Examining the role of Axl inhibition in Chk1 inhibitor-resistant triple negative breast cancers

Abstract

Triple negative breast cancers as a category pose a challenge in the clinic. As our understanding of the breast cancer proteome expands, we can identify new targets for treatment. The Colavito lab previously identified Chk1 as a target in treating triple negative breast cancer and developed a model of Chk1 inhibitor resistance to further examine the mechanisms of this treatment. Preliminary screenings identified that these Chk1 inhibitor resistant cells had elevated levels of activation in the protein Axl. This study examines the role Axl plays in Chk1 inhibitor resistance in the hope of identifying a possible treatment combination for patients struggling with triple negative breast cancer. Through dose response assays, it was identified that Axl inhibition sensitized Chk1 inhibitor resistant cells to the Chk1 inhibitor AZD7762. Western blotting confirmed that DNA damage increased in AZD7762 resistant cells treated with both AZD7762 and the Axl inhibitor R428. Flow cytometry confirmed that apoptosis was not the mechanism of growth inhibition. RT-qPCR showed little change in epithelial or mesenchymal gene expression, but migration assays showed that AZD7762-resistant cells migrate less than their parents. Finally, colony formation assays show that combining Axl inhibition with AZD7762 greatly reduced the colony forming capacity of these cells. This work clearly identifies that Axl plays a role in Chk1 inhibitor resistance, and encourages further work into understanding which mechanisms are at play in this pathway.