Significant increase in the water dispersibility of zinc phthalocyanine nanowires and applications in cancer phototherapy

Abstract

The phototherapy is one of the widely accepted noninvasive clinical methodologies to eradicate cancer cells owing to its minimal side effects and high selectivity to the light of specific wavelength. As represented by photodynamic (PD) and photothermal (PT) therapy, the phototherapy requires light and photosensitizer to generate reactive oxygen species and heat, respectively. Zinc phthalocyanine (ZnPc) is one of the promising photosensitizers as it has a strong absorption cross-section in the spectral range of 650–900 nm that guarantees maximum tissue penetration. One critical issue in using Pc molecule, including ZnPc as a biocompatible sensitizer is the poor water solubility. To increase water solubility, various chemical modifications inducing hydrophilicity have been widely attempted to introduce various functional groups in the ZnPc backbone. We report that ZnPc nanowires (NWs) directly grown from ZnPc powder by vaporization–condensation–recrystallization process show surprisingly increased water dispersibility without any functionalization. The ZnPc NW solution exhibits highly efficient dual PD and PT effects upon the irradiation of near infrared (808 nm) laser. The dual phototherapeutic effect of ZnPc NW is proven to enhance cytotoxic efficiency according to both in vitro and in vivo experimental results. Hee Cheul Choi, Sang Ho Lee and co-workers have devised a way to improve the dispersibility of light-sensitive molecules in water. Using light to treat medical conditions, including tumours, can be less invasive and toxic than other approaches. Such photodynamic and photothermal therapies rely on a light-sensitive molecule — a photo-sensitizer — that is excited under irradiation to release either reactive oxygen species or heat, respectively, which in turn can destroy targeted cells. Most photo-sensitizers, however, suffer from poor solubility in aqueous physiological media, which hinders their applications in the body. This is the case for zinc phthalocyanine, a macrocyclic compound hosting a zinc atom in its central cavity. Rather than trying to alter its chemical composition, the researchers have now observed that converting the powder form into crystalline nanowires significantly increased its dispersibility in water. Furthermore, the nanowires were found to be promising for both photothermal and photodynamic therapies. Water-dispersed nanowires for phototherapy: Without passivation of any water-friendly functional groups in its backbone, one-dimensional zinc phthalocyanine nanowires show remarkably increased dispersibility in water. Upon irradiation with near infrared light, the zinc phthalocyanine nanowires exhibit dual photodynamic and photothermal properties, which enhance the cytotoxic efficiency against tumor cells.