Login to Access Video or Poster Abstract: MP83-02
Sources of Funding: This work was supported by JSPS KAKENHI Grant Number 15K20109 and 26861299.

Introduction

Recently we demonstrated that the activated PI3K-Akt-mTOR signaling pathway induced by androgen deprivation therapy or docetaxel explains at least in part the aggressiveness in CRPC. Inhibitors of PI3K-Akt-mTOR signaling pathway have potential as next generation anti-CRPC drug. However, there have been little reports that monotherapy with a PI3K-Akt-mTOR signaling inhibitor was effective to CRPC. PIM1 is a kinase which induces expression of receptor tyrosine kinases and it has been reported to contribute Akt inhibitor resistance in lymphoma. We investigated the anti-tumor effect of PIM1 inhibitor for CRPC.

Methods

Two cell lines were used: LNCaP, a androgen-dependent PCa cell line with PTEN deficiency; and C4-2AT6, a castration-resistant prostate cancer cell line with PTEN deficiency and elevated Akt signaling pathways. We investigated the therapeutic efficacy of PIM1 inhibitor; AZD1208 and PI3K/mTOR dual inhibitor; BEZ235.

Results

We compared the cytotoxic effect of docetaxel (DTX) on LNCaP and C4-2AT6 cells by cell viability assay. In LNCaP and C4-2AT6 cells, the relative cell viability treated with 1nM DTX was 68.8 % ± 0.1 % and 87.5% ± 1.9 %, respectively. These results indicated that C4-2AT6 cells showed significantly higher resistance to DTX than LNCaP cells. Next we examined the cytotoxic effect of BEZ235 on LNCaP and C4-2AT6 cells by cell viability assay. In LNCaP and C4-2AT6 cells, the relative cell viability treated with 10nM BEZ235 was 90.2% ± 0.7 % and 89.9% ± 2.3 %, respectively. Western blotting showed increased expression of PIM1 and EGFR in BEZ235 treated cells. These results indicated that PI3K/mTOR inhibitor induced EGFR expression through PIM1 up-regulation. We evaluated the cytotoxic effect of AZD1208 on LNCaP and C4-2AT6. The relative cell viability was 67.9 ± 1.0 % and 67.5 ± 3.1 % with 10µM AZD1208, respectively. AZD1208 significantly inhibited cell proliferation of LNCaP and C4-2AT6. In addition, we examined synergic effect of AZD1208 and DTX/BEZ235. The relative cell viability treated with 10µM AZD1208 and 1nM DTX was 63.8 ± 1.1 % and 48.0 ± 0.6 %. The relative cell viability treated with 10µM AZD1208 and BEZ235 was 55.9 ± 1.6 % and 46.9 ± 1.5 %. We found AZD1208 also had synergic effect with DTX and BEZ235 (Figure).

Conclusions

PIM1 inhibition can overcome the drug resistant mechanism induced by targeting PI3K/Akt/mTOR pathways in docetaxel resistant CRPC.

Funding

This work was supported by JSPS KAKENHI Grant Number 15K20109 and 26861299.