Phase I/II first-in-human study to evaluate the safety and efficacy of tissue factor-ADC MRG004A in patients with solid tumors.

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3002 Background: Tissue factor (TF) overexpression is associated with thrombosis, metastasis and poor prognosis in solid tumors, including cervical and pancreatic cancer. MRG004A is a novel anti-TF monoclonal antibody conjugated (ADC) to MMAE payload (drug-to-antibody ratio: 3.8), utilizing Glycoconnect site-specific conjugation technology. Herein, we present the preliminary safety and efficacy data from phase I/II MRG004A-001. Methods: This is an interim report (Data cutoff: Dec 15, 2023) of first-in-human, dose-escalation and expansion study ongoing in the USA and China. Pts with ECOG 0-1 with unresectable/metastatic solid tumor with measurable disease per RECIST v1.1 that progressed on prior systemic therapy, received MRG004A monotherapy Q3W intravenously. The primary objectives were to assess the safety, activity, maximal tolerated dose (MTD) and recommended phase 2 dose (RP2D). Baseline tissue was evaluated for the association of TF expression with objective response rate (ORR) and disease control rate (DCR). Results: Sixty-three pts were enrolled with 43 in dose-escalation phase (8 dose levels [0.3-2.6mg/kg]) and 20 in dose-expansion phase (15 at 2.0mg/kg and 5 at 2.4mg/kg). Median age 58 (38-75). ECOG0: 8 (13%) pts. Female: 37 (59%) pts. Median 3 prior lines of therapy: 3 (1-10). MTD was not reached. Sixteen baseline samples were evaluated for overall % membrane positivity by immunohistochemistry. Nineteen were pancreatic cancer (PC) and 68% (13/19) had TF ≥50% and 2 or 3 (+). Five received dose <2 mg/kg Q3W. Significant anti-tumor activity of MRG004A was observed in pts with PC. Among 12 evaluable pts with PC in the 2.0mg/kg cohort, who have received median 3 lines of prior therapy, there were 4 PR and 6 SD. ORR was 33.3% (4/12) and DCR was 83.3% (10/12). Among them, 5 pts with PC of TF expression ≥50% and 3+ intensity and ≤2 prior lines of therapy received MRG004A at 2mg/kg. 4 of 5 TF-overexpressed PC achieved PR and 1 SD. Also, MRG004A showed efficacy in other cancers. In 4 pts with heavily-treated triple-negative breast cancer (TNBC), ORR and DCR were 25% (1/4) and 50% (2/4), respectively. In 2 pts with cervical cancer with four prior therapy lines, 1 PR and 1 SD. Common treatment-related adverse events (TRAE) of any grade include conjunctivitis (27%), anemia (17%), and hypoalbuminemia (13%) and 7.9% (5/63) pts had serious adverse events. One pt with TNBC treated at 1.8mg/kg experienced G3 Steven Johnson Syndrome, a dose-limiting toxicity (DLT), but resolved. No other DLT was observed and dose expansion and matured outcome evaluation is ongoing. Conclusions: MRG004A demonstrated a manageable toxicity and a striking antitumor activity across multiple tumor types with high TF expression in heavily pretreated setting, including pancreatic cancers. These encouraging findings warrant further evaluation of MRG004A, particularly in the context of TF-overexpressed solid tumors. Clinical trial information: NCT03941574 .