Salivary gland tissue chip screening identifies candidate radioprotective drugs.

BACKGROUND: Most head and neck cancer patients treated with ionizing radiation loose salivary gland function. Patients with decreased saliva have trouble eating, speaking and are predisposed to oral infections and tooth decay. Amifostine is the only FDA approved drug to prevent radiation-induced hyposalivation. However, it has intolerable side-effects that limit its use, motivating the discovery of alternative therapeutics. METHODS: We leveraged our salivary gland tissue chip platform for high-content drug discovery that we developed using submandibular gland tissue from female SKH1 hairless mice, backcrossed 6 generations with C57BL/6 J mice. We developed in-chip assays to quantify reduced glutathione and cellular senescence, which are accepted biomarkers of radiation damage. We validated radioprotection using WR-1065, the active form of Amifostine and tested other reported radioprotective drugs including Edaravone, Tempol, N-acetylcysteine, Rapamycin, Ex-Rad, and Palifermin. Next, a Selleck Chemicals library of FDA-approved drugs was screened for radioprotection. Lead hits were tested in mouse models. RESULTS: We identify 25 candidate compounds and down-select them using EC50 values and published pharmacologic data. This lead us to test Phenylbutazone (an anti-inflammatory), Enoxacin (a fluoroquinolone antibiotic), and Doripenem (a carbapenem antibiotic) for in vivo radioprotection in mice. Results confirm that these three drugs exhibit radioprotection equivalent to Amifostine but with superior EC50 values, ranging from 140 to 6900-fold lower values. CONCLUSIONS: This body of work demonstrates the development and validation of assays using a tissue chip platform for high-content drug screening and the successful discovery and in vivo validation of candidate radioprotective drugs with non-antioxidant primary modes of action. These results point to possible unknown mechanisms of radioprotection. These drugs can be developed to improve radioprotection efficacy and clinical administration without adverse side-effects.