Fig. 6: Pharmacological inhibition of OPRK1 suppresses tumor growth in multiple in vivo castration-resistant prostate cancer models.

a Mice bearing VCaP cell-derived xenograft were castrated. Four weeks later, when the tumor started castration-resistant growth, mice were untreated or treated with OPRK1 inhibitor nor-BNI (n = 5 each). b Mice bearing VCaP cell-derived xenograft were castrated and untreated or treated with nor-BNI (n = 5 each) at the same time. c AILNCaP cells were inoculated to castrated mice. When the cell-derived xenograft tumors were engrafted and started growing, mice were untreated or treated with nor-BNI (n = 5 each). d Single-sample GSEA (ssGSEA) showing differentially enriched gene sets in VCaP cells treated with siRNA for AR (siAR) alone vs those treated with siAR and siRNA for OPRK1 (siORPK1). A gene set involved in SMAD6 pathway (red column) is enriched as well as some gene sets involved in neuronal pathways (light blue) and G-protein-related pathways (magenta). e Expressions of six genes involved in the SMAD6 pathway (JEON_SMAD6_TARGETS_UP) were evaluated using quantitative RT-PCR in VCaP or AIVCaP cells under AR signal suppression between siNTC and siOPRK1 treatments. f Representative photomicrograph images of hematoxylin and eosin (H&E) and immunohistochemical stains for OPRK1 in non-cancer prostate (benign), castration-sensitive (CSPC) prostate cancer, prostate cancer treated with neoadjuvant androgen deprivation therapy (NAADT), and castration-resistant prostate cancer (CRPC) tissues. g Immunostainability of OPRK1 classified into negative (none), weakly (weak), and strongly (strong) positive in benign, hormone-naïve (HNPC), PCa after neoadjuvant hormone therapy (NAHT), and CRPC. h Immunostainability of OPRK1 in HNPC tissues with regard to AR immunostainability. i Immunostainability of OPRK1 in CRPC tissues with regard to AR immunostainability.