271P First-in-human, phase I dose escalation and expansion study of anti-HER2 ADC MRG002 in patients with HER2 positive solid tumors

Abstract

MRG002 is an ADC composed of a humanized anti-HER2 mAb conjugated to MMAE via a vclinker. MRG002 is presently being investigated as monotherapy in an ongoing phase I study for safety, tolerability, PK, and preliminary antitumor activity in patients (pts) with HER2+ advanced or metastatic solid tumors. In phase Ia dose escalation utilizing a “3+3” design, a total of 25 pts with BC (19), SGC (3), GC (2), and CRC (1) were enrolled to identify MTD/RP2D. The median age was 53 (30, 66) years. The median number of prior therapies was 5 (1, 11). The starting dose of MRG002 was 0.3 mg/kg, followed by 0.6, 1.2, 1.8, 2.2, 2.6, and 3.0 mg/kg, all pts with BC and GC had HER2+ per CAP guidelines. For the other cancers, pts had an IHC status of 2+ or 3+, regardless of HER2 FISH results. Each pt received MRG002 Q3W for a maximum of 8 cycles. Commonly observed TRAEs were neutrophil count decrease (56%), AST increase (56%), WBC decrease (56%), lactate dehydrogenase increase (44%), alopecia (44%), CPK increase (40%), ALT increase (36%), triglyceride increase (32%), cholesterol increase (32%), GGT increase (32%), appetite decrease (32%), and hypoaesthesia (32%). Majority of AEs were mild to moderate in severity. The most commonly reported TRAEs ≥ Grade 3 were neutrophil count decrease and triglycerides increase in 3 pts (12%), respectively. The treatment-related SAEs were reported in 6 pts (24%) including GGT increase, AST/ALT increase, neutrophil count decrease, LEVF decrease, fatigue, peripheral neuropathy. There was no death due to AEs. Among 21 pts who had at least one tumor assessment, 9 PR (43%), 8 SD (38%), and 4 PD (19%). The investigator assessed ORR was 43% and the DCR was 81%. Of these 21 pts, 16 pts were HER2+ breast cancer, 8 PR, 5 SD, and ORR was 50% (8/16), DCR was 81%(13/16). There were two DLTs at 3.0 mg/kg including LVEF decrease and CPK elevation. Accordingly, the RP2D determined at 2.6 mg/kg which is currently being evaluated in the phase Ib dose expansion. The dose escalation of MRG002 showed manageable safety profile and encouraging antitumor activity in pts with HER2+ solid tumors including BC, GC and other cancer types, which will be further investigated in phase II studies.