Agonistic antibodies against the T cell costimulatory receptor 4-1BB (CD137) have proved to be very efficacious anti-tumor agents in preclinical animal models. However, clinical development of 4-1BB agonistic antibodies has met with limited success thus far. Anti-4-1BB monoclonal antibodies have either been reported to cause significant dose-limiting hepatotoxicity or demonstrated limited efficacy as single agent therapeutics. Here we describe the generation of a tumor-targeted 4-1BB agonist aimed at inducing more effective triggering of 4-1BB without associated systemic toxicity. Tumor targeting is achieved via fibroblast activation protein (FAP) which is abundantly expressed by cancer associated fibroblasts present in many solid tumors. Drug candidate MP0310 comprises DARPin domains binding to 4-1BB and FAP and is devoid of an antibody Fc domain. Compared to first generation monoclonal antibodies targeting 4-1BB, MP0310 shows high potency in vitro and less systemic activation in vivo. In vitro reporter and T cell assays indicate that MP0310 is a potent T cell co-stimulator whose activity is restricted to the presence of FAP-expressing cells. In humanized mouse xenograft studies, FAP-targeted 4-1BB activation induced potent co-stimulation of CD8 T cells leading to tumor growth inhibition. On the other hand, the DARPin molecule did not induce effects associated with strong systemic activation such as hepatotoxicity or exacerbation of graft versus host disease observed in such models, unlike the first generation FcγR-dependent 4-1BB antibodies. In addition, no systemic activation of T cell proliferation was observed in the absence of FAP-positive tumors. In healthy cynomolgus monkeys, administration of MP0310 did not induce systemic stimulation of memory T cell proliferation in contrast to an anti-4-1BB antibody despite MP0310 being fully cross-reactive to cyno 4-1BB and binding effectively to cyno FAP. Therefore, we conclude that the tumor-restricted co-stimulation of 4-1BB may prevent toxicities caused by systemic 4-1BB activation and provide a safe and effective way to boost anti-tumor T cell responses. This could allow more effective dosing and better combination therapies with checkpoint inhibitors and other immune stimulating drugs. MP0310 is in preparation to enter clinical development.

Citation Format: Alexander Link, Julia Hepp, Christian Reichen, Patricia Schildknecht, Ivana Tosevski, Joanna Taylor, Laurent Juglair, Alexander Titz, Mirela Matzner, Ralph Bessey, Christof Zitt, Guy Lemaillet, Joerg Herbst, Keith M. Dawson, Hong Ji, Victor Levitsky, Dan Snell, Michael T. Stumpp, Andreas Harstrick, Elmar vom Baur. Preclinical pharmacology of MP0310: A 4-1BB/FAP bispecific DARPin drug candidate promoting tumor-restricted T-cell costimulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3752.