Comparison Of An Fap-Targeted, Cd137 Activating Darpin Drug Candidate With A Non-Targeted, Cd137 Activating Antibody In A Human Pbmc Transplanted Ht-29 Mouse Tumor Model.

e14626Background: Urelumab (BMS-663513) is a humanized monoclonal antibody binding to CD137 which, upon Fc-clustering, leads to activation of T-cells. Urelumab is currently in Phase 2 clinical development and has been reported to cause significant hepatotoxicities (around 15% Grade ≥2 ALT and AST elevation) when given as infusion every 3 weeks at doses ≥0.3 mg/kg. Currently ongoing clinical trials report decreased systemic toxicity but limited efficacy at lower doses of urelumab. We hypothesized that more effective triggering of CD137 without associated systemic toxicity may be achieved by targeting a CD137 agonistic engager without Fc to fibroblast activation protein (FAP) which is abundantly expressed in the stroma of many solid tumors. To achieve this, a targeted molecule belonging to the DARPin family of binding proteins was composed of one FAP- and two CD137-binding domains in a “beads on a string” format and tested in a mouse model with human PBMCs. Methods: Human PBMCs were used to reconstitute the...