Metastatic castration resistant prostate cancer (mCRPC) is the leading cause of death among prostate cancer (PCa) patients. Patients of African American (AA) origin are particularly disproportionately affected as they are less responsive to current therapies, mainly androgen deprivation therapy (ADT) that target androgen receptor signalling, which is less expressed in AA patients. Receptor tyrosine kinases (RTKs) have been implicated in cancer development and progression and inhibition of their activities has been effective in inhibiting cancer progression in other cancers. However, targeting RTK signalling has not yielded satisfactory results in PCas. The objective of this study was to identify precise RTKs that may be targetable in mCRPCs. An in-vitro model for primary vs mCRPC was developed from AA PCa cell lines: RC77T and RC43T. Briefly, invasive RC77T and RC43T cells were isolated in a cell invasion chamber. The invasive sublines were gradually exposed to increasing concentration (up to 10µM) of MDV3100 over a nine-month period to develop castration resistance. The resulting invasive and castration resistant sublines: RCMI77-CR3 and RCMI43-CR3 were subsequently cultured and maintained in K-SFM containing 10µM of MDV3100. Human Receptor Tyrosine Kinase Phosphorylation Antibody Array and Co-Immunoprecipitation protocols were used to identify differences in RTK activation. TCGA patient data was analysed using R to identify correlation between RTK mRNA expression and PCa progressiveness. MTT assay was used to evaluate effect of RTK inhibitors and MDV3100 treatment on cell survival. The RC77T and RC43T cells were epithelial in appearance, while RCMI77-CR3 and RCMI43-CR3 cells tended to be mesenchymal. The RCMI77-CR3 and RCMI43-CR3 sublines were more resistance to MDV3100 compared to their primary PCa counterparts. Human RTK Array identified four RTKs: KIT, LYN, ITK and RYK to be hyperphosphorylated in RCMI77-CR3 and RCMI43-CR3 relative to RC77T and RC43T, while three RTKs including EphA3, EphB1 and ErbB3 were hypo-phosphorylated. Immunoprecipitation and western blot analysis revealed differential expression of phosphotyrosine kinases between RC77T and RCMI77-CR3 cells. Analysis of TCGA patient data showed, mRNA expression level of only LYN and RYK differed significantly (p<0.05) significantly with disease progression. Analysis of effect of tyrosine kinase inhibitors on cell proliferation showed RCMI77-CR3 to be more responsive to dasatinib and axitinib compared to RC77T. No similar differences in response was observed for the inhibitors; SU6656, IWR-1, ICG-001 and BMS. The current study suggests, activation of specific RTKs are involved survival and drug resistance in mCRPC cells. Inhibiting these specific RTK signalling pathways in segments of patients with specific RTK hyperactivation could significantly improve survival.

Citation Format: Raven A. Williams, Joakin Mori, Hui-Xian Lin, Alahni Becks, Clayton Yates, Honghe Wang. Receptor tyrosine kinases are differentially phosphorylated in metastatic castration resistant 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 1331.