Abstract 4823: Alvocidib enhances the efficacy of cytarabine and daunorubicin (7+3) in non-clinical models of acute myeloid leukemia

Abstract

Abstract The ‘7+3' induction regimen has been the standard of care for frontline acute myeloid leukemia (AML) for more than 30 years. There are still significant unmet needs for frontline patients, particularly those with high-risk features. Alvocidib, a potent CDK9 inhibitor, has shown clinical activity in multiple studies of frontline and relapsed/refractory AML. In some clinical studies, alvocidib has been administered as part of the ACM (alvocidib, cytarabine, and mitoxantrone) regimen. The ACM regimen has demonstrated greater clinical responses compared to 7+3 in frontline intermediate and high-risk AML patients. The ACM regimen is now being evaluated in a multi-institution, Phase II study using a MCL-1 dependency biomarker to select patients likely to be sensitive to the alvocidib-containing regimen. Alvocidib activity is primarily driven by its inhibition of CDK9/RNA-polymerase II and the subsequent suppression of key anti-apoptotic proteins, including MCL-1. Alvocidib induces apoptosis and potentiates the activity of apoptosis-inducing agents, such as cytarabine and mitoxantrone. The synergy of the ACM regimen led us to hypothesize that alvocidib may enhance the anti-leukemia activity of the 7+3 regimen in preclinical models as well. Cell viability and apoptosis measurements were made following treatment using the CellTiter-Glo and Caspase-Glo assays according to manufacturer protocol. MCL-1 mRNA expression and the expression of additional markers was determined using RT-qPCR. Protein expression was determined using standard immunoblotting techniques. Alvocidib and the 7+3 regimen were also tested in vivo in the MV4-11 AML xenograft model. Here, it was observed that the 72-hour viability assays yielded single agent IC50 values of alvocidib, cytarabine, or daunorubicin in cultured AML cells ranging from 2.2 nM to 567 nM. In apoptosis assays, a modest induction was observed with cytarabine, daunorubicin, or alvocidib. However, the three-drug combination more than doubled the induction of apoptosis compared to any of the agents alone. We also observed that MCL-1 was suppressed in the combination treatment. In a xenograft study, 21.1 and 48.5% tumor growth inhibition (TGI) was observed following either single agent treatment of daunorubicin (0.5 mg/kg) or cytarabine (60 mg/kg), respectively. Treatment of alvocidib (1.25 mg/kg) yielded 60.0% TGI. Combination treatment, however, resulted in tumor shrinkage, yielding 116.2% TGI. While we have reported previously that alvocidib synergizes with cytarabine and mitoxantrone preclinically in the ACM regimen, our data here demonstrates that alvocidib potentiates the activity of cytarabine and daunorubicin as well. Our results here provide additional scientific rationale for an investigational Phase Ib clinical study employing alvocidib in combination with 7+3 in frontline AML patients, which is currently ongoing. Citation Format: Wontak Kim, Clifford J. Whatcott, Adam Siddiqui-Jain, David J. Bearss, Steven L. Warner. Alvocidib enhances the efficacy of cytarabine and daunorubicin (7+3) in non-clinical models of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4823.