A-ring-fused pyrazoles of dihydrotestosterone targeting prostate cancer cells via the downregulation of the androgen receptor

Abstract

High expression of the androgen receptor (AR) and the disruption of its regulation are strongly responsible for the development of prostate cancer (PCa). Therapeutically relevant non-steroidal or steroidal antiandrogens are able to block the AR effect by eliminating AR-mediated signalling. Herein we report the synthesis of novel steroidal pyrazoles derived from the natural sex hormone 5α-dihydrotestosterone (DHT). 2-Ethylidene or 2-(hetero)arylidene derivatives of DHT obtained by regioselective Claisen-Schmidt condensation with acetaldehyde or (hetero)aromatic aldehydes in alkaline ethanol were reacted with monosubstituted hydrazines to give A-ring-fused 1,5-disubstituted pyrazoles as main or exclusive products, depending on the reaction conditions applied. Spontaneous or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)-induced oxidation of the primarily formed pyrazolines resulted in the desired products in moderate to good yields, while 17-oxidation also occurred by using the Jones reagent as a strong oxidant. Transcriptional activity of the AR in a reporter cell line was examined for all novel compounds, and several previously synthesized similar DHT-based pyrazoles with differently substituted heteroring were also included to obtain information about the structure-activity relationship. Two specific regioisomeric groups of derivatives significantly diminished the transcriptional activity of the AR in reporter cell line in 10 μM concentration, and displayed reasonable antiproliferative activity in AR-positive PCa cell lines. Lead compound (3d) was found to be a potent AR antagonist (IC₅₀ = 1.18 μM), it generally suppressed AR signalling in time and dose dependent manner, moreover, it also led to a sharp decrease in wt-AR protein level probably caused by proteasomal degradation. We confirmed the antiproliferative activity of 3d in AR-positive PCa cell lines (with GI₅₀ in low micromolar ranges), and its cellular, biochemical and in silico binding in AR ligand-binding domain. Moreover, compound 3d was shown to be potent even ex vivo in patient-derived tissues, which highlights the therapeutic potential of A-ring-fused pyrazoles.

Keywords: A-ring-fused pyrazoles; Androgen receptor; Prostate cancer; Protein degradation; Structure-activity relationship; Transcriptional activity.