Abstract
Type I interferons (IFNα/β) are cytokines with a broad spectrum of antitumor activities including antiproliferative, proapoptotic, and immunostimulatory effects, and are potentially useful in the treatment of B-cell malignancies and other cancers. To improve antitumor potency and diminish the systemic side effects of IFN, we recently developed anti-CD20-IFNα fusion proteins with in vitro and in vivo efficacy against both mouse and human lymphomas expressing CD20. As IFNβ binds more tightly to the IFNα/β receptor (IFNAR) and has more potent antitumor activities, we have now constructed an anti-CD20 fusion protein with murine IFNβ (mIFNβ). Anti-CD20-mIFNβ was more potent than recombinant mIFNβ and anti-CD20-mIFNα in inhibiting the proliferation of a mouse B-cell lymphoma expressing human CD20 (38C13-huCD20). Growth inhibition was accompanied by caspase-independent apoptosis and DNA fragmentation. The efficacy of anti-CD20-mIFNβ required the physical linkage of mIFNβ to anti-CD20 antibody. Importantly, anti-CD20-mIFNβ was active against tumor cells expressing low levels of IFNAR (38C13-huCD20 IFNAR). In vivo, established 38C13-huCD20 tumors were largely insensitive to rituximab or a nontargeted mIFNβ fusion protein, yet treatment with anti-CD20-mIFNβ eradicated 83% of tumors. Anti-CD20-mIFNβ was also more potent in vivo against 38C13-huCD20 than anti-CD20-mIFNα, curing 75% versus 25% of tumors (P=0.001). Importantly, although anti-CD20-mIFNα could not eradicate 38C13-huCD20 IFNAR tumors, anti-CD20-mIFNβ treatment prolonged survival (P=0.0003), and some animals remained tumor-free. Thus, antibody fusion proteins targeting mIFNβ to tumors show promise as therapeutic agents, especially for use against tumors resistant to the effects of mIFNα.