Presentation Authors: Yoshitaka Sekine*, Daisuke Oka, Hiroshi Nakayama, Yoshiyuki Miyazawa, Hidekazu Koike, Hiroshi Matsui, Yasuhiro Shibata, Kazuhiro Suzuki, Maebashi, Japan
Introduction: Olaparib is reported to have antitumor effects for castration-resistant prostate cancer patients with germline mutations in DNA repair genes. Our microarray data showed that simvastatin downregulated DNA repair genes in androgen independent prostate cancer PC-3 cells. In this study, we investigated the combination therapy with Olaparib and simvastatin for castration-resistant and taxane-resistant prostate cancer.
Methods: Androgen independent PC-3, 22Rv1 and androgen dependent LNCaP human prostate cancer cell lines and PrSC human non-transformed prostate cell were used. We have developed androgen-independent LNCaP cells (LNCaP-LA) by making a trade of FBS for charcoal stripped-FBS gradually. Microarray analyses were performed, followed by Ingenuity Pathway Analysis. mRNA and protein expressions were evaluated by quantitative real-time PCR and Western blot analysis, respectively. To knockdown a candidate gene, cells were transfected with siRNA. Cell viability was determined by MTS assay and cell counts.
Results: Simvastatin altered many gene expressions in PC-3 cells. Microarray data and Ingenuity Pathway Analysis showed that the number of differentially expressed genes was the biggest in the pathway of â€œRole of BRCA1 in DNA Damage Responseâ€ (Fig.1). In the validation, mRNA levels of BRCA1, BRCA2, RAD51, BARD1, FANCD2, RFC3, RFC4, RFC5, MRE11A, FANCA and FANCG, which were listed in â€œRole of BRCA1 in DNA Damage Responseâ€, were decreased significantly by simvastatin in PC-3 cells. Simvastatin decreased the expressions of BRCA1, FANCD2, RFC3, MRE11A and FANCG in 22Rv1 cells, BRCA2, RAD51, BARD1, RFC3 and RFC5 in LNCaP-LA cells, respectively. On the other hand, the expressions of all these genes were not changed in androgen dependent LNCaP cells after treatment of simvastatin. Moreover, simvastatin increased the expressions of all these genes in PrSC. The reduction in BRCA1 and BRCA2 expressions following siRNA transfection increased cytocidal effects of Olaparib in PC-3 and LNCaP-LA cells. The combination of Olaparib and simvastatin further enhanced the inhibition of cell proliferation compared with treatment with either drug alone in PC-3, 22Rv1 and LNCaP-LA, but not in PrSC. Moreover, we developed 22Rv1 having acquired resistance to Cabazitaxel (22Rv1-CR). In 22Rv1-CR cells, simvastatin also decreased the expressions of BRCA1, BRCA2 and FANCA, and the combination of Olaparib and simvastatin further enhanced the inhibition of cell proliferation compared with treatment with either drug alone.
Conclusions: Simvastatin alters the expressions of many genes concerned with DNA repair in castration-resistant and taxane-resistant prostate cancer cells. The combination of PARP inhibitor and the drugs, which decrease the expressions of DNA repair genes, can potentially affect castration-resistant and taxane-resistant prostate cancer growth.