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Antibodies targeting PD-1 have been demonstrated durable anti-cancer activity in certain cancer types. However, the anti-PD-1 antibodies are less or not efficacious in many situations, which might be attributed to co-expression of multiple inhibitory receptors or presence of immunosuppressive cells in the tumor microenvironment. Most of the anti-PD-1 antibodies used in clinical studies are of IgG4 isotype with the S228P mutation (IgG4S228P). The functional impact by the interaction of anti-PD-1 IgG4S228P antibody with Fc gamma receptors (FcγRs) is poorly understood. To assess the effects, we generated a pair of anti-PD-1 antibodies: BGB-A317/IgG4S228P and BGB-A317/IgG4-variant (abbreviated as BGB-A317), with the same variable regions but two different IgG4 Fc-hinge sequences. There was no significant difference between these two antibodies in binding to PD-1. However, BGB-A317/IgG4S228P binds to human FcγRI with high affinity and mediates crosslinking between PD-1 and FcγRI. In contrast, BGB-A317 does neither. Further cell-based assays showed that such crosslinking could reverse the function of an anti-PD-1 antibody from blocking to activating. More importantly, the crosslinking induces FcγRI+ macrophages to phagocytose PD-1+ T cells. In a mouse model transplanted with allogeneic human cancer cells and PBMCs, BGB-A317 showed significant tumor growth inhibition, whereas BGB-A317/IgG4S228P had no such inhibition. Immunohistochemistry study revealed an inverse correlation between FcγRI+ murine macrophage infiltration and the density of CD8+PD-1+ human T cells within tumors in the BGB-A317/IgG4S228P-treated group. These evidences suggested that FcγRI+ binding and crosslinking had negative impact on the anti-PD-1 antibody-mediated anti-cancer activity. Electronic supplementary material The online version of this article (10.1007/s00262-018-2160-x) contains supplementary material, which is available to authorized users.

Phosphoinositide 3-kinases (PI3Ks) are a family of enzymes capable of phosphorylating phosphatidylinositol to phosphoinositides, which are important secondary messengers involved in various cell signaling and functions. PI3Kδ is one of four isoforms (PI3Kα, β, δ and γ) of the PI3K class I family. It is restrictively expressed in leukocytes. PI3Kδ is a key signal transduction component for normal and malignant B cells and also important for the homeostasis and function of T-regulatory cells (Treg), making it a promising target for treatment of both hematologic malignancies and solid tumors. BGB-10188 is a highly selective inhibitor of PI3Kδ, showing no significant inhibition over 376 protein kinases and 17 lipid kinases, and more than three-thousand folds selectivity over PI3Kα, PI3Kβ, and PI3Kγ. BGB-10188 potently inhibited PI3Kδ in biochemical, cellular and human whole blood assays with IC50s ranging from 1.7-16 nM. It also showed a long-lasting and strong target inhibition activity in mouse pharmacodynamics (PD) studies at doses as low as 10mg/kg. The elimination half-life (t1/2) of BGB-10188 in plasma was 12.6 hours and 10.4 hours in rats and dogs, respectively. BGB-10188 showed significant antitumor effects in different types of B cell Lymphoma xenograft models. The liver toxicities of BGB-10188 were evaluated in mice and significantly improved safety margin was observed for BGB-10188 in comparison with other PI3Kδ inhibitors. In summary, BGB-10188 is a novel PI3Kδ inhibitor with high selectivity, potency and improved safety profile shown in preclinical studies, which is promising and warrants the testing of the compound in human. Citation Format: Xiao Yang, Xiaolong Yang, Xinxin Cui, Dan Su, Yue Wu, Xuebing Sun, Jingyuan Wang, Huichen Bai, Wei Wei, Jing Li, Xi Yuan, Ye Liu, Fan Wang, Zhiwei Wang, Lai Wang, Xuesong Liu, Xiaomin Song. BGB-10188, a highly selective PI3Kδ inhibitor with improved safety profile and superior anti-tumor activities in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 664.