ASC-J9 Suppresses Castration-Resistant Prostate Cancer Growth through Degradation of Full-length and Splice Variant Androgen Receptors

Abstract

Early studies suggested androgen receptor (AR) splice variants might contribute to the progression of prostate cancer (PCa) into castration resistance. However, the therapeutic strategy to target these AR splice variants still remains unresolved. Through tissue survey of tumors from the same patients before and after castration resistance, we found that the expression of AR3, a major AR splice variant that lacks the AR ligand-binding domain, was substantially increased after castration resistance development. The currently used antiandrogen, Casodex, showed little growth suppression in CWR22Rv1 cells. Importantly, we found that AR degradation enhancer ASC-J9 could degrade both full-length (fAR) and AR3 in CWR22Rv1 cells as well as in C4-2 and C81 cells with addition of AR3. The consequences of such degradation of both fAR and AR3 might then result in the inhibition of AR transcriptional activity and cell growth in vitro. More importantly, suppression of AR3 specifically by short-hairpin AR3 or degradation of AR3 by ASC-J9 resulted in suppression of AR transcriptional activity and cell growth in CWR22Rv1-fARKD (fAR knockdown) cells in which DHT failed to induce, suggesting the importance of targeting AR3. Finally, we demonstrated the in vivo therapeutic effects of ASC-J9 by showing the inhibition of PCa growth using the xenografted model of CWR22Rv1 cells orthotopically implanted into castrated nude mice with undetectable serum testosterone. These results suggested that targeting both fAR- and AR3-mediated PCa growth by ASC-J9 may represent the novel therapeutic approach to suppress castration-resistant PCa. Successful clinical trials targeting both fAR and AR3 may help us to battle castration-resistant PCa in the future.

Differential Androgen Deprivation Therapies with Anti-androgens Casodex/Bicalutamide or MDV3100/Enzalutamide versus Anti-androgen Receptor ASC-J9® Lead to Promotion versus Suppression of Prostate Cancer Metastasis

“…We noticed that although both Casodex and MDV3100 have significant anti-growth effects in LNCaP, C81, and C4-2 cells, both anti-androgen drugs showed less effect on CWR22Rv1 cell growth, which could be due to the existence of the AR variant, AR3, (27,38). Recent reports have documented that Casodex failed to suppress AR3 transactivation, and this is probably due 6 ) were mixed with Matrigel and injected into both anterior prostates of nude mice.…”

“…Moreover, Hu et al (39) also found in both in vitro and in vivo studies that MDV3100 or abiraterone treatment increased AR3 expression, which might then enhance cell cycle-related genes to promote PCa progression. In contrast, ASC-J9 could degrade both full-length AR and AR3 (27), providing another explanation of why ASC-J9 showed better therapeutic effects in battling both PCa cell growth and metastasis.…”

“…to the lack of an androgen-binding domain (27,38,39). Moreover, Hu et al (39) also found in both in vitro and in vivo studies that MDV3100 or abiraterone treatment increased AR3 expression, which might then enhance cell cycle-related genes to promote PCa progression.…”

“…We investigated the possibility that any newly developed anti-androgen/AR compounds have both anti-PCa cell growth and invasion capacity so that they can simultaneously suppress PCa growth and metastasis. We first focused on two anti-AR compounds, the AR degradation enhancer ASC-J9 (8,11,27) and CTS (12), the tanshinone extracted from the Chinese herb danshen. Unlike the currently used anti-androgens that reduce or prevent androgen binding to AR, the newly developed anti-AR compound, ASC-J9, has the unique capability to degrade AR protein in selective cells.…”

ATM Inhibition Potentiates Death of Androgen Receptor-inactivated Prostate Cancer Cells with Telomere Dysfunction

“…Notably, telomere dysfunction and the activation of ATM kinase by AR inactivation also occurs in AR-positive castration-resistant 22Rv1 cells (Fig. 1F) that are resistant to the growth inhibitory effect of AR antagonists such as Casodex (34). This suggests that telomere dysfunction and FIGURE 1.…”