Engineering and biological assessment of double core nanoplatform for co-delivery of hybrid fluorophores to human melanoma

We investigated new development in photodynamic therapy (PDT), aiming at enhanced tumor selectivity and biocompatibility, which included application of a third-generation photosensitizing agent, i.e. xanthene-origin Rose Bengal (RB) co-encapsulated with up-converting NaYF4 nanoparticles (NPs) co-doped with lanthanide ions: Er3+ (2%) and Yb3+ (20%). The hybrid fluorophores were applied as components of double core nanocarriers (NCs) obtained by double (multiple) emulsion solvent evaporation process. Next, to improve the biocompatibility and photodynamic activity, biodegradable polymer: poly(lactide-co-glycolide) – PLGA and non-ionic surfactants with different hydrophobicity: Span 80 and Cremophor A25, were used. After the engineering process, controlled by dynamic light scattering (DLS) measurements, ζ-potential evaluation, transmission electron and atomic force microscopy (TEM and AFM) imaging, as well as optical analysis provided by measurements of the up-conversion emission spectra and luminescence kinetics for encapsulated only NaYF4:Er3+,Yb3+ NPs and co-encapsulated RB + NaYF4:Er3+,Yb3+ molecules, spherical polyester NCs with average size <200 nm, were tested on human melanoma (Me-45 and MeWo) cells and a control human keratinocyte (HaCaT) cell line. The photodynamic action of the investigated NCs was assessed by oxidoreductive potential measurements with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, that corresponds to percentage of the viable cells. Immunofluorescence and the NCs internalization studies were visualized by confocal laser scanning microscopy (CLSM studies). Our results indicated effective photosensitizer delivery into the cancer cells and significant photodynamic efficiency enhanced by the near infrared (NIR)-activation of the encapsulated hybrid cargo in the skin melanoma cells.