Purpose: RC48 contains the novel humanized anti-HER2 antibody hertuzumab conjugated to MMAE via a cleavable linker. A phase I study was initiated to evaluate the toxicity, MTD, PK, and antitumor activity of RC48 in patients with HER2-overexpressing locally advanced or metastatic solid carcinomas, particularly gastric cancer.
Patients and methods: This was a 2-part phase I study. Successive cohorts of patients received escalating doses of RC48 (0.1 mg/kg, 0.5 mg/kg, 1.0 mg/kg, 2.0 mg/kg, 2.5 mg/kg, and 3.0 mg/kg). Dose expansion proceeded at the dose of 2.0 mg/kg Q2W. The efficacy and safety set included all patients who received at least one dose of RC48.
Results: Fifty-seven patients were enrolled, the MTD was unavailable due to termination of 3.0 mg/kg cohort; 2.5 mg/kg Q2W was declared the RP2D. RC48 was well tolerated, the most frequent grade 3 or worse TRAEs included neutropenia (19.3%), leukopenia (17.5%), hypoesthesia (14.0%), and increased conjugated blood bilirubin (8.8%). Four deaths occurred during the whole study, three of which were believed to be related to RC48. Overall, ORR and DCR were 21.0% (12/57) and 49.1% (28/57). Notably, patients who were HER2 IHC2+/FISH- responded similarly to those who were IHC2+/FISH+ and IHC3+, with ORRs of 35.7% (5/14), 20% (2/10), and 13.6% (3/22), respectively. In patients who were pretreated with HER2-targeted drugs, RC48 also showed promising efficacy, with ORR of 15.0% (3/20) and DCR of 45.0% (9/20).
Conclusion: RC48 was well tolerated and showed promising antitumor activity in HER2-positive solid tumors, including gastric cancer with HER2 IHC 2+/FISH- status.
Clinical trial information: NCT02881190.
Keywords: Gastric cancer; HER2; RC48-ADC; Solid tumors.