Abstract 2858: Binding characteristics of the immunocytokine hu14.18-IL2 and induction of human effector functions as anticipated mode of action.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Immunotherapy of neuroblastoma with anti-GD2 antibodies in combination with interleukin-2 (IL2) emerges as an important treatment option as shown in several clinical trials. In consequence, an antibody-IL2 fusion protein (hu14.18-IL2; immunocytokine) was designed that combines the targeting and effector functions of an anti-GD2 antibody and the immune modulation activity of IL2. In addition to mediation of typical effector functions such as CDC and ADCC this immunocytokine targets IL2 to GD2+ tumor cells and thereby links tumor cells to IL2-receptor bearing effector cells via an Fc-gamma independent mechanism. This concept has already shown encouraging results in Phase I/II trials in relapsed/refractory neuroblastoma patients. Here, we report the antigen binding characteristics and in vitro anti-neuroblastoma activity of a new GMP preparation of hu14.18-IL2 (APN301). Binding of APN301 to its nominal antigen GD2 was analyzed by solid phase ELISA and compared to other antibodies of the 14G2a family. Affinities of APN301 to GD2 and to anti-14.18 anti-idiotype antibodies were also determined by Biacore® analysis. GD2 specific ADCC, CDC and whole blood cytotoxicity were analyzed in cytotoxicity assays in vitro (calcein-release, 51Cr release) using GD2+ neuroblastoma target cell lines. We demonstrate similar binding characteristics of APN301 to GD2 compared to parent 14.18 antibodies (murine and chimeric). The anti-14.18 anti-id antibody ganglidiomab fully inhibits binding of APN301 to the nominal antigen GD2, thereby proving internal image properties. The dissociation constants of APN301 to GD2 and ganglidiomab as determined in Biacore analyses are in the 10-9M and 10-7M range, respectively, similar to those determined for the naked chimeric 14.18 antibody. Relevant for the prediction of clinical activity we demonstrate potent specific lysis of GD2+ human neuroblastoma cells mediated by APN301 in a whole blood cytotoxicity assay in vitro, utilizing whole blood of healthy donors as well as whole blood of high-risk neuroblastoma patients in advanced disease stage. Further clinical trials with APN301 in neuroblastoma patients are being planned, taking into account the found potent whole blood cytolytic activity and the pharmakokinetic properties of this immunocytokine. Citation Format: Hans Loibner, Manfred Schuster, Evelyne Janzek, Stefan Stranner, Bernhard Peball, Susanne Wiederkum, Oliver Mutschlechner, Nikolai Siebert, Holger Lode. Binding characteristics of the immunocytokine hu14.18-IL2 and induction of human effector functions as anticipated mode of action. [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 2858. doi:10.1158/1538-7445.AM2013-2858 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.