,
Griss
T
,
Samborska
B
,
Dong
Z
, et al
AMPK is a negative regulator of the Warburg effect and suppresses tumor growth in vivo
.
Cell Metab
2013
;
17
:
113
24
.
22.
Scaglia
N
,
Tyekucheva
S
,
Zadra
G
,
Photopoulos
C
,
Loda
M
. 
De novo fatty acid synthesis at the mitotic exit is required to complete cellular division
.
Cell Cycle
2014
;
13
:
859
68
.
23.
Brusselmans
K
,
De Schrijver
E
,
Verhoeven
G
,
Swinnen
JV
. 
RNA interference-mediated silencing of the acetyl-CoA-carboxylase-alpha gene induces growth inhibition and apoptosis of prostate cancer cells
.
Cancer Res
2005
;
65
:
6719
25
.
24.
Chajes
V
,
Cambot
M
,
Moreau
K
,
Lenoir
GM
,
Joulin
V
. 
Acetyl-CoA carboxylase alpha is essential to breast cancer cell survival
.
Cancer Res
2006
;
66
:
5287
94
.
25.
Lee
JH
,
Koh
H
,
Kim
M
,
Kim
Y
,
Lee
SY
,
Karess
RE
, et al
Energy-dependent regulation of cell structure by AMP-activated protein kinase
.
Nature
2007
;
447
:
1017
20
.
26.
Banko
MR
,
Allen
JJ
,
Schaffer
BE
,
Wilker
EW
,
Tsou
P
,
White
JL
, et al
Chemical genetic screen for AMPKalpha2 substrates uncovers a network of proteins involved in mitosis
.
Mol Cell
2011
;
44
:
878
92
.
27.
Thaiparambil
JT
,
Eggers
CM
,
Marcus
AI
. 
AMPK regulates mitotic spindle orientation through phosphorylation of myosin regulatory light chain
.
Mol Cell Biol
2012
;
32
:
3203
17
.
28.
Vazquez-Martin
A
,
Oliveras-Ferraros
C
,
Menendez
JA
. 
The active form of the metabolic sensor: AMP-activated protein kinase (AMPK) directly binds the mitotic apparatus and travels from centrosomes to the spindle midzone during mitosis and cytokinesis
.
Cell Cycle
2009
;
8
:
2385
98
.
29.
Vazquez-Martin
A
,
Oliveras-Ferraros
C
,
Lopez-Bonet
E
,
Menendez
JA
. 
AMPK: Evidence for an energy-sensing cytokinetic tumor suppressor
.
Cell Cycle
2009
;
8
:
3679
83
.
30.
Merlen
G
,
Gentric
G
,
Celton-Morizur
S
,
Foretz
M
,
Guidotti
JE
,
Fauveau
V
, et al
AMPKalpha1 controls hepatocyte proliferation independently of energy balance by regulating Cyclin A2 expression
.
J Hepatol
2014
;
60
:
152
9
.
31.
Shen
CH
,
Yuan
P
,
Perez-Lorenzo
R
,
Zhang
Y
,
Lee
SX
,
Ou
Y
, et al
Phosphorylation of BRAF by AMPK impairs BRAF-KSR1 association and cell proliferation
.
Mol Cell
2013
;
52
:
161
72
.
32.
Chou
CC
,
Lee
KH
,
Lai
IL
,
Wang
D
,
Mo
X
,
Kulp
SK
, et al
AMPK reverses the mesenchymal phenotype of cancer cells by targeting the Akt-MDM2-Foxo3a signaling axis
.
Cancer Res
2014
;
74
:
4783
95
.
33.
Pineda
CT
,
Ramanathan
S
,
Fon Tacer
K
,
Weon
JL
,
Potts
MB
,
Ou
YH
, et al
Degradation of AMPK by a cancer-specific ubiquitin ligase
.
Cell
2015
;
160
:
715
28
.
34.
Horman
S
,
Vertommen
D
,
Heath
R
,
Neumann
D
,
Mouton
V
,
Woods
A
, et al
Insulin antagonizes ischemia-induced Thr172 phosphorylation of AMP-activated protein kinase alpha-subunits in heart via hierarchical phosphorylation of Ser485/491
.
J Biol Chem
2006
;
281
:
5335
40
.
35.
Zheng
B
,
Jeong
JH
,
Asara
JM
,
Yuan
YY
,
Granter
SR
,
Chin
L
, et al
Oncogenic B-RAF negatively regulates the tumor suppressor LKB1 to promote melanoma cell proliferation
.
Mol Cell
2009
;
33
:
237
47
.
36.
