High dose acetaminophen re-polarizes CD11b+ cells in the tumor microenvironment towards an activated macrophage...

High dose acetaminophen (AAP) has demonstrated promising results in early phase clinical trials for treatment of advanced malignancies. When administered concurrently with the CYP2E1 inhibitor fomepizole, AAP can be dose-escalated 100-fold relative to standard dosing without liver toxicity and without compromising anti-tumor activity.

The current study used a 23-plex flow cytometry panel to study AAP-induced changes in the tumor immune microenvironment of syngeneic mouse breast tumors. Effects of AAP on macrophage function and antigen presentation, alone and in combination with PD-1 antibodies, were evaluated.

Findings demonstrated that the vast majority of CD45+ cells in the triple negative breast cancer model are CD11b+ cells of the innate immune system. The CD11b+ cells in the tumor micro-environment of vehicle-treated mice were mostly comprised of GR1+ myeloid derived suppressor cells. On the other hand, the CD11b+ cells in the high dose AAP-treated mice were mostly of the activated macrophage phenotype (F4/80+CD80+MHCII+). In vitro studies were performed to better understand AAP effects on macrophage function. It was demonstrated that AAP enhances phagocytosis as well as antigen presentation by macrophages to antigen-reactive T-cells. These effects are amplified when PD-1 antibodies are combined with AAP in the in vitro antigen presentation assay. Furthermore, AAP has synergistic anti-tumor activity in vivo when combined with PD-1 antibody therapy, an effect that is macrophage dependent.

The present study demonstrates profound AAP-induced changes in the tumor immune microenvironment including the differentiation of CD11b+ cells towards an activated "M1" macrophage phenotype.