A first in-human study of A166 in patients with locally advanced/metastatic solid tumors which are HER2-positive or HER2-amplified who did not respond or stopped responding to approved therapies.

Abstract

1049 Background: HER2 is an effective therapeutic target for breast and gastric cancer. A166 is an antibody-drug conjugate composed of a novel cytotoxic drug site-specifically conjugated to transtuzumab sequence via a stable protease-cleavable valine citrulline linker. Methods: This was a single arm, open-label, multicenter, dose escalating Phase 1 first-in-human study of A166 as monotherapy in solid tumor patients. Dose escalation and MTD identification was directed using a Bayesian logistic regression model with overdose control. The following dose levels were evaluated in this study: 0.3, 1.2, 3.6, 4.8 mg/kg. (ClinicalTrials.gov NCT03602079) Results: As of November 1, 2019 35 pts have completed the DLT evaluation period across 4 dose levels. Overall, A166 had an acceptable toxicity profile with no unexpected toxicities related to the study drug. No adverse events recorded met the protocol specified definition of a dose limiting toxicity at any studied dose level. Most frequently (≥10%) occurring TEAEs include were Keratitis, Decreased appetite, Dry eye, Vision blurred etc. Overall incidence of ophthalmic toxicities in the 3.6 mg/kg cohort was 80% and in the 4.8 mg/kg cohort it was 83%. Among the 27 patients evaluable for efficacy, best response was progression of disease in 11 patients (41%), stable disease in 9 patients (33%) and partial response in 7 patients (26%), for the total disease control rate of 59%.Responses were seen only at the dose levels of 3.6 mg/kg and 4.8 mg/kg. Conclusions: A166 demonstrated clinically meaningful efficacy in heavily pretreated patients with relapsed or refractory advanced solid cancers. The achievement of an ORR of 36% at efficacious dose levels and up to 100% in HER2 positive patients regardless of histology (2 CRC, 1 BC and 1 NSCLC) at the highest studied dose level exceed Clinical trial information: NCT03602079 .