A Bispecific Antibody-IFNα2b Immunocytokine Targeting CD20 and HLA-DR Is Highly Toxic to Human Lymphoma and Multiple Myeloma Cells

The short circulating half-life and side effects of IFN alpha affect its dosing schedule and efficacy. Fusion of IFN alpha to a tumor-targeting monoclonal antibody (MAb-IFN alpha) can enhance potency due to increased tumor localization and improved pharmacokinetics. We report the generation and characterization of the first bispecific MAb-IFNa, designated 20-C2-2b, which comprises two copies of IFN alpha 2b and a stabilized F(ab)(2) of hL243 (humanized anti-HLA-DR; IMMU-114) site-specifically linked to veltuzumab (humanized anti-CD20). In vitro, 20-C2-2b inhibited each of four lymphoma and eight myeloma cell lines, and was more effective than mono-specific CD20-targeted MAb-IFN alpha or a mixture comprising the parental antibodies and IFN alpha in all but one (HLA-DR-/CD20(-)) myeloma line, suggesting that 20-C2-2b should be useful in the treatment of various hematopoietic malignancies. 20-C2-2b displayed greater cytotoxicity against KMS12-BM (CD20(+)/HLA-DR+ myeloma) compared with monospecific MAb-IFN alpha, which targets only HLA-DR or CD20, indicating that all three components in 20-C2-2b could contribute to toxicity. Our findings indicate that a given cell's responsiveness to MAb-IFN alpha depends on its sensitivity to IFN alpha and the specific antibodies, as well as the expression and density of the targeted antigens. Cancer Res; 70(19); 7600-9. (C) 2010 AACR.