Preclinical studies on targeted delivery of multiple IFNα2b to HLA-DR in diverse hematologic cancers

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 mAb (mAb-IFN alpha) can enhance potency because of increased tumor localization and improved pharmacokinetics. We used the Dock-and-Lock method to generate C2-2b-2b, a mAb-IFN alpha comprising tetrameric IFN alpha 2b site-specifically linked to hL243 ( humanized anti-HLA-DR). In vitro, C2-2b-2b inhibited various B-cell lymphoma leukemia and myeloma cell lines. In most cases, this immunocytokine was more effective than CD20-targeted mAb-IFN alpha or a mixture comprising the parental mAb and IFN alpha. Our findings indicate that responsiveness depends on HLA-DR expression/density and sensitivity to IFN alpha and hL243. C2-2b-2b induced more potent and longer-lasting IFN alpha signaling compared with nontargeted IFN alpha. Phosphorylation of STAT1 was more robust and persistent than that of STAT3, which may promote apoptosis. C2-2b-2b efficiently depleted lymphoma and myeloma cells from whole human blood but also exhibited some toxicity to B cells, monocytes, and dendritic cells. C2-2b-2b showed superior efficacy compared with nontargeting mAb-IFN alpha, peginterferonalfa-2a, or a combination of hL243 and IFN alpha, using human lymphoma and myeloma xenografts. These results suggest that C2-2b-2b should be useful in the treatment of various hematopoietic malignancies. (Blood. 2011;118(7):1877-1884)