Patient stem cell (SC)-derived prostate cancer (PC) organoids (Org) to recreate clonal heterogeneity of PC foci and measure therapeutic response potential.

252 Background: In spite of significant outcome gains in recurrent and de novo metastatic PC, resistance inevitably develops to androgen deprivation (ADT) and chemotherapy. Resistance is supported by clonal heterogeneity due to complex genomic and epigenetic alterations within PC foci in the primary and metastases (mets) and by the enrichment of residual tumor foci with PC SCs that survive therapy. PCSCs maintain self-renewal capacity, adapt over time to different microenvironments and retain tumor propagating activity leading to castration resistant (CR) PC progression. To study these processes, we generated patient SC-derived PC Org from primary and mets specimens. Methods: We isolated cells from normal epithelium and PC foci of 4 histopathologically mapped radical prostatectomy specimens and 2 CRPC mets. We developed a 3D culture system utilizing single tumor initiating cells expressing CD29hi/CD49bhi/CD44hiand co-cultured with epithelial/mesenchymal growth factors. Org growth peaked at 2 weeks, and Or...