Abstract 1803: HLA-DR-targeting tetrameric IFNα2b immunocytokine has potent in vitro and in vivo activity in myelomas, lymphomas and leukemias (2011)

Abstract Introduction: IFNα2 has been used in therapy of a variety of hematopoietic neoplasias, including myeloma (MM), NHL, hairy cell leukemia (HCL), and CML. However, its therapeutic potential is limited by its short circulating half-life and systemic toxicity. Fusion of IFNα2 to a monoclonal antibody (mAb) improves solubility and stability, and markedly increases circulating half-life. In addition to allowing less frequent and lower doses via extended Pk, targeting of IFNα2 to tumor sites using a tumor-directed mAb can reduce systemic concentrations and increase local concentration and tumor retention of IFNα2, thereby improving the therapeutic index. Increased tumor concentrations of IFNα2 can augment its direct anti-proliferative, apoptotic and anti-angiogenic activity, as well as prime an antitumor immune response. Methods: We previously used the DNL method to generate stably-tethered immunocytokines (Rossi et al., Blood 2009;114:3864-71; Rossi et al., Cancer Res 2010;70:7600-9), which include 20-2b-2b (CD20-targeted mAb-IFNα comprising tetrameric IFNα2b and veltuzumab) and 20-C2-2b (bispecific CD20/HLA-DR-targeting dimeric IFNα2b). Here we describe the potent in vitro and in vivo anti-tumor activities of a third immunocytokine, C2-2b-2b, comprising tetrameric IFNα2b and the anti-HLA-DR mAb, hL243, against myeloma, lymphoma and leukemia cell lines. Results: C2-2b-2b bound target cells with similar avidity to hL243 and exhibited high IFNα specific activity. In vitro, C2-2b-2b inhibited a panel of 20 cell lines comprising NHL (Burkitt, mantle cell &amp; follicular), leukemia (HCL, AML, ALL &amp; CLL), and MM, and in most cases was more effective than CD20-targeted mAb-IFNα or a mixture comprising hL243 and IFNα. Our findings indicate that a given cell's responsiveness depends on HLA-DR expression/density and its sensitivity to IFNα and hL243. C2-2b-2b was remarkably potent in vivo, where a single 1 μg dose significantly improved survival in advanced Daudi (NHL) and CAG (MM) xenograft models, and doses of ≥10 μg resulted in 70-100% long-term survivors (cures). C2-2b-2b showed superior anti-tumor efficacy compared to hL243 IgG, hL243 + rIFNα2b, Peginterferonalfa-2a or non-targeting mAb-IFNα. Ex-vivo pharmacodynamics studies using whole blood spiked with either NHL or MM cells showed that C2-2b-2b depleted either tumor cell type more efficiently than normal B cells and monocytes, did not deplete T cells, and was cytotoxic to dendritic cells, with myeloid DCs more susceptible than plasmacytoid DCs. Conclusions: The DNL method provides a modular approach to efficiently tether multimeric cytokines onto a targeting antibody, resulting in higher in vivo potency than the original cytokines due to improved pharmacokinetics, targeting and reduced systemic toxicity. These results suggest that C2-2b-2b might be useful in the treatment of various hematopoietic malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1803. doi:10.1158/1538-7445.AM2011-1803