WASHINGTON, April 9, 2013 (GLOBE NEWSWIRE) -- Immunomedics, Inc. (Nasdaq:IMMU), a biopharmaceutical company primarily focused on the development of monoclonal antibody-based products for the targeted treatment of cancer, autoimmune and other serious diseases, today announced that its proprietary antibody-drug conjugate (ADC), labetuzumab-SN-38, appears to be safe and reasonably well tolerated within a clinically effective dosage range in patients with advanced colorectal cancer. Results from this Phase I study were presented by Dr. Neil H. Segal from the Memorial Sloan Kettering Cancer Center, New York, NY. Labetuzumab-SN-38 is one of three agents from the Company's robust ADC program that are in clinical development. Labetuzumab is a slowly-internalizing antibody that recognizes the carcinoembryonic antigen (CEA; CEACAM5 or CD66e), which is expressed in many solid cancers, including more than 80% of colorectal cancer. In prior clinical trials, the antibody was shown to be safe when administered unconjugated or bound to the radioisotope, iodine-131, for radioimmunotherapy. SN-38 is the active metabolite of irinotecan, which is a standard therapy for patients with metastatic colorectal cancer, but has major gastrointestinal and hematologic toxicity. By targeting SN-38 directly to CEA-expressing tumors, delivery of SN-38 may be increased while mitigating systemic toxicity. Preclinical studies have shown that the antibody-drug linkage was susceptible to cleavage in serum, with 50% of SN-38 released in ~1.0 day, leading to a locally enhanced concentration within the tumor site. In animal models of human colorectal cancer, the ADC exhibited high anti-tumor activity. The goal of this single-arm, dose-escalation study was to determine the maximum-tolerated dose of labetuzumab-SN-38 in patients with metastatic colorectal cancer. Patients who had previously been treated with at least one prior irinotecan-containing regimen were enrolled to receive 2 doses of the ADC separated by 14 days. In the absence of unacceptable toxicity or disease progression, treatment continues for at least 24 weeks for a total of 12 cycles. Treatment may continue past 24 weeks if the patient reports a partial response or stable disease, with no unacceptable toxicity.