Immunomedics Reports First Clinical Results of New Antibody-Directed Radiation Therapy for Colorectal Cancer

Immunomedics, Inc. IMMU today reported that pretargeted radiation therapy with TF2, a humanized bispecific antibody owned by the Company, appears to be safe and tolerable in patients with advanced colorectal cancer. Results from the Phase I study were released by SNM at its 58th Annual Meeting Press Conference. In this study, a new approach to antibody-directed radiation therapy, or radioimmunotherapy (RAIT), called pretargeting, was used. Developed by IBC Pharmaceuticals, Inc., the Company's majority-owned subsidiary, pretargeted RAIT (PT-RAIT) requires the use of a different type of antibody called a bispecific antibody. Unlike traditional antibodies having both arms binding only to one receptor, bispecific antibodies have been engineered so that each arm recognizes two different targets, one for the tumor and the other for the agent that carries radioactive materials. TF2, created by the Company's patented Dock-and-Lock (DNL) protein engineering platform, recognizes carcinoembryonic antigen (CEA or CEACAM5) expressed by many human cancers, as well as a small radioisotope-carrying peptide called HSG (histamine-succinyl-glycine). A key feature of PT-RAIT is that radioactive materials are introduced in a second step through the injection of a small peptide that the bound antibody also recognizes. The agent either attaches quickly to the antibody localized at the tumors or, due to its small size, is rapidly excreted in the urine, thereby minimizing the body's exposure to radiation. Another advantage of PT-RAIT is in the higher radiation dose level delivered selectively to the tumors. The aims of the Phase I study are to determine and optimize the pharmacokinetics and tumor targeting of TF2 and the radiolabeled peptide, as well as to evaluate the therapeutic potential and the safety and toxicity of this PT-RAIT in patients with advanced colorectal cancer. Results from 4 cohorts of patients who received 75 or 150 mg of TF2 followed 1 or 5 days later with 25 or 100 µg of the radioactive peptide were presented at the annual meeting by investigators from the University Medical Center in Nijmegen, The Netherlands. Pretargeting with TF2 and the specific labeled peptide target tumor lesions in colorectal cancer patients rapidly and produced high tumor-to-background ratios. TF2 is cleared quickly from the blood. As a result, a short interval between the infusion of TF2 and the injection of peptide is preferred. Moreover, high doses of radiolabeled peptide can be administered safely with only bone marrow toxicity as dose-limiting. "This is 1 of 2 investigator-sponsored studies in Europe involving TF2 for pretargeted imaging and radioimmunotherapy of colorectal and lung cancers," commented Cynthia L. Sullivan, President and CEO. "We will initiate our own clinical trials of TF2 in patients with metastatic colorectal cancer, where patient enrollment is anticipated to begin this summer at several U.S. investigational sites," Ms. Sullivan added.