Overcoming ABCB1 mediated multidrug resistance in castration resistant prostate cancer

The few available therapies for mCRPC patients include taxanes docetaxel (DTX) and cabazitaxel (CBZ). However, development of resistance limits their clinical use. PCa that relapses after hormonal therapies, referred to as castration resistant prostate cancer (CRPC), often presents with metastases (mCRPC) that are the major cause of mortality. The few available therapies for mCRPC patients include taxanes docetaxel (DTX) and cabazitaxel (CBZ). However, development of resistance limits their clinical use. To study taxanes resistance, we produced CBZ resistant C4-2B cells (RC4-2B) and documented resistance to both CBZ and DTX in cell culture and in 3D prostaspheres settings. RNAseq identified increased expression of ABCB1 in RC4-2B, that was confirmed by immunoblotting and immunofluorescent analysis. ABCB1-specific inhibitor elacridar reversed CBZ and DTX resistance in RC4-2B cells, confirming ABCB1-mediated resistance mechanism. To study taxanes resistance in CRPC, we have produced CBZ-resistant mCRPC C4-2B cell line following the next experimental procedure: after 72 h of CBZ treatment, cells were recovered for one week, re-plated, and the cycle was repeated with increased concentration of CBZ starting at 0.1nM and ending at 20nM. After 4 months, we completed the production of CBZ resistant subclone RC4-2B. We characterized CBZ resistance of RC4-2B cells using metabolic viability (Alamar Blue) and colony formation assays. These complementary methods revealed that IC50 for CBZ is ~10x higher in RC4-2B cells compared to the parental C4-2B cells. To understand mechanisms of taxanes resistance, we performed transcriptome analysis in C4-2B and RC4-2B cells.