Vaterite submicron particles designed for photodynamic therapy in cells

Abstract

Background: Calcium carbonate (CaCO₃) is one of the most abundant materials in the world. It has several different crystalline phases as present in the minerals: calcite, aragonite and vaterite, which are anhydrous crystalline polymorphs. Regarding the preparation of these microparticles, the most important aspect is the control of the polymorphism, particle size and material morphology. This study aimed to develop porous microparticles of calcium carbonate in the vaterite phase for the encapsulation of chloro-aluminum phthalocyanine (ClAlPc) as a photosensitizer (PS) for application in Photodynamic Therapy (TFD).

Methods: In this study, spherical vaterite composed of microparticles are synthesized by precipitation route assisted by polycarboxylate superplasticizer (PSS). The calcium carbonate was prepared by reacting a mixed solution of Na₂CO₃ with a CaCl₂ solution at an ambient temperature, 25 °C, in the presence of polycarboxylate superplasticizer as a stabilizer. The photosensitizer was incorporated by adsorption technique in the CaCO₃ microparticles. The CaCO₃ microparticles were studied by scanning electron microscopy, steady-state, and their biological activity was evaluated using in vitro cancer cell lines by trypan blue exclusion method. The intracellular localization of ClAlPc was examined by confocal microscopy.

Results: The CaCO₃ microparticles obtained are uniform and homogeneously sized, non-aggregated, and highly porous microparticles. The calcium carbonate microparticles show an average size of 3 μm average pore size of about 30-40 nm. The phthalocyanine derivative loaded-microparticles maintained their photophysical behavior after encapsulation. The captured carriers have provided dye localization inside cells. The in vitro experiments with ClAlPc-loaded CaCO₃ microparticles showed that the system is not cytotoxic in darkness, but exhibits a substantial phototoxicity at 3 μmol.L^-1 of photosensitizer concentration and 10 J.cm^-2 of light. These conditions are sufficient to kill about 80 % of the cells.

Conclusions: All the performed physical-chemical, photophysical, and photobiological measurements indicated that the phthalocyanine-loaded CaCO3 microparticles are a promising drug delivery system for photodynamic therapy and photoprocesses.

Keywords: Calcium carbonate; Photodynamic therapy; Photosensitizer; Vaterite submicron particles.