The Role of DLX1 As a Biomarker and Novel Target in Poor Prognostic Prostate Cancer

Introduction: Previous work from our lab has identified a molecularly distinct subgroup of primary prostate cancers with biology similar to metastatic prostate cancers. These “met-like” cancers can be identified by a 70 gene classifier and are statistically more likely to result in distant metastases than their “non-met like” counterparts. This study aimed to identify exploitable biology common to both “met-like” primary tumours and metastatic prostate cancer. Experimental procedures: Differential gene expression and Ingenuity pathway analysis (IPA) was used to identify nodal genes upregulated in both “met-like” primary prostate cancers and metastatic prostate cancers. siRNA screening was performed on 40 nodal genes in a panel of normal, primary and metastatic prostate cancers. Cell viability was assessed using cell titer-glo luminescent Assay. Relative levels of apoptosis were assessed using PARP, caspase-8 and caspase-3 cleavage Western Blots. siRNA mediated knockdowns were confirmed by Western Blot and rtPCR. Results: We have identified upregulation of the homeobox transcription factor DLX1 in “met-like” primary prostate cancers and metastatic prostate cancers. High levels of DLX1 expression were found to be independently predicative of biochemical recurrence and metastatic disease in primary prostate cancers. DLX1 knockdown resulted in significantly decreased cell viability in primary and metastatic prostate cancer cell lines with minimal reduction of viability in normal prostate cells. Additionally DLX1 knockdown was shown to result in increased PARP, caspase-8 and caspase-3 cleavage providing evidence of apoptotic cell death. Furthermore knockdown of DLX1 resulted in significantly increased transcript levels of the pro-apoptotic BH3 protein BIK, suggesting its involvement in the observed apoptotic cell death. Conclusion: DLX1 has previously been identified as a marker of prostate cancer metastasis with increased expression being observed in both primary and metastatic prostate cancers. However we have observed increased DLX1 expression in a subset of primary prostate cancers that developed metastatic diseased compared to primary tumors that did not metastasise. The elucidation of apoptotic mechanisms following DLX1 knockdown may uncover potential exploitable biology that may be used for the treatment of prostate cancer. Citation Format: Nicholas Forsythe, Cathal McKinney, Nuala McCabe, Richard D. Kennedy. The role of DLX1 as a biomarker and novel target in poor prognostic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 370.