Acute myeloid leukemia (AML) is a serious disease. The 5-year survival rates remain frustratingly low (65% for children and 26% for adults). Resistance to frontline chemotherapy (usually cytarabine) often develops; therefore a new treatment modality is needed. Bcl-2 family proteins play an important role in balancing cell survival and apoptosis. The antiapoptotic Bcl-2 family proteins have been found to be dysregulated in AML. ABT-199, a BH3 mimetic, was developed to target antiapoptotic protein Bcl-2. Although ABT-199 has demonstrated promising results, resistance occurs. Previous studies in AML show that ABT-199 alone decreases the association of proapoptotic protein Bim with Bcl-2, but this is compensated by increased association of Bim with prosurvival protein Mcl-1, stabilizing Mcl-1, resulting in resistance to ABT-199. In this study, we investigated the antileukemic activity of the Mcl-1-selective inhibitor A-1210477 in combination with ABT-199 in AML cells. We found that A-1210477 synergistically induced apoptosis with ABT-199 in AML cell lines and primary patient samples. The synergistic induction of apoptosis was decreased upon Bak, Bax and Bim knockdown. While A-1210477 treatment alone also increased Mcl-1 protein levels, combination with ABT-199 reduced binding of Bim to Mcl-1. Our results demonstrate that sequestration of Bim by Mcl-1, a mechanism of ABT-199 resistance, can be abrogated by combined treatment with the Mcl-1 inhibitor A-1201477.

The antiapoptotic Bcl‐2 family proteins play critical roles in resistance to chemotherapy in acute myeloid leukaemia (AML). The Bcl‐2‐selective inhibitor ABT‐199 (Venetoclax) shows promising antileukaemic activity against AML, though Mcl‐1 limits its antileukaemic activity. XPO1 is a nuclear exporter overexpressed in AML cells and its inhibition decreases Mcl‐1 levels in cancer cells. Thus, we hypothesized that the XPO1‐selective inhibitor KPT‐330 (Selinexor) can synergize with ABT‐199 to induce apoptosis in AML cells through down‐regulation of Mcl‐1. The combination of KPT‐330 and ABT‐199 was found to synergistically induce apoptosis in AML cell lines and primary patient samples and cooperatively inhibit colony formation capacity of primary AML cells. KPT‐330 treatment decreased Mcl‐1 protein after apoptosis initiation. However, binding of Bim to Mcl‐1 induced by ABT‐199 was abrogated by KPT‐330 at the same time as apoptosis initiation. KPT‐330 treatment increased binding of Bcl‐2 to Bim but was overcome by ABT‐199 treatment, demonstrating that KPT‐330 and ABT‐199 reciprocally overcome apoptosis resistance. Mcl‐1 knockdown and overexpression confirmed its critical role in the antileukaemic activity of the combination. In summary, KPT‐330 treatment, alone and in combination with ABT‐199, modulates Mcl‐1, which plays an important role in the antileukaemic activity of the combination.

As the mainstay treatment for advanced prostate cancer, androgen deprivation therapy (ADT) targets the action of androgen receptor (AR) by reducing androgen level and/or by using anti-androgen to compete with androgens for binding to AR. Albeit effective in extending survival, ADT is associated with dose-limiting toxicity and the development of castration-resistant prostate cancer (CRPC) after prolonged use. Because CRPC is lethal and incurable, developing effective strategies to enhance the efficacy of ADT and circumvent resistance becomes an urgent task. Continuous AR signaling constitutes one major mechanism underlying the development of CRPC. The present study showed that methylseleninic acid (MSA), an agent that effectively reduces AR abundance, could enhance the cancer-killing efficacy of the anti-androgen bicalutamide in androgen-dependent and CRPC cells. We found that the combination of MSA and bicalutamide produced a robust downregulation of prostate-specific antigen and a recently identified AR target, telomerase, and its catalytic subunit, human telomerase reverse transcriptase. The downregulation of hTERT occurs mainly at the transcriptional level, and reduced AR occupancy of the promoter contributes to downregulation. Furthermore, apoptosis induction by the two agents is significantly mitigated by the restoration of hTERT. Our findings thus indicate that MSA in combination with anti-androgen could represent a viable approach to improve the therapeutic outcome of ADT. Given the critical role of hTERT/telomerase downregulation in mediating the combination effect and the fact that hTERT/telomerase could be measured in blood and urine, hTERT/ telomerase could serve as an ideal tumor-specific biomarker to monitor the efficacy of the combination therapy noninvasively. Mol Cancer Ther; 9(7); 2016-25. ©2010 AACR.