Blocking GRP/GRP-R signaling decreases expression of androgen receptor splice variants and inhibits tumor growth in castration-resistant prostate cancer

Thomas C Case; Alyssa Merkel; Marisol Ramirez-Solano; Qi Liu; Julie A Sterling; Renjie Jin

doi:10.1016/j.tranon.2021.101213

Blocking GRP/GRP-R signaling decreases expression of androgen receptor splice variants and inhibits tumor growth in castration-resistant prostate cancer

Transl Oncol. 2021 Nov;14(11):101213. doi: 10.1016/j.tranon.2021.101213. Epub 2021 Aug 27.

Authors

Thomas C Case¹, Alyssa Merkel², Marisol Ramirez-Solano³, Qi Liu³, Julie A Sterling², Renjie Jin⁴

Affiliations

¹ Department of Urology, Vanderbilt University Medical Center, A1329, MCN, 1161 21st Ave. South, Nashville, TN 37232, USA.
² Department of Cancer Biology, Medicine, Division of Clinical Pharmacology, Bone Biology Center, and Biomedical Engineering, Vanderbilt University Medical Center, Nashville, TN, USA.
³ Department of Biostatistics, Vanderbilt University Medical Center, Nashville, TN, USA.
⁴ Department of Urology, Vanderbilt University Medical Center, A1329, MCN, 1161 21st Ave. South, Nashville, TN 37232, USA. Electronic address: renjie.jin@vumc.org.

Abstract

Clinical management of castration-resistant prostate cancer (CRPC) resulting from androgen deprivation therapy (ADT) remains challenging. Many studies indicate that androgen receptor splice variants (ARVs) play a critical role in the development of CRPC, including resistance to the new generation of inhibitors of androgen receptor (AR) action. ARVs are constitutively active and lack the ligand-binding domain (LBD), thereby allowing prostate cancer (PC) to maintain AR activity despite therapies that target the AR (full-length AR; AR-FL). Previously, we have reported that long-term ADT increases the neuroendocrine (NE) hormone - Gastrin Releasing Peptide (GRP) and its receptor (GRP-R) expression in PC cells. Further, we demonstrated that activation of GRP/GRP-R signaling increases ARVs expression by activating NF-κB signaling, thereby promoting cancer progression to CRPC. Most importantly, as a cell surface protein, GRP-R is easily targeted by drugs to block GRP/GRP-R signaling. In this study, we tested if blocking GRP/GRP-R signaling by targeting GRP-R using GRP-R antagonist is sufficient to control CRPC progression. Our studies show that blocking GRP/GRP-R signaling by targeting GRP-R using RC-3095, a selective GRP-R antagonist, efficiently inhibits NF-κB activity and ARVs (AR-V7) expression in CRPC and therapy-induced NEPC (tNEPC) cells. In addition, blocking of GRP/GRP-R signaling by targeting GRP-R can sensitize CRPC cells to anti-androgen treatment (such as MDV3100). Further, preclinical animal studies indicate combination of GRP-R antagonist (targeting ARVs) with anti-androgen (targeting AR-FL) is sufficient to inhibit CRPC and tNEPC tumor growth.

Keywords: Androgen receptor variants; Castration-resistant prostate cancer; GRP/GRP-R; NF-kappa B; neuroendocrine prostate cancer.