Kinase experiment:

Human embryonic kidney cells (HEK293) expressing TLR2, 3, 4, 5, 7, 8, or 9 are cultured in Dulbecco's Modified Eagle's Media containing 4.5 g/L L-glucose and 10% FBS. The activity of specific TLR agonists is assessed using the secretory embryonic alkaline phosphatase (SEAP) reporter gene that is linked to NF-κB activation in response to TLR stimulation. Measurement of SEAP activity using the Quanti-blue substrate after TLR agonist treatment is carried out similarly[1].

Cell experiment:

PBMCs or purified NK cells are prepared, and the purity of NK cells is approximately 99%. NK cell-mediated cytotoxicity is assessed by Calcein AM release from labeled target cells. In brief, PBMCs or purified NK cells are cultured for 48 hours in RPMI medium in the presence of Motolimod (167 or 500 nM) before incubation with target cells[1].

Animal experiment:

Monkeys[2] The male monkeys (2.9-4.9 kg) are housed individually (cage dimensions of 0.76 m wide×0.74 m deep×0.81 m in height), but commingled periodically as part of the environmental enrichment program. The animals are also given fruit, vegetable, or additional supplements as a form of environmental enrichment, as well as given various cage enrichment devices. Animals are given Certified Primate Diet, two times daily and water ad libitum. Motolimod is administered as a bolus subcutaneous (SC) injection in the intrascapular area at doses of 1 and 10 mg/kg. Blood samples are collected at baseline (pre-dose), and 6, 12, 24, and 96 h post injection to monitor levels of IL-1β and IL-18 in the plasma using the human MAP v.1.6 inflammation panel.

Target: TLR8

IC50: 100 nM (EC50)

Motolimod (VTX-2337) is a small molecule, selective Toll-like receptor (TLR) 8 agonist with EC50 value of 100 nM [1]. VTX-2337 is currently in clinical development as an immunotherapy for multiple oncology indications, including ovarian cancer and squamous cell carcinoma of the head and neck [2]. TLR8 is located in the endosome where it functions in the recognition of foreign nucleic acids from intracellular pathogens. TLR8 has emerged as a potential target for anticancer immunotherapies [1].

In vitro: VTX-2337 (800 nmol/L) activated NK cells, leading to increased TNFα and IL-12, IFNγ production and VTX-2337 (167 or 500 nmol/L) augmented rituximab- and trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) [1]. Moreover, VTX-2337 (3 or 10 μM) induced mature IL-1β and IL-18 production through NLRP3 inflammasome activation in THP-1 cells [2].

In vivo: VTX-2337 (1 or 10 mg/kg, subcutaneous injection) induced IL-1β and IL-18 production in male cynomolgus monkeys [2].

Clinical trial: In a phase I dose-finding study, VTX-2337 (0.1–3.9 mg/m2, subcutaneous administration) was well tolerated and active with a predictable pharmacologic profile in adult subjects with advanced solid tumors or lymphoma [3].

References:
1.  Lu H, Dietsch GN, Matthews MA, Yang Y, Ghanekar S, Inokuma M, et al. VTX-2337 is a novel TLR8 agonist that activates NK cells and augments ADCC. Clin Cancer Res. 2012;18(2):499-509.
2.  Dietsch GN, Lu H, Yang Y, Morishima C, Chow LQ, Disis ML, et al. Coordinated Activation of Toll-Like Receptor8 (TLR8) and NLRP3 by the TLR8 Agonist, VTX-2337, Ignites Tumoricidal Natural Killer Cell Activity. PLoS One. 2016;11(2):e0148764.
3.  Northfelt DW, Ramanathan RK, Cohen PA, Von Hoff DD, Weiss GJ, Dietsch GN, et al. 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. Clin Cancer Res. 2014;20(14):3683-91.