Caino
MC
,
Chae
YC
,
Vaira
V
,
Ferrero
S
,
Nosotti
M
,
Martin
NM
, et al
Metabolic stress regulates cytoskeletal dynamics and metastasis of cancer cells
.
J Clin Invest
2013
;
123
:
2907
20
.
37.
Tong
WH
,
Sourbier
C
,
Kovtunovych
G
,
Jeong
SY
,
Vira
M
,
Ghosh
M
, et al
The glycolytic shift in fumarate-hydratase-deficient kidney cancer lowers AMPK levels, increases anabolic propensities and lowers cellular iron levels
.
Cancer Cell
2011
;
20
:
315
27
.
38.
Rodriguez
M
,
Potter
DA
. 
CYP1A1 regulates breast cancer proliferation and survival
.
Mol Cancer Res
2013
;
11
:
780
92
.
39.
Egan
DF
,
Shackelford
DB
,
Mihaylova
MM
,
Gelino
S
,
Kohnz
RA
,
Mair
W
, et al
Phosphorylation of ULK1 (hATG1) by AMP-activated protein kinase connects energy sensing to mitophagy
.
Science
2011
;
331
:
456
61
.
40.
Hardie
DG
,
Pan
DA
. 
Regulation of fatty acid synthesis and oxidation by the AMP-activated protein kinase
.
Biochem Soc Trans
2002
;
30
:
1064
70
.
41.
Zaugg
K
,
Yao
Y
,
Reilly
PT
,
Kannan
K
,
Kiarash
R
,
Mason
J
, et al
Carnitine palmitoyltransferase 1C promotes cell survival and tumor growth under conditions of metabolic stress
.
Genes Dev
2011
;
25
:
1041
51
.
42.
Bungard
D
,
Fuerth
BJ
,
Zeng
PY
,
Faubert
B
,
Maas
NL
,
Viollet
B
, et al
Signaling kinase AMPK activates stress-promoted transcription via histone H2B phosphorylation
.
Science
2010
;
329
:
1201
5
.
43.
Jeon
SM
,
Chandel
NS
,
Hay
N
. 
AMPK regulates NADPH homeostasis to promote tumour cell survival during energy stress
.
Nature
2012
;
485
:
661
5
.
44.
Zhong
D
,
Liu
X
,
Khuri
FR
,
Sun
SY
,
Vertino
PM
,
Zhou
W
. 
LKB1 is necessary for Akt-mediated phosphorylation of proapoptotic proteins
.
Cancer Res
2008
;
68
:
7270
7
.
45.
Vincent
EE
,
Coelho
PP
,
Blagih
J
,
Griss
T
,
Viollet
B
,
Jones
RG
. 
Differential effects of AMPK agonists on cell growth and metabolism
.
Oncogene
2014
Sep 22. [Epub ahead of print]
.
46.
Laderoute
KR
,
Calaoagan
JM
,
Chao
WR
,
Dinh
D
,
Denko
N
,
Duellman
S
, et al
5′-AMP-activated protein kinase (AMPK) supports the growth of aggressive experimental human breast cancer tumors
.
J Biol Chem
2014
;
289
:
22850
64
.
47.
Rios
M
,
Foretz
M
,
Viollet
B
,
Prieto
A
,
Fraga
M
,
Costoya
JA
, et al
AMPK activation by oncogenesis is required to maintain cancer cell proliferation in astrocytic tumors
.
Cancer Res
2013
;
73
:
2628
38
.
48.
Rios
M
,
Foretz
M
,
Viollet
B
,
Prieto
A
,
Fraga
M
,
Garcia-Caballero
T
, et al
Lipoprotein internalisation induced by oncogenic AMPK activation is essential to maintain glioblastoma cell growth
.
Eur J Cancer
2014
;
50
:
3187
97
.
49.
Hindupur
SK
,
Balaji
SA
,
Saxena
M
,
Pandey
S
,
Sravan
GS
,
Heda
N
, et al
Identification of a novel AMPK-PEA15 axis in the anoikis-resistant growth of mammary cells
.
Breast Cancer Res
2014
;
16
:
420
.
50.
Liu
L
,
Ulbrich
J
,
Muller
J
,
Wustefeld
T
,
Aeberhard
L
,
Kress
TR
, et al
Deregulated MYC expression induces dependence upon AMPK-related kinase 5
.
Nature
2012
;
483
:
608
12
.
51.
Owen
MR
,
Doran
E
,
Halestrap
AP
. 
Evidence that metformin exerts its anti-diabetic effects through inhibition of complex 1 of the mitochondrial respiratory chain
.
Biochem J
2000
;
348
Pt 3
:
607
14
.
52.
Evans
JM
,
Donnelly
LA
,
Emslie-Smith
AM
,
Alessi
DR
,
Morris
AD
. 
