Background: OM is a common, painful, and costly toxicity associated with cytotoxic regimens used to treat H&N cancers, which may result in radiotherapy treatment interruptions to negatively impact tumor control. There are currently no approved interventions to successfully prevent or delay OM onset among patients being treated with radiation therapy, with or without concomitant chemotherapy (CRT). Oxidative stress is a critical event in OM’s pathogenesis. Through its effect on Nrf2, ST-617 has marked anti-oxidative activity/properties. Supportive Therapeutics is developing ST-617, a dithioethione, for the attenuation of OM onset, duration and severity. The objective of this trial was to assess the safety, tolerability, PK, PD and efficacy of ST-617 in patients at high risk of severe OM (SOM). Methods: A dose escalation trial in which ST-617 administered as an oral suspension, 1-2 hours before the administration of daily RT fractions was performed at 9 study sites in South Africa and Australia. Eighteen patients with diagnoses of oral or oropharyngeal CA were enrolled (up to 6 pts/dose). Patients received concomitant cisplatin either weekly or tri-weekly. ST-617 was administered 3 days prior to CRT, and then continuing daily until the end of treatment. Safety outcomes, using CTCAE criteria (v 4.03) were used. Dose escalation occurred in the absence of toxicity. OM occurrence and severity were assessed by trained and validated evaluators using WHO, NCI-CTC and RTOG criteria; scores were centrally assigned. The primary efficacy endpoints included the incidence and duration of SOM (WHO grades 3 or 4) vs historical controls. PD tracking measured total ROS/RNS, GSH/GSSG, regulation in plasma and buccal epithelial cells. Results: 17 pts completed the 50, 100 and 150mg/day with no safety issues. No early dose limiting toxicity (DLT) or serious Adverse Event linked to ST-617 were observed. AEs observed were mainly nausea which is usually associated with CRT as expected. The 100 mg/day dose has been well tolerated with no grade 4 OM. No CRT dose interruptions or delays due to OM has been observed. Total ROS/RNS levels in plasma and buccal samples show significant decrease with increased ST-617 dosing from 50 to 100 mg/day. Conclusions: ST-617 administration was safe at all doses tested. The course and severity of patients treated with ST-617 compared favorably with historical controls. Mechanistic correlation between ROS/RNS levels was seen. A randomized, controlled, double blind trial is planned with the recommended dose of 100mg/day. Clinical trial information: 20180138.