Mechanisms of AT101 [(-)-gossypol] induced cytotoxicity in malignant peripheral nerve sheath tumors.

摘要

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive Schwann cell-derived sarcomas and are the leading cause of mortality in patients with neurofibromatosis type 1 (NF1). Current treatment modalities have been largely ineffective resulting in a high rate of MPNST recurrence and poor five year patient survival. This necessitates the exploration of alternative chemotherapeutic options for MPNST patients. By evading apoptosis and utilizing protective mechanisms such as autophagy, cancer cells develop resistance to chemo- and radio-therapy. The overall goal of my thesis studies is to evaluate chemotherapeutic agents that can modulate both apoptosis and autophagy, thus target both cell death pathways and cell survival mechanisms. BH3 mimetics are a novel class of drugs that can induce both apoptosis and autophagy and thus can be effective in MPNST therapy. My studies elucidate the cytotoxic mechanisms of AT101 [(-)-gossypol], a BH3 mimetic, in MPNSTs and further identify key modulators and pathways involved. These studies aim to advance the current knowledge about this new drug and how to harness its cytotoxic capabilities to formulate effective chemotherapy for MPNSTs.;Since MPNSTs overexpress anti-apoptotic BCL2 proteins which mediate resistance to chemotherapy, my studies sought to assess the effect of the AT101 on MPNST cells in vitro. My studies demonstrate that AT101 caused caspase-independent MPNST cell death, which was mediated in part by cytotoxic autophagy and HIF-1alpha induced expression of the atypical BH3-only protein BNIP3. These effects were mediated by intracellular iron chelation, a previously unreported mechanism of AT101 cytotoxicity. Additionally, I also found that AT101 could modulate the CXCL12/CXCR4 autocrine signaling axis in MPNSTs. Recent studies have shown that MPNST cells express CXCL12 and utilize it in an autocrine fashion to promote survival and proliferation. Therefore, the CXCL12-CXCR4 signaling pathway is a viable target for chemotherapy in MPNSTs. My studies also demonstrate that by suppressing CXCL12 expression and downregulating its downstream mediators, cyclin D1 and beta-catenin, AT101 can significantly inhibit proliferation of MPNST cells. These novel properties of AT101 along with its significant effect on MPNST cell proliferation and cell death suggest that it may be particularly effective in these hard to treat tumors.