In bacteria, nucleotide excision repair (NER) plays a major role in repairing DNA damage from a wide variety of sources. Therefore, its inhibition offers potential to develop a new antibacterial in combination with adjuvants, such as UV light. To date, only one known chemical inhibitor of NER is 2-(5-Amino-1,3,4-thiadiazol-2-ylbenzo(f)chromen-3-one) (ATBC) exists and targets Mycobacterium tuberculosis NER. To enable the design of future drugs we need to understand its mechanism of action. To determine the mechanism of action, we used in silico structure-based prediction, which identified the ATP binding pocket of E. coli UvrA as a probable target. Growth studies in E. coli showed it was non-toxic alone, but able to impair growth when combined with DNA damaging agents, and as we predicted it reduced by ~70% UvrA’s ATPase rate. Since UvrA’s ATPase activity is necessary for effective DNA binding, we used single molecule microscopy to directly observe DNA association. We measured a ~7-fold reduction in UvrA molecules binding to a single molecule of dsDNA suspended between optically trapped beads. These data provide a clear mechanism of action for ATBC, and show that targeting UvrA’s ATPase pocket is effective and ATBC provides an excellent framework for the derivation of more soluble inhibitors that can be tested computationally for activity.

Cancer chemotherapeutics kill rapidly dividing cells, which includes cells of the immune system. The resulting neutropenia predisposes patients to infection, which delays treatment and is a major cause of morbidity and mortality. Here we have exploited the cytotoxicity of the anti-cancer compound cisplatin to screen for FDA-approved drugs that impair bacterial nucleotide excision DNA repair (NER), the primary mechanism bacteria use to repair cisplatin lesions. Five compounds have emerged of which three possess ideal antimicrobial properties including cell penetrance, specific activity for NER, and the ability to kill a multi-drug resistant clinically relevant E. coli strain. Targeting NER offers a new therapeutic approach for infections in cancer patients by combining antimicrobial activity with cancer chemotherapy.