Metformin and reduced risk of cancer in diabetic patients
.
BMJ
2005
;
330
:
1304
5
.
53.
Kalender
A
,
Selvaraj
A
,
Kim
SY
,
Gulati
P
,
Brule
S
,
Viollet
B
, et al
Metformin, independent of AMPK, inhibits mTORC1 in a rag GTPase-dependent manner
.
Cell Metab
2010
;
11
:
390
401
.
54.
Ben Sahra
I
,
Regazzetti
C
,
Robert
G
,
Laurent
K
,
Le Marchand-Brustel
Y
,
Auberger
P
, et al
Metformin, independent of AMPK, induces mTOR inhibition and cell-cycle arrest through REDD1
.
Cancer Res
2011
;
71
:
4366
72
.
55.
Viollet
B
,
Guigas
B
,
Sanz Garcia
N
,
Leclerc
J
,
Foretz
M
,
Andreelli
F
. 
Cellular and molecular mechanisms of metformin: an overview
.
Clin Sci (Lond)
2012
;
122
:
253
70
.
56.
Liu
X
,
Chhipa
RR
,
Pooya
S
,
Wortman
M
,
Yachyshin
S
,
Chow
LM
, et al
Discrete mechanisms of mTOR and cell cycle regulation by AMPK agonists independent of AMPK
.
Proc Natl Acad Sci U S A
2014
;
111
:
E435
44
.
57.
Hardie
DG
,
Alessi
DR
. 
LKB1 and AMPK and the cancer-metabolism link – ten years after
.
BMC Biol
2013
;
11
:
36
.
58.
Faubert
B
,
Vincent
EE
,
Poffenberger
MC
,
Jones
RG
. 
The AMP-activated protein kinase (AMPK) and cancer: Many faces of a metabolic regulator
.
Cancer Lett
2015
;
356
:
165
70
.
59.
Laderoute
KR
,
Calaoagan
JM
,
Madrid
PB
,
Klon
AE
,
Ehrlich
PJ
. 
SU11248 (sunitinib) directly inhibits the activity of mammalian 5′-AMP-activated protein kinase (AMPK)
.
Cancer Biol Ther
2010
;
10
:
68
76
.
60.
Huang
X
,
Wullschleger
S
,
Shpiro
N
,
McGuire
VA
,
Sakamoto
K
,
Woods
YL
, et al
Important role of the LKB1-AMPK pathway in suppressing tumorigenesis in PTEN-deficient mice
.
Biochem J
2008
;
412
:
211
21
.
61.
Hadad
SM
,
Hardie
DG
,
Appleyard
V
,
Thompson
AM
. 
Effects of metformin on breast cancer cell proliferation, the AMPK pathway and the cell cycle
.
Clin Transl Oncol
2014
;
16
:
746
52
.
62.
Lea
MA
,
Pourat
J
,
Patel
R
,
desBordes
C
. 
Growth inhibition of colon cancer cells by compounds affecting AMPK activity
.
World J Gastrointest Oncol
2014
;
6
:
244
52
.
63.
Choudhury
Y
,
Yang
Z
,
Ahmad
I
,
Nixon
C
,
Salt
IP
,
Leung
HY
. 
AMP-activated protein kinase (AMPK) as a potential therapeutic target independent of PI3K/Akt signaling in prostate cancer
.
Oncoscience
2014
;
1
:
446
56
.
64.
Lee
KH
,
Hsu
EC
,
Guh
JH
,
Yang
HC
,
Wang
D
,
Kulp
SK
, et al
Targeting energy metabolic and oncogenic signaling pathways in triple-negative breast cancer by a novel adenosine monophosphate-activated protein kinase (AMPK) activator
.
J Biol Chem
2011
;
286
:
39247
58
.
65.
Zadra
G
,
Photopoulos
C
,
Tyekucheva
S
,
Heidari
P
,
Weng
QP
,
Fedele
G
, et al
A novel direct activator of AMPK inhibits prostate cancer growth by blocking lipogenesis
.
EMBO Mol Med
2014
;
6
:
519
38
.
66.
Jurmeister
S
,
Ramos-Montoya
A
,
Neal
DE
,
Fryer
LG
. 
Transcriptomic analysis reveals inhibition of androgen receptor activity by AMPK in prostate cancer cells
.
Oncotarget
2014
;
5
:
3785
99
.
67.
Shen
M
,
Zhang
Z
,
Ratnam
M
,
Dou
QP
. 
The interplay of AMP-activated protein kinase and androgen receptor in prostate cancer cells
.
J Cell Physiol
2014
;
229
:
688
95
.
68.
