ICG-ALA complex for improved phototherapy of cancer

Abstract

5-Aminolevulinic acid (ALA) based photodynamic therapy (PDT) is a clinically approved therapeutic method for cancer treatment. Indocyanine green (ICG) is on the other hand an FDA-approved fluorescent dye that has been widely used in medical imaging in the near-infrared (NIR), and lately recognized as an agent to induce photothermal therapy (PTT). However, the hydrophilicity of ALA and rapid degradation of ICG in aqueous or physiological media as well as their instability limit their clinical application. Besides, the combination of PDT and PTT is a promising alternative to a single therapy approach. Herein, electrostatic binding of ALA to ICG is proposed to bypass such handicaps and provide enhanced therapeutic outcomes with simultaneous PDT and PTT combination. ICG-ALA exhibited excellent biocompatibility up to 50 μg ICG/mL-10 mM ALA in the dark in both SKBR3 and MDA-MB-231 cell lines with higher cell uptake compared to free ALA or ICG. ICG-ALA treatment coupled with 640/808 nm 5 min co-irradiation caused significantly stronger phototoxicity in both cancer cell lines at very low concentrations, reaching near complete loss of viability at 2.5 μg ICG /mL-0.5 mM ALA equivalent concentration of the ICG-ALA. The temperature increase observed during irradiation of the cells and the elevated oxidative stress resulting in the release of caspase 3/7 agrees well with the onset of PTT and PDT. In addition, ICG-ALA demonstrates visualization of cancer cells in both NIR (ICG) and visible (PpIX) regions allowing imaging-guided phototherapy.