Orally Bioavailable Androgen Receptor Degrader, Potential Next-Generation Therapeutic for Enzalutamide-Resistant Prostate Cancer

Clin Cancer Res. 2019 Nov 15;25(22):6764-6780. doi: 10.1158/1078-0432.CCR-19-1458. Epub 2019 Sep 3.

Abstract

Purpose: Androgen receptor (AR)-targeting prostate cancer drugs, which are predominantly competitive ligand-binding domain (LBD)-binding antagonists, are inactivated by common resistance mechanisms. It is important to develop next-generation mechanistically distinct drugs to treat castration- and drug-resistant prostate cancers.

Experimental design: Second-generation AR pan antagonist UT-34 was selected from a library of compounds and tested in competitive AR binding and transactivation assays. UT-34 was tested using biophysical methods for binding to the AR activation function-1 (AF-1) domain. Western blot, gene expression, and proliferation assays were performed in various AR-positive enzalutamide-sensitive and -resistant prostate cancer cell lines. Pharmacokinetic and xenograft studies were performed in immunocompromised rats and mice.

Results: UT-34 inhibits the wild-type and LBD-mutant ARs comparably and inhibits the in vitro proliferation and in vivo growth of enzalutamide-sensitive and -resistant prostate cancer xenografts. In preclinical models, UT-34 induced the regression of enzalutamide-resistant tumors at doses when the AR is degraded; but, at lower doses, when the AR is just antagonized, it inhibits, without shrinking, the tumors. This indicates that degradation might be a prerequisite for tumor regression. Mechanistically, UT-34 promotes a conformation that is distinct from the LBD-binding competitive antagonist enzalutamide and degrades the AR through the ubiquitin proteasome mechanism. UT-34 has a broad safety margin and exhibits no cross-reactivity with G-protein-coupled receptor kinase and nuclear receptor family members.

Conclusions: Collectively, UT-34 exhibits the properties necessary for a next-generation prostate cancer drug.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Androgen Receptor Antagonists / administration & dosage
  • Androgen Receptor Antagonists / adverse effects
  • Androgen Receptor Antagonists / pharmacokinetics
  • Androgen Receptor Antagonists / pharmacology*
  • Animals
  • Antineoplastic Agents / administration & dosage
  • Antineoplastic Agents / adverse effects
  • Antineoplastic Agents / pharmacokinetics
  • Antineoplastic Agents / pharmacology*
  • Biomarkers, Tumor
  • Cell Line, Tumor
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Drug Resistance, Neoplasm* / genetics
  • Gene Expression
  • Humans
  • Male
  • Mice
  • Mutation
  • Phenylthiohydantoin / administration & dosage
  • Phenylthiohydantoin / adverse effects
  • Phenylthiohydantoin / analogs & derivatives*
  • Phenylthiohydantoin / pharmacology
  • Prostatic Neoplasms / drug therapy
  • Prostatic Neoplasms / metabolism*
  • Prostatic Neoplasms / pathology
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Binding
  • Proteolysis
  • Rats
  • Receptors, Androgen / genetics
  • Receptors, Androgen / metabolism
  • Signal Transduction / drug effects
  • Ubiquitin / metabolism
  • Xenograft Model Antitumor Assays

Substances

  • Androgen Receptor Antagonists
  • Antineoplastic Agents
  • Biomarkers, Tumor
  • Receptors, Androgen
  • Ubiquitin
  • Phenylthiohydantoin
  • enzalutamide
  • Proteasome Endopeptidase Complex