A small-molecule inhibitor of human DNA polymerase eta potentiates the effects of cisplatin in tumor cells.

Translesion DNA synthesis (TLS) performed by human DNA polymerase eta (hpol eta) allows tolerance of damage from cis-diamminedichloroplatinum(II) (CDDP or cisplatin). We have developed hpol eta inhibitors derived from N-aryl-substituted indole barbituric acid (IBA), indole thiobarbituric acid (ITBA), and indole quinuclidine scaffolds and identified 5-((5-chloro-1-(naphthalen-2-ylmethyl)-1H-indol-3-yl)methylene)-2-thioxodihydropyrimidine-4,6-(1H,5H)-dione (PNR-7-02), an ITBA derivative that inhibited hpol eta activity with an IC50 value of 8 mu M and exhibited 5-10-fold specificity for hpol eta over replicative pols. We conclude from kinetic analyses, chemical footprinting assays, and molecular docking that PNR-7-02 binds to a site on the little finger domain and interferes with the proper orientation of template DNA to inhibit hpol eta. A synergistic increase in CDDP toxicity was observed in hpol eta-proficient cells co-treated with PNR-7-02 (combination index values = 0.4-0.6). Increased gamma H2AX formation accompanied treatment of hpol eta-proficient cells with CDDP and PNR-7-02. Importantly, PNR-7-02 did not impact the effect of CDDP on cell viability or gamma H2AX in hpol eta-deficient cells. In summary, we observed hpol eta-dependent effects on DNA damage/replication stress and sensitivity to CDDP in cells treated with PNR-7-02. The ability to employ a small-molecule inhibitor of hpol eta to improve the cytotoxic effect of CDDP may aid in the development of more effective chemotherapeutic strategies.