Abstract 1882: Clinical approach and biomarker strategy for HFB301001, a novel OX40 agonistic antibody

Agonist OX40 antibodies have shown promising pre-clinical activities, but their clinical activities have been limited thus far. Several reasons may account for this limited clinical activity, including sub-optimal antibody design, dose selection, and lack of a biomarker strategy for indication selection and patient enrichment. Previous clinical trials selected doses that maximized receptor occupancy, but some patients responded at lower doses, indicating nuances to choosing the correct therapeutic doses for an agonist antibody. In addition, preclinical work has demonstrated a so-called “hook” effect whereby agonist activity decreases at higher concentrations, which further emphasizes the need to develop a novel anti-OX40 therapeutic antibody that addresses the previously encountered challenges. HFB301001 is a novel human IgG1 agonist antibody that binds to a unique epitope on OX40. This allows for agonistic activity that does not compete with the endogenous OX40 ligand. Relative to other clinical stage OX40 antibodies, HFB301001 has reduced OX40 downregulation following co-stimulation of T cells, and it has demonstrated superior in vivo anti-tumor activity and pharmacodynamic immune modulation in a human OX40 knock-in mouse model. HFB301001 is well tolerated in cynomolgus monkeys. To progress into clinical studies, we have determined human dose projections for clinical evaluation of HFB301001 using PKPD modeling, serum exposure in non-human primates, antitumor efficacy in mouse models and immune cell pharmacodynamics. We also took advantage of Fc variants to delineate the relative contributions of Treg depletion versus enhancing T cell activity by agonism to efficacy of HFB301001. To further enhance probability of success (POS) in clinical studies, we are applying our single-cell Drug Intelligent Science (DIS™) platform to rationally identify cancer indications and to define novel predictive response biomarkers. We have used single-cell profiling to identify unique tumor-infiltrating T cell signatures that may help identify patients more likely to response to HFB301001 treatment, inform indication selection, and establish a patient stratification biomarker strategy. Finally, we show here our phase I trial design for HFB301001 that implements these findings. In conclusion, HFB301001 is a highly differentiated therapeutic antibody which is well positioned to enter a global, multi-center Phase I clinical trial to explore optimal biologically active dose and evaluate predictive biomarker hypotheses. Here, we present results supporting the rationale for indication selection, biomarker identification, dose selection, and phase I clinical trial design. Citation Format: Ross Fulton, Jinping Gan, Yun-Yueh Lu, Julianna Crivello, Zachery Duda, Zhiyuan Wang, Rebecca Silver, Alexandra Staskus, Charina Ortega, Sami Ellouze, Carine George, Sophie Foulon, Wenhua Xu, Xing Cai, Joyce Pi, Dean Lee, Monika Manne, Ruina Jin, Yuan Wang, Hongkai Zhang, Nicola Beltraminelli, Francisco Adrian, Robert Petit, Liang Schweizer, Andreas Raue. Clinical approach and biomarker strategy for HFB301001, a novel OX40 agonistic antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1882.