Valtorta
S
,
Nicolini
G
,
Tripodi
F
,
Meregalli
C
,
Cavaletti
G
,
Avezza
F
, et al
A novel AMPK activator reduces glucose uptake and inhibits tumor progression in a mouse xenograft model of colorectal cancer
.
Invest New Drugs
2014
;
32
:
1123
33
.
69.
Hawley
SA
,
Fullerton
MD
,
Ross
FA
,
Schertzer
JD
,
Chevtzoff
C
,
Walker
KJ
, et al
The ancient drug salicylate directly activates AMP-activated protein kinase
.
Science
2012
;
336
:
918
22
.
70.
Davies
SP
,
Carling
D
,
Munday
MR
,
Hardie
DG
. 
Diurnal rhythm of phosphorylation of rat liver acetyl-CoA carboxylase by the AMP-activated protein kinase, demonstrated using freeze-clamping. Effects of high fat diets
.
Eur J Biochem
1992
;
203
:
615
23
.
71.
Park
HU
,
Suy
S
,
Danner
M
,
Dailey
V
,
Zhang
Y
,
Li
H
, et al
AMP-activated protein kinase promotes human prostate cancer cell growth and survival
.
Mol Cancer Ther
2009
;
8
:
733
41
.
72.
Tennakoon
JB
,
Shi
Y
,
Han
JJ
,
Tsouko
E
,
White
MA
,
Burns
AR
, et al
Androgens regulate prostate cancer cell growth via an AMPK-PGC-1alpha-mediated metabolic switch
.
Oncogene
2014
;
33
:
5251
61
.
73.
Hadad
SM
,
Baker
L
,
Quinlan
PR
,
Robertson
KE
,
Bray
SE
,
Thomson
G
, et al
Histological evaluation of AMPK signalling in primary breast cancer
.
BMC Cancer
2009
;
9
:
307
.
74.
Zhang
Y
,
Storr
SJ
,
Johnson
K
,
Green
AR
,
Rakha
EA
,
Ellis
IO
, et al
Involvement of metformin and AMPK in the radioresponse and prognosis of luminal versus basal-like breast cancer treated with radiotherapy
.
Oncotarget
2014
;
5
:
12936
49
.
75.
Su
YW
,
Lin
YH
,
Pai
MH
,
Lo
AC
,
Lee
YC
,
Fang
IC
, et al
Association between phosphorylated AMP-activated protein kinase and acetyl-CoA carboxylase expression and outcome in patients with squamous cell carcinoma of the head and neck
.
PLoS One
2014
;
9
:
e96183
.
76.
Baba
Y
,
Nosho
K
,
Shima
K
,
Meyerhardt
JA
,
Chan
AT
,
Engelman
JA
, et al
Prognostic significance of AMP-activated protein kinase expression and modifying effect of MAPK3/1 in colorectal cancer
.
Br J Cancer
2010
;
103
:
1025
33
.
77.
Zulato
E
,
Bergamo
F
,
De Paoli
A
,
Griguolo
G
,
Esposito
G
,
De Salvo
GL
, et al
Prognostic significance of AMPK activation in advanced stage colorectal cancer treated with chemotherapy plus bevacizumab
.
Br J Cancer
2014
;
111
:
25
32
.
78.
Kang
BW
,
Jeong
JY
,
Chae
YS
,
Lee
SJ
,
Lee
YJ
,
Choi
JY
, et al
Phosphorylated AMP-activated protein kinase expression associated with prognosis for patients with gastric cancer treated with cisplatin-based adjuvant chemotherapy
.
Cancer Chemother Pharmacol
2012
;
70
:
735
41
.
79.
Kim
JG
,
Lee
SJ
,
Chae
YS
,
Kang
BW
,
Lee
YJ
,
Oh
SY
, et al
Association between phosphorylated AMP-activated protein kinase and MAPK3/1 expression and prognosis for patients with gastric cancer
.
Oncology
2013
;
85
:
78
85
.
80.
Zheng
L
,
Yang
W
,
Wu
F
,
Wang
C
,
Yu
L
,
Tang
L
, et al
Prognostic significance of AMPK activation and therapeutic effects of metformin in hepatocellular carcinoma
.
Clin Cancer Res
2013
;
19
:
5372
80
.
81.
William
WN
,
Kim
JS
,
Liu
DD
,
Solis
L
,
Behrens
C
,
Lee
JJ
, et al
The impact of phosphorylated AMP-activated protein kinase expression on lung cancer survival
.
Ann Oncol
2012
;
23
:
78
85
.
82.
Zupa
A
,
Improta
G
,
Silvestri
A
,
Pin
E
,
Deng
J
,
Aieta
M
, et al
A pilot characterization of human lung NSCLC by protein pathway activation mapping
.
