Antibody-Interferon-Alpha Fusion Protein Therapy for the Treatment of B-Cell Non-Hodgkin Lymphoma: Enhanced ADCC, Inhibition of Proliferation, and In Vivo Eradication of CD20+ Human Lymphomas

Background:  Interferon-alpha (IFNα) is a pleiotrophic cytokine with direct anti-tumor and immunostimulatory effects.  Currently IFNα is approved for the treatment of multiple hematologic malignancies, including non-Hodgkin lymphoma (NHL).  However, its clinical utility has been hindered by dose-limiting toxicitiy due to systemic activation of the interferon receptor.  To overcome this limitation, we engineered anti-tumor antibody-IFNα fusion proteins to selectively increase delivery of IFN to the tumor site and reduce systemic toxicity.  We previously reported that IGN002, an anti-CD20-IFNα fusion protein, exhibits enhanced complement-dependent cytotoxicity (CDC) compared to rituximab, and inhibits proliferation and induces apoptosis of human B-cell NHL (Yamada et al, ASCO 2013).  We now extend these previous findings and show that IGN002 possesses enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) effector function and superior in vivo anti-tumor activity against B-cell NHL, compared to rituximab. 

Methods:  IGN002 was evaluated against a panel of human Burkitt and diffuse large B-cell lymphoma (DLBCL) cell lines.  Proliferation was measured by [³H]-thymidine incorporation, STAT1 activation by flow cytometry, ADCC by lactate dehydrogenase release using human PBMC effectors, and IFN bioactivity by encephalomyocarditis (EMC) viral protection assay.  NHL xenografts were grown in SCID mice.

Results:  IGN002 more potently inhibited the growth of NHL cell lines expressing CD20 than rituximab or unfused IFNα.  Intrinsic IFNα activity of IGN002 was reduced in viral protection and anti-proliferation assays using cells lacking CD20 expression.  STAT1 activation by IGN002 was enhanced on cells expressing the target antigen, whereas a control antibody-IFNα fusion protein showed reduced STAT activation activity compared to unfused IFNα. Together, these results indicate that fusion of IFNα to the antibody results in reduced IFN effects on cells not bearing the tumor antigen target.  IGN002 exhibited enhanced ADCC activity compared to rituximab against Daudi, Ramos, and Raji NHL cells in long-term (overnight incubation) assays, demonstrating both higher potency and higher maximal cytotoxicity.  This result is possibly due to activation of the effector cell populations by the fused IFNα moiety, as IFN is known to activate both NK cells and monocytes.  The in vivo anti-tumor efficacy of IGN002 was compared to rituximab and a control antibody-IFNα fusion protein against 10-day established Raji NHL xenografts.  IGN002 was superior to both rituximab and the control fusion protein, achieving a longer median survival and higher long-term survival rate (p = 0.0015 and < 0.0001 vs. rituximab and control fusion protein, respectively).  The in vivo anti-tumor efficacy of IGN002 was also compared to rituximab at three equimolar dose levels (5 mg/kg, 1 mg/kg, and 0.2 mg/kg antibody) against 10-day established Daudi NHL xenografts.  IGN002 showed superior efficacy compared to rituximab at all doses (p < 0.001), achieving tumor eradication (100% long-term survival) in all mice treated at all three dose levels, whereas rituximab only delayed tumor progression.

Conclusions:  IGN002 demonstrated more robust direct anti-proliferative and antibody effector functions than rituximab against human NHL cells in vitro, and also showed the ability to eradicate established NHL xenografts in vivo.  Against cells expressing the CD20 target antigen, IGN002 exhibited greater anti‑proliferative potency than unfused IFNα.  In contrast, the anti-proliferative and anti-viral potency of IGN002 was reduced against cells lacking CD20, compared to unfused IFNα.  These findings support the hypothesis that tumor antigen-targeted IFN therapeutics may possess a broader therapeutic index than unfused IFNα, inhibiting tumor growth by multiple mechanisms while reducing systemic toxicity.  These results support the further development of IGN002 for the treatment of B-cell NHL, and a first-in-human phase I clinical study will begin later this year in the United States.