Multicenter, Open-Label, Phase I Study of DSP-7888 Dosing Emulsion in Patients with Advanced Malignancies

Background Wilms' tumor 1 (WT1) is overexpressed in various malignancies. DSP-7888 Dosing Emulsion, also known as ombipepimut-S (United States Adopted Name; International Nonproprietary Name: adegramotide/nelatimotide), is an investigational therapeutic cancer vaccine comprising two synthetic peptides derived from WT1 to promote both cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte-mediated immune responses against WT1-expressing tumors. Objective The aim of this study was to report the results from a phase I dose-escalation study (NCT02498665) that evaluated DSP-7888, administered either intradermally (ID) or subcutaneously (SC), in patients with recurrent or advanced malignancies associated with overexpression of WT1. Patients and Methods In this phase I dose-escalation study, patients with recurrent or advanced malignancies associated with overexpression of WT1 who progressed on, were intolerant to, or not a candidate for standard therapy or who presented with a malignancy that had no definite standard therapy received escalating doses of ID or SC DSP-7888 in a rolling-six study design. DSP-7888 3.5, 10.5, or 17.5 (ID only) mg was administered until disease progression or other discontinuation event. Primary objectives were safety, tolerability, and identification of the recommended phase II dose (RP2D). Overall survival (OS) and WT1-specific CTL induction were included as secondary and exploratory objectives, respectively. Results Twenty-four patients received either ID (3.5 mg, n = 4; 10.5 mg, n = 3; 17.5 mg, n = 3) or SC DSP-7888 (3.5 mg, n = 9; 10.5 mg, n = 5). No dose-limiting toxicity was observed. The most frequent treatment-emergent adverse event was injection site reactions (ID, 100% [10/10]; SC, 35.7% [5/14]); all were grade 1 or 2. Four patients (ID 17.5 mg, n = 1; SC 3.5 mg, n = 1; SC 10.5 mg, n = 2) had stable disease, 16 had progressive disease, and four were not evaluable. Median (95% confidence interval) OS duration was 180.0 (136.0-494.0) days. Among evaluable patients, WT1-specific CTL induction was observed in 66.7% (6/9) and 41.7% (5/12) of those administered ID and SC DSP-7888, respectively. Conclusions DSP-7888 Dosing Emulsion was well tolerated, with no dose-limiting toxicities, in patients with recurrent or advanced malignancies. Higher WT1-specific CTL induction activity was noted with ID compared with SC administration; because of this, the ID route was selected for further evaluation in the clinical program.