Ceramide is a bioactive sphingolipid-derived second messenger that has been demonstrated to induce apoptosis and cell cycle arrest in various cancer cell culture systems. Although in vitro tumor cell culture models have illuminated the potential therapeutic utility of a cell-permeable analog of ceramide, C6, in vivo delivery is impeded by the extreme hydrophobicity and physical-chemical properties of this bioactive lipid. Previously, we have demonstrated that the incorporation of C6 into pegylated liposomal vesicles is an effective anti-cancer drug delivery strategy in vitro and in vivo. Here, we report the utilization of a novel multi-functional polymeric drug delivery system designed to therapeutically target C6 to solid tumor tissue. This delivery system is a hydrolytically degradable and temperature-sensitive linear-dendritic nanoparticle with a lower critical solution temperature (LCST) of 30 °C. C6 was effectively loaded into the nanoparticles, and released continuously for at least 1 month in vitro, measured by mass spectroscopy. The preferential uptake of fluorescein isothiocyanate-labeled linear-dendritic nanoparticles into human MDA-MB-231 breast adenocarcinoma cells at temperature above the LCST (37 °C) was confirmed by confocal microscopy and quantified by flow cytometry. The accumulation of NBD-C6 into MDA-MB-231 cells was highly enhanced by the thermoresponsive linear-dendritic nanoparticles, but not by non-thermoresponsive liposome and PEG-dendritic polymer, at temperature above the LCST (37 °C). The linear-dendritic nanoparticles alone were not toxic, but their complexes with C6 caused significant growth inhibition and apoptosis to MDA-MB-231 cells at 37 °C. The designed thermoresponsive and biodegradable linear-dendritic nanoparticles have great potential for thermally targeted and sustained release of C6 for the treatment of solid tumors with hyperthermia.
"The micelle formed by these polymers tends to have uniform size . Several hydrophobic drugs and fluorescent probes have been physically encapsulated into these micelles    . However, the crowded molecular structure of the dendritic block may restrict encapsulation of some drugs into these micelles. "
[Show abstract][Hide abstract] ABSTRACT: We have developed a nanocarrier drug-delivery system based on micelles formed by a new class of well-defined linear PEGylated two-arm oligomer of cholic acids in aqueous solution. By varying the length of the linear PEG chains and the configuration of cholic acid oligomer, one can easily fine-tune the physicochemical properties of the amphiphilic polymers and the resulting micelles. These include particle size, critical micelle concentration, and drug-loading capacity. High level of hydrophobic anticancer drugs such as PTX, etoposide and SN-38 can be readily loaded into such nanocarriers. The loading capacity of the nanocarrier for PTX (PTX) is extremely high (12.0mg/mL), which is equivalent to 37.5% (w/w) of the total mass of the micelle. PTX-loaded nanocarriers are much more stable than Abraxane (PTX/human serum albumin nanoaggregate) when stored in bovine serum albumin solution or dog plasma. PTX release profile from the micelles is burst-free and sustained over a period of seven days. The anti-tumor activity of PTX-loaded nanocarriers against ovarian cancer cell line in vitro, with continuous drug exposure, is similar to Taxol (formulation of PTX dissolved in Cremophor EL and ethanol) or Abraxane. Targeted drug delivery to tumor site with these novel micelles was demonstrated by near infrared fluorescence (NIRF) imaging in nude mice bearing ovarian cancer xenograft. Furthermore, PTX-loaded nanocarriers demonstrated superior anti-tumor efficacy compared to Taxol at equivalent PTX dose in ovarian cancer xenograft model.
"Drug-loaded micelles in the specific temperature or acidity can be easily depolymerized and released the drugs   . Thomas  reported a new type of temperature-sensitive nanoparticles. The critical solution temperature is 30℃. "
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