Discovery of Highly Potent and Efficient PROTAC Degraders of Androgen Receptor (AR) by Employing Weak Binding Affinity VHL E3 Ligase Ligands

Abstract

Androgen receptor (AR) is a validated therapeutic target for the treatment of metastatic castration-resistant prostate cancer (mCRPC). We report herein our design, synthesis, and biological characterization of highly potent smallmolecule proteolysis targeting chimera (PROTAC) AR degraders using a potent AR antagonist and E3 ligase ligands with weak binding affinities to VHL protein. Our study resulted in the discovery of 11 (ARD-266), which effectively induces degradation of AR protein in AR-positive (AR+) LNCaP, VCaP, and 22Rv1 prostate cancer cell lines with DC 50 values of 0.2−1 nM. ARD-266 is capable of reducing the AR protein level by >95% in these AR+ prostate cancer cell lines and effectively reduces ARregulated gene expression suppression. For the first time, we demonstrated that an E3 ligand with micromolar binding affinity to its E3 ligase complex can be successfully employed for the design of highly potent and efficient PROTAC degraders and this finding may have a significant implication for the field of PROTAC research.

Current strategies for the design of PROTAC linkers: a critical review

“…Pfaff et al [100], identified that the difference in linker length between the trans and cis azobenzene isomers was approximately 3-4 A� , which has a great similarity to the critical difference in linker length between active and inactive degraders for several published PROTACs (around 3 A� ). They used an ortho-F 4 -azobenzene to generate a bistable "photoPROTAC" (79), which could be switched between photostationary states (PSS) by irradiation at 415 nm or 530 nm. Irradiation at 415 nm gave rise to a PSS with 95% trans-79, whilst irradiation at 530 nm led to a PSS with 68% cis-79.…”

Extended pharmacodynamic responses observed upon PROTAC-mediated degradation of RIPK2

“…Although PROTAC technology was first described nearly 20 years ago 4 , there has been a dramatic increase in interest and activity catalysed by improvements in the embedded E3 ligase binders [5][6][7][8] which have delivered higher cell permeability. These improvements have increased cellular protein degradation potency of PROTACs from the high micromolar range to the low or even sub-nanomolar range [9][10][11][12] .…”

Prey for the Proteasome: Targeted Protein Degradation—A Medicinal Chemist's Perspective

“…On the other hand, due to its catalytic mode of action already a low concentration of PROTAC can be sufficient for effective degradation. Half maximal degradation concentrations (DC 50 s) in the low‐ and sub nanomolar range are commonly observed even when binding to the E3 ligase or the target protein are only in the micromolar range . However, membrane permeability poses a significant challenge for molecules of this size and polarity.…”

“…While several assays have been described for the in vitro optimization of PROTACs very little is known about how to design PROTACs for in vivo applications. Despite various xenograft studies using PROTACs are reported, optimization strategies for in vivo experiments are only beginning to emerge . The recently published study on improving bioavailability of a previously unstable Bruton's tyrosine kinase PROTAC to yield a compound with reduced clearance, increased half‐life and exposure is the beginning of hopefully many more examples to follow .…”