Fig. 2

Intracellular accumulation and endo/lysosomal escape capability of the PEI-modified nanoparticle. A Intracellular PTX accumulation of MCF-7/Taxol cells coincubated with PP@PTX, P@PTX and free PTX before and after drug efflux. Blue fluorescence shows nuclei from DAPI; red fluorescence shows DiI-labeled PP@PTX NPs and P@PTX NPs; green fluorescence shows FTIC-labeled free PTX. The scale bar is 100 μm. B Intracellular PTX retention in MCF-7/Taxol cells at various times after DiI-labeled PP@PTX, P@PTX and free FITC-PTX treatment. C The colocalization of NPs and endo/lysosomes in MCF-7/Taxol cells after coincubation with DiI-labeld PP@PTX and P@PTX. Lysotracker stains the endo/lysosomes (green), and the NPs trapped in endo/lysosomes are labeled as yellow dots. Colocation scatterplots of PP@PTX and P@PTX vs endo/lysosomes are analyzed by Image J. The scale bar is 25 μm. D Corresponding Pearson’s correlation coefficient (PCC) values of PP@PTX and P@PTX vs endo/lysosomes after 6 h coincubation, n = 5 per group. E Integrity of endo/lysosomal membrane with calcein after conincubation with PP@PTX and P@PTX. The scar bar is 25 μm. F Bio-TEM images of MCF-7/Taxol cells incubated with PP@PTX for 6 h. The ROI (yellow square in the image) reveals the membrane rupture and burst of lysosomes. L lysosome, N nucleu, M mitochondria, ER endoplasmic reticulum. G Relative cell viability of MCF-7/Taxol cells after incubation with P@PTX, PP@PTX, and pretreated PP@PTX (pre-immersed in PBS at pH 6.3 for 2 h) at different concentrations for 24 h. All data are presented as mean ± SD, *p < 0.05, **p < 0.01