Inhibitors of cullin-RING E3 ubiquitin ligase 4 with antitumor potential

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 8
• Main Authors: Wu, Kenneth, Huynh, Khoi Q, Lu, Iris, Moustakim, Moses, Miao, Haibin, Yu, Clinton, Haeusgen, Matthew J, Hopkins, Benjamin D, Huang, Lan, Zheng, Ning, Sanchez, Roberto, DeVita, Robert J, Pan, Zhen-Qiang
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 23.02.2021
• Subjects: Animals; Antineoplastic Agents - chemistry; Antineoplastic Agents - pharmacology; Apoptosis; Biological Sciences; Biomarkers, Tumor - genetics; Biomarkers, Tumor - metabolism; Cell Proliferation; Enzyme Inhibitors - chemistry; Enzyme Inhibitors - pharmacology; Female; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Neoplastic - drug effects; Humans; Leukemia, Myeloid, Acute - drug therapy; Leukemia, Myeloid, Acute - enzymology; Leukemia, Myeloid, Acute - pathology; Mice; Mice, Inbred BALB C; Mice, Nude; Tumor Cells, Cultured; Ubiquitin - metabolism; Ubiquitin-Protein Ligases - antagonists & inhibitors; Ubiquitination; Xenograft Model Antitumor Assays; cullin4; tumor inhibition; E3 CRL4; protein degradation; small-molecule inhibitors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2007328118

Cullin-RING (really intersting new gene) E3 ubiquitin ligases (CRLs) are the largest E3 family and direct numerous protein substrates for proteasomal degradation, thereby impacting a myriad of physiological and pathological processes including cancer. To date, there are no reported small-molecule inhibitors of the catalytic activity of CRLs. Here, we describe high-throughput screening and medicinal chemistry optimization efforts that led to the identification of two compounds, 33-11 and KH-4-43, which inhibit E3 CRL4 and exhibit antitumor potential. These compounds bind to CRL4's core catalytic complex, inhibit CRL4-mediated ubiquitination, and cause stabilization of CRL4's substrate CDT1 in cells. Treatment with 33-11 or KH-4-43 in a panel of 36 tumor cell lines revealed cytotoxicity. The antitumor activity was validated by the ability of the compounds to suppress the growth of human tumor xenografts in mice. Mechanistically, the compounds' cytotoxicity was linked to aberrant accumulation of CDT1 that is known to trigger apoptosis. Moreover, a subset of tumor cells was found to express cullin4 proteins at levels as much as 70-fold lower than those in other tumor lines. The low-cullin4-expressing tumor cells appeared to exhibit increased sensitivity to 33-11/KH-4-43, raising a provocative hypothesis for the role of low E3 abundance as a cancer vulnerability.