Abstract PR8: Novel tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for immunotherapy of cancer. (2013)

Abstract Introduction: IL-2 therapy can lead to durable responses in a modest proportion of cancer patients, but the treatment is associated with significant toxicity. Over the last decades, various IL-2-based immunocytokines have been generated by fusing IL-2 to tumor-targeting antibodies. However, none of these molecules have progressed beyond Phase II trials and they are hampered by various liabilities: 1) High functional affinity (low pM) for IL-2Rabg on immune cells and on pulmonary vascular endothelium (Krieg et al., PNAS, 2010) compromising preferential tumor targeting due to fusion of two IL-2 moieties to the antibody. This is further compounded when the immunocytokine binds to FcgRs on the same cells. 2) Rapid systemic clearance and short half-life due to high affinity IL-2Rabg binding. 3) Preferential activation of Tregs over immune effectors due to use of wildtype IL-2. Here, we describe a novel monomeric tumor-targeted immunocytokine where a single, engineered IL-2 variant (IL-2v) with abolished IL-2Ra (CD25) binding is fused to the C-terminus of a tumor-specific hIgG1 antibody with a heterodimeric Fc-part. FcgR and C1q binding is completely abolished by a novel Fc mutation. For targeting, human(-ized) high affinity antibodies against CEA (GA504, CEA-IL2v) or FAP (GA501, FAP-IL2v) were chosen. Experimental procedures: CEA- and FAP-IL2v were recombinantly produced and characterized by surface plasmon resonance. Induction of P-STAT5, proliferation, activation induced cell death (AICD), various activation markers and cytokine release were determined on effector cells. Safety, pharmacokinetics (PK), tumor targeting by imaging, immune-pharmacodynamics and anti-tumor efficacy were analyzed in immunocompromised Scid and immunocompetent C57BL/6 mice. Results: IL-2v completely lacks binding to CD25, but retains IL-Rbg binding. In line with this, FAP- and CEA-IL2v do not bind to CD25 or preferentially activate Tregs, and do not cause AICD. However, IL-2Rbg bioactivity is retained and they are still able to activate NK, CD4 and CD8 T cells as shown by concentration dependent increase in activation markers and induction of proliferation. In particular, CEA- and FAP-IL2v expand and activate NK cells and skew the CD4:CD8 ratio towards activated CD8 T cells in vivo. In C57BL/6 mice CEA- and FAP-IL2v demonstrate improved safety despite of ca. 2-fold higher exposure and t1/2 than a wildtype IL-2-based IgG immunocytokine. SPECT/CT imaging revealed FAP-mediated tumor targeting and accumulation of FAP-IL2v with low normal tissue uptake. Notably, FAP-IL2v tumor targeting was similar to the parental FAP antibody with low accumulation in lymphoid tissues; clearly superior to an FAP-targeted wt IL-2 immunocytokine that showed preferential homing to the spleen. Studies in tumor bearing mice showed dose dependent efficacy of CEA- and FAP-IL2v in established xenograft and immunocompetent syngeneic mouse models in terms of survival. Conclusion: CEA- and FAP-IL2v demonstrate superior safety, PK and tumor targeting, while lacking preferential induction of Tregs due to abolished CD25 and FcgR binding, monovalency and high-affinity tumor-targeting as compared to conventional immunocytokines. They retain the capacity to activate NK and T effector cells through IL 2Rbg; in particular once targeted and immobilized in the tumor microenvironment. These preclinical properties support further investigation for the immunotherapy of CEA/FAP-positive tumors. This abstract is also presented as Poster A23. Citation Format: Christian Klein, Waldhauer Inja, Valeria Nicolini, Dunn Claire, Anne Freimoser, Anne Freimoser, Sylvia Herter, Edwin Geven, Otto Boerman, Erwin van Puijenbroek, David Wittig, Samuel Moser, Oliver Ast, Ralf Hosse, Sabine Lang, Sebastian Neumann, Adelbert Grossmann, Ingo Gorr, Stefan Evers, Pavel Pisa, Jennifer Fretland, Victor Levitsky, Christian Gerdes, Marina Bacac, Ekkehard Moessner, Ekkehard Moessner, Pablo Umaña. Novel tumor-targeted, engineered IL-2 variant (IL-2v)-based immunocytokines for immunotherapy of cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr PR8.