High dose acetaminophen with concurrent CYP2E1 inhibition has profound anti-cancer activity without liver toxicity .

Acetaminophen (AAP) is metabolized by a variety of pathways such as sulfation, glucuronidation and fatty acid amide hydrolase-mediated conversion to the active analgesic metabolite AM404. CYP2E1-mediated metabolism to the hepatotoxic reactive metabolite NAPQI (N-acetyl-p-benzoquinone imine) is a minor metabolic pathway that has not been clearly linked to AAP therapeutic benefits yet definitely leads to AAP liver toxicity. N-acetylcysteine (NAC) (an anti-oxidant) and fomepizole (a CYP2E1 inhibitor) are clinically used for the treatment of AAP toxicity. Mice treated with AAP in combination with fomepizole (+/- NAC) were assessed for liver toxicity by histology and serum chemistry. Anti-cancer activity of AAP with NAC and fomepizole rescue was assessed in vitro and in vivo. Fomepizole with or without NAC completely prevented AAP-induced liver toxicity. In vivo, high dose AAP with NAC/fomepizole rescue had profound anti-tumor activity against commonly used 4T1 breast tumor and LLC lung tumor models and no liver toxicity was detected. The anti-tumor efficacy was reduced in immune-compromised NSG mice, suggesting an immune mediated mechanism of action. In conclusion, using fomepizole-based rescue, we were able to treat mice with 100-fold higher than standard dosing of AAP (650 mg/kg) without any detected liver toxicity and substantial anti-tumor activity. Significance Statement Concurrent CYP2E1 inhibition allows for dose escalation of acetaminophen to levels needed for anti-cancer activity without liver toxicity. High dose acetaminophen has anti-cancer activity against commonly used syngeneic models of lung cancer (lewis lung cancer) and breast cancer (4T1) known to be resistant to first line therapies such as PD-1 antibody therapy and cisplatin.