Aspirin-based esters for carboxylesterase 2-targeted bioimaging and drug delivery

Bio-activated esters containing a functional alcohol and an acid moiety as recognition unit have emerged in bioimaging and drug discovery. When the alcohol moiety is designated as an imaging dye or a drug, disease-related enzyme activity can be visualized, or the drug can be delivered to disease lesions with aberrant enzyme expression. However, although the carboxylic acid moiety is co-delivered to enzyme-overexpressing sites along with the alcohol part, the leaving acid groups are typically non-functional. Therefore, we sought to develop a dual-functional ester design platform by incorporating a biologically active acid with functional alcohol moieties. In this study, we selected carboxylesterase 2 (CES2) as the target enzyme and first proposed aspirin-based esters as a potential CES2-targeting scaffold. A prototype compound ( HFC-AS ) was initially constructed and characterized as a dual-functional ester, which exhibited high sensitivity and specificity for CES2 sensing and significantly improved antitumor efficacy compared to the combined addition of HFC-OH and aspirin. Subsequently, an aspirin-based fluorescent probe ( DDX-AS ) was developed, displaying an ultrafast reaction rate toward CES2 while maintaining high sensitivity and selectivity. Consequently, CES2 activity in living systems could be rapidly detected with high specificity, enabling imaging of both subcutaneous transplanted and pulmonary metastatic melanoma. Furthermore, an aspirin-based prodrug ( SN-38-AS ) was developed and demonstrated a higher tumor growth inhibition rate (98%) than the clinically used prodrug irinotecan (89%), while also exhibiting an improved safety profile. Collectively, a new strategy for CES2-targeted bioimaging and drug delivery was proposed and evaluated, showing great potential for disease diagnosis and drug development.