Login to Access Video or Poster Abstract: MP99-15
Sources of Funding: This work is supported in part by grants NIH/NCI This work was supported in part by grants NIH/NCI CA140468, CA168601, CA179970, and DOD PCRP PC150040.

Introduction

Docetaxel (DTX) is one of the primary drugs used for treating castration resistant prostate cancer (CRPC). Unfortunately, over time patients invariably develop resistance to DTX therapy and their disease will continue to progress. The mechanisms by which resistance develops is still incompletely understood. This study seeks to determine the involvement of miRNAs, specifically miR-181a, in DTX resistance in CRPC.

Methods

Total RNA from parental C4-2B prostate cancer cells and DTX resistant C4-2B cells (C4-2B TaxR) was submitted for small RNA deep sequencing. Data was analyzed to ascertain which miRNAs expressions were most altered in C4-2B TaxR cells compared to parental cells. Having identified an increase in miR-181a in resistant cells, its expression was modulated in C4-2B and C4-2B TaxR cells by transfecting them with miR-181a mimics or antisense, respectively. Following transfection, cell number was determined after 48 h with or without DTX. Cross resistance to cabazitaxel induced by miR-181a was also determined. Western blots were used to determine ABCB1 protein expression and rhodamine assays used to assess activity. Phospho-p53 expression was assessed by western blot and apoptosis was measured by ELISA in C4-2B TaxR cells with inhibited miR-181a expression with or without DTX.

Results

miR-181a is significantly upregulated in C4-2B TaxR cells compared to parental C4-2B cells as analyzed by small RNA sequencing. Overexpression of miR-181a in C4-2B cells confers DTX and cabazitaxel resistance. Knockdown of miR-181a in C4-2B TaxR cells re-sensitizes them to treatment with both DTX and cabazitaxel. miR-181a knockdown alone induced apoptosis in C4-2B TaxR cells which is further enhanced by DTX. We next assessed if miR-181a altered expression or activity of ABCB1, which is overexpressed/active in C4-2B TaxR cells and promotes resistance to DTX by pumping the drug out of cells. We found that miR-181a does not impact ABCB1 expression or activity. Since we previously demonstrated that phospho-p53 can modulate DTX sensitivity, we determined if miR-181a can alter p53 expression in C4-2B TaxR cells. Knockdown of miR-181a in C4-2B TaxR cells induced phospho-p53 expression, suggesting that miR-181a induced resistance to DTX is mediated by inhibition of phospho-p53 expression.

Conclusions

Overexpression of mir-181a in C4-2B TaxR cells contributes to their resistance to DTX and inhibition of mir-181a expression can restore treatment response. This is due, in part, to modulation of p53 phosphorylation and induction of apoptosis.

Funding

This work is supported in part by grants NIH/NCI This work was supported in part by grants NIH/NCI CA140468, CA168601, CA179970, and DOD PCRP PC150040.