title: Coordinated Activation of Toll-Like Receptor8 (TLR8) and NLRP3 by the TLR8 Agonist, VTX-2337, Ignites Tumoricidal Natural Killer Cell Activity.
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.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT01334177.
authors.affiliation: VentiRx Pharmaceuticals, Seattle, WA, United States of America.
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Dietsch
authors.affiliation: Tumor Vaccine Group, Center for Translational Medicine in Women's Health, University of Washington, Seattle, WA, United States of America.
authors.forename: Hailing
authors.initials: H
authors.lastname: Lu
authors.affiliation: Tumor Vaccine Group, Center for Translational Medicine in Women's Health, University of Washington, Seattle, WA, United States of America.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Tumor Vaccine Group, Center for Translational Medicine in Women's Health, University of Washington, Seattle, WA, United States of America.|Department of Laboratory Medicine, University of Washington, Seattle, WA, United States of America.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Morishima
authors.affiliation: Department of Medicine, University of Washington, Seattle, WA, United States of America.
authors.forename: Laura Q
authors.initials: LQ
authors.lastname: Chow
authors.affiliation: Tumor Vaccine Group, Center for Translational Medicine in Women's Health, University of Washington, Seattle, WA, United States of America.
authors.forename: Mary L
authors.initials: ML
authors.lastname: Disis
authors.affiliation: VentiRx Pharmaceuticals, Seattle, WA, United States of America.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Hershberg
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology* / Q000627:therapeutic use; D002352:Carrier Proteins / Q000819:agonists*; D020170:Caspase 1 / Q000378:metabolism; D015550:Cell Degranulation / Q000187:drug effects / Q000276:immunology; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic / Q000276:immunology; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D058847:Inflammasomes / Q000378:metabolism; D020382:Interleukin-18 / Q000096:biosynthesis; D053583:Interleukin-1beta / Q000096:biosynthesis; D020014:K562 Cells; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000276:immunology* / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D008252:Macaca fascicularis; D008297:Male; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D009369:Neoplasms / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D017452:Receptors, IgG / Q000378:metabolism; D051200:Toll-Like Receptor 8 / Q000819:agonists*
chemical_list: D001552:Benzazepines; D002352:Carrier Proteins; D058847:Inflammasomes; D020382:Interleukin-18; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D017452:Receptors, IgG; D051200:Toll-Like Receptor 8; C573973:VTX-2337; D020170:Caspase 1