In this study, the therapeutic efficacy of SN-38 conjugated to labetuzumab was evaluated in two animal models of human colon cancer. Labetuzumab is a non-internalizing humanized antibody that binds to the carcinoembryonic antigen expressed by many solid cancers. The company has conducted clinical trials with the naked and radiolabeled antibody in patients with colorectal, breast and pancreas cancers.
In a lung metastatic model of colon carcinoma, therapy with labetuzumab-SN-38 conjugate increased median survival time (MST) 1.9- to 3.4-fold compared to various controls, with 20% of animals alive at the end of the study.
In another colon cancer model, MST for the immunoconjugate treatment group increased four-fold to 86 days compared to untreated animals, and was significantly better than all controls, including irinotecan administered at its maximum tolerated dose, which is a 50-fold increase in the amount of free drug than SN-38 in the immunoconjugate dose.
Cynthia Sullivan, president and CEO of Immunomedics, said: We believe these results suggest that targeted chemotherapy of colorectal cancer with labetuzumab-SN-38 should enhance the bioavailability and reduce the toxicity of the clinically validated drug, irinotecan. More preclinical evidences are being collected to support the human testing of this new drug immunoconjugate.