Downregulation of Androgen Receptor Transcription by Promoter G-Quadruplex Stabilization as a Potential Alternative Treatment for Castrate-Resistant Prostate Cancer

Abstract

Androgen receptor (AR) signaling remains an important regulatory pathway in castrate-resistant prostate cancer, and its transcriptional downregulation could provide a new line of therapy. A number of small-molecule ligands have previously demonstrated the ability to stabilize G-quadruplex structures and affect gene transcription for those genes whose promoters contain a quadruplex-forming sequence. Herein, we report the probable formation of new G-quadruplex structure present in the AR promoter in a transcriptionally important location. NMR spectroscopy, circular dichroism, UV spectroscopy, and UV thermal melting experiments for this sequence are consistent with G-quadruplex formation. Fluorescence resonance energy transfer (FRET) melting studies have identified a novel compound, MM45, which appears to stabilize this G-quadruplex at submicromolar concentrations. The effects of MM45 have been investigated in prostate cancer cell lines where it has been shown to inhibit cell growth. A reporter assay intended to isolate the effect of MM45 on the G-quadruplex sequence showed dose-dependent transcriptional repression only when the AR promoter G-quadruplex sequence is present. Dose-dependent transcriptional repression of the AR by MM45 has been demonstrated at both a protein and mRNA level. This proof of concept study paves the route toward a potential alternative treatment pathway in castrate-resistant prostate cancer.

Permanganate/S1 Nuclease Footprinting Reveals Non-B DNA Structures with Regulatory Potential across a Mammalian Genome

“…After gene name mapping, we found 374 human and mouse homologous oncogenes. Non-B DNA structures at promoter regions of AR, CSF1R, HRAS, KIT, PDGFRB, RET human cancer-related genes had previously been proposed to have regulatory function (Brooks and Hurley, 2009;Mitchell et al, 2013;Qin et al, 2010;Ray and Ray, 2015). The statistical significance of the oncogene analysis was assessed using the hypergeometric test (no p value correction was needed).…”

Telomerase Inhibition, Telomere Shortening, and Cellular Uptake of the Perylene Derivatives PM2 and PIPER in Prostate Cancer Cells

“…20) In the same manner, G-quadruplex ligands have been shown to stabilize the G-quadruplex structure on the G-quadruplex motif from the promoters of several genes controlling cellular proliferation, such as c-MYC, c-KIT, k-RAS, and vascular endothelial growth factor (VEGF), among others, leading to the down-regulation of these genes and antiproliferative activity in cancer cell lines. 21) Moreover, Gquadruplex ligands were also found to facilitate G-quadruplex formation at the androgen receptor (AR) promoter, leading to the down-regulation of AR gene expression in AR-positive prostate cancer cells. 22,23) Several perylene derivatives have been found to be Gquadruplex ligands and telomerase inhibitors.…”

Discovery of new G-quadruplex binding chemotypes

“…Comparison with the behaviour of a tetra-substituted naphthalenediimide compound previously examined by us 20 , shows that 1–6 exhibit only moderate ΔT m values with the AR G4, which are generally lower than with other G4s. Compounds 1–6 produced slightly reduced but still significant stabilisation with the c- KIT 2 and k- RAS 21 G4s, suggesting that these compounds have the ability to act simultaneously on multiple G4 targets (G4 poly-targeting).…”

“…The ten most active compounds were subsequently screened against an expanded panel of fluorescently-labelled promoter G4-forming sequences, with HSP90A, HSP90B (heat shock protein 90 promoter sequences), 12 k-RAS 21 (in the promoter of the k-RAS oncogene) 19 and AR, a G4 recently identified in the promoter of the androgen receptor (involved in prostate cancer development). 20 …”