A Novel Imidazoquinoline With TLR 7/8, STING, and Inflammasome Activity Demonstrates Antitumor Efficacy in Mouse Melanoma and Neu-Driven Mammary Adenocarcinoma

Activation of endosomal Toll-like receptors 7 and 8 in antigen-presenting cells typically results in the induction of type I interferons (IFN). We previously reported a series of imidazoquinolines that potently activate TLR7/8. The potency and selectivity of these compounds can be tuned via substitutions to the N1 and C2 positions of the tricycle. Furthermore, C2-alkyl substitutions that project into a hydrophobic pocket at the dimer interface of the receptor significantly affect TLR7 and TLR8 activities. In the current study, we show that these compounds induce the expression of IFN-γ, a type II IFN, in addition to the classic type I IFNs. To understand the mechanism of type II IFN induction, we utilized global proteomics to evaluate the effect of our lead TLR7/8 agonist 4-amino-1-(4-(aminomethyl)benzyl)-2-butyl-7-methoxycarbonyl-1H-imidazo[4, 5-c]quinoline (558) on dendritic cells (DCs). These studies show 558 activated STING and inflammasome pathways, in addition to its effect on TLR7/8. Based on the multifactorial mechanism of action, we also investigated the therapeutic benefit of 558 as a single agent. The effect of 558 dosing on various immune cell populations was investigated in tumor-bearing and healthy mice. Further, the effect of 558 on tumor multiplicity and tumor burden was studied in the transgenic Balb-neuT mice, which develop neu-driven mammary adenocarcinomas. 558 reversed the tumor-induced declines in antitumor immune cells in the bone marrow and lymph nodes of tumor-bearing mice. In vivo studies showed that 558 significantly reduced the rate of tumor growth, likely due to enhanced DC activation in the lymph nodes and CD8 T cell infiltration into the tumor tissue.