In Vitro and In Vivo Targeting and Therapy of an Antibody-Drug Conjugate (IMMU-110) in B-Cell Malignancies.

IMMU-110 is a drug immunoconjugate comprised of doxorubicin (DOX) conjugated to the humanized anti-CD74 monoclonal antibody (mAb), hLL1, at a DOX:mAb (mol/mol) ratio of 8:1. CD74 is a rapidly internalizing type-II transmembrane chaperone molecule associated with HLA-DR, and has high expression on human non-Hodgkin’s lymphoma (NHL) and multiple myeloma (MM) clinical specimens and cell lines. Here, we investigated the in vitro and in vivo efficacy of IMMU-110 in xenograft models of human NHL (Raji, Daudi) and MM (MC/CAR). In vitro cell binding of IMMU-110 with the CD74-positive cells was significantly higher than that of a non-specific isotype-matched mAb-DOX conjugate (DOX conjugated to a mAb against epithelial glycoprotein-1; DOX-hRS7), and was similar to that of naked hLL1. Both IMMU-110 and naked hLL1 bound CD74 with subnanomolar affinity. The in vitro cytotoxicity of IMMU-110 was significantly higher than non-specific antibody-DOX conjugate, DOX-hRS7, and was similar to free DOX in MC/CAR, Raji or Daudi human Burkitt’s lymphoma cells. In CD74-negative cell lines, IMMU-110 was significantly less toxic than free DOX, having similar cytotoxicity to DOX-hRS7. In vivo, IMMU-110 displayed a pharmacokinetic and biodistribution profile almost identical to that of hLL1 mAb. Both hLL1 mAb and IMMU-110 had a biphasic clearance from the circulation; the α and β half-life (t_1/2) of IMMU-110 were 4.6 h and 157.9 h, respectively, and those of hLL1 were 5.4 h and 151.5 h, respectively. In biodistribution studies, no significant difference was observed between IMMU-110 and naked hLL1 with regards to normal tissue uptake. Neither IMMU-110 nor naked hLL1 mAb had a significant association with any normal body tissue. In therapy experiments, a single i.v. protein dose of 350 μg IMMU-110, injected 5 days after implantation of MC/CAR cells in SCID mice, resulted in curing 70% of the animals. Similar cure rates were observed when treatment with IMMU-110 was given 10 days after transplantation of MC/CAR cells. In the Raji xenograft model, 100% of animals were cured with a single protein dose of 120 μg IMMU-110, injected 5 days after implantation of cells. In survival studies, the efficacy of IMMU-110 was significantly better than naked hLL1, the combination of naked hLL1 and free DOX, or of a non-specific antibody-DOX conjugate, DOX-hRS7. In a tolerability study in SCID mice, no toxic effect of IMMU-110 was observed even at the highest dose tested (2.5 mg /mouse). In conclusion, treatment of B-cell lymphoma and myeloma xenograft models with single injections of IMMU-110 resulted in high levels of response and long-term survivors. IMMU-110 is being further developed as a potential therapeutic for the treatment of CD74-positive tumors.