Impact of elevated anti-apoptotic MCL-1 and BCL-2 on the development and treatment of MLL-AF9 AML in mice

Abstract

Many acute myeloid leukaemias (AMLs) express high levels of BCL-2 and MCL-1, especially after therapy. To test the impact of these anti-apoptotic proteins on AML development and treatment, we used haemopoietic reconstitution to generate MLL-AF9 AMLs expressing BCL-2 or Mcl-1 transgenes. AMLs with elevated BCL-2 or MCL-1 had a higher proportion of mature myeloid cells but, like conventional MLL-AF9 AMLs, were readily transplantable. Short-term cell lines established from multiple primary AMLs of each genotype were tested in vitro for susceptibility to chemotherapeutics currently used for treating AML (daunorubicin, etoposide, cytarabine); the proteasome inhibitor bortezomib; CDK7/9 inhibitors; and BH3 mimetics, which bind and inhibit pro-survival proteins. The BH3 mimetics tested, alone and in combination with the other drugs, were: ABT-737 which, like its clinical counterpart navitoclax, targets BCL-2, BCL-XL and BCL-W; BCL-2-specific ABT-199 (venetoclax); BCL-XL-specific A-1331852; and S63845, a new MCL-1-specific BH3 mimetic. As single agents, daunorubicin and bortezomib had the greatest efficacy. Elevated MCL-1 or BCL-2 reduced sensitivity to daunorubicin but, surprisingly, not to bortezomib. MCL-1 markedly enhanced resistance to ABT-737 and ABT-199 but not S63845, and BCL-2 increased resistance to S63845 but not to ABT-737 or ABT-199. Notable synergies were achieved by combining BH3 mimetics with daunorubicin: S63845 increased the sensitivity of both MCL-1 and BCL-2 overexpressing MLL-AF9 AMLs, and ABT-737 aided in killing those overexpressing BCL-2. Synergy between daunorubicin and ABT-199 was also apparent in vivo, although not curative. Impressive synergistic responses were achieved for human MLL-fusion AML cell lines treated with daunorubicin plus either ABT-737, ABT-199 or S63845, and with ABT-199 plus S63845, with or without daunorubicin. Our data suggest that AML patients may benefit from combining conventional cytotoxic drugs with BH3 mimetics targeting BCL-2 or MCL-1 or, if tolerated, both these agents.

Leukemic IL‐17RB signaling regulates leukemic survival and chemoresistance

“…We observed that the IL-17B-IL-17RB axis can be specifically induced by Ara-C. Our data support the strategy of targeting the IL-17B-IL-17RB axis to overcome chemoresistance in AML, and suppression of IL-17B or IL-17RB is accompanied by a modulation of bcl-2 family proteins that prime the cell for apoptosis after chemotherapy. In agreement with this observation, recent studies have demonstrated that inhibition of bcl-2 family proteins render AML cells more susceptible to chemotherapeutic agents (49,50). However, bcl-2 family proteins are essential for survival and function during many important developmental process (51)(52)(53)(54), and inhibition of bcl-2 may have an unacceptable side effect.…”

Ubiquitination and deubiquitination of MCL1 in cancer: deciphering chemoresistance mechanisms and providing potential therapeutic options

“…The sudden emergence of effective MCL1 inhibitors has broadened the horizon for strategies used to target MCL1, and studies have also confirmed the efficacy of using MCL1 inhibitors in combination with other BCL-2 family inhibitors 98 , 102 – 104 . Several MCL1 inhibitors, including S63845 95 , AMG 176 96 , AZD5991 97 , S64315 105 , and AMG 397 ( https://clinicaltrials.gov ), are already being investigated in the clinical stage, and the future of their application in the treatment of chemoresistance is encouraging.…”

Targeting Bim via a lncRNA Morrbid Regulates the Survival of Preleukemic and Leukemic Cells

“…Indeed, venetoclax (ABT-199), an oral BCL-2 inhibitor, has been approved for the treatment of chronic lymphocytic leukemia and elderly patients with AML ( DiNardo et al, 2019 ). Similarly, inhibition of MCL-1 via S64315 or AMG-176 as a single-agent therapy or in combination with BCL-2 inhibitor and other drugs is in clinical trials for AML treatment ( Anstee et al, 2019 ; Caenepeel et al, 2018 ; Ramsey et al, 2018 ; Teh et al, 2018 ). Although BCL-2 itself is an important player in tumorigenesis and represents an important therapeutic target, in vivo stimulation of the expression of pro-apoptosis proteins in AML treatment (e.g., BIM) has not been studied in preclinical models ( Shukla et al, 2017 ).…”