Abstract 1098: TIMP-1: A potential biomarker of neuroendocrine differentiation in metastatic castration-resistant prostate cancer (mCRPC)

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA BACKGROUND: Tissue inhibitor of metalloproteinases-1 (TIMP-1) is a 28.5 kDa secreted glycoprotein that inhibits matrix metalloproteinase (MMP) activity. Recent studies have demonstrated that TIMP-1 promotes tumor growth in an MMP-independent manner. We have previously shown that elevated plasma TIMP-1 predicts worse survival in mCRPC patients; however, the mechanism underpinning this association is unknown. Normal and malignant neuroendocrine (NE) cells, from various organs, express TIMP-1 as measured by immunohistochemistry (IHC). We hypothesized that elevated blood levels of TIMP-1 in mCRPC patients results from androgen deprivation therapy-induced NE differentiation. METHODS: In this study, we used qPCR, ELISA and IHC to correlate the expression of TIMP-1 and NE markers such as chromogranin A (CGA) in 7 prostate cancer cell lines, 37 patient serum samples and prostate cancer (adenocarcinoma and NE cancer) tissue microarrays. RESULTS: We first examined TIMP-1 and NE marker (NSE and PTHLH) mRNA expression in 7 prostate cancer cell lines. Our results show that PC-3, PC-3M, DU145 cells express high levels of TIMP-1 as well as NE markers. On the other hand, LNCAP, VCAP and LAPC-4 cells had barely detectable levels of TIMP-1 and much lower expression of NE markers. We then measured serum TIMP-1 and CGA levels from CRPC patient samples by ELISA. Patients with castration resistant disease had significantly higher serum TIMP-1 levels (mean value of 373.5 ng/ml) than patients with hormone sensitive disease (mean value of 304.8 ng/ml) (p=0.01), suggesting that castration resistance in prostate cancer patients is associated with increased TIMP-1 production. Interestingly, when we divided patients using a cutoff of 100 ng/ml (based on cutoffs reported in published literature), serum TIMP-1 was significantly higher in the high CGA group (p=0.018), indicating an association between TIMP-1 production and existing NE markers. We also compared PSA values between low and high CGA groups and found that the high CGA group was associated with lower PSA levels (p=0.029). Next, we explored TIMP-1 expression in NE tumor tissues. We performed TIMP-1 and CGA IHC staining in archival liver neuroendocrine and thyroid cancers and found that TIMP-1 expression was associated with CGA expression. In prostate cancer specimens, normal prostate epithelial cells expressed high levels of TIMP-1, but the expression was lost in adenocarcinomas. In contrast, prostatic neuroendocrine cancers expressed high levels of TIMP-1 as well as the NE marker CGA. CONCLUSIONS: These observations support the further evaluation of TIMP-1 as a tissue and serum biomarker for NE differentiation in CRPC. Note: This abstract was not presented at the meeting. Citation Format: Yixuan Gong, Uma Chippada-Venkata, Xudong Dai, Matthew D. Galsky, Jiaoti Huang. TIMP-1: A potential biomarker of neuroendocrine differentiation in metastatic castration-resistant prostate cancer (mCRPC). [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 1098. doi:10.1158/1538-7445.AM2014-1098