J Thorac Oncol
2012
;
7
:
1755
66
.
83.
Nanjundan
M
,
Byers
LA
,
Carey
MS
,
Siwak
DR
,
Raso
MG
,
Diao
L
, et al
Proteomic profiling identifies pathways dysregulated in non–small cell lung cancer and an inverse association of AMPK and adhesion pathways with recurrence
.
J Thorac Oncol
2010
;
5
:
1894
904
.
84.
Li
C
,
Liu
VW
,
Chiu
PM
,
Yao
KM
,
Ngan
HY
,
Chan
DW
. 
Reduced expression of AMPK-beta1 during tumor progression enhances the oncogenic capacity of advanced ovarian cancer
.
Mol Cancer
2014
;
13
:
49
.
85.
Tsavachidou-Fenner
D
,
Tannir
N
,
Tamboli
P
,
Liu
W
,
Petillo
D
,
Teh
B
, et al
Gene and protein expression markers of response to combined antiangiogenic and epidermal growth factor targeted therapy in renal cell carcinoma
.
Ann Oncol
2010
;
21
:
1599
606
.
86.
Cancer Genome Atlas Research N
. 
Comprehensive molecular characterization of clear cell renal cell carcinoma
.
Nature
2013
;
499
:
43
9
.
87.
Bhandaru
M
,
Martinka
M
,
Li
G
,
Rotte
A
. 
Loss of AMPKalpha1 expression is associated with poor survival in melanoma patients
.
J Invest Dermatol
2014
;
134
:
1763
6
.
88.
Wangsa
D
,
Heselmeyer-Haddad
K
,
Ried
P
,
Eriksson
E
,
Schaffer
AA
,
Morrison
LE
, et al
Fluorescence in situ hybridization markers for prediction of cervical lymph node metastases
.
Am J Pathol
2009
;
175
:
2637
45
.
89.
Hoffman
AE
,
Demanelis
K
,
Fu
A
,
Zheng
T
,
Zhu
Y
. 
Association of AMP-activated protein kinase with risk and progression of non-Hodgkin lymphoma
.
Cancer Epidemiol Biomarkers Prev
2013
;
22
:
736
44
.
90.
Buckendahl
AC
,
Budczies
J
,
Fiehn
O
,
Darb-Esfahani
S
,
Kind
T
,
Noske
A
, et al
Prognostic impact of AMP-activated protein kinase expression in ovarian carcinoma: correlation of protein expression and GC/TOF-MS-based metabolomics
.
Oncol Rep
2011
;
25
:
1005
12
.
91.
Li
C
,
Liu
VW
,
Chiu
PM
,
Chan
DW
,
Ngan
HY
. 
Over-expressions of AMPK subunits in ovarian carcinomas with significant clinical implications
.
BMC Cancer
2012
;
12
:
357
.
92.
Vetvik
KK
,
Sonerud
T
,
Lindeberg
M
,
Luders
T
,
Storkson
RH
,
Jonsdottir
K
, et al
Globular adiponectin and its downstream target genes are up-regulated locally in human colorectal tumors: ex vivo and in vitro studies
.
Metabolism
2014
;
63
:
672
81
.
93.
Warden
SM
,
Richardson
C
,
O'Donnell
J
 Jr
,
Stapleton
D
,
Kemp
BE
,
Witters
LA
. 
Post-translational modifications of the beta-1 subunit of AMP-activated protein kinase affect enzyme activity and cellular localization
.
Biochem J
2001
;
354
:
275
83
.
94.
Vidal
AP
,
Andrade
BM
,
Vaisman
F
,
Cazarin
J
,
Pinto
LF
,
Breitenbach
MM
, et al
AMP-activated protein kinase signaling is upregulated in papillary thyroid cancer
.
Eur J Endocrinol
2013
;
169
:
521
8
.
95.
Huang
FY
,
Chiu
PM
,
Tam
KF
,
Kwok
YK
,
Lau
ET
,
Tang
MH
, et al
Semi-quantitative fluorescent PCR analysis identifies PRKAA1 on chromosome 5 as a potential candidate cancer gene of cervical cancer
.
Gynecol Oncol
2006
;
103
:
219
25
.
96.
Ros
S
,
Santos
CR
,
Moco
S
,
Baenke
F
,
Kelly
G
,
Howell
M
, et al
Functional metabolic screen identifies 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 as an important regulator of prostate cancer cell survival
.
Cancer Discov
2012
;
2
:
328
43
.
97.
Stevens
RJ
,
Ali
R
,
Bankhead
CR
,
Bethel
MA
,
Cairns
BJ
,
Camisasca
RP
, et al
Cancer outcomes and all-cause mortality in adults allocated to metformin: systematic review and collaborative meta-analysis of randomised clinical trials
.
