C(6)-Ceramide-Coated Catheters Promote Re-Endothelialization of Stretch-Injured Arteries.

OBJECTIVE: Drug eluting stents have recently been associated with the increased risk of adverse thrombogenic events and/or late luminal loss, which is highly associated with incomplete re-endothelialization. The increased risks behoove the design of alternative delivery modalities and/or drugs that do not compromise the re-endotheliaization process. The objective of the present study is to elucidate the biological mechanism(s) by which non-stent-based delivery modalities for the anti-proliferative lipid metabolite, C(6)-ceramide, could lead to a reduction in arterial injury after angioplasty. RESULTS: Immunohistochemical studies in rabbit and porcine models suggest that C(6)-ceramide-coated balloon catheters limit arterial stenosis without inhibiting endothelial wound healing responses. Specifically, C(6)-ceramide-coated balloon catheters reduce internal elastica injury with a corresponding reduction in medial fracture length in a 28-day porcine coronary artery stretch model. In addition, C(6)-ceramide decreases the formation of the fibrin matrix to possibly augment the subsequent wound healing response. We hypothesized that differential metabolism of exogenous ceramide by coronary endothelial and smooth muscle cells could explain the apparent discrepancy between the anti-proliferative actions of ceramide and the pro-wound healing responses of ceramide. Human coronary artery endothelial cells (HCAEC), in contrast to human coronary artery smooth muscle cells (HCASMC), preferentially express ceramide kinase and form ceramide-1-phosphate, which promotes endothelial cell survival. CONCLUSION: Differential metabolism of ceramide between HCASMC and HCAEC offers a mechanism by which ceramide preferentially limits smooth muscle cell growth, in the presence of active wound healing. The combinatorial ability of ceramide to limit vascular smooth muscle proliferation and promote re-endothelialization, offers the potential for C(6)-ceramide-coated catheters to serve as adjuncts to stent-based modalities or as a stand-alone treatment.

Thermoresponsive and biodegradable linear-dendritic nanoparticles for targeted and sustained release of a pro-apoptotic drug.

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, C(6), 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 C(6) 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 C(6) 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 degrees C. C(6) 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 degrees C) was confirmed by confocal microscopy and quantified by flow cytometry. The accumulation of NBD-C(6) 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 degrees C). The linear-dendritic nanoparticles alone were not toxic, but their complexes with C(6) caused significant growth inhibition and apoptosis to MDA-MB-231 cells at 37 degrees C. The designed thermoresponsive and biodegradable linear-dendritic nanoparticles have great potential for thermally targeted and sustained release of C(6) for the treatment of solid tumors with hyperthermia.

Ceramide recruits and activates protein kinase C zeta (PKC zeta) within structured membrane microdomains.

We have previously demonstrated that hexanoyl-D-erythro-sphingosine (C(6)-ceramide), an anti-mitogenic cell-permeable lipid metabolite, limited vascular smooth muscle growth by abrogating trauma-induced Akt activity in a stretch injury model of neointimal hyperplasia. Furthermore, ceramide selectively and directly activated protein kinase C zeta (PKC zeta) to suppress Akt-dependent mitogenesis. To further analyze the interaction between ceramide and PKC zeta, the ability of ceramide to localize within highly structured lipid microdomains (rafts) and activate PKC zeta was investigated. Using rat aorta vascular smooth muscle cells (A7r5), we now demonstrate that C(6)-ceramide treatment results in an increased localization and phosphorylation of PKC zeta within caveolin-enriched lipid microdomians to inactivate Akt. In addition, ceramide specifically reduced the association of PKC zeta with 14-3-3, a scaffold protein localized to less structured regions within membranes. Pharmacological disruption of highly structured lipid microdomains resulted in abrogation of ceramide-activated, PKC zeta-dependent Akt inactivation, whereas molecular strategies suggest that ceramide-dependent PKC zeta phosphorylation of Akt3 at Ser(34) was necessary for ceramide-induced vascular smooth muscle cell growth arrest. Taken together, these data demonstrate that structured membrane microdomains are necessary for ceramide-induced activation of PKC zeta and resultant diminished Akt activity, leading to vascular smooth muscle cell growth arrest.

Systemic delivery of liposomal short-chain ceramide limits solid tumor growth in murine models of breast adenocarcinoma.

In vitro tumor cell culture models have illuminated the potential therapeutic utility of elevating the intracellular concentration of the antimitogenic and proapoptotic sphingolipid, ceramide. However, although cell-permeable, short-chain ceramide is an effective apoptotic agent in vitro, its use as an in vivo, systemically delivered therapeutic is limited by its inherent lipid hydrophobicity and physicochemical properties. Here, we report that the systemic i.v. delivery of C6-ceramide (C6) in a pegylated liposomal formulation significantly limited the growth of solid tumors in a syngeneic BALB/c mouse tumor model of breast adenocarcinoma. Over a 3-week treatment period, a well-tolerated dose of 36 mg/kg liposomal-C6 elicited a >6-fold reduction in tumor size compared with empty ghost liposomes. Histologic analyses of solid tumors from liposomal-C6-treated mice showed a marked increase in the presence of apoptotic cells, with a coincident decrease in cellular proliferation and in the development of a microvessel network. Liposomal-C6 accumulated within caveolae and mitochondria, suggesting putative mechanisms by which ceramide induces selective cancer cell cytotoxicity. A pharmacokinetic analysis of systemic liposomal-C6 delivery showed that the pegylated liposomal formulation follows first-order kinetics in the blood and achieves a steady-state concentration in tumor tissue. Confirming the therapeutic utility of i.v. liposomal-C6 administration, we also shown diminution of solid tumor growth in a human xenograft model of breast cancer. Together, these results indicate that bioactive ceramide analogues can be incorporated into pegylated liposomal vehicles for improved solubility, drug delivery, and antineoplastic efficacy.