The estrogen receptor (ER) is a validated target for the treatment of estrogen receptor-positive (ER+) breast cancer. Here, we describe the design, synthesis, and extensive structure–activity relationship (SAR) studies of small-molecule ERα degraders based on the proteolysis targeting chimeras (PROTAC) concept. Our efforts have resulted in the discovery of highly potent and effective PROTAC ER degraders, as exemplified by ERD-308 (32). ERD-308 achieves DC50 (concentration causing 50% of protein degradation) values of 0.17 and 0.43 nM in MCF-7 and T47D ER+ breast cancer cell lines, respectively, and induces >95% of ER degradation at concentrations as low as 5 nM in both cell lines. Significantly, ERD-308 induces more complete ER degradation than fulvestrant, the only approved selective ER degrader (SERD), and is more effective in inhibition of cell proliferation than fulvestrant in MCF-7 cells. Further optimization of ERD-308 may lead to a new therapy for advanced ER+ breast cancer.

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.

We report herein the discovery of exceptionally potent and orally bioavailable PROTAC AR degraders with ARD-2585 being the most promising compound. ARD-2585 achieves DC50 values of ≤0.1 nM in the VCaP cell line with AR gene amplification and in the LNCaP cell line carrying an AR mutation. It potently inhibits cell growth with IC50 values of 1.5 and 16.2 nM in the VCaP and LNCaP cell lines, respectively, and achieves excellent pharmacokinetics and 51% of oral bioavailability in mice. It is more efficacious than enzalutamide in inhibition of VCaP tumor growth and does not cause any sign of toxicity in mice. ARD-2585 is a promising AR degrader for extensive investigations for the treatment of advanced prostate cancer.

Proteolysis targeting chimera (PROTAC) small-molecule degraders have emerged as a promising new type of therapeutic agents, but the design of PROTAC degraders with excellent oral pharmacokinetics is a major challenge. In this study, we present our strategies toward the discovery of highly potent PROTAC degraders of androgen receptor (AR) with excellent oral pharmacokinetics. Employing thalidomide to recruit cereblon/cullin 4A E3 ligase and through the rigidification of the linker, we discovered highly potent AR degraders with good oral pharmacokinetic properties in mice with ARD-2128 being the best compound. ARD-2128 achieves 67% oral bioavailability in mice, effectively reduces AR protein and suppresses AR-regulated genes in tumor tissues with oral administration, leading to the effective inhibition of tumor growth in mice without signs of toxicity. This study supports the development of an orally active PROTAC AR degrader for the treatment of prostate cancer and provides insights and guidance into the design of orally active PROTAC degraders.

CuBr and ZnI(2) have been developed as catalysts or subcatalysts for the efficient asymmetric synthesis of axially chiral allenols with up to 97% ee from readily available propargylic alcohols, aliphatic or aromatic aldehyde, pyrrolidine, and commerically available ligands. The alcohol unit in the terminal alkynes plays a very important role for ensuring high enantioselectivity via coordination.