MCL-1 and BCL-xL-dependent resistance to the BCL-2 inhibitor ABT-199 can be overcome by preventing PI3K/AKT/mTOR activation in lymphoid malignancies

Abstract

Overexpression of anti-apoptotic BCL-2 family members is a hallmark of many lymphoid malignancies, including chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) that can be targeted with small molecule inhibitors. ABT-199 is a rationally designed BCL-2 homology (BH)-3 mimetic that specifically binds to BCL-2, but not to MCL-1 and BCL-xL. Although the thrombocytopenia that occurs with navitoclax treatment has not been a problem with ABT-199, clinical trials in CLL could benefit by lowering the ABT-199 concentration through targeting other survival pathways. In this study, we investigated the mechanisms of resistance that develops to ABT-199 therapy by generating ABT-199-resistant (ABT199-R) cell lines via chronic exposure of NHL cell lines to ABT-199. Acquired resistance resulted in substantial AKT activation and upregulation of MCL-1 and BCL-xL levels that sequestered BIM. ABT199-R cells exhibited increased MCL-1 stability and failed to activate BAX in response to ABT-199. The ABT-199 acquired and inherent resistant cells were sensitized to treatment with ABT-199 by inhibitors of the PI3K, AKT, and mTOR pathways, NVP-BEZ235 and GS-1101. NVP-BEZ235, a dual inhibitor of p-AKT and mTOR, reduced MCL-1 levels causing BIM release from MCL-1 and BCL-xL, thus leading to cell death by BAX activation. The PI3Kδ inhibitor GS-1101 (idelalisib) downregulated MCL-1 and sensitized ABT199-R cells through AKT-mediated BAX activation. A genetic approach, through siRNA-mediated down-regulation of AKT, MCL-1, and BCL-xL, significantly decreased cell survival, demonstrating the importance of these cell survival factors for ABT-199 resistance. Our findings suggest a novel mechanism that modulates the expression and activity of pro-survival proteins to confer treatment resistance that could be exploited by a rational combination therapeutic regimen that could be effective for treating lymphoid malignancies.

Development of venetoclax for therapy of lymphoid malignancies

“…Similarly, targeted agents that impact on MCL-1 expression through phosphatidylinositol 3-kinase (PI3K) or mammalian target of rapamycin kinase (mTOR), such as idelalisib 10 or NVP-BEZ235, were also effective. 51 We found that increased BCL-xL expression was inversely correlated with that of miR-377 in ABT-199-resistant DLBCL cell lines and that high BCL-xL/low miR-377 expression conferred resistance to venetoclax in CLL patients. 52 Using a hypomethylating agent, 5-azacytidine restored the response by increasing levels of miR-377 and, as a consequence, decreasing levels of BCL-xL.…”

“…50 Our previous study showed that acquired resistance could be obtained after chronic exposure to venetoclax in DLBCL cell lines, resulting in substantial AKT activation and upregulation of MCL-1 and BCL-xL levels that sequestered BIM (Figure 1). 51 Importantly, genetic suppression of AKT, BCL-xL, or MCL-1 could restore sensitivity to venetoclax. Similarly, targeted agents that impact on MCL-1 expression through phosphatidylinositol 3-kinase (PI3K) or mammalian target of rapamycin kinase (mTOR), such as idelalisib 10 or NVP-BEZ235, were also effective.…”

“…51 Another study also showed that BEZ235 could synergize with venetoclax by an alternative mechanism, by inducing the accumulation of BAD and BIM in DLBCL cells. 68 In another study, cerdulatinib, a dual SYK/JAK inhibitor, was shown to induce apoptosis of CLL cells following inhibition of the BCR/IL-4 signaling pathways and could thus overcome nurse-like cell or anti-IgM/CD40L + IL-4-mediated protection in CLL primary cells from patients.…”

Restraining FOXO3-dependent transcriptional BMF activation underpins tumour growth and metastasis of E-cadherin-negative breast cancer

“…42,43 Recent studies indicated that BH3-mimetics can be used to treat nonlymphoid cancers but mostly in combination with oestrogen antagonists, proteasome inhibitors, specific PI3K-mTOR inhibitors or chemotherapy. 24,[44][45][46][47][48][49] As previous findings from our laboratory demonstrated that E-cadherin-negative lobular breast cancer depends on p120-catenin-mediated activation of RhoA, Rock and subsequent actomyosin contraction, 26 we anticipate that dual inhibition of these pathways might be successful in E-cadherin-negative cancers that are not driven by oncogenic activation of GFR pathways. Although we do not yet know whether RhoA-Rock signals converge onto the GFR-AKT-FOXO axis in the regulation of anoikis resistance, the fact that FOXO expression had no effect on survival of B-RAF/KRAS-mutated MDA-MB-231 cells seems to be in line with this assumption.…”

Targeting BET proteins improves the therapeutic efficacy of BCL-2 inhibition in T-cell acute lymphoblastic leukemia

“…Nevertheless, venetoclax sensitivity is variable between different T-ALL patient samples and the emergence of resistance to venetoclax (11)(12)(13) as well as the occurrence of dose-limiting toxicities (14) provides a rationale for the evaluation of venetoclax as part of a combination therapy.…”