Conjugated anisotropic gold nanoparticles through pterin derivatives for a selective plasmonic photothermal therapy: in vitro studies in HeLa and normal human endocervical cells

This article reports a simple one-step method for anisotropic gold nanoparticle synthesis for plasmonic photothermal therapy medical purposes, using 1,4-bis[(2-ethylhexyl) oxy]-1,4-dioxo-2-butanesulfonic acid-sodium (AOT) reverse micelles as nanoreactor, where under specific condition, AOT acts as both a reducing and stabilizing agent. Obtained AuNPs were functionalized by attaching compounds derived from 2-aminopteridin-4(3H)-ona (pterin family) such as (2S)-2-[(4-{[(2-amino-4-hydroxypteridin-6-yl) methyl] amino} phenyl) formamido] pentanedioic acid (folic acid/FA) and 2-amino-4-hydroxypteridine-6-carboxylic acid (PCA) in order to evaluate its effect as targets for folate receptor-mediated cellular uptake in HeLa and normal human endocervical cells. The nanoconjugates were characterized through transmission electron microscopy (TEM), ultraviolet-visible, fluorescence, and Fourier transform infrared spectroscopies. Results showed an effective photothermal response of AuNPs in solution under NIR exposure with concentration dependence and none effect of the conjugation. In vitro studies in HeLa cells showed a concentration-dependent cytotoxicity of AuNPs; thus, conjugation to biomolecules such as FA or PCA has provided a biocompatible coating onto AuNPs and made them highly cytocompatible. Results demonstrated despite AF and PCA are analogue molecules, the folate receptors in HeLa cells are specific, and the different chemical groups available on the AuNPs surface have drastically different cell membrane penetration properties. The specific cell uptake through folate receptor (FR) was observed for short treatment time, while for a long treatment time, other mechanisms as penetration or adhesion were shown involved. In the particular case, of AF@AuNPs, the cell uptake through FR-mediated endocytosis was evidenced to have been decreasing cell viability in 24% after 2 h of treatment and 5 min under NIR exposure. This was confirmed by morphological changes in cells, as well the selective uptake of the FA@AuNPs by HeLa cells compared to normal cells, due folate receptor overexpression in HeLa cells. The findings from this study will have implications in the chemical design of nanostructures for plasmonic photothermal therapy. The obtained results provide evidences at in vitro level to support the fact that AF@AuNP nanoconjugate will accumulate in the affected tissue preferentially through the EPR (enhanced permeability and retention) effect by folate-targeting mechanism which will significantly enhance the efficacy of NIR-induced local photothermal effects.