Abstract 607: Targeting PIM1 kinase enhances 1,25-dihydroxyvitamin D3-mediated anti-tumor activity in bladder cancer cells (2014)

Abstract Bladder cancer is the 5th most common in the United States. 30% of cases are advanced stage requiring multimodality therapy at diagnosis and many which are first diagnosed when superficial will progress to more advanced disease. High recurrence and progression rate and drug resistance highlight the need for new therapeutic strategies to improve clinical outcomes. 1,25-dihydroxyvitamin D3 (1,25D3), the most active vitamin D metabolite, has demonstrated broad spectrum antitumor activities in vitro and in vivo. In addition, 1,25D3 potentiates the antitumor effects of common chemotherapeutic agents in several cancer cell types including bladder cancer. 24-hydroxylase, encoded by the CYP24A1 gene, plays a key role in degrading 1,25D3. Increased expression of CYP24A1 has been found in several human tumors. Several studies reveal that the protein kinase signaling pathways including PIM1 are involved in the regulation of CYP24A1 expression. The PIM kinases are a family of serine/threonine kinases (PIM-1, PIM-2, PIM-3) that have been associated with tumorigenesis and drug resistance. PIM1 has been extensively studied in lymphoma and upregulation of PIM kinase expression has been reported in many malignancies. We analyzed mRNA expression of CYP24A1 and PIM1 in 17 bladder cancer cell lines by qRT-PCR. We found that CYP24A1 expression is increased in 12 out of 17 bladder cancer cell lines and PIM1 expression is increased in 8 out of 17 bladder cancer cell lines compared to expression in a benign bladder cancer cell line. Therefore, we hypothesized that inhibition of PIM kinase activity would suppress CYP24A1 expression and thus enhancing 1,25D3-mediated anti-tumor activity. Using the PIM1 inhibitor, JP11646, we found that inhibition of PIM1 kinase activity reduces CYP24A1 expression at transcriptional level in bladder cancer cells RT112 and RT112D21 which express high level of PIM1 and CYP24A1. We further evaluated the efficacy of the PIM1 inhibitor alone and in combination with 1,25D3. Inhibition of PIM1 kinase activity by JP11646 reduces cell growth in a panel of bladder cancer cell lines in a dose-dependent manner as measured by MTT assays. MTT assays detected a significant inhibition of cell proliferation by 50% compared to the control when cells were treated with 128 nM of JP11646 for 72 h in 6 of bladder cancer cell lines tested. Furthermore, inhibition of PIM1 kinase activity enhances 1,25D3-mediated inhibitory effect on cell growth in bladder cancer cells RT112 and RT112D21. This study provides the first evidence that inhibition of PIM kinase activity may be an attractive therapeutic strategy to facilitate the optimization of antitumor therapy of vitamin D in bladder cancer. This study was supported by NIH/NCI grants 5R01CA067267 and 5R01CA095045 Citation Format: Wei Luo, Carmen M. Baldino, Justin Caserta, Yingyu Ma, Candace Johnson, Donald L. Trump. Targeting PIM1 kinase enhances 1,25-dihydroxyvitamin D3-mediated anti-tumor activity in bladder cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 607. doi:10.1158/1538-7445.AM2014-607