Small molecule TSC01682 inhibits osteosarcoma cell growth by specifically disrupting the CUL4B-DDB1 interaction and decreasing the ubiquitination of CRL4B E3 ligase substrates.

The direct interaction between Cullin 4B (CUL4B) and DNA damage-binding protein 1 (DDB1) is required for the assembly of Cullin4B-RING E3 ligase complex (CRL4B), which are involved in the tumorigenesis of osteosarcoma through ubiquitinating and degrading multiple tumor suppressors and cell cycle regulators. Thus, targeting CUL4B-DDB1 interaction to prevent the assembly of CRL4B may be a potent approach to inhibit osteosarcoma cell growth. In the present study, we identified six naturally-sourced small molecules that can specifically disrupt the CUL4B-DDB1 interaction using an in vitro high-throughput screening (HTS) system in yeast. We focused our investigation on revealing the molecular effects of TSC01682, the most active compound capable of inhibiting osteosarcoma cell growth. Biochemically, TSC01682 significantly repressed the CUL4B-DDB1 interaction in both yeast cells and osteosarcoma cells. Moreover, TSC01682 treatment in osteosarcoma cells also caused a decrease of other CRL4B components including CUL4-associated factor 11 (DCAF11) and DCAF13, but an increase of two CRL4B substrates including cyclin-dependent kinase inhibitor 1A (CDKN1A, also known as p21) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) through inhibiting their ubiquitination. Consistent with these molecular changes, TSC01682 treatment significantly inhibited cell proliferation, colony formation, invasion, and in vivo tumor growth. Collectively, our results suggest that TSC01682 is a potent compound capable of disrupting the CUL4B-DDB1 interaction, and it may be developed as a chemotherapeutic drug for osteosarcoma treatment. AJCR