Abstract 605: Apogossypolone Derivative -BI97D6 Effectively Targets MCL1 Overexpressing Acute Myeloid Leukemia Cells.

Abstract Aberrant expression of anti-apoptotic proteins such as BCL2, MCL1, and BCL-XL is observed in many tumors including Acute Myeloid Leukemia (AML). An obvious strategy for AML therapy would be to target the anti-apoptotic BCL2 family members. While compounds such as ABT-737 have shown promise for treatment of some malignancies, the compound binds poorly to MCL1 and thus cells that overexpress MCL1 usually display high resistance to the drug. Furthermore, ABT-737 activates ERK signaling resulting in MCL1 overexpression in surviving cells (Konopleva, et al, Leukemia 2011). The apogossypolone derivative -BI97D6 binds MCL1 and BCL2, BCL-XL, BFL1 with high affinities (Wei, et al, J Med Chem 2010). We recently reported that -BI97D6 (a) efficiently kills AML cell lines even in the presence of protective mesenchymal stroma cells, (b) interferes with the association between MCL1/BIM and BCL2/BAX, (c) stimulates BAX conformational change, (d) requires BAX or BAK for cell killing, and (e) does not induce ER stress. These data suggests that -BI97D6, unlike other gossypol or apogossypol compounds, acts mainly as a BH3 mimetic. In the current study, we first examined the role of MCL1 in -BI97D6-mediated killing. OCI-AML3 cells are extremely resistant to ABT-737 due to its high expression of MCL1. MCL1 expression was suppressed by lenti-viral shRNA in OCI-AML3 cells and knockdown of MCL1 protein by 80% was achieved as determined by quantitative western blot. Compared to cells with non-specific control shRNA, cells with MCL1 shRNA were greatly sensitized to ABT-737, and significantly sensitized to AraC, while -BI97D6, which binds MCL1 with high affinity, is almost equipotent in knockdown and control cells. Since results with AML cell lines have been promising, we examined the efficacy of -BI97D6 on primary AML samples. Flow cytometry analysis revealed that -BI97D6 potently induced apoptosis in AML blast cells at low nM concentration (EC50<50nM). -BI97D6 also effectively killed putative CD34+CD38- leukemia stem cells (LSC). Importantly, primary AML with FLT3-ITD and FLT3-D835 mutations showed similar sensitivity as those without FLT3 mutations (EC50<50nM). As FLT3 mutations are associated with poor prognosis in AML, these findings suggests that -BI97D6 can target AML LSC and could benefit even high risk patients. In summary, compound -BI97D6 may be a promising drug candidate for MCL1-targeted AML therapy. Citation Format: Rongqing Pan, Vivian Ruvolo, Maurizio Pellecchia, Jun Wei, Marina Konopleva, John C. Reed, Peter Ruvolo, Michael Andreeff. Apogossypolone derivative -BI97D6 effectively targets MCL1 overexpressing Acute Myeloid Leukemia cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 605. doi:10.1158/1538-7445.AM2013-605