Lipoic acid decreases Mcl-1, Bcl-xL and up regulates Bim on ovarian carcinoma cells leading to cell death.

BACKGROUND: Ovarian carcinoma is the leading cause of death from gynecological cancer because there is risk of chemoresistance. As previously demonstrated in our laboratory, Alpha-lipoic acid (LA), a co-factor for metabolic enzymes, suppresses the tumor growth. In this study, we have researched the mechanisms that are responsible for the activity of LA. METHODS: We have studied the mechanisms of LA in two ovarian cancer cell lines, a cisplatin sensitive one, IGROV1 and its resistant counterpart, IGROV1-R10. These cells have been exposed to lipoic acid at various concentrations. Cell proliferation, cell cycle repartition and nuclear staining with DAPI were recorded. Western blot analyses were performed to detect various proteins implied in apoptotic cell death pathways. To investigate the formation of ROS, the oxidation of CM-DCFH2-DA were also determined. FINDINGS: LA suppressed growth proliferation and induced apoptosis in both ovarian cell lines. Moreover, LA provoked a down regulation of two anti-apoptotic proteins, Mcl-1 and Bcl-xL protein and a strong induction of the BH3-only protein Bim. Furthermore, LA induced ROS generation which could be involved in the CHOP induction which is known to activate the Bim translation. CONCLUSIONS: Our results reveal novel actions of LA which could explain the anti-tumoral effects of the LA. Therefore, LA seems to be a promising compound for ovarian cancer treatment.

The metabolic cooperation between cells in solid cancer tumors.

Cancer cells cooperate with stromal cells and use their environment to promote tumor growth. Energy production depends on nutrient availability and O2 concentration. Well-oxygenated cells are highly proliferative and reorient the glucose metabolism towards biosynthesis, whereas glutamine oxidation replenishes the TCA cycle coupled with OXPHOS-ATP production. Glucose, glutamine and alanine transformations sustain nucleotide and fatty acid synthesis. In contrast, hypoxic cells slow down their proliferation, enhance glycolysis to produce ATP and reject lactate which is recycled as fuel by normoxic cells. Thus, glucose is spared for biosynthesis and/or for hypoxic cell function. Environmental cells, such as fibroblasts and adipocytes, serve as food donors for cancer cells, which reject waste products (CO2 , H⁺, ammoniac, polyamines…) promoting EMT, invasion, angiogenesis and proliferation. This metabolic-coupling can be considered as a form of commensalism whereby non-malignant cells support the growth of cancer cells. Understanding these cellular cooperations within tumors may be a source of inspiration to develop new anti-cancer agents.

Inhibition of Mcl-1 expression by citrate enhances the effect of Bcl-xL inhibitors on human ovarian carcinoma cells.

The inhibition of two major anti-apoptotic proteins, Bcl-xL and Mcl-1, appears essential to destroy chemoresistant cancer cells. We have studied their concomitant inhibition, using ABT 737 or siRNA targeting XL1 and citrate, a molecule which reduces the expression level of Mcl-1.Two cisplatin-chemoresistant ovarian cell lines (SKOV3 and IGROV1-R10) were exposed to ABT 737 or siRNA targeting XL1 and citrate at various individual concentrations, or combined. Cell proliferation, cell cycle repartition and nuclear staining with DAPI were recorded. Western blot analyses were performed to detect various proteins implied in apoptotic cell death pathways.Mcl-1 expression was barely reduced when cells were exposed to citrate alone, whereas a mild reduction was observed after ABT 737 treatment. Concomitant inhibition of Bcl-xL and Mcl-1 using ABT 737 or siXL1 associated with citrate was far more effective in inhibiting cell proliferation and inducing cell death than treatment alone.Given that few, if any, specific inhibitors of Mcl-1 are currently available, anti-glycolytic agents such as citrate could be tested in association with synthetic inhibitors of Bcl-xL.