Abstract 693: ASKG843, a bifunctional fusion protein of PD1/TGF-βRII, demonstrates potent in vitro/in vivo activities, and excellent pharmacokinetic properties in non-human primates (NHPs) with good safety profiles

Abstract

Introduction: Antibodies targeting the immune checkpoint PD1/PD-L1 are emerging as effective cancer immunotherapies, but most cancers fail to respond to these as single agents. Tumor cells and the tumor microenvironment (TME) frequently express transforming growth factor-β (TGF-β) to either drive immune cell dysfunction in the microenvironment or to exclude immune cell infiltration into tumors. Concurrently targeting the immunosuppressive/immune-excluding TGF-β pathway represents a rational and promising strategy to enhance PD1/PD-L1-based immunotherapies. ASKG843 is a bifunctional molecule designed to simultaneously block PD1/PD-L1 pathway and disable all three TGF-β isoforms in the TME. Here we report the functional evaluation of ASKG843 in vitro, anti-tumor activity in vivo, pharmacokinetic (PK) and pharmacodynamic (PD) properties in cynomolgus monkeys as well as its safety profiles following 5-repeat weekly dosing in NHPs. Methods: ASKG843 was constructed comprising αhPD1 Ab with the C-terminus of the heavy chain fused to the ECD of human TGF-βRII via flexible linkers. Bispecific binding properties were evaluated by Fortebio and bispecific ELISA. Respective signaling blockade for PD1 and TGF-β were assessed using either PD1/NFAT-luciferase reporter system or TGF-β/SMAD-luciferase reporter cell line. The anti-tumor activity of ASKG843 was determined in human PBMC-engrafted NSG mice-bearing A375 xenografts. The PK/PD and safety profiles of ASKG843 were assessed in NHPs. Results: Fortebio and bispecific ELISA analyses demonstrated the ability of ASKG843 to simultaneously bind both human PD1 and TGF-β1-3. ASKG843 not only dose-dependently blocked PD1/PD-L1 inhibitory axis with similar potency to parental αPD1 Ab in PD1 bioassay, but also thwarted TGF-β canonical signaling with IC50 =14.7 ng/mL in TGF-β bioassay. In human PBMC-reconstituted A375 xenograft model ASKG843 promoted strong anti-tumor response with efficacy comparable to the reference molecule (PD-L1/TGF-βRII) at the same dose/dosing frequency. In cynomolgus monkeys ASKG843 demonstrated superior PK to PD-L1/TGF-βRII reference molecule resulting in sustained depletion of TGF-β in peripheral blood for at least 10 days following single injection at 5 mg/kg dose, and no toxicity-related sign observed which contrasted with the reference molecule. Most encouragingly ASKG843 maintained very good safety profiles in cynomolgus monkeys following multiple injections at dose up to 100 mg/kg. Conclusions: ASKG843 demonstrated potent bi-functional activities in vitro and in vivo endowed by its design. Superior PK to the reference molecule yet maintaining better safety profiles in NHPs support further development of ASKG843 as an effective immunotherapeutic candidate. Citation Format: Liqin Liu, Shiwen Zhang, Kurt Shanebeck, Mouzhong Xu, Yunxia Yuan, Ming Li, Lu Li, Ray Chuang, Yong Wen, Yuefeng Lu, Jeff Lu. ASKG843, a bifunctional fusion protein of PD1/TGF-βRII, demonstrates potent in vitro/in vivo activities, and excellent pharmacokinetic properties in non-human primates (NHPs) with good safety profiles [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 693.