Mechanistically-driven investigation of pegcrisantaspase combination therapy against acute myeloid leukemia

Introduction: Novel, more efficacious, and better tolerated therapy for acute myeloid leukemia (AML) is needed, as current treatment options result in only 35-40% 5 year survival in patients younger than 60 years of age. Targeting cellular metabolism, specifically by disrupting glutamine metabolism, is a promising approach to treat AML since altering metabolism appears to affect AML cell growth more compared to normal cells. L-asparaginases, which are approved for use in acute lymphoblastic leukemia, has been shown to alter glutamine metabolism in AML cells. In a recently published clinical trial, we found that Erwinaze, Erwina chrysanthemi asparaginase, is capable of depletion of plasma glutamine levels and is well tolerated in adult patients with AML with no occurrence of dose-limiting toxicity (DLT). Here, we report the anti-AML activity of pegcrisantaspase, a novel long-acting Erwinia chrysanthemi L-asparaginase, in combination with clinically relevant chemotherapeutic agents in vitro and in vivo. Materials and Methods: In this study we investigated the cytotoxic effect of pegcrisantaspase along with 12 other clinically relevant chemotherapeutic agents. In vitro anti-proliferative activity of each agent was determined in 7 different AML cell lines (MV4-11, MOLM-14, MonoMac-6, U937, THP-1, HL60, K562) using the WST-1 cell proliferation reagent. In combination studies, cell survival was measured by Trypan blue staining. For determination of synergism, results of the WST-1 cell proliferation assay were analyzed by median effect analysis and used to determine a combination index (CI), with synergism defined as CI values Results: Pegcrisantaspase inhibited AML cell growth in six of seven cell lines tested, with IC50s ranging from 0.0001 IU/mL to 0.049 IU/mL. At higher concentrations, pegcrisantaspase was synergistic with the proteasome inhibitors ixazomib and carfilzomib. When pegcrisantaspase was combined with the Bcl-2 inhibitor, venetoclax, pegcrisantaspase potentiated the effect of venetoclax in AML cells by more than 10 fold. Additionally, pegcrisantaspase showed significant anti-AML effects compared to control in our mouse xenograft model. Conclusions and Future Directions: Our data demonstrates the meaningful anti-AML activity of pegcrisantaspase in vitro and in vivo. The results also suggest that combination of pegcrisantaspase with proteasome and Bcl-2 inhibitors is potentially efficacious at treating AML. Mechanistic experiments to examine the phosphorylation state of key downstream targets of mTOR are ongoing. Furthermore, future in vivo studies will involve combining the above chemotherapies with pegcrisantaspase in our mouse xenograft model. Citation Format: Hannah Kaizer, Binny Bhandary, Brandon A. Carter-Cooper, Eun Yong Choi, Bandish Kapadia, Elizabeth T. Chang, Rena G. Lapidus, Ronald B. Gartenhaus, Ashkan Emadi. Mechanistically-driven investigation of pegcrisantaspase combination therapy against 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 884.