Introduction: Cabazitaxel (CBZ) has been identified as the most effective cytotoxic agent for improving survival in men with docetaxel-refractory castration-resistant prostate cancer (CRPC). However, the development of acquired resistance to CBZ was inevitable. The study aimed to use bioinformatic analysis to screen for candidate drugs that could overcome CBZ-resistance of human whole genome array data.
Methods: Two CRPC cell lines, DU145 and PC3, were used in this study. We incubated the cell lines with gradually increasing concentrations of CBZ to establish CBZ-resistant cell lines, DU145CR and PC3CR. In addition, we analyzed the gene expression profile of CBZ-resistant prostate cancer biopsy tissue collected at our institution and performed screening tests for candidate drugs that could overcome CBZ-resistance. A cell viability assay was used to determine the combined cytotoxic effects of CBZ and a candidate drug on CBZ-resistant cell lines.
Results: We compared the cytotoxic effect of CBZ on CBZ-resistant cells using a cell viability assay. The half maximal inhibitory concentration (IC50) of CBZ in DU145CR and PC3CR were three times higher than that in parental cells. The Broad Institute’s connectivity map analysis of human whole genome array data identified a candidate drug, DCN176. The relative cell viability of DU145 and PC3 cells treated with 10 µM DCN176 were 73.1% ± 1.0% and 68.0% ± 1.3% and that of DU145CR and PC3CR cells treated with 10 µM DCN176 were 61.9% ± 0.6% and 58.7% ± 1.2%.DCN176 appeared to have an anti-tumor effect on CBZ-resistant prostate cancer. CBZ and DCN176 showed a synergic effect in DU145CR and PC3CR cells (Combination Index: 0.76 and 0.81). DCN176 also had an anti-tumor effect in DU145CR and PC3CR xenograft mice models in vivo. To explore the mode of action of DCN176, we analyzed genomic and phosphorylation changes by exon sequencing and liquid chromatography-mass spectrometry (LC-MS). Exon sequencing revealed chromosomal instability in CBZ-resistant cell lines. LC-MS demonstrated an inhibitory effect of DCN176 on the DNA mismatch repair (MMR) pathway. Survival analysis using The Cancer Genome Atlas cohort data showed that loss of MMR genes was a factor for poor prognosis. We tested the sensitivity for DNA damage in CBZ-resistant models by radiation exposure and found that 4-Gy radiation significantly induced more ?H2AX accumulation in CBZ-resistant cells than in CBZ-sensitive cells.
Conclusions: Targeting DNA repair pathways with DCN176 can overcome CBZ-resistance in CRPC. Source of
Funding: This study was supported by Grants-in-Aid for Scientific Research (#17K16813 to H. Hongo and #17K11158 to T. Kosaka) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.
