Folate-targeted gold nanoparticles for doxorubicin delivery in tumor spheroids

Targeted drug delivery systems represent a promising strategy for enhancing the efficacy and specificity of cancer therapy. In this study, 35 nm folate-targeted gold nanoparticles are presented as nanoparticle-drug conjugates obtained by anchoring on their surface lipoyl terminating doxorubicin prodrug (proDoxo) releasable at the endolysosomal acidic pH to prevent off-site toxic effects. Colloidal stable nanoparticles with a density of proDoxo up to 1000 molecules/particle and 2 kDa mPEG-SH coating were obtained. At pH 5, Doxo was completely released from the nanoparticles in 5 days while only 13% was released over the same period at pH 7.4. The nanoparticle decoration with folic acid as a targeting agent bestowed nanosystems with selective drug delivery to folate receptor (FR)-overexpressing cancer cells and controlled intracellular release. This led to enhanced cancer cell killing by folated nanoparticles compared to their nontargeted counterparts. Moreover, folated nanoparticles were found to distribute more homogeneously inside KB^FR+ cancer cell spheroids than non-targeted nanoparticles, resulting in higher spheroid volume reduction.