Phase I Trial of the Trifunctional Anti-HER2 × Anti-CD3 Antibody Ertumaxomab in Metastatic Breast Cancer

Abstract Purpose: Ertumaxomab is an intact bispecific antibody targeting HER2/neu and CD3 with selective binding to activatory Fcγ type I/III receptors, resulting in the formation of a tri-cell complex between tumor cells, T cells, and accessory cells. Patients with metastatic breast cancer were enrolled into a multicenter phase I dose-escalating trial. Experimental Design: Three ascending doses of ertumaxomab (10-200 μg) were administered i.v. on day 1, 7 ± 1, and 13 ± 1. Safety and tolerability were the primary objectives. Secondary objectives were antitumor activity and different immunologic variables. Results: Fifteen out of 17 enrolled patients completed the study. One hundred micrograms was identified as the maximal tolerable single dose. Most drug-related adverse events were mild and transient including fever (94%), rigors (47%), headache (35%), nausea (29%), vomiting (29%). Grades 3 and 4 (Common Toxicity Criteria) were lymphocytopenia (76%) and elevation of liver enzymes (47%). One patient (200 μg dose) developed severe hypotension and respiratory distress syndrome, another patient (150 μg dose) developed a systemic inflammatory response syndrome and acute renal failure. Aggravation of congestive heart failure was seen in one patient with preexisting ventricular dysfunction after administration of the third dose (200 μg). All adverse events were fully reversible. Antitumor response was seen in 5 out of 15 evaluable patients (one with a complete response, two with partial responses, two with stable disease) at dose levels of ≥100 μg. Measurements of cytokines (interleukin-6, interleukin-2, tumor necrosis factor-α, and IFN-γ) suggest a strong T helper cell type 1–associated immune response. The induction of human anti-mouse/anti-rat antibodies was detected in 5 out of 16 (31%) patients. Discussion: Treatment with triple infusions of ertumaxomab yields a strong immunologic response. Doses up to 100 μg can be safely infused with close monitoring of patients. The observed clinical responses are encouraging and indicate antitumor efficacy.