In Cellulo Multistep Synthesis of Antitumor Zwitterionic Heterocycles Triggered by Cancer-Specific Acrolein

Zwitterionic heterocycles hold significant therapeutic potential; however, their application is often hindered by poor membrane permeability and limited target-cell selectivity. Here, we report an innovative strategy for the in situ synthesis of these compounds within cancer cells, using a rationally designed precursor that is nontoxic, non-ionic, and membrane permeable. The synthesis is initiated by endogenous acrolein, an oncometabolite elevated in cancer cells, which triggers a cascade involving 1,3-dipolar cycloaddition, diazo formation, carbamate cleavage, imine formation, intramolecular 6π-azaelectrocyclization, oxidative aromatization, and ester hydrolysis. We validated this methodology in human lung adenocarcinoma (A549) cells, where the in situ-synthesized zwitterionic heterocycle exhibited anticancer activity. Conversely, its pre-synthesized congener showed minimal cytotoxicity, underscoring the poor membrane permeability of the zwitterionic form. Precursor optimization resulted in a lead compound that, upon administration to A549 cells, converted into a cytotoxic zwitterionic heterocycle with a half-maximal inhibitory concentration (IC₅₀) of 6.2 µM. The lead precursor showed exceptional selectivity, with no cytotoxicity in normal human diploid (TIG3) cells. This selectivity arises because healthy cells contain low acrolein levels, insufficient to trigger the activation cascade. Our approach effectively addresses the key therapeutic challenges associated with zwitterionic heterocycles.