The Defined TLR3 Agonist, Nexavant, Exhibits Anti-Cancer Efficacy and Potentiates Anti-PD-1 Antibody Therapy by Enhancing Immune Cell Infiltration

Simple Summary Nexavant, a newly reported TLR3 agonist, has advantages over Poly(I:C) in terms of quality control and pre-clinical efficacy. Here, we further investigated the physicochemical properties, downstream signaling pathways, anti-cancer efficacy, and mechanism of action of Nexavant. The Nexavant was homogenous in solution and less sensitive to RNase A, and showed thermostability compared with Poly(I:C). Unlike Poly(I:C), which activates TLR3, RIG-I, and MDA5, Nexavant only activated TLR3 and RIG-I, not MDA5. The administration of Nexavant via either the intratumoral route or the intranasal route suppressed tumor growth in various cancer models. Combination therapy with anti-PD-1 antibodies resulted in better, synergistic tumor growth inhibition compared to the respective monotherapies. This study demonstrated that Nexavant could be more suitable for clinical use than Poly(I:C) and applied as an anti-cancer agent in the presence or absence of anti-PD-1 antibodies.Abstract Nexavant was reported as an alternative to the TLR3 agonist of Poly(I:C) and its derivatives. The physicochemical properties, signaling pathways, anti-cancer effects, and mechanisms of Nexavant were investigated. The distinctive characteristics of Nexavant compared to that of Poly(I:C) were demonstrated by precise quantification, enhanced thermostability, and increased resistance to RNase A. Unlike Poly(I:C), which activates TLR3, RIG-I, and MDA5, Nexavant stimulates signaling through TLR3 and RIG-I but not through MDA5. Compared to Poly(I:C), an intratumoral Nexavant treatment led to a unique immune response, immune cell infiltration, and suppression of tumor growth in various animal cancer models. Nexavant therapy outperformed anti-PD-1 antibody treatment in all the tested models and showed a synergistic effect in combinational therapy, especially in well-defined cold tumor models. The effect was similar to that of nivolumab in a humanized mouse model. Intranasal instillation of Nexavant led to the recruitment of immune cells (NK, CD4+ T, and CD8+ T) to the lungs, suppressing lung metastasis and improving animal survival. Our study highlighted Nexavant's defined nature for clinical use and unique signaling pathways and its potential as a standalone anti-cancer agent or in combination with anti-PD-1 antibodies.