Diabetologia
2012
;
55
:
2593
603
.
98.
Thakkar
B
,
Aronis
KN
,
Vamvini
MT
,
Shields
K
,
Mantzoros
CS
. 
Metformin and sulfonylureas in relation to cancer risk in type II diabetes patients: a meta-analysis using primary data of published studies
.
Metabolism
2013
;
62
:
922
34
.
99.
Franciosi
M
,
Lucisano
G
,
Lapice
E
,
Strippoli
GF
,
Pellegrini
F
,
Nicolucci
A
. 
Metformin therapy and risk of cancer in patients with type 2 diabetes: systematic review
.
PLoS One
2013
;
8
:
e71583
.
100.
Suissa
S
,
Azoulay
L
. 
Metformin and the risk of cancer: time-related biases in observational studies
.
Diabetes Care
2012
;
35
:
2665
73
.
101.
Gandini
S
,
Puntoni
M
,
Heckman-Stoddard
BM
,
Dunn
BK
,
Ford
L
,
DeCensi
A
, et al
Metformin and cancer risk and mortality: a systematic review and meta-analysis taking into account biases and confounders
.
Cancer Prev Res
2014
;
7
:
867
85
.
102.
Kim
YI
,
Kim
SY
,
Cho
SJ
,
Park
JH
,
Choi
IJ
,
Lee
YJ
, et al
Long-term metformin use reduces gastric cancer risk in type 2 diabetics without insulin treatment: a nationwide cohort study
.
Aliment Pharmacol Ther
2014
;
39
:
854
63
.
103.
Preston
MA
,
Riis
AH
,
Ehrenstein
V
,
Breau
RH
,
Batista
JL
,
Olumi
AF
, et al
Metformin use and prostate cancer risk
.
Eur Urol
2014
;
66
:
1012
20
.
104.
Tsilidis
KK
,
Capothanassi
D
,
Allen
NE
,
Rizos
EC
,
Lopez
DS
,
van Veldhoven
K
, et al
Metformin does not affect cancer risk: a cohort study in the U.K. Clinical Practice Research Datalink analyzed like an intention-to-treat trial
.
Diabetes Care
2014
;
37
:
2522
32
.
105.
Luo
J
,
Beresford
S
,
Chen
C
,
Chlebowski
R
,
Garcia
L
,
Kuller
L
, et al
Association between diabetes, diabetes treatment and risk of developing endometrial cancer
.
Br J Cancer
2014
;
111
:
1432
9
.
106.
Mamtani
R
,
Pfanzelter
N
,
Haynes
K
,
Finkelman
BS
,
Wang
X
,
Keefe
SM
, et al
Incidence of bladder cancer in patients with type 2 diabetes treated with metformin or sulfonylureas
.
Diabetes Care
2014
;
37
:
1910
7
.
107.
Margel
D
,
Urbach
DR
,
Lipscombe
LL
,
Bell
CM
,
Kulkarni
G
,
Austin
PC
, et al
Metformin use and all-cause and prostate cancer-specific mortality among men with diabetes
.
J Clin Oncol
2013
;
31
:
3069
75
.
108.
He
XX
,
Tu
SM
,
Lee
MH
,
Yeung
SC
. 
Thiazolidinediones and metformin associated with improved survival of diabetic prostate cancer patients
.
Ann Oncol
2011
;
22
:
2640
5
.
109.
Wu
W
,
Merriman
K
,
Nabaah
A
,
Seval
N
,
Seval
D
,
Lin
H
, et al
The association of diabetes and anti-diabetic medications with clinical outcomes in multiple myeloma
.
Br J Cancer
2014
;
111
:
628
36
.
110.
Currie
CJ
,
Poole
CD
,
Jenkins-Jones
S
,
Gale
EA
,
Johnson
JA
,
Morgan
CL
. 
Mortality after incident cancer in people with and without type 2 diabetes: impact of metformin on survival
.
Diabetes Care
2012
;
35
:
299
304
.
111.
Ko
EM
,
Walter
P
,
Jackson
A
,
Clark
L
,
Franasiak
J
,
Bolac
C
, et al
Metformin is associated with improved survival in endometrial cancer
.
Gynecol Oncol
2014
;
132
:
438
42
.
112.
Nevadunsky
NS
,
Van Arsdale
A
,
Strickler
HD
,
Moadel
A
,
Kaur
G
,
Frimer
M
, et al
Metformin use and endometrial cancer survival
.
Gynecol Oncol
2014
;
132
:
236
40
.
113.
