A phase 1 trial of intravenous 4-( N -( S -glutathionylacetyl)amino) phenylarsenoxide (GSAO) in patients with advanced solid tumours

Background 4-( N -( S -glutathionylacetyl)amino) phenylarsenoxide (GSAO) is a water-soluble mitochondrial toxin that binds to adenine nucleotide translocase in the inner mitochondrial membrane, thereby targeting cell proliferation. This phase 1 study investigated safety, dose-limiting toxicities (DLTs), maximum tolerated dose (MTD) and pharmacokinetics (PK) of GSAO as a daily 1-h infusion for 5 days a week for 2 weeks in every three. Pharmacodynamics of GSAO was evaluated by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and circulating markers of angiogenesis. Methods Patients with advanced solid tumours received GSAO in a dose-escalation trial according to a standard ‘3 + 3’ design that was guided by toxicity and, for the final dose escalation, by arsenic PK data. Results A total of 34 patients were treated with GSAO across 9 dose levels (1.3–44.0 mg/m 2 ). Treatment was well tolerated with few adverse events. An additional three patients were enrolled at the 12.4 mg/m 2 dose level following a DLT of derangement of liver function tests (grade 4). At the 44.0 mg/m 2 dose level, two out of three patients had DLTs (reversible encephalopathy; paroxysmal atrial fibrillation). Conclusions The MTD of GSAO was 22.0 mg/m 2 /day. There was no biomarker evidence from DCE-MRI or circulating markers of angiogenesis of an anti-vascular effect of GSAO.