Pharmacologic studies of CDH17/CD3 bispecific antibodies to treat colorectal and pancreatic cancers.

116 Background: Immunotherapy has emerged as a new hope for cancer patients who do not respond to conventional therapies. In addition to the widely investigated immune checkpoint inhibitors such as PD-L1 antibody, bispecific T cell redirecting antibodies have also drawn much attention from pharmaceutical companies. The popularity of bispecific T cell engager has been increasing since the US FDA’s accelerated approval of blinatumomab for treatment of haematological malignancies. The clinical efficacy of such engagers in solid tumors have however remained to be demonstrated. Cadherin-17 (CDH17) is a promising immunotherapeutic target for gastrointestinal (GI) cancers. It is a highly tumor-specific antigen with restricted expression limited to the tight junction of intestine that is normally inaccessible to biologics. CDH17 overexpression correlates with tumor burden and poor prognosis. Methods: Fully humanized CDH17/CD3 bispecific antibodies were generated. T cell-mediated cytotoxicity was tested in vitro and in vivo. Safety was addressed in cynomolgus monkeys with intestinal CDH17 level equivalent to that of human. Results: One lead antibody, ARB202 exhibited high-affinity binding to CDH17 and CD3. In the presence of CDH17-positive pancreatic cancer cells, ARB202 stimulated in vitro IL-2 release in CD3/CD28-expanded PBMC. In the absence of tumor cells ARB202 stimulated cytokine production in PBMCs required over 600-fold greater concentrations. ARB202 specifically directed in vitro T cell killing of GI cancer cells expressing CDH17, but not of cells lacking CDH17 expression. In mouse xenograft models reconstituted with human immune cells, ARB202 demonstrated significant tumor growth inhibition with concomitant IL-2 response. No dose-dependent toxicities on cynomolgus monkeys were observed over a 3-log dose range. ARB202 displayed favourable in vivo pharmacokinetic profiles in mice and monkeys. ARB202 is a stable bispecific antibody retaining functional activity after incubation for a month at 37°C at pH6.0. Conclusions: ARB202 is a promising candidate for clinical trials. A proprietary cell line is generated for the pilot manufacturing of ARB202 for IND enabling studies.