Rieken
M
,
Xylinas
E
,
Kluth
L
,
Crivelli
JJ
,
Chrystal
J
,
Faison
T
, et al
Association of diabetes mellitus and metformin use with oncological outcomes of patients with non-muscle-invasive bladder cancer
.
BJU Int
2013
;
112
:
1105
12
.
114.
Rieken
M
,
Xylinas
E
,
Kluth
L
,
Crivelli
JJ
,
Chrystal
J
,
Faison
T
, et al
Effect of diabetes mellitus and metformin use on oncologic outcomes of patients treated with radical cystectomy for urothelial carcinoma
.
Urol Oncol
2014
;
32
:
49
e7–14
.
115.
Peeters
PJ
,
Bazelier
MT
,
Vestergaard
P
,
Leufkens
HG
,
Schmidt
MK
,
de Vries
F
, et al
Use of metformin and survival of diabetic women with breast cancer
.
Curr Drug Saf
2013
;
8
:
357
63
.
116.
He
X
,
Esteva
FJ
,
Ensor
J
,
Hortobagyi
GN
,
Lee
MH
,
Yeung
SC
. 
Metformin and thiazolidinediones are associated with improved breast cancer-specific survival of diabetic women with HER2+ breast cancer
.
Ann Oncol
2012
;
23
:
1771
80
.
117.
Allott
EH
,
Abern
MR
,
Gerber
L
,
Keto
CJ
,
Aronson
WJ
,
Terris
MK
, et al
Metformin does not affect risk of biochemical recurrence following radical prostatectomy: results from the SEARCH database
.
Prostate Cancer Prostatic Dis
2013
;
16
:
391
7
.
118.
Kaushik
D
,
Karnes
RJ
,
Eisenberg
MS
,
Rangel
LJ
,
Carlson
RE
,
Bergstralh
EJ
. 
Effect of metformin on prostate cancer outcomes after radical prostatectomy
.
Urol Oncol
2014
;
32
:
43
e1–7
.
119.
Lega
IC
,
Austin
PC
,
Gruneir
A
,
Goodwin
PJ
,
Rochon
PA
,
Lipscombe
LL
. 
Association between metformin therapy and mortality after breast cancer: a population-based study
.
Diabetes Care
2013
;
36
:
3018
26
.
120.
Bayraktar
S
,
Hernadez-Aya
LF
,
Lei
X
,
Meric-Bernstam
F
,
Litton
JK
,
Hsu
L
, et al
Effect of metformin on survival outcomes in diabetic patients with triple receptor-negative breast cancer
.
Cancer
2012
;
118
:
1202
11
.
121.
Mitsuhashi
A
,
Kiyokawa
T
,
Sato
Y
,
Shozu
M
. 
Effects of metformin on endometrial cancer cell growth in vivo: a preoperative prospective trial
.
Cancer
2014
;
120
:
2986
95
.
122.
Schuler
KM
,
Rambally
BS
,
DiFurio
MJ
,
Sampey
BP
,
Gehrig
PA
,
Makowski
L
, et al
Antiproliferative and metabolic effects of metformin in a preoperative window clinical trial for endometrial cancer
.
Cancer Med
2015
;
4
:
161
73
.
123.
Laskov
I
,
Drudi
L
,
Beauchamp
MC
,
Yasmeen
A
,
Ferenczy
A
,
Pollak
M
, et al
Anti-diabetic doses of metformin decrease proliferation markers in tumors of patients with endometrial cancer
.
Gynecol Oncol
2014
;
134
:
607
14
.
124.
Joshua
AM
,
Zannella
VE
,
Downes
MR
,
Bowes
B
,
Hersey
K
,
Koritzinsky
M
, et al
A pilot ‘window of opportunity’ neoadjuvant study of metformin in localised prostate cancer
.
Prostate Cancer Prostatic Dis
2014
;
17
:
252
8
.
125.
Kwong
SC
,
Brubacher
J
. 
Phenformin and lactic acidosis: a case report and review
.
J Emerg Med
1998
;
16
:
881
6
.
126.
Pernicova
I
,
Korbonits
M
. 
Metformin–mode of action and clinical implications for diabetes and cancer
.
Nat Rev Endocrinol
2014
;
10
:
143
56
.
127.
Knapen
LM
,
Dittrich
ST
,
de Vries
F
,
Starup-Linde
J
,
Vestergaard
P
,
Henry
RM
, et al
Use of biguanides and the risk of colorectal cancer: a register-based cohort study
.
Curr Drug Saf
2013
;
8
:
349
56
.
128.
Algra
AM
,
Rothwell
PM
. 
Effects of regular aspirin on long-term cancer incidence and metastasis: a systematic comparison of evidence from observational studies versus randomised trials
.
