Salivary gland tissue chip screening identifies candidate radioprotective drugs

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. 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. 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. 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. Salivary glands are often damaged in patients undergoing radiation therapy to treat head and neck cancers. Lack of saliva results in a poor quality of life for these patients. Currently there are no good drugs that patients can take to protect their salivary glands from radiation damage. We used a system that models the salivary gland called a tissue chip to test a large panel of drugs to see if they can prevent damage by radiation. We identified several drug candidates that could protect mouse salivary glands from radiation. These drugs should now be further investigated as they could potentially be used to protect the salivary glands of patients undergoing radiation therapy. Piraino, Chen, Mereness et al use a salivary gland tissue chip for high-content radioprotective drug discovery. Three drugs are identified that exhibit higher potency and equivalent radioprotection to Amifostine, the only FDA approved drug that is rarely used clinically due to severe side effects and lack of efficacy.