Paclitaxel-Loaded pH-Sensitive Liposome: New Insights on Structural and Physicochemical Characterization.

A long-circulating and pH-sensitive liposome containing paclitaxel (SpHL-PTX) was recently developed by our group. Once in an acidic environment, for example, tumors, these liposomes undergo destabilization, releasing the encapsulated drug. In this way, the aim of this study was to evaluate the molecular and supramolecular interactions between the lipid bilayer and PTX in similar biological environment conditions. High-sensitivity analyses of SpHL-PTX structures were obtained by the small-angle X-ray scattering technique combined with other techniques such as dynamic light scattering, asymmetric flow field-flow fractionation, transmission electron microscopy, and high-performance liquid chromatography. The results showed that PTX incorporation in the liposomal bilayer clearly leads to changes in supramolecular organization of dioleoylphosphatidylethanolamine (DOPE) molecules, inducing the formation of more ordered structures. Changes in supramolecular organization were observed at lower pH, indicating that pH sensitivity was preserved even in the presence of fetal bovine serum proteins. Furthermore, morphological and physicochemical characterization of SpHL-PTX evidenced the formation of nanosized dispersion suitable for intravenous administration. In conclusion, a stable nanosized dispersion of PTX was obtained at pH 7.4 with suitable parameters for intravenous administration. At lower pH conditions, the pH sensitivity of the system was clearly evidenced by changes in the supramolecular organization of DOPE molecules, which is crucial for the delivery of PTX into the cytoplasm of the targeted cells. In this way, the results obtained by different techniques confirm the feasibility of SpHL as a promising tool to PTX delivery in acidic environments, such as tumors.

Phase behavior of dioleyphosphatidylethanolamine molecules in the presence of components of pH-sensitive liposomes and paclitaxel.

Paclitaxel is a potent antimicrotubule chemotherapeutic agent widely used for clinical treatment of a variety of solid tumors. However, the low solubility of the drug in aqueous medium and the toxic effects of the commercially available formulation, Taxol(®), has hindered its clinical application. To overcome these paclitaxel-related disadvantages, several drug delivery approaches have been thoroughly investigated. In this context, our research group has developed long-circulating and pHsensitive liposomes containing paclitaxel composed of dioleylphosphatidylethanolamine, cholesterylhemisuccinate and distearoylphosphatidylethanolamine-polyethylene glycol2000, which have shown to be very promising carriers for this taxane. For the destabilization of pH-sensitive liposomal systems and the release of the encapsulated drug in the cytoplasm of tumor cells, the occurrence of a phase transition from a lamellar to a non-lamellar phase of dioleylphosphatidylethanolamine molecules is essential. Two techniques, differential scanning calorimetry and small angle X-ray scattering, were used to investigate the influence of the liposomal components and paclitaxel in the phase transition process of dioleylphosphatidylethanolamine molecules and to evaluate the pH-sensitivity of the formulation under low hydration conditions. The findings clearly evidence the phase transition of dioleylphosphatidylethanolamine molecules in the presence and absence of PTX indicating that the introduction of the drug in the system does not bring damage to the pH-sensitivity of the system, which resulting in liposome destabilization at low pH regions and encapsulated paclitaxel release preferentially in a desired target tissue.

99mTc-phytate as a diagnostic probe for assessing inflammatory reaction in malignant tumors.

OBJECTIVE: Once administered intravenously, technetium-99m (99mTc)-labeled phytate binds to calcium in the serum and behaves as a nanoparticle. On the basis of the high permeability of the tumor vasculature, 99mTc-phytate is expected to leak and accumulate specifically in inflammatory cells. The aim of this study was to evaluate the potential of 99mTc-phytate in assessing the degree of inflammation in Ehrlich solid tumors in mice. MATERIALS AND METHODS: 99mTc-phytate was prepared by adding pertechnetate to a solution containing phytic acid and stannous chloride. The blood half-life of this particle following intravenous injection was determined using blood samples from healthy animals, whereas its size was measured by photon correlation spectroscopy. Scintigraphic imaging and biodistribution studies were carried out in tumor-bearing mice at 30 min and 2 h after injection. RESULTS: The average size of the particles was in the range of 200 nm, suggesting that they are capable of passively passing through fenestrations in tumor vessels, which are 200-2000 nm in size. The blood half-life for 99mTc-phytate was found to be 2.1 min, a result that is in agreement with previous studies. Data from tumor-bearing mice showed high tumor uptake at 2 h after 99mTc-phytate administration. As a result, a high tumor-to-muscle ratio was achieved (T/M = 25.9 ± 7.54). CONCLUSION: These findings indicate that 99mTc-sodium phytate has promising properties for identifying the type of tumor. This approach will have significant implications for characterizing tumor biology and treatment of malignant lesions.

Participation of nitric oxide pathway in the relaxation response induced by E-cinnamaldehyde oxime in superior mesenteric artery isolated from rats.

For many years, nitric oxide (NO) has been studied as an important mediator in the control of vascular tone. Endothelial deficiencies that diminish NO production can result in the development of several future cardiovascular diseases, such as hypertension and arteriosclerosis. In this context, new drugs with potential ability to donate NO have been studied. In this study, 3 aromatic oximes [benzophenone oxime, 4-Cl-benzophenone oxime, and E-cinnamaldehyde oxime (E-CAOx)] induced vasorelaxation in endothelium-denuded and intact superior mesenteric rings precontracted with phenylephrine. E-CAOx demonstrated the most potent effect, and its mechanism of action was evaluated. Vascular reactivity experiments demonstrated that the effect of E-CAOx was reduced by the presence of 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, 1H[1,2,4,]oxadiazolo[4,3-a]quinoxalin-1-one, and (Rp)-8-(para-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate, suggesting the participation of NO/sGC/PKG pathway. NO donation seems to be mediated through nicatinamide adenine dinucleotide phosphate-dependent reductases because 7-ethoxyresorufin decreased the effect of E-CAOx on vascular reactivity and reduced NO formation as detected by flow cytometry using the NO indicator diaminofluorescein 4,5-diacetate. Further downstream of NO donation, K+ subtype channels were also shown to be involved in the E-CAOx vasorelaxant effect. The present study showed that E-CAOx acts like an NO donor, activating NO/sGC/PKG pathway and thus K+ channels.