1058 Development of AZD9793 for GPC3+solid tumor treatment: a next generation CD8-guided T cell engager with superior therapeutic index versus conventional formats

Background

Hepatocellular carcinoma (HCC) is a significant cause of cancer-related deaths globally. Glypican-3 (GPC3) is an onco-fetal protein reactivated in various tumors, including 70–80% of HCC cases, and is linked to poor prognosis. Its tumor-restricted surface expression makes it an ideal target for T cell engagers (TCE). While current bispecific TCE-based treatments have been effective against hematological malignancies and certain solid tumors, they are also linked to substantial toxicity, including CRS and ICANS. This toxicity restricts their therapeutic window and potential for combination therapies in clinical settings.

Methods

Our goal was to develop a TCE with a favorable safety/efficacy profile through CD8 preferential engagement. This approach involves leveraging CD8+ T cell biological functions while minimizing CD4+ T cell activation, thereby limiting cytokine release as CD4+ T cells are the main driver of CRS-risk. AZD9793, a novel CD8-guided TCE, is an asymmetric trispecific IgG1 monoclonal antibody comprising 2 Fab binding domains to human GPC3, one VHH binding domain to human TCR, and one VHH binding domain to human CD8 co-receptor. AZD9793 biological activity were evaluated in vitro and in vivo, in comparison to a conventional GPC3xCD3 TCE.

Results

In preclinical in vitro experiments, AZD9793 demonstrated potent GPC3-specific T cell dependent cellular cytolysis activity across various HCC cell lines expressing different levels of GPC3 (HepG2, Hep3B, Huh7, and PLC/PRF/5). Compared to a conventional TCE that broadly activates CD3+ T cells, AZD9793 induced preferential engagement of CD8+ T cells through CD8/TCR binding and potent killing, with limited CD4+ T cell activation and lower cytokine secretion profiles. Pre-clinical in vivo assessment confirmed that AZD9793 exhibits dose-dependent anti-tumor effects in humanized mouse models with HCC xenografts. Notably, when comparable anti-tumor efficacy was achieved in vivo, AZD9793 induced significantly less systemic cytokine production than a conventional GPC3xCD3 TCE, with circulating levels of TNF-α, IL-6, IFN-g, IL-10, IL-2 and IL-17A similar to those in vehicle-treated animals. Furthermore, AZD9793 demonstrated bystander killing activity, leading to growth inhibition of heterogeneously expressing GPC3 tumor cells, in both in vitro and in vivo settings.

Conclusions

AZD9793 is a first-in-class TCE for the treatment of GPC3+ solid tumor with the potential of a significantly improved therapeutic index over conventional GPC3xCD3 engagers. Bivalent GPC3 binding, CD8-biased engagement, and low affinity TCR binding improve AZD9793 cytotoxic potency on tumor cells while decreasing the risk of cytokine release and associated toxicity. These attributes provide a rational for the evaluation of AZD9793 in clinic.

Ethics Approval

The in vivo studies were conducted according to Institutional Animal Care and Use Committee approved protocols in the Laboratory Animal Resources facility at AstraZeneca, an Association for Animal Accreditation of Laboratory Animal Care and United States Department of Agriculture-licensed facility. Human PBMCs were used in accordance with Informed Consent Form (ICF).