Abstract C125: Preclinical pharmacodynamic biomarker and combination strategy of RG7386, a novel FAP-DR5 bispecific antibody for targeting solid tumors

Introduction RG7386 is a novel bispecific antibody, binding with high affinity to fibroblast activation protein (FAP) and with low affinity to death receptor 5 (DR5). Avidity-driven binding of the bispecific antibody mediates hyper-clustering of DR5 thus triggering tumor cell death. Induction of FAP dependent apoptosis translated into strong efficacy in vivo using patient derived xenografts thereby proposing RG7386 as an attractive therapeutic approach for the treatment of stroma rich FAP-positive solid tumors as well as FAP positive sarcomas. However, thus far DR5 targeting strategies failed to show clinical efficacy likely due to lack of hyperclustering and intrinsic resistance mechanisms. Preclinical translational studies were conducted to demonstrate the on-target mode of action, to ensure maximal activity and to guide pharmacodynamic (PD) analysis to unravel potential resistance mechanisms. Material and Methods Based on strong anti-tumor efficacy of RG7386 alone and in combination with irinotecan in a colorectal cancer (CRC) cell line based xenograft model (DLD-1) co-injected with fibroblasts a kinetic study was designed. Tumors were explanted 6, 16, 72 and 168 hours after RG7386 single agent treatment and harvested for immunohistochemical (IHC) and ELISA based protein analysis of apoptosis markers, such as cleaved caspase 3 (cc3), cleaved PARP and activated caspase 8 and 9. Additionally, PD effects of RG7386 treatment as single agent and in combination with doxorubicin were investigated in a FAP positive desmoplastic melanoma cell line derived model (LOX-IMVI). Results We observed significant time-dependent induction of apoptosis upon treatment with RG7386 by IHC and ELISA in xenograft tumors expressing FAP in stroma or on tumor cells directly. High, transient levels of apoptosis markers such as cc3 were observed by IHC early after treatment compared to vehicle control. Analysis of equivalent tissue lysates by ELISA revealed also rapid induction of cc3, cleaved PARP and activated caspase 8 and 9 in monotherapy in the DLD-1 CRC xenograft model which was superior when given together with doxorubicin in the LOX-IMVI desmoplastic melanoma model. Conclusion We identified that RG7386 strongly induces tumor cell apoptosis in vivo shortly after injection independently if FAP was expressed on tumor stroma or at tumor cells and discovered optimal pharmacodynamic markers and time points for sampling and analysis. As a result, early clinical trials of RG7386 will be designed to increase the therapeutic potential by choosing the right combination partner and to ensure demonstration of the postulated mode of action by pharmacodynamic data. Citation Format: Thomas Friess, Ann-Marie Broeske, Stefanie Lechner, Esther Abraham, Gabriele Hoelzlwimmer, Hadassa Sade, Peter Bruenker, Oliver Krieter. Preclinical pharmacodynamic biomarker and combination strategy of RG7386, a novel FAP-DR5 bispecific antibody for targeting solid tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C125.