Coordinated Activation of Toll-Like Receptor8 (TLR8) and NLRP3 by the TLR8 Agonist, VTX-2337, Ignites Tumoricidal Natural Killer Cell Activity.

Gregory N Dietsch,Mary L Disis,Chihiro Morishima,Yi Yang,Laura Q Chow,Hailing Lu,Robert M Hershberg,Hiroyoshi Nishikawa

doi:10.1371/journal.pone.0148764

Abstract

VTX-2337 (USAN: motolimod) is a selective toll-like receptor 8 (TLR8) agonist, which is in clinical development as an immunotherapy for multiple oncology indications, including squamous cell carcinoma of the head and neck (SCCHN). Activation of TLR8 enhances natural killer cell activation, increases antibody-dependent cell-mediated cytotoxicity, and induces Th1 polarizing cytokines. Here, we show that VTX-2337 stimulates the release of mature IL-1β and IL-18 from monocytic cells through coordinated actions on both TLR8 and the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome complex. In vitro, VTX-2337 primed monocytic cells to produce pro-IL-1β, pro-IL-18, and caspase-1, and also activated the NLRP3 inflammasome, thereby mediating the release of mature IL-1β family cytokines. Inhibition of caspase-1 blocked VTX-2337-mediated NLRP3 inflammasome activation, but had little impact on production of other TLR8-induced mediators such as TNFα. IL-18 activated natural killer cells and complemented other stimulatory pathways, including FcγRIII and NKG2D, resulting in IFNγ production and expression of CD107a. NLRP3 activation in vivo was confirmed by a dose-related increase in plasma IL-1β and IL-18 levels in cynomolgus monkeys administered VTX-2337. These results are highly relevant to clinical studies of combination VTX-2337/cetuximab treatment. Cetuximab, a clinically approved, epidermal growth factor receptor-specific monoclonal antibody, activates NK cells through interactions with FcγRIII and facilitates ADCC of tumor cells. Our preliminary findings from a Phase I open-label, dose-escalation, trial that enrolled 13 patients with recurrent or metastatic SCCHN show that patient NK cells become more responsive to stimulation by NKG2D or FcγRIII following VTX-2337 treatment. Together, these results indicate that TLR8 stimulation and inflammasome activation by VTX-2337 can complement FcγRIII engagement and may augment clinical responses in SCCHN patients treated with cetuximab.Trial Registration: ClinicalTrials.gov NCT01334177

Highlights

Natural killer (NK) cells play an important, well-documented role in cancer immune surveillance and form a bridge to transition innate immune responses to adaptive responses
antibody-dependent cell-mediated cytotoxicity (ADCC) is a well-established effector pathway that contributes to the therapeutic activity of monoclonal antibodies such as cetuximab, an epidermal growth factor receptor (EGFR)-specific mAb approved for treatment of patients with squamous cell carcinoma of the head and neck (SCCHN)
These results indicate that toll-like receptor 8 (TLR8) stimulation and inflammasome activation by VTX-2337 can complement FcγRIII engagement and may augment clinical responses in SCCHN patients treated with cetuximab

Summary

Introduction

Natural killer (NK) cells play an important, well-documented role in cancer immune surveillance and form a bridge to transition innate immune responses to adaptive responses. Activating receptors, such as NKG2D expressed by NK cells, recognize stress-induced ligands on virally infected and malignant cells. NK cell recognition of antibody coated tumor cells through surface FcγRIII/CD16, provides a potent activation signal leading to antibody-dependent cell-mediated cytotoxicity (ADCC), [1, 2]. Increased ADCC by NK cells may lead to a more vigorous anti-tumor response in the short term, which can help shape tumor-directed adaptive immune responses with the potential for long-term, durable clinical responses [6]

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Results

Conclusion