Abstract 1618: A highly selective and potent TLR8 agonist ZG0895 in preclinical studies of anti-tumor activities

Abstract Toll-like receptor 8 (TLR8) recognizes ssRNA fragments from pathogens and initiate both innate and adaptive immune responses. TLR8 activation can reverse Treg and myeloid-derived suppressor cells (MDSC) mediated immune suppression by tumors that lead to a restore of immune response to inhibit tumor growth. ZG0895 is a potent and novel TLR agonist that shows a highly selective activation of TLR8 and has a more than 300-fold potency over TLR7 in EC50 values. The agonist screening results further confirmed that ZG0895 without activation of TLR isoforms like TLR2, 4 or 9 in cells. In pharmacokinetics and pharmacodynamics, ZG0895 has a preferable ADME and PK profile and can activate immune system via subcutaneous (s.c.) administration. For in vivo anti-tumor efficacy studies, ZG0895 at 1~30 mg/kg exhibited significant dose-dependent inhibition of tumor growth in immunocompetent myeloid-sufficient murine models with CT26, EMT6 or HH subcutaneous xenografts. Furthermore, ZG0895 administration resulted in a complete tumor regression by ZG0895 at high dose via s.c. injection. Mechanism studies of ZG0895 in ex vivo human PBMC assay showed a strong induction of TLR8 related cytokines. In vivo study in tumor-bearing mouse demonstrated that pro-inflammatory cytokines, such as TNFα, IL12p40, IL6 and IL10, were quickly released after ZG0895 treatment but soon returned to normal that can avoid continuous activation of systemic immunity and reduce the risk of cytokine release storm. Consistently, in vivo cynomolgus monkey study by consecutive treatments with ZG0895 (day 30) resulted in a significant increase of immune system cells including intermediate monocytes, non-classic monocytes, cDCs and NK cells, along with notable decrease of classical monocytes but unchanged pDCs, suggesting a possible reversion of tumor-initiated MDSC via TLR8 activation. All these changes were back to normal after period of recovery (day 57), indicated the immune effect of ZG0895 was restrained. These preclinical results support that ZG0895 as a highly TLR8-selective agonist inhibits tumor growth via the activation of TLR8 eliciting immune responses but under a better safety than other conventional TLR8 agonists, and it is worth to be further explored as an anti-cancer drug candidate. Citation Format: Dawei Cui, Ruifeng Liu, Huanyi Yang, Bing Zhu, Zelin Sheng, Binhua Lv. A highly selective and potent TLR8 agonist ZG0895 in preclinical studies of anti-tumor activities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1618.