Tumor metastasis emerges as a crucial target for tumor therapy. In this study, a tumor metastasis targeting peptide（TMT） was conjugated to a lipid material（PEG-DSPE） to obtain the targeting compound（TMT-PEG-DSPE）, which was used to construct the targeted liposomal doxorubicin（TMT-LS-DOX）. We showed that TMT-LS-DOX presented satisfactory pharmaceutical characteristics. This metastasis-specific delivery system was tested in two highly metastatic breast cancer cell lines（MDA-MB-435S and MDA-MB-231） with a non-metastatic breast cancer cell line（MCF-7） as the control. The free TMT peptide itself showed no cytotoxicity even at the concentration of 100 μg/mL. Importantly, the enhanced cellular uptake of TMT-LS-DOX to both MDA-MB-435S and MDA-MB-231 cell lines was demonstrated as compared to MCF-7 cells, via a TMT-mediated mechanism demonstrated by a receptor competition study. In conclusion, the TMT modified nanocarriers might provide a strategy to enhance the specificity of chemotherapeutic agents to highly metastatic breast cancer.
Liposome is one of the most successful drug delivery systems applying nanotechnology topotentiate the therapeutic efficacy and reduce toxicities of conventional medicines. Sincethe first doxorubicin-loaded liposome reached the market, numerous researches have beencarried out to develop new liposomal formulations over the past decade and have givenbirth to a series of commercial products. Therapeutic agents, most of which are anti-cancerdrugs, are encapsulated in the aqueous core or lipid bilayers of liposomes to improve theirdelivery to the targeted tissue. There are several liposomal formulations, such as EndoTAG-1 (paclitaxel-loaded cationic liposomes), Lipoplatin (cisplatin-loaded long circulating liposomes) and Stimuvax (a cancer vaccine), showing promising therapeutic value in clinicalstudies. Besides, new designs including environmentally sensitive liposomes, liposomaldrug combinations and liposomal vaccines are now tested in clinical trials.
Nanotechnology has been widely used in the field of medicine, and it can significantly improve the bioavailability and the target efficiency of medicines. However, after administration, nanomedicines can adsorb biomolecules that can influence their effects. It was reported that the adsorption of plasma proteins can change the surface properties of nanoparticles. When nanoparticles pass through cells, they may carry some cellular proteins out of cells. Currently, it is unclear whether the adsorbed proteins affect the uptake of nanoparticles in the next cell layer. To simplify this complex biological process, BSA-capped gold nanoparticles were prepared and incubated with Caco-2 cell lysate to simulate conditions of transcytosis through epithelial cells. The surface morphology of nanoparticles was examined by TEM. SRB was used to evaluate the cytotoxicity of the nanoparticles. The uptake and cellular distribution of the nanoparticles were detected by ICP-MS and CLSM. The results suggested that the adsorption of cell proteins could enhance the adhesion and uptake of gold nanoparticles. The gold nanoparticles were mainly located in lysosomes, and there were some Lysate-capped AuNPs in the mitochondria whereas no BSA-capped AuNPs appeared there.
Rho GTPases play an important role on the regulation of cytoskeleton, which can affect the cell morphogenesis, cell migration, endocytosis and vesicle transport by controlling the growth and maintenance of microfilaments and microtubules. It has been known that regulation of cell cytoskeleton is inseparable from the cell uptake of nano-medicine or nano-drug delivery systems. However, only few studies have focused on the impacts of Rho GTPases on cell uptake of nano-medicine or nano-drug delivery systems. This study selected single-walled carbon nanohoms （SWCNHs）, which have emerged as promising drug delivery systems, to explore the impacts of Rho GTPases on cell uptake of nano-drug delivery systems. SWCNHs were oxidized with concentrated nitric acid and prepared into nano dispersion by ultrasonic dispersion. Confocal laser scanning microscope （CLSM） and transmission electron microscopy （TEM） were used to observe the cell uptake and intracellular distribution of nanoparticles after incubated A549 cells with the dispersion mentioned above. Mechanism of cell uptake was assessed using various inhibitors. The results showed that the cell uptake of oxSWCNHs was significantly reduced when RhoA was inhibited. The oxSWCNHs were internalized through clathrin-mediated endocytosis and mainly positioned in lysosomes ofA549 cells.
It was reported previously that tamoxifen （TAM） could increase the intracellular accumulation of drug-loaded liposomes, but the exact mechanism is unknown although it was supposed that TAM might enhance the cell uptake by inhibiting the drug efflux caused by P-glycoprotein （P-gp）. To identify the mechanism of increased cellular uptake of liposomes induced by tamoxifen, PEGgylated liposomes （SSL） ofP-gp-substrate doxorubicin （DOX） or non-P-gp-substrate coumarin （Cou） were prepared with or without TAM. The cell uptake of these liposome systems was investigated in cell lines with different P-gp-expressing levels and the interaction of TAM with lipid membrane was also studied. As the results, the co-encapsulation of TAM with DOX-SSL increased the intracellular uptake in all three tumor cell lines. In P-gp-highly-expressing MCF-7/Adr cells, the effect of TAM was the strongest and in negative control Hela cells, the impact weakened but still significant. The improvement was also observed in the cellular uptake of Cou-SSL. Surface plasmon resonance （SPR） studies demonstrated that TAM-SSL exhibited a much stronger atYmity with model biomembrane compared with empty SSL, and ft^her test with isothermal titration calorimetry （ITC） showed that free TAM had an obvious interaction with lipid membrane. In conclusion, TAM could increase the affinity of liposomes with biomembrane and enhance the intracellular accumulation of liposomes via both TAM-mediated P-gp inhibition and the increased interaction between hydrophobic TAM molecules and lipid membrane.