Lancet Oncol
2012
;
13
:
518
27
.
129.
Rothwell
PM
,
Price
JF
,
Fowkes
FG
,
Zanchetti
A
,
Roncaglioni
MC
,
Tognoni
G
, et al
Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials
.
Lancet
2012
;
379
:
1602
12
.
130.
Rothwell
PM
,
Wilson
M
,
Price
JF
,
Belch
JF
,
Meade
TW
,
Mehta
Z
. 
Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials
.
Lancet
2012
;
379
:
1591
601
.
131.
Fraser
DM
,
Sullivan
FM
,
Thompson
AM
,
McCowan
C
. 
Aspirin use and survival after the diagnosis of breast cancer: a population-based cohort study
.
Br J Cancer
2014
;
111
:
623
7
.
132.
Holmes
MD
,
Chen
WY
,
Li
L
,
Hertzmark
E
,
Spiegelman
D
,
Hankinson
SE
. 
Aspirin intake and survival after breast cancer
.
J Clin Oncol
2010
;
28
:
1467
72
.
133.
McCowan
C
,
Munro
AJ
,
Donnan
PT
,
Steele
RJ
. 
Use of aspirin post-diagnosis in a cohort of patients with colorectal cancer and its association with all-cause and colorectal cancer specific mortality
.
Eur J Cancer
2013
;
49
:
1049
57
.
134.
Reimers
MS
,
Bastiaannet
E
,
van Herk-Sukel
MP
,
Lemmens
VE
,
van den Broek
CB
,
van de Velde
CJ
, et al
Aspirin use after diagnosis improves survival in older adults with colon cancer: a retrospective cohort study
.
J Am Geriatr Soc
2012
;
60
:
2232
6
.
135.
Liao
X
,
Lochhead
P
,
Nishihara
R
,
Morikawa
T
,
Kuchiba
A
,
Yamauchi
M
, et al
Aspirin use, tumor PIK3CA mutation, and colorectal-cancer survival
.
N Engl J Med
2012
;
367
:
1596
606
.
136.
Walker
AJ
,
Grainge
MJ
,
Card
TR
. 
Aspirin and other non-steroidal anti-inflammatory drug use and colorectal cancer survival: a cohort study
.
Br J Cancer
2012
;
107
:
1602
7
.
137.
Bastiaannet
E
,
Sampieri
K
,
Dekkers
OM
,
de Craen
AJ
,
van Herk-Sukel
MP
,
Lemmens
V
, et al
Use of aspirin postdiagnosis improves survival for colon cancer patients
.
Br J Cancer
2012
;
106
:
1564
70
.
138.
Chia
WK
,
Ali
R
,
Toh
HC
. 
Aspirin as adjuvant therapy for colorectal cancer–reinterpreting paradigms
.
Nat Rev Clin Oncol
2012
;
9
:
561
70
.
139.
Choe
KS
,
Cowan
JE
,
Chan
JM
,
Carroll
PR
,
D'Amico
AV
,
Liauw
SL
. 
Aspirin use and the risk of prostate cancer mortality in men treated with prostatectomy or radiotherapy
.
J Clin Oncol
2012
;
30
:
3540
4
.
140.
Flahavan
EM
,
Bennett
K
,
Sharp
L
,
Barron
TI
. 
A cohort study investigating aspirin use and survival in men with prostate cancer
.
Ann Oncol
2014
;
25
:
154
9
.
141.
Cardwell
CR
,
Flahavan
EM
,
Hughes
CM
,
Coleman
HG
,
O'Sullivan
JM
,
Powe
DG
, et al
Low-dose aspirin and survival in men with prostate cancer: a study using the UK Clinical Practice Research Datalink
.
Cancer Causes Control
2014
;
25
:
33
43
.
142.
Dhillon
PK
,
Kenfield
SA
,
Stampfer
MJ
,
Giovannucci
EL
,
Chan
JM
. 
Aspirin use after a prostate cancer diagnosis and cancer survival in a prospective cohort
.
Cancer Prev Res
2012
;
5
:
1223
8
.
143.
Holmes
MD
,
Olsson
H
,
Pawitan
Y
,
Holm
J
,
Lundholm
C
,
Andersson
TM
, et al
Aspirin intake and breast cancer survival – a nation-wide study using prospectively recorded data in Sweden
.
BMC Cancer
2014
;
14
:
391
.
144.
Cardwell
CR
,
Kunzmann
AT
,
Cantwell
MM
,
Hughes
C
,
Baron
JA
,
Powe
DG
, et al
Low-dose aspirin use after diagnosis of colorectal cancer does not increase survival: a case–control analysis of a population-based cohort
.
Gastroenterology
2014
;
146
:
700
8
e2
.