Development and validation of an immuno-PET tracer for patient stratification and therapy monitoring of antibody-drug conjugate therapy.

11006 Background: SAR566658 is an antibody-drug immunoconjugate consisting of a humanized monoclonal antibody (huDS6) against the tumor-associated MUC1-sialoglycotope, CA6, conjugated to a cytotoxic maytansinoid (DM4). SAR566658 is currently undergoing phase I clinical trials in patients with CA6-positive solid tumors. A companion diagnostic based on huDS6 may facilitate patient stratification and early evaluation of therapeutic efficacy. The present study describes the development and preclinical evaluation of three novel Copper-64 (t½= 12.7h) labeled antibody fragments (two Fabs and a diabody) derived from the huDS6 antibody. One fragment was chosen based on imaging figures of merit for further specificity evaluations. Methods: The affinity of all fragments and their DOTA conjugates to CA6 was validated using flow cytometry. The DOTA conjugates were labeled with Copper-64 and evaluated in human serum stability studies, in vivo small animal PET imaging and 24-hour biodistribution studies in nude mice bea...