Development and Clinical Trial of M701, an Anti-EpCAM × Anti-CD3 Bispecific Antibody: A Targeted Intraperitoneal Therapy for Malignant Ascites Stemming from Advanced Solid Tumors

Background Malignant ascites (MA) is one of the major complications in advanced epithelial cancer patients and is associated with poor prognosis, poor quality of life, and severe symptoms. No efficient medicine is available for treating MA worldwide. Only paracentesis is recommended by the guidelines in most countries, but with limited efficacy and a short control time. Thus, novel treatments are needed to control MA. Methods An anti-EpCAM × anti-CD3 bispecific antibody, M701, was constructed as a T-cell engager to eliminate tumor cells in the peritoneal cavity. A phase 2 study was performed to evaluate the efficacy and safety of the intraperitoneal (IP) infusion of M701 in advanced epithelial tumor patients with moderate-to-large-scale MA. In this study, 84 patients were enrolled, with 43 in the M701 group receiving paracentesis and IP M701 infusion and 41 in the control group receiving paracentesis alone. Results The major endpoint, median puncture-free survival (PuFS), was 75 days in the M701 group and 25 days in the control group, with a significant difference (p = 0.0065). Subgroup analysis indicated that different types of cancer, including gastric, colorectal, and ovarian cancers, all benefited from the M701 infusion. Patients with higher relative lymphocyte counts (≥ 13%) at baseline received better effects. Compared to those in the control group, the overall survival (OS) of patients in the M701 group was longer (mOS 110 days vs 76 days, p = 0.1443, HR = 0.68). The 6-month survival rates were 33.3% and 12.1% in the two groups, respectively. No additional serious adverse events (SAEs) were detected in the M701 group. The most frequent treatment-related adverse events were anemia and low white blood cell count, which were manageable. M701 infusions did not cause a greater risk than paracentesis alone in the control arm, while all patients were administered systemic treatment. Conclusion When treated with M701, patients with MA had significantly longer puncture intervals and trend of longer survival times. The results were encouraging for patients with MA. A phase III clinical trial of M701 aimed at further validation is ongoing.