CES3 (carboxylesterase 3) is a phase I drug metabolizing enzyme that catalyzes the hydrolysis of ester, amide, and carbamate compounds 1. The protein is primarily expressed in liver and localizes to the endoplasmic reticulum, with tissue-specific expression also found in gastrointestinal tract, lungs, and brain regions including cerebellum 123. CES3 demonstrates relatively low catalytic efficiency compared to other carboxylesterases, showing poor substrate conversion for the anticancer prodrug CPT-11 (irinotecan) to its active metabolite SN-38 41. Beyond xenobiotic metabolism, CES3 plays crucial roles in lipid metabolism and metabolic regulation. It promotes lipid storage in adipocytes and is essential for β-adrenergic signaling-stimulated thermogenesis and lipolysis in adipose tissue 56. In liver, CES3 contributes to metabolic dysfunction-associated steatotic liver disease (MASLD) development by promoting de novo lipogenesis, with CES3 loss protecting against Western diet-induced hepatic steatosis 2. CES3 expression is downregulated in various cancers including hepatocellular carcinoma and colorectal adenocarcinoma, where higher expression correlates with better prognosis and enhanced immunotherapy response 78. The enzyme represents a potential therapeutic target for metabolic disorders and cancer treatment.