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Novel inhibitors of Rad6 ubiquitin conjugating enzyme: design, synthesis, identification, and functional

Matthew A Sanders1,2, Ghali Brahemi3, Pratima Nangia-Makker1,4

  • 1Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan.

Molecular Cancer Therapeutics
|January 23, 2013
PubMed

Insights

Researchers developed the first small molecule inhibitors (SMIs) targeting the E2 enzyme Rad6B, crucial for DNA repair and cancer progression. These inhibitors show promise in blocking cancer cell growth and reducing key cancer-associated proteins.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Oncology

Background:

  • Protein ubiquitination is vital for cellular processes including DNA repair and signaling, with dysregulation frequently observed in cancer.
  • Ubiquitin-conjugating enzymes (E2) are key mediators of ubiquitination, offering a target for specific cancer therapies.
  • Selective E2 small molecule inhibitors (SMIs) promise greater specificity compared to proteasome inhibitors.

Purpose of the Study:

  • To synthesize and functionally characterize the first small molecule inhibitors (SMIs) of the human E2 enzyme Rad6B.
  • To identify novel E2 inhibitor candidates using a pharmacophore model and virtual screening.
  • To evaluate the efficacy of identified SMIs in inhibiting Rad6B activity and impacting cancer cell behavior.

Main Methods:

  • Generation of a pharmacophore model for E2 ubiquitin-binding sites for virtual screening.
  • In silico molecular docking of triazine (TZ) analogs to the Rad6B X-ray structure.
  • In vitro verification of inhibitor effects on Rad6B-mediated histone H2A ubiquitination.
  • Assessment of cancer cell proliferation, colony formation, migration, cell cycle arrest, and apoptosis.
  • Analysis of endogenous Rad6 activity and β-catenin protein levels in treated cancer cells.

Main Results:

  • Twelve triazine (TZ) analogs were screened, with TZs #8 and 9 showing high complementarity to the Rad6B catalytic site.
  • TZs #1, 2, 8, and 9 effectively inhibited Rad6B-ubiquitin thioester formation and histone H2A ubiquitination.
  • SMI #9 demonstrated selectivity, not affecting UbcH5-mediated BCA2 ubiquitination.
  • SMI #9 potently inhibited breast cancer cell proliferation, colony formation, and migration, inducing G2-M arrest and apoptosis.
  • Treatment with SMIs #8 and 9 decreased endogenous Rad6 activity and reduced β-catenin protein levels.

Conclusions:

  • The study successfully identified and characterized the first small molecule inhibitors (SMIs) targeting the human E2 enzyme Rad6B.
  • These novel Rad6B SMIs demonstrate potent anti-cancer effects, including inhibition of proliferation and induction of apoptosis in breast cancer cells.
  • The findings highlight Rad6B as a promising therapeutic target in cancer, with potential for developing more specific and effective cancer treatments.

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