Inhibition of Rspo-Lgr4 Facilitates Checkpoint Blockade Therapy by Switching Macrophage Polarization.

Qingyun Liu,Min Qian,Jie Zhang,Binghe Tan,Stefan Siwko,Honghui Han,Na Zhang,Kendra Carmon,Bing Du,Juliang Qin,Mingyao Liu,Hua Ren,Xiujuan Shi

doi:10.1158/0008-5472.can-18-0152

Abstract

Therapies targeting immune checkpoints have shown great clinical potential in a subset of patients with cancer but may be hampered by a failure to reverse the immunosuppressive tumor microenvironment (TME). As the most abundant immune cells in TME, tumor-associated macrophages (TAM) play nonredundant roles in restricting antitumor immunity. The leucine-rich repeat-containing G-protein-coupled receptor 4 (Lgr4, also known as Gpr48) has been associated with multiple physiologic and pathologic functions. Lgr4 and its ligands R-spondin 1-4 have been shown to promote the growth and metastasis of tumor cells. However, whether Lgr4 can promote tumor progression by regulating the function of immune cells in the tumor microenvironment remains largely unknown. Here, we demonstrate that Lgr4 promotes macrophage M2 polarization through Rspo/Lgr4/Erk/Stat3 signaling. Notably, urethane-induced lung carcinogenesis, Lewis lung carcinoma (LLC), and B16F10 melanoma tumors were all markedly reduced in Lgr4fl/flLyz2cre/+ mice, characterized by fewer protumoral M2 TAMs and increased CD8+ T lymphocyte infiltration in the TME. Furthermore, LLC tumor growth was greatly depressed when Rspo/Lgr4/Erk/Stat3 signaling was blocked with either the LGR4 extracellular domain or an anti-Rspo1 antibody. Importantly, blocking Rspo-Lgr4 signaling overcame LLC resistance to anti-PD-1 therapy and improved the efficacy of PD-1 immunotherapy against B16F10 melanoma, indicating vital roles of Rspo-Lgr4 in host antitumor immunity and a potential therapeutic target in cancer immunotherapy.Significance: This study identifies a novel receptor as a critical switch in TAM polarization whose inhibition sensitizes checkpoint therapy-resistant lung cancer to anti-PD-1 therapy.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/17/4929/F1.large.jpg Cancer Res; 78(17); 4929-42. ©2018 AACR.

Highlights

Cancer immunotherapy has shown marvelous efficacy in trials targeting negative immune checkpoint regulators including CTLA-4 and PD-1 [1]; only a small subset of patients respond to these treatments that target T cells
Rspo/Lgr4 facilitates M2 macrophage polarization To characterize the potential of Lgr4 in Tumorassociated macrophages (TAM), we checked whether the expression level of Lgr4 is affected by polarization to an M2-like state, as most TAMs are M2 macrophages
We demonstrated that Lgr4 is remarkably upregulated in IL4induced M2 macrophages (Fig. 1A)

Summary

Introduction

Cancer immunotherapy has shown marvelous efficacy in trials targeting negative immune checkpoint regulators including CTLA-4 and PD-1 [1]; only a small subset of patients respond to these treatments that target T cells. Tumorassociated macrophages (TAM), which constitute the major leukocytic infiltrate found within the stroma of many tumor types, along with the other tumor-associated components of innate immunity, appear unaffected by current negative immune checkpoint approaches. Accumulating preclinical and clinical observations demonstrated that modulate macrophage polarization in the TME may represent an additional approach for cancer treatment, either alone or in combination with immune checkpoint therapies [5,6,7,8]. Given that immune checkpoint blockade (ICB) anticancer therapies are currently effective in only a fraction of patients, and primarily function through activation of T-cell responses, we hypothesized that activating the innate immune response through targeting TAMs would augment the efficacy and broaden the target patient population of immune checkpoint blockade approaches

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Results

Conclusion