The chelating agent diethylenetriaminepentaacetic acid (DTPA) inhibits human cytomegalovirus replication. Since chelating agents are known to exhibit anti-cancer effects, DTPA-induced cytotoxicity was evaluated in breast cancer cells (MCF-7) and neuroblastoma cells (UKF-NB-3). DTPA inhibited cancer cell growth in threefold lower concentrations compared to human foreskin fibroblasts (HFF). Antiviral and anti-cancer activity of chelating agents is caused by intracellular complexation of metal ions. DTPA, an extracellular chelator, was covalently coupled to human serum albumin (HSA) molecules, HSA nanoparticles (HSA-NP), gelatin type B (GelB) molecules, and GelB nanoparticles (GelB-NP) to increase cellular uptake. Coupling of DTPA to drug carrier systems increased its cytotoxic and antiviral activity by 5- to 8-fold. Confocal laser scanning microscope examination revealed uptake of DTPA-HSA-NP in UKF-NB-3 cells and HFF. Therefore, coupling of DTPA to protein-based drug carrier systems increases its antiviral and anti-cancer activity probably by mediating cellular uptake.