Enhanced photosensitizing properties of protein bound curcumin

The naturally occurring compound curcumin has been proposed for a number of pharmacological applications. In spite of the promising chemotherapeutic properties of the molecule, the use of curcumin has been largely limited by its chemical instability in water. In this work, we propose the use of water soluble proteins to overcome this issue in perspective applications to photodynamic therapy of tumors. Curcumin was bound to bovine serum albumin and its photophysical properties was studied as well as its effect on cell viability after light exposure through MTT assay and confocal imaging. Bovine serum albumin binds curcumin with moderate affinity and solubilizes the hydrophobic compound preserving its photophysical properties for several hours. Cell viability assays demonstrate that when bound to serum albumin, curcumin is an effective photosensitizer for HeLa cells, with better performance than curcumin alone. Confocal fluorescence imaging reveals that when curcumin is delivered alone, it preferentially associates with mitochondria, whereas curcumin bound to bovine serum albumin is found in additional locations within the cell, a fact that may be related to the higher phototoxicity observed in this case. The higher bioavailability of the photosensitizing compound curcumin when bound to serum albumin may be exploited to increase the efficiency of the drug in photodynamic therapy of tumors.