Abstract 1791: LBL-015, a novel anti-PD-1 fused with TGF-βRII, shows a great anti-tumor activity in a mouse MC38 model
Authors: Huang Xiao , Sun Jianming , Qin Yurong , Lin Huan , Guan Jing , Lai Shoupeng , Kang Xiaoqiang , Ling Hong 
Published: July 2021

Abstract
Objective: Blocking PD-1 with monoclonal antibodies is a highly promising onco-immune therapy and has elicited durable antitumor responses and long-term remissions with a broad spectrum of cancers, However, the response to anti-PD-1 therapy is restricted to only a subset of patients with around 25% response rate in cancer patients. TGF-β, a growth factor, plays a pivotal role in tumor development and progression, by inducing tumor immune evasion, activating cancer associated fibroblasts with induction of migration and invasiveness of tumor cells, and promoting angiogenesis in tumor microenvironment. Therefore, a tetravalent bispecific fusion protein (LBL-015), targeting both PD-1/PD-L1 axis and TGF-β signaling pathway was developed to achieve maximal anti-tumor immunity, while blocking the factors implicated in the tumor microenvironment and overcoming the resistance of tumor cells to anti-PD-1 therapy.
Methods: The bispecific fusion protein was designed as 2:2 antibody-cytokine fusion format, using our unique Mab fusion platform. The binding affinity of LBL-015 to human PD-1 and TGF-β1 was determined by Fortebio. The activity of LBL-015 was determined using several in vitro assays, including PD-1/NFAT, TGFβ1/SBE-Luc reporter gene and PBMC activation assays. The in vivo anti-tumor activity of LBL-015 was investigated in the human PD-1 knock-in mouse model (Shanghai Model Organisms) implanted with MC38-OVA cells.
Results: The binding affinity of LBL-015 was measured as 5.24 nM to human PD-1 and 0.14 nM to human TGF-β1, respectively. In vitro LBL-015 could block PD-1-PD-L1 interaction, recovering NFAT reporter gene signal, with EC50 of 0.1565 nM, which was much more potent than M7824 (EC50 of 0.5412 nM). In TGF-β1/SBE-Luc reporter gene assay, LBL-015 inhibited SMAD signaling induced by TGF-β1, with IC50 of 0.00576 nM, which was comparable to M7824. In pre-activated human PBMCs, the release of IFN-γ by PBMCs was completely suppressed with TGF-β1 addition. LBL-015 could relieve the suppression of IFN-γ release induced by PD-1 or TGF-β1, in a dose dependent manner. Surprisingly, M7824 didn't show any effect in this assay system. In a model of huPD-1 knock-in mice (Shanghai Model Organisms) implanted with MC38-OVA cells. LBL-015 was shown significant tumor growth inhibition (TGI) of 84.36% and 55.27% at the dose of 20 mg/kg and 10 mg/kg respectively (p&lt;0.001 compared with vehicle treated mice), indicating its potent anti-tumor activity of this bi-functional fusion protein.
Conclusions: LBL-015, an anti-PD-1 and TGF-β bispecific fusion protein was shown a great synergetic anti-tumor efficacy in vitro to antagonize both tumor immune evasion and aberrant microenvironment induced by PD-1 and TGF-β1, also in a mouse tumor model, LBL-015 strongly inhibited tumor growth in a dose dependent manner, hence a promising bispecific fusion protein for further clinical development.
Citation Format: Xiao Huang, Jianming Sun, Yurong Qin, Huan Lin, Jing Guan, Shoupeng Lai, Xiaoqiang Kang, Hong Ling. LBL-015, a novel anti-PD-1 fused with TGF-βRII, shows a great anti-tumor activity in a mouse MC38 model [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 1791.