MFTZ-1 regulates both constitutive and inducible HIF-1α accumulation at translational level via targeting Akt and MAPK

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The macrolide compound 14-ethyl-2,5,11-trimethyl-4,13,19,20-tetraoxa-Tricyclo [14.2.1.1^7,10]eicosane-3, 12-dione (MFTZ-1) has been identified as a novel topoisomerase II (Top2) inhibitor with potent in vitro and in vivo anti-tumor activities (Xie et al, Mol Cancer Ther, in press). We further found that MFTZ-1 exhibited potent antiangiogenesis. In this study, we aimed to elucidate the possible mechanisms involved in this critical event. Western blot analyses showed that MFTZ-1 at subcytotoxic concentrations reduced HIF-1α protein accumulation driven by hypoxia, or epidermal growth factor (EGF) or insulin-like growth factor-1 (IGF-1) in human breast cancer MDA-MB-231 cells. We also repeated the result under hypoxic conditions in a panel of cell lines originated from different tissues. Further studies demonstrated that MFTZ-1 drove HIF-1α accumulation neither via degradation pathway nor at its transcriptional level. Rather, MFTZ-1 apparently inhibited constitutive and inducible activation of both Akt and p42/p44 MAPK pathway in MDA-MB-231 cells exposed to either hypoxia, EGF or IGF-1, which subsequently caused a marked reduction of downstream phosph-4EBP and phosph-p70s6k. All these suggest that MFTZ-1’s antagonism against cellular accumulation of HIF-1α is regulated at the translational level. Moreover, MFTZ-1 dramatically diminished the constitutive and inducible secretion of VEGF of MDA-MB-231 cells. MFTZ-1 abrogated the HIF-1α-driven transcription of VEGF mRNA and removed the increase in hypoxia-induced VEGF secretion. On the other hand, MFTZ-1 also lowered the basal level of VEGF secretion in normoxia and hypoxia. Therefore, MFTZ-1 is capable of combating both constitutive, HIF-1α-independent and inducible, HIF-1α-dependent VEGF secretion. As a consequence, MFTZ-1 disrupted the tube formation of human umbilical vein endothelial cells (HUVEC) under hypoxia with low-concentration serum or normoxia with high-concentration serum, and inhibited HUVEC cells migration and microvessel outgrowth from rat aortic ring under normoxia. All these favor the potent anti-angiogenic impact of MFTZ-1 under different conditions. Collectively, our findings, together with its Top2-involved anti-tumor activities, highlight the importance of MFTZ-1 as a promising lead molecule in cancer therapy.