5-Bromouracil-gracillin (5BrU-G) complex: an APOBEC3-activated therapeutic strategy exploiting cancer-specific enzymatic activity for selective cytotoxicity.

Recent cancer treatment development has focused on smart drugs, primarily using nanomaterials as carriers. However, concerns about nanomaterial fate and body clearance have led to exploring alternative approaches. This study presents a novel targeted smart drug that uses normal lymphocytic cells as carriers and exploits cancer microenvironment characteristics for drug release, avoiding systemic damage. The research investigated a complex combining gracillin (natural carrier) and the chemotherapeutic agent 5-bromouracil (5-BrU). Molecular docking showed the 5BrU-G complex had superior binding affinity (- 7.96 kcal mol) to glycosylated adhesion domain of human T lymphocyte glycoprotein CD2 (1CDB) cell surface receptors in silico. The complex was successfully synthesized through double replacement, precipitation, and neutralization reactions, confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cytotoxic and genotoxic studies revealed the selectivity of 5BrU-G against cancer cells (MDA-MB-231 and Caco-2) while saving normal cells (MCF-10A and CCD 841 CoN). Unlike 5-BrU alone, which showed significant genotoxicity in normal cells, the 5BrU-G complex demonstrated minimal toxic effects. The selective targeting mechanism of 5BrU-G relies on APOBEC3 enzyme activity, which is elevated in cancer cells but is absent in normal cells. This was confirmed when APOBEC3 inhibition prevented the complex's cancer-killing activity. This novel approach offers promising alternatives for improving cancer therapy efficacy while reducing side effects.