Presentation Authors: Vito Cucchiara*, Joy Yang, Chengfei Liu, Sacramento, CA, Hans Adomat, Emma Guns, Martin Gleave, Vancouver, Canada, Allen Gao, Christopher Evans, Sacramento, CA
Introduction: Hormone therapy is currently the mainstay in the management of locally advanced and metastatic prostate cancer (PCa). Degarelix (Firmagon, Deg), a GnRH receptor antagonist demonstrated some advantages over the LHRH agonist Leuprolide (Leup) by avoiding â€œtestosterone flareâ€ and lower FSH levels. We compared the effect of Deg and Leup on prostate cancer (PC) cell progression in vitro and in vivo.
Methods: RT-qPCR was conducted for GnRH type 2 receptor in PC cell lines. PSA-Luc assays were performed coupled with or without AR-V7 transfection in C4-2B cells. PC cell proliferation in the presence of Leup and Deg was evaluated by cell counts. Western blotting analysis and RT-qPCR were performed to examine the levels of AR-FL and AR variants (V7) upon treatments with Leup and Deg alone or in combination with antiandrogens (abiraterone acetate, AA or enzalutamide, Enza). In vivo VCaP xenographs were treated with control, castration, Leup or Deg in a 6-week period of time. Tumor progression was monitored by biweekly calliper measurement. Harvested tumors were stained for Ki67 and subjected to steroid measurement by LC-MS.
Results: GnRHR2 was readily detectable in PC cells. AR transcriptional activity reported by PSA-Luc assay was modulated by both Leup and Deg. In LNCaP and C4-2B MDVR cells, 20ÂµM Deg significantly reduced the cell viability (p < 0.01). GnRH-antagonist (alone or in combination with AA or Enza) counteracted the transactivation activity of AR by reducing AR-FL and AR variants at the protein level. In C4-2BMDVR cells, Deg reduced AR-V7 protein expression by 26 to 40% alone or combined with AA and Enza compared to control. Leup, however, enhanced variant expression. Deg reduced AR-variant levels from 17 to 41% in monotherapy or combinations compared to control. In mice, Leup slightly suppressed tumor growth compared to controls (p>0.05). However, tumors in Deg-treated group were 1.5-fold smaller than Leup-treated group but 1.7-fold bigger than surgical castration-group. Ki67 IHC staining confirmed the difference in tumor proliferation among groups. Measurements of intratumoral steroids by LC-MS from tumors, serum samples or cell pellets confirmed that Deg decreased the levels of testosterone and steroidogenesis pathway intermediates, comparable to surgical castration; while Leup had no inhibitory effect.
Conclusions: Our results suggest a selective mechanism of action of Deg against AR-variants. The present study provides additional molecular insights regarding the mechanism of Deg compared to GnRH agonist therapy which may have clinical implications.
Source of Funding: Ferring