TLR1/2 Specific Small-Molecule Agonist Suppresses Leukemia Cancer Cell Growth by Stimulating Cytotoxic T Lymphocytes

Toll-like receptor 2 (TLR2) expressed on antigen presenting cells evokes a series of critical cytokines, which favor the development of tumor-specific cytotoxic T lymphocytes (CTLs). Therefore, TLR2 represents an attractive cancer immunotherapeutic target. Here, a synthetic library of 14 000 compounds together with a series of newly developed compounds for NF-kappa B activation using HEK-Blue hTLR2 cells is initially screened. Following further screening in a variety of cells including HEK-Blue hTLRs reporter cells, murine, and human macrophage cell lines, a potent small molecule agonist 23 (SMU-Z1) is identified, which specifically activates TLR2 through its association with TLR1, with a EC50 of 4.88 +/- 0.79 x 10(-9) M. Toxicology studies, proinflammatory cytokines (e.g., TNF-alpha, IL-1 beta, IL-6, and nitric oxide) and target-protein based biophysical assays demonstrate the pharmacologically relevant characteristics of SMU-Z1. In addition, SMU-Z1 promotes murine splenocyte proliferation and upregulates the expression of CD8(+) T cells, NK cells and DCs, which results in a significant antitumor effect in a murine leukemia model. Finally, the induced tumors in three out of seven mice disappear after administration of SMU-Z1. Our studies thus identify a novel and potent TLR1/2 small molecule agonist, which displays promising immune adjuvant properties and antitumor immunity.