The antitumor toxin CD437 is a direct inhibitor of DNA polymerase [alpha]

ARTICLE

PUBLISHED ONLINE: 16 MAY 2016 | http://dx.doi.org/10.1038/nchembio.2082

Web End =DOI: 10.1038/NCHEMBIO.2082

The antitumor toxin CD437 is a direct inhibitor of DNA polymerase

Ting Han1, Maria Goralski2, Emanuela Capota2, Shae B Padrick3, Jiwoong Kim4,5, Yang Xie4,5 & Deepak Nijhawan1,2,5*

CD437 is a retinoid-like small molecule that selectively induces apoptosis in cancer cells, but not in normal cells, through an unknown mechanism. We used a forward-genetic strategy to discover mutations in POLA1 that coincide with CD437 resistance (POLA1R). Introduction of one of these mutations into cancer cells by CRISPR-Cas9 genome editing conferred CD437 resistance, demonstrating causality. POLA1 encodes DNA polymerase , the enzyme responsible for initiating DNA synthesis during the S phase of the cell cycle. CD437 inhibits DNA replication in cells and recombinant POLA1 activity in vitro. Both effects are abrogated by the identified POLA1 mutations, supporting POLA1 as the direct antitumor target of CD437. In addition, we detected an increase in the total fluorescence intensity and anisotropy of CD437 in the presence of increasing concentrations of POLA1 that is consistent with a direct binding interaction. The discovery of POLA1 as the direct anticancer target for CD437 has the potential to catalyze the development of CD437 into an anticancer therapeutic.

npg 201 6 Nature America, Inc. All rights reserved.

CD437, a retinoid-like small molecule, is a promising cancer drug lead on the basis of its potential to achieve a high therapeutic index (Fig. 1a). CD437 is toxic to numerous cancer cell

lines derived from different primary tumor types, including ovarian cancer, non-small-cell lung cancer, leukemia, breast cancer, and squamous cell carcinoma15. After CD437 treatment, cancer cells accumulate in the S phase of the cell cycle and then undergo apoptosis, characterized by loss of mitochondrial membrane potential, cytochrome c release, and caspase activation6,7. By contrast, CD437 does not induce apoptosis in normal human cells. Rather, both primary keratinocytes and normal human lung epithelial cells undergo arrest in the G1/S phase of the cell cycle, which is not followed by cell death8,9. Indeed, peritoneal administration of CD437 over 3 weeks led to regression of mouse xenograft tumors derived from human cancer cell lines, without any signs of toxicity3. The promise of CD437 as a therapeutic lead has inspired extensive chemical optimization yielding both potent and bioavailable derivatives,...