First-in-human phase I study of the DNA-repair inhibitor DT01 in combination with radiotherapy in patients with skin metastases from melanoma

Background: DT01 is a DNA-repair inhibitor preventing recruitment of DNA-repair enzymes at damage sites. Safety, pharmacokinetics and preliminary efficacy through intratumoural and peritumoural injections of DT01 were evaluated in combination with radiotherapy in a first-in-human phase I trial in patients with unresectable skin metastases from melanoma. Methods: Twenty-three patients were included and received radiotherapy (30 Gy in 10 sessions) on all selected tumour lesions, comprising of two lesions injected with DT01 three times a week during the 2 weeks of radiotherapy. DT01 dose levels of 16, 32, 48, 64 and 96mg were used, in a 3+3 dose escalation design, with an expansion cohort at 96 mg. Results: The median follow-up was 180 days. All patients were evaluable for safety and pharmacokinetics. No dose-limiting toxicity was observed and the maximum-tolerated dose was not reached. Most frequent adverse events were reversible grades 1 and 2 injection site reactions. Pharmacokinetic analyses demonstrated a systemic passage of DT01. Twenty-one patients were evaluable for efficacy on 76 lesions. Objective response was observed in 45 lesions (59%), including 23 complete responses (30%). Conclusions: Intratumoural and peritumoural DT01 in combination with radiotherapy is safe and pharmacokinetic analyses suggest a systemic passage of DT01.