20(S)-protopanaxadiol regio-selectively targets androgen receptor: anticancer effects in castration-resistant prostate tumors

Abstract

We have explored the effects of 20(S)-protopanaxadiol (aPPD), a naturally derived ginsenoside, against androgen receptor (AR) positive castration resistant prostate cancer (CRPC) xenograft tumors and have examined its interactions with AR. In silico docking studies for aPPD binding to AR, alongside transactivation bioassays and in vivo efficacy studies were carried out in the castration-resistant C4-2 xenograft model. Immunohistochemical (IHC) and Western blot analyses followed by evaluation of AR, apoptotic, cell cycle and proliferative markers in excised tumors was performed. The growth of established CRPC tumors was inhibited by 53% with aPPD and a corresponding decrease in serum PSA was seen compared to controls. The IHC data revealed that Ki-67 was significantly lower for aPPD treated tumors and was associated with elevated p21 and cleaved caspase-3 expression, compared to vehicle treatment. Furthermore, aPPD decreased AR protein expression in xenograft tumors, while significantly upregulating p27 and Bax protein levels. In vitro data supporting this suggests that aPPD binds to and significantly inhibits the N-terminal or the DNA binding domains of AR. The AR androgen binding site docking score for androgen (dihydrotestosterone) was −11.1, while that of aPPD was −7.1. The novel findings described herein indicate aPPD potently inhibits PCa in vivo partly via inhibition of a site on the AR N-terminal domain. This manifested as cell cycle arrest and concurrent induction of apoptosis via an increase in Bax, cleaved-caspase-3, p27 and p21 expression.

Anti-Tumor Effects of Ginsenoside 20(S)-Protopanaxadiol and 1,25-Dihydroxyvitamin D3 Combination in Castration Resistant Prostate Cancer

“…Treatment Pharmacokinetic interactions between calcitriol and aPPD can lead to increased antitumor effects in vivo. We have shown that aPPD and calcitriol independently demonstrate anticancer effects in prostate cancer models [21,25]. Our lab has also shown that CYP3A4 is responsible for the hepatic metabolism and inactivation of calcitriol and aPPD is a CYP3A4 inhibitor [72,73].…”

“…Mooso et al (2010) have shown that the increase in AR expression caused a decrease in VDR levels, which was mediated through the shared coregulators [55]. Calcitriol can increase AR protein expression in LNCaP prostate cancer cells [55], while we have previously shown that aPPD significantly inhibited AR protein expression and activities in vivo in the C4-2 xenograft mouse model [25]. Cao et al (2014) reported suppression of full length and splice variant AR expression in castration-resistant 22Rv1 xenograft tumors [28].…”

“…Tumor volume measurements were taken twice every week. Calipers were used to measure the three perpendicular axes of each tumor (volume = 1 4 length × width × weight × 0.5326) [25]. During the treatment period, animals were monitored twice per week for changes in body weight (g) and monitored daily for the appearance and signs of acute toxicity including death, lethargy, blindness, and disorientation.…”

“…Among several ginseng derivatives, aPPD has been characterized as one of the most potent ginsenoside metabolite with reported anticancer effects in prostate cancer, breast cancer, and leukemia [21][22][23][24]. The work from our laboratory has demonstrated that aPPD can demonstrate anticancer effects in androgen-dependent LNCaP and androgen-independent C4-2 cells in vitro and inhibits PCa xenograft growth in preclinical models [21,22,[25][26][27][28][29][30]. In addition, aPPD has the antioxidant and anti-inflammatory properties, which can positively affect the anticancer mechanism [31].…”

Preclinical and Clinical Research Models of Prostate Cancer: A Brief Overview

“…Because steroidogenic enzyme levels are relatively higher in tissues than in secondary cell lines, the measurement of steroidogenesis is much more robust and measurable in HPH [ 34 ]. Both the classical and backdoor steroidogenesis pathways are observed in HPH with DHT as the end product [ 107 , 108 , 109 ]. SRD5A isoforms and CYP17A1 enzymes are detected in Western blot and activity studies in HPH [ 104 ] which provides mechanistic insight into steroidogenesis and its inhibitors.…”