Fatty acid synthase inhibition activates AMP-activated protein kinase in SKOV3 human ovarian cancer cells Free

4465

Fatty acid synthase (FAS), catalyzes the reductive de novo synthesis of fatty acids utilizing malonyl-CoA, acetyl-CoA, and NADPH as substrates. FAS is highly expressed in ovarian cancers and most common human carcinomas. Recently, AMP-activated protein kinase (AMPK) has been shown to play a role in cancer development as the kinase that phosphorylates and activates AMPK is LKB-1, the Peutz-Jegher tumor suppressor gene. AMPK is activated in cells as a response to metabolic stresses that lead to the depletion of cellular ATP levels and thus increase the AMP/ATP ratio. AMPK is a heterotrimeric complex consisting of a catalytic subunit α1 or α2, and regulatory β and γ subunits which function as a serine/threonine kinase. Once activated by phosphorylation, AMPK inactivates anabolic biosynthetic enzymes for cholesterol synthesis such as HMG-CoA reductase, and for fatty synthesis such as acetyl-CoA carboxylase (ACC), curbing ATP utilization. Concomitantly, AMPK stimulates catabolic processes which enhance ATP production such as glucose uptake, glycolysis, and fatty acid oxidation. Both inhibition of FAS or activation of AMP-activated protein kinase (AMPK) has been shown to be cytotoxic to human cancer cells in vitro and in vivo. In this study, we explore the cytotoxic mechanism of action of FAS inhibition and show that C93, a synthetic FAS inhibitor, increases the AMP/ATP ratio activating AMPK in SKOV3 human ovarian cancer cells leading to cytotoxicity. As a physiological consequence of AMPK activation in the SKOV3 cells following C93 treatment, acetyl-CoA carboxylase (ACC), the rate limiting enzyme of fatty acid synthesis, was phosphorylated and inhibited while glucose oxidation was increased. Despite these attempts to conserve energy, the AMP/ATP ratio increased with worsening cellular redox status in the cancer cells. Pretreatment of SKOV3 cells with Compound C, an AMPK inhibitor, substantially rescued the cells from C93 cytotoxicity indicating its dependence on AMPK activation. TOFA, an ACC inhibitor did not activate AMPK despite inhibiting fatty acid synthesis pathway activity, and was not significantly cytotoxic to SKOV3 cells. This indicates that substrate accumulation from FAS inhibition triggering AMPK activation, not end-product depletion of fatty acids, are likely responsible for AMPK activation. C93 also exhibited significant anti-tumor activity and apoptosis against SKOV3 xenografts in athymic mice without significant weight loss or cytotoxicity to proliferating cellular compartments such as bone marrow, gastrointestinal tract or skin. Thus, pharmacological FAS inhibition selectively activates AMPK in ovarian cancer cells inducing cytotoxicity, while sparing the pleiotropic effects of AMPK activation in most normal human tissues.