Efficacy of abemaciclib in palbociclib-resistant hormone receptor positive breast cancer cell lines: MCF-7 and T47D

Resistance to CDK4/6 inhibitors plus endocrine therapy, standard of care for HR+/HER2-neg metastatic breast cancer (MBC) patients, remains as a clinical problem with limited therapeutic options after disease progression. Treatment with abemaciclib after progression on a prior CDK4/6i has received increasing interest. However, molecular predictors of cross-resistance and unique mechanism of resistance to each CDK4/6i are unknown. In this study, multiomics analyses revealed =30 differentially altered pathways between palbociclib and abemaciclib resistant models. Mechanistic, preclinical and retrospective clinical evidence showed that HR+/HER2-neg MBC tumors refractory to palbociclib still may be responsive to abemaciclib. Based on the unique mechanisms of resistance to each CDK4/6i, we propose that patients who would benefit from abemaciclib treatment post progression on palbociclib could be selected based on the Hallmark gene set enrichment of G2/M pathway, while those who most probably would be refractory could be identified base on the gene set enrichment of OXPHOS pathway. Overall design: Comparative gene expression profiling analysis of RNA-seq data for palbociclib vs abemaciclib resistant cells. In total 11 resistant cell lines were analyzed by triplicate. MCF7 parental cell line included 6 replicates.