The endosomes thus formed are eventually converted into the lysosomes and ultimately result in the drug release [102]. Liu et al. developed SWCNT conjugated with paclitaxel (PTX) and reported the nonreceptor mediated endocytosis mechanism for the cellular uptake in murine 4T1 breast carcinoma cells [110]. Islam et al. investigated the cellular uptake of pluronic copolymer-stabilized, purified ~145nm long single walled carbon nanotubes (SWCNTs) through a series of complementary cellular, cell-mimetic, and in vitro model membrane experiments. The Raman intensity distribution, obtained from the G-band (1590cm−1), shows SWCNT concentration Inhibitors,research,lifescience,medical localized to the MK2206 midplane of a fixed, hematoxylin-labelled

cell. SWCNTs were preferentially Inhibitors,research,lifescience,medical located within cells versus the extracellular regions, and most SWCNTs were localized in the perinuclear region. SWCNTs localized within fluorescently labelled endosomes and confocal Raman spectroscopy showed a dramatic reduction in SWCNT uptake into the hematoxylin-labeled HeLa cell at 4°C compared with 37°C, after being incubated for 2 days. These data suggested energy-dependent

endocytosis. Inhibitors,research,lifescience,medical To confirm this, a direct measurement to check the endocytosis was conducted in which endocytosis in HeLa cells was visualized using a Green Fluorescent Protein, GFP-tagged RhoB-GTPase, which labels endosomes in mammalian cells. On confocal imaging it was confirmed that the internalization of SWCNTs was occurring through the endocyte formation as there was a slight increase

in Inhibitors,research,lifescience,medical endosome numbers per cell with increased time of exposure to SWCNTs, with a statistically significant increase in endosome number at 20 and 25 minutes [111]. In endocytosis independent pathway there is a direct translocation of CNT through the plasma membrane into the cytoplasm which has been termed by some researchers as the “nanoneedle” mechanism [100]. This pathway includes processes such as diffusion, membrane fusion, and direct pore transport Inhibitors,research,lifescience,medical (Figure 5(c)). Individually dispersed CNTs in aqueous solutions have been experimentally demonstrated to be able to enter the cytoplasm of cells by directly crossing the cell membrane. Such cellular uptake of CNT, which is not influenced by the presence of endocytosis inhibitor (such as sodium azide), suggests the endocytosis Oxalosuccinic acid independent pathway of internalization [112]. The mechanism of how CNT enters cells via the insertion and diffusion is poorly understood. Some theoretical studies suggest a two-step process in which, first, the tubes accommodate onto the lipid cell membrane and then orient to adopt the transmembrane configuration. In this model, the internalization of nanotubes into the cells was spontaneous and was mediated by the lipid membrane and that the hydrophilic interactions and/or static charge interactions between the tubes and the lipid membrane which drove the translocation of the nanotubes [113].