WNC0901 is a novel DNA-PK inhibitor and potent radiosensitizer of otherwise radioresistant solid tumors

Therapeutic resistance limits the efficacy of radiation therapy in many tumors and provides a compelling rationale to develop novel treatments to enhance radiation sensitivity. DNA-dependent protein kinase (DNA-PK) is a major mediator of DNA repair following radiation, and DNA-PK inhibitors are effective radiosensitizers. WNC0901 is a potent DNA-PK inhibitor in both a cell-free kinase assay (IC50 = 0.073 nM) and a cell-based assay (IC50 = 76 nM). WNC0901 has a 30-fold specificity for DNA-PK relative to other PI3K-related kinases. In a broader kinome screen (363 kinases), 1 μM WNC0901 resulted in >25% inhibition of only five other kinases. There is robust inhibition of radiation-induced DNA-PK autophosphorylation (Ser-2056), as analyzed by Western blotting, with maximal effect at 300 nM WNC0901 in A549 (lung carcinoma), U2OS (osteosarcoma), and HT29 (colorectal) cells. The efficacy of WNC0901 as a radiosensitizer was evaluated in clonogenic assays across these same three radioresistant tumor models. Following treatment with graded concentrations of WNC0901 (0-1000 nM) combined with 2.5 Gy radiation, maximal effects were observed at a 300 nM concentration in A549 (88-fold reduction in relative clonogenic survival compared to RT alone, p<0.001), U2OS (5.8-fold decrease, p=0.002), and HT29 (59-fold decrease, p=0.008) In a full radiation clonogenic, the sensitizer enhancement ratio at 10% survival (SER10) was 3.8 (A549), 2.3 (U2OS), and 1.8 (HT29). In vitro metabolism studies have identified demethylated WNC0901 (WNC0901-M) as a major metabolite. Similar to the parent drug, WNC0901-M is a potent DNA-PK inhibitor with maximal radiosensitizing effects of the metabolite observed at 300nM with SER10 of 2.4 (A549), 1.9 (U2OS), and 1.8 (HT29). The in vivo efficacy of 50 mg/kg WNC0901 combined with 8 Gy was evaluated and compared to another DNA-PK inhibitor, 50 mg/kg peposertib, in A549 tumor heterotopic xenografts. Compared to placebo (median time to endpoint 63 days) or RT alone (median 72 days), the combination of WNC0901 and RT significantly delayed tumor regrowth (median 169 days; p=0.002 compared to RT). Interestingly, peposertib + RT was ineffective (median 83 days; p=0.332 compared to RT). In a second study, similarly robust sensitizing effects of WNC0901 was observed in HT29 xenografts (placebo - median 45 days; RT - median 75 days; RT + WNC0901 - median >110 days; p=.03 relative to RT). Together, these findings demonstrate the robust radiosensitizing effects of WNC0901 in radioresistant tumors and provide a rationale for continued development of this drug.