Abstract 482: Tipping the balance in the tumor microenvironment: An engineered cytokine (NKTR-214) with altered IL2 receptor binding selectivity and improved efficacy.

Introduction Immunotherapy offers the potential for durable responses in a growing list of cancer indications.1 One approach towards stimulating the immune system is to target the heterotrimeric interleukin2 receptor, IL2R. Binding of ligand to the β subunit leads to expansion of tumor killing memory effector T cells, whereas engagement of the α subunit expands undesirable regulatory T cells, promoting immune suppression in the tumor.2 NKTR-214 uses polymer technology to engineer a cytokine that has reduced affinity for the IL2Rα subunit, diminishing the expansion of regulatory T cells in the tumor, while maintaining affinity for the β subunit expands memory effector T cells. The selective immunological profile in the tumor tips the balance towards tumor killing and results in superior efficacy and tolerability in a resistant mouse melanoma model. Methods The affinity of NKTR-214 to IL2Rα and IL2Rβ was measured directly by SPR and compared to that of clinically available IL2 (Aldesleukin). C57BL/6 mice bearing subcutaneous B16F10 melanoma were treated with NKTR-214 (IV, Q9dx3), Aldesleukin (BIDx5, 2 cycles) or vehicle. Immune cell populations in the tumor microenvironment were characterized by flow cytometry. Anti-tumor efficacy was measured by monitoring tumor volumes over time. Data The affinity of the activated form of NKTR-214 to IL2Rα was reduced by ∼8x compared to clinically available Aldesleukin. Mice receiving NKTR-214 showed an increase of ∼8-fold in CD8 memory effector T cells in the tumor compared to Aldesleukin .Conversely, mice receiving NKTR-214 showed a ∼6-fold decrease of CD4 regulatory T cells in the tumor compared to Aldesleukin. Improved survival and substantial tumor growth delay were observed in the NKTR-214 treated mice as compared to Aldesleukin, despite using 10-fold fewer moles of protein. The mice in the NKTR-214 treated group were not moribund, did not shiver, and showed an 84% decrease in mortality as compared to the Aldesleukin treated group. Conclusions Engineering a cytokine through polymer modification leads to a differential IL2 receptor binding profile and an improved tumor infiltrating T cell profile. The modification increases CD8 memory effector T cells and decreases suppressive regulatory T cells in the tumor compared to a clinically available IL2 (Aldesleukin). The reduced level of immune suppression in the tumor may explain the substantially improved therapeutic index observed for NKTR-214, despite using 10-fold fewer moles of protein, and infrequent dosing (Q9Dx3). The drug was well tolerated by the mice, with an 84% decrease in mortality compared to Aldesleukin. The results demonstrate that polymer engineering of a cytokine can have a profound differentiating effect on its in vitro and in vivo behavior. 1L. Calabro, Semin Oncol 2010 37 460-467 2O. Boyman, J. Sprent Nature Reviews Immunology 2012 12 180 Citation Format: Deborah Charych, Steven Lee, Murali Addepalli, Thomas Chang, Peter Kirk, Marina Konakova, Laurie Vanderveen, Rupesh Kanhere, Dennis Fry, Cherie Ali, Stephen Harrison, Seema Kantak, Stephen Doberstein. Tipping the balance in the tumor microenvironment: An engineered cytokine (NKTR-214) with altered IL2 receptor binding selectivity and improved efficacy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 482. doi:10.1158/1538-7445.AM2013-482