Discovery of a small molecule TLR3 agonist adjuvant

Pattern-recognition receptor (PRR) agonists are valuable agents across multiple medical applications, from vaccinology to immune-oncology. However, well-defined and potent small molecule agonists for many PRRs still await discovery and development. Screening of chemical libraries of ~200,000 small molecules for maturation of human monocytic cells by quantifying NF-κB activation and cell adherence was completed. From this screen, we selected a thiazole benzamide derivative, PVP-057, for its robust immunomodulatory properties, low toxicity profile, and concentration-dependent activity. In vitro investigation of pathway and receptor activation reveals that PVP-057 is a Toll-like receptor 3 (TLR3) agonist. As a single-component adjuvant, administered intramuscularly or intradermally to female mice, PVP-057 enhances long-term humoral immunogenicity of varicella-zoster virus glycoprotein E to levels comparable to those induced by the clinical grade standard benchmark adjuvant, AS01B, while concurrently inducing cell-mediated immunity. To demonstrate the large-scale and precise synthesis necessary for the efficient mass production of a small molecule agonist, a green chemistry approach was completed, devising a three-step, 24-hour synthesis scheme for PVP-057, with a reliable purity of ~98%. Featuring highly efficient and scalable synthesis, a distinct TLR3-dependent mechanism of action, and robust adjuvanticity, the PVP-057 pharmacophore has prophylactic and therapeutic potential. Adjuvants are an important component of modern vaccines. Here, the authors employ a phenotypic screen of ~200k compounds and identify PVP-057, a TLR3 agonist with a simple scalable 3-step synthesis, as an adjuvant that induces durable humoral and cellular immunity to varicella-zoster virus (VZV) gE in mice.