Developing Inhibitors that Exploit ABCG2 and Cancer Dependencies to Improve Therapeutic Outcome

Abstract

Multidrug efflux transporters such as ABCG2 limit drug penetration into cancer cells and limit therapeutic effectiveness of many chemotherapeutic drugs. We have shown previously that inhibition of ABCG2, when combined with a conventional chemotherapy, improved treatment efficacy in murine models of acute myeloid leukemia and medulloblastoma (1,2). In this study, we sought to identify ABCG2 inhibitors that are also capable of targeting a cancer cell‐specific pathway. By combining these ABCG2 inhibitors with conventional chemotherapeutic drugs that are ABCG2 substrates, we anticipate synergistic cytotoxic effects that will produce superior treatment outcomes. A high‐throughput functional ABCG2 inhibition screen was performed using a library containing ~12,000 bioactive compounds including FDA‐approved drugs. Hit compounds were validated in a dose dependent manner, and compounds that were cytotoxic and had a low IC50 (< 1 μM) for ABCG2 inhibition were selected for further investigation. We identified kinase inhibitors (KIs) that have not been previously reported to be ABCG2 inhibitors and confirmed the direct interaction of one KI to ABCG2 using a membrane protein cellular thermal shift assay (CETSA). We investigated if the combination of a conventional cancer chemotherapeutic drug, mitoxantrone, and the KI produced an increase in efficacy against primary leukemic cells. In vitro testing of this combination on murine myeloid leukemia cells produced synergistic cell killing with an IC50 value ~10‐fold lower for each compound compared to the IC50 value for normal hematopoietic progenitors. Murine leukemia cells were then treated either singly or with the mitoxantrone‐KI combination ex vivo, followed by transplantation into lethally irradiated congenic recipient mice. The mice that received cells treated with mitoxantrone and the KI had a significant increase in their overall survival. We are extending our findings to other cancers that overexpress ABCG2 as this may be a viable therapeutic approach that improves treatment response in cancers that specifically express ABCG2 and are treated with ABCG2 substrates.Support or Funding InformationThis work was supported by NIH and by the ALSAC.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.