An improvement in photodynamic therapy (PDT) efficiency against a human gastric cancer cell line (MKN45) with 5-aminolevulinic acid (ALA) and lanthanide nanoparticles (LNPs) is described. An endogenous photosensitizer, protoporphyrin IX, biosynthesized from ALA and selectively accumulated in cancer cells, is sensitizable by the visible lights emitted from up-conversion LNPs, which can be excited by a near-infrared light. Ten kinds of surface modifications were performed on LNPs, NaYF₄(Sc/Yb/Er) and NaYF₄(Yb/Tm), in an aim to distribute these irradiation light sources near cancer cells. Among these LNPs, only the amino-functionalized LNPs showed affinity to MKN45 and HeLa cancer cells. A PDT assay with MKN45 demonstrated that amino-modified NaYF₄(Sc/Yb/Er) gave rise to a dramatically enhanced PDT effect, reaching almost perfect lethality, whereas NaYF₄(Yb/Tm)-based systems caused little improvement in PDT efficiency. The improvement of PDT effect with the amino-modified NaYF₄(Sc/Yb/Er) is promising for a practical PDT against deep cancer cells that are reachable only by near-infrared lights.
Keywords: ALA; lanthanide nanoparticle; near-infrared; up-conversion luminescence.