VTX-2337 Is a Novel TLR8 Agonist That Activates NK Cells and Augments ADCC

Abstract

Purpose: We aim to characterize VTX-2337, a novel Toll-like receptor (TLR) 8 agonist in clinical development, and investigate its potential to improve monoclonal antibody-based immunotherapy that includes the activation of natural killer (NK) cells.Experimental Design: HEK-TLR transfectants were used to compare the selectivity and potency of VTX-2337, imiquimod, CpG ODN2006, and CL075. The ability of VTX-2337 to induce cytokine and chemokine production from human peripheral blood mononuclear cells (PBMC) and activation of specific immune cell subsets was examined. The potential for VTX-2337 to activate NK cell activity through direct and indirect mechanisms was also investigated. Finally, we tested the potential for VTX-2337 to augment antibodydependent cell-mediated cytotoxicity (ADCC), especially in individuals with low-affinity FcgR3A singlenucleotide polymorphism (SNP).Results: VTX-2337 selectively activates TLR8 with an EC 50 of about 100 nmol/L and stimulates production of TNFa and interleukin (IL)-12 from monocytes and myeloid dendritic cells (mDC). VTX-2337 stimulates IFNg production from NK cells and increases the cytotoxicity of NK cells against K562 and ADCC by rituximab and trastuzumab. Effects of VTX-2337 on NK cells were, in part, from direct activation as increased IFNg production and cytotoxic activity were seen with purified NK cells. Finally, VTX-2337 augments ADCC by rituximab in PBMCs with different FcgR3A genotypes (V

A Phase I Dose-Finding Study of the Novel Toll-like Receptor 8 Agonist VTX-2337 in Adult Subjects with Advanced Solid Tumors or Lymphoma

“…We have extensively characterized the in vitro response of human peripheral blood mononuclear cells, monocytes, mDC, and NK cells to VTX-2337 (6). It should be noted that many of the prominent cytokines induced in vitro via TLR8 activation (notably, IL12, IL1, IFNg) are not detected in the plasma of subjects dosed with VTX-2337.…”

“…Recent X-ray crystallographic data have confirmed that this LRR is associated with ligand binding (10). In all other species, TLR8 is a potent activator of innate immunity, and in humans TLR8 is expressed in the endosomal compartment of monocytes and mDC (6,11). This is in clear distinction to the expression of human TLR7 and TLR9 in the endosome of plasmacytoid dendritic cells-a population of DC with a very different phenotype and biology compared with mDC (12,13).…”

“…VTX-2337 is a novel, selective, small-molecule agonist for TLR8 that mimics the natural ligand of viral single-stranded ribonucleic acid (ssRNA) (6). TLR8 is interesting amongst the family of TLRs in that murine and rat cells respond weakly to synthetic or natural ligands to TLR8 (7,8) due to a small deletion in a defined leucine-rich repeat (LRR) in the linear structure of the receptor (9).…”

“…The only unexpected observation in toxicology studies in the cynomolgus monkey was ocular inflammation, albeit at dose levels considerably higher than would be expected to be used in human clinical applications. Treatment of human peripheral blood cells in vitro with VTX-2337 resulted in increased production of TNFa and IL12 from monocytes and mDC and increased production of interferon gamma (IFNg) from NK cells (6).…”

Critical role of Toll-like receptor signaling in NK cell activation

“…And more important is that unlike other TLR7/8 agonists, these ssRNAs can mediate the activation of NK cells directly, represented as up-regulation of cytotoxicity against HNSCC cell lines BHY, PCI-1 and PCI-13, induction production of IFN-, granzyme B and perforin by NK cells [53]. VTX-2337, a novel small-molecular TLR8 agonist, is recently found to be able to activate NK cells directly and augment ADCC by rituximab in PBMCs [54]. Stimulation with imiquimod, also known as a TLR7 ligand, enhances the cytotoxic activity of expanded NK and  T cells from cancer patients in vitro [55].…”