Development of a tumor extracellular pH-responsive nanocarrier by terminal histidine conjugation in a star shaped poly(lactic-co-glycolic acid)

[Display omitted] •A histidine modified star-shaped PLGA was synthesized.•NPs prepared with this polymer exhibited pH-responsive behaviour.•The NPs showed endosomal escape and uniform cellular distribution.•In the tumor spheroid model, deep penetration was observed with this NP. After reaching the tumor site, nanoparticles (NPs) mostly accumulate in the periphery of the tumor, as their intra-tumoral penetration is prevented due to the low perfusion, high interstitial fluid pressure, and dense matrix present in the tumor. A pH-responsive carrier can improve tumor permeation by releasing the drug quickly in the acidic tumor pH, helping its uniform tumor distribution through diffusion. In the current study, we have developed a histidine modified star-shaped PLGA (sPLGA-His) for the tumor-targeted delivery of the drug combination of docetaxel and disulfiram. The sPLGA-His NPs exhibited a rapid pH-responsive drug release behavior, with significantly increased drug release at pH 6.5 compared to pH 7.4 in 12 h. In-vitro cytotoxicity analysis showed that the pH-sensitive sPLGA-His NPs had enhanced efficacy in both 2D and 3D cell culture models. In the cell uptake study, the sPLGA-His NPs exhibited endosomal escape and uniform cellular distribution, whereas sPLGA NPs were found to be accumulated in the endosomes. In the tumor spheroid model, deep penetration was observed with the sPLGA-His NPs, while sPLGA NPs were found to be accumulated in the periphery. Using fluorescent colocalization as well as FRET analysis, increased release of the encapsulated cargo was noticed with the sPLGA-His NPs, compared to sPLGA NPs. Altogether, the sPLGA-His NPs can be used as a tumor extracellular pH-responsive nanocarrier for efficient drug delivery to the tumor.