The Dual Androgen Receptor and Glucocorticoid Receptor Antagonist CB-03-10 as Potential Treatment for Tumors that have Acquired GR-mediated Resistance to AR Blockade.

CB-03-10 (cortexolone 17α-valerate-21-propionate) is a synthetic steroidal compound derived from cortexolone (11-deoxycortisone), an intermediate in cortisol biosynthesis. Characterization of the activity of CB-03-10 and its main related compound CB-03-05 (cortexolone 17α-valerate) included in vitro binding to the androgen and glucocorticoid receptors (AR and GR), antagonism of AR and GR transcriptional activities, and screening for antitumor activity across a selected panel of human prostate and in triple-negative breast cancer cell lines. CB-03-10 cytotoxic activity in these cancer cell lines was in the low micromolar range and was primarily associated with induction of the apoptotic cascade via activation of caspases. The compound's potential for antitumor activity was verified in a murine xenograft model utilizing the AR-positive LNCaP prostate cancer cell line as well as in an orthotopic model utilizing AR-negative/GR-positive MDA-MB-231 breast cancer cell line. Orally administered CB-03-10 inhibited prostate tumor growth and orthotopically implanted breast tumor growth in these mice and maintained body weight, as compared with vehicle-treated mice. On the basis of AR/GR binding affinities, antagonism of androgen and glucocorticoid-dependent transcriptional activities, and AR/GR mRNA and protein expression, the mechanism of tumor growth suppression is related to AR and GR antagonist activities. Importantly, these compounds lack biologically relevant AR/GR agonist activities. Overall, these preclinical findings support the selection of CB-03-10 for further development as an anticancer agent in cases where resistance to AR-targeted therapy or chemotherapy, via upregulation of GR activity, continues to limit the efficacy and duration of clinical benefit with these interventions.

Rifamycin SV exhibits strong anti-inflammatory in vitro activity through pregnane X receptor stimulation and NFκB inhibition.

Rifamycin SV (rifamycin), is a member of the ansamycin family of antimicrobial compounds which kills bacteria commonly associated with infectious diarrhea and other enteric infections. Rifamycin has been found to be effective in experimental animal models of gut inflammation and its efficacy in these settings has been attributed partially to immunomodulatory non-bactericidal activities. This study aimed to further evaluate the anti-inflammatory activities of rifamycin by analyzing its effect on two key regulators of inflammation: PXR and NFκB. Rifamycin stimulated PXR transcriptional activity in two PXR reporter cell lines and induced expression of two genes known to be regulated by PXR and are directly involved in cellular detoxification: CYP3A4 and PgP. Moreover, CYP3A4 metabolic activity was induced by rifamycin in HepG2 cells. Rifamycin also antagonized TNFα and LPS-induced NFκB activities and inhibited IL1ß-induced synthesis of inflammatory chemokine, IL8. Although reciprocal regulation of PXR and NFkB by rifamycin was not directly addressed, the data suggest that in the absence of PXR, inhibition of NFκB by rifamycin is not dependent on PXR stimulation. Thus, rifamycin exhibits potent anti-inflammatory activities, characterized by in vitro PXR activation and concomitant CYP3A4 and PgP induction, in parallel with potent NFκB inhibition and concomitant IL8 inhibition.

Cortexolone 17α-propionate (Clascoterone) Is a Novel Androgen Receptor Antagonist that Inhibits Production of Lipids and Inflammatory Cytokines from Sebocytes In Vitro

Cortexolone 17α-propionate (clascoterone) is a novel topical androgen antagonist that is being analyzed for its ability to treat acne. The pathogenesis of acne is attributed to multiple factors, including altered sebum production, inflammatory processes, dysregulation of the hormone microenvironment, and the proliferation of the skin commensal bacteria, Propionibacterium acnes (P. acnes). Androgens induce the proliferation and differentiation of sebocytes, (cells that comprise the sebaceous gland), help regulate the synthesis of the lipids that are incorporated into sebum and stimulate the production of cytokines that are found in inflammatory acne lesions. Several studies have established that clascoterone is a potent antiandrogen that is well tolerated and has selective topical activity. Its potency as an acne therapeutic is currently being analyzed in a large phase 3 clinical trial. The study described herein elucidates for the first time the mechanism of action of clascoterone. Clascoterone was found to bind the androgen receptor (AR) with high affinity in vitro, inhibit AR-regulated transcription in a reporter cell line, and antagonize androgen-regulated lipid and inflammatory cytokine production in a dose-dependent manner in human primary sebocytes. In particular, when compared to another AR antagonist, spironolactone, clascoterone was significantly better at inhibiting inflammatory cytokine synthesis from sebocytes. Therefore, clascoterone may be an excellent candidate to be the first topical antiandrogen to treat acne. J Drugs Dermatol. 2019;18(5):412-418.