Immunomedics reports CD22 antibody produced significant anti-tumor response

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 reported that epratuzumab, the Company's humanized anti-CD22 antibody, conjugated with SN-38, the active component of irinotecan, produced significant anti-tumor responses in a mouse model of human lymphoma. Furthermore, combining the antibody-drug conjugate (ADC) with veltuzumab, a second-generation humanized anti-CD20 antibody, enhanced its therapeutic activity without additional toxicity. Results from these preclinical studies were presented at the 52^nd annual meeting of the American Society of Hematology.

While monoclonal antibody therapy has had a significant impact on the management of B-cell malignancies, it is most often used in combination with chemotherapy.  An improved approach could be to attach the agent directly onto an antibody for targeted delivery of the drug to the tumor. Epratuzumab is an ideal candidate for ADC development because it is an internalizing antibody and clinical studies have shown it to be potentially safe and efficacious as a naked antibody. The potential therapeutic activity of epratuzumab-SN-38 is the combined effect of both the antibody and the drug.

The activity of the ADC was assessed in several hematopoietic tumor cell lines and in mice, inoculated subcutaneously or intravenously with the cell lines. In vivo studies also examined combination therapy using the ADC and veltuzumab. 

Studies in 4 B-cell lymphoma cell lines and 4 acute lymphoblastic leukemia cell lines confirmed the potent in vitro activity of epratuzumab-SN-38 in the nanomolar range.  Significant anti-tumor activity was also observed in mice bearing human lymphoma cells. Treatments of animals 5 days after tumor cell implantation with 300 micrograms of the conjugate given twice-weekly for 4 weeks increased median survival from 42 days in untreated animals to 63 days.

Substantial improvement in therapeutic activity was observed when veltuzumab was included. The addition of 35 micrograms of veltuzumab prolonged median survival to more than 160 days with 6 of 10 animals surviving. These results indicate that the epratuzumab-SN-38 conjugate is a potentially potent therapeutic, which can be significantly enhanced when combined with anti-CD20 immunotherapy, representing a new ADC treatment regimen.

"Targeted delivery of drug by an antibody is an exciting approach in cancer treatment. We plan to continue to develop ADCs looking specifically for agents that have a wide therapeutic window with minimal side effects," remarked Cynthia L. Sullivan, President and Chief Executive Officer. "The SN-38 conjugate of epratuzumab is one of several agents created by our ADC program. We are pleased to report these encouraging results and look forward to bringing it into the clinic in the future," Ms. Sullivan added.