Ultrastructural analysis of Lyophilized Human Spermatozoa.

OBJECTIVE: Lyophilization is potentially more practical and cost-effective alternative for sperm preservation. However, there are no studies that evaluate the ultrastructure of human spermatozoa after lyophilization. Therefore, the aim of our study was to evaluate the ultrasctructure of lyophilized spermatozoa using Transmission Electron Microscopy. METHODS: From a total of 21 donated seminal samples, 30 aliquots were originated and divided into two aliquots so that one could have been submitted to cryopreservation/thaw and the other for lyophilization/rehydration. The liquefied aliquots were homogenized at room temperature. Samples assigned for cryopreservation were placed in straws and samples assigned for lyophilization were placed in the appropriate vials. Cryopreservation samples were placed at -30oC for 30 minutes subsequently for 30 minutes at vapour phase and then plunged into liquid nitrogen. Lately, were warmed in water bath at 37oC for 10 minutes followed by 10 minutes centrifugation. The pellet was resuspended and analysed in a Makler chamber. The semen vials assigned for lyophilization were loaded into a pre-fixed freeze-drying chamber. Following lyophilization, vials were removed from the freeze-drying chamber and kept at 4oC until rehydration. TEM was performed after rehydration and thawing. Sperm samples were fixed, rinsed in buffer, post fixed and dehydration was carried out in escalating concentrations of alcohol solution, acetone and then, embedding in Epon resin. Ultrathin sections were stained and examined in a Transmission Electron Microscope. RESULTS: Analysis of sperm after freezing/thawing using Transmission Electron Microscopy showed lesions to the midpiece, with some mitochondria degeneration and random rupture of plasma membrane. In the head, we identified intact plasma membrane, nucleus and acrosome, as in the flagellum all main structures remained intact including the plasma membrane, the longitudinal columns of dense fibers and the semicircular fibers. Analysis by Transmission Electron Microscopy showed that spermatozoa heads had ruptured plasma membranes, absence of acrosomes, nuclei with heterogeneous and decompressed chromatin. Mitochondria were deteriorated in the midpiece. Longitudinal columns of dense fibers were absent in the flagellum. Axonemes, in cross-sections, were disrupted with disorganized structures. CONCLUSIONS: To our knowledge, our study demonstrated, for the first time, the structure of the human spermatozoa after lyophilization using Transmission Electron Microscopy. The use of a fixed lyophilization protocol with media containing cryoprotectants might explain the damage to the structures. More studies are necessary to improve the results of sperm lyophilization. In the future, the use of lyophilization of spermatozoa might reduce the costs of fertility preservation, since there will be no need for storage space and transportation is simpler.

Topical photodynamic therapy with chloroaluminum phthalocyanine liposomes is as effective as systemic pentavalent antimony in the treatment of experimental cutaneous leishmaniasis.

BACKGROUND: In the Americas, one of the main causative species of cutaneous leishmaniasis is Leishmania (Leishmania) amazonensis. The systemic antimonials remain the most largely used option for disease control. However, this drug has significant toxicity. The development of new alternative therapies, including the identification of effective drugs for topical treatment of cutaneous leishmaniasis, is of utmost interest. In this sense, photodynamic therapy emerges as a new strategy. The aim of this study was to develop the chloroaluminum phthalocyanine-loaded liposome, characterize it, and evaluate its stability and efficacy in the topical treatment of cutaneous leishmaniasis caused by L. (L.) amazonensis. METHODS: Liposomes composed of egg phosphatidylcholine were prepared by Bangham's method. Storage stability of phthalocyanine-loaded liposomes was evaluated at 30 and 60 days after preparation. For the in vivo evaluation, the animals were infected with L. (L.) amazonensis and divided into groups: chloroaluminium phthalocyanine-loaded liposome, blank liposome, meglumine antimoniate (200 mgSb+5/Kg/day), and control. The lesion size was determined weekly after the beginning of the treatment. Upon completion, parasites were recovered from the skin lesion and spleen and evaluated by limiting dilution assay. RESULTS: Chloroaluminum phthalocyanine-loaded liposomes were stable and showed adequate characteristics for topical administration. The topical chloroaluminum phthalocyanine-loaded liposome was as effective as systemic pentavalent antimony in reducing the parasitic load in the lesion and spleen in infected animals. CONCLUSIONS: The present study showed that photodynamic therapy with chloroaluminum phthalocyanine-loaded liposomes is a promising strategy for the treatment of American cutaneous leishmaniasis caused by L. (L.) amazonensis.

Influence of PEG coating on the biodistribution and tumor accumulation of pH-sensitive liposomes.

Liposomes are lipid vesicles widely used as nanocarriers in targeted drug delivery systems for therapeutic and/or diagnostic purposes. A strategy to prolong the blood circulation time of the liposomes includes the addition of a hydrophilic polymer polyethylene glycol (PEG) moiety onto the surface of the vesicle. Several studies claim that liposome PEGylation by a single chain length or a combination of PEG with different chain lengths may alter the liposomes' pharmacokinetic properties. Therefore, the purpose of this study was to evaluate the influence of PEG on the biodistribution of pH-sensitive liposomes in a tumor-bearing animal model. Three liposomal formulations (PEGylated or not) were prepared and validated to have a similar mean diameter, monodisperse distribution, and neutral zeta potential. The pharmacokinetic properties of each liposome were evaluated in healthy animals, while the biodistribution and scintigraphic images were evaluated in tumor-bearing mice. High tumor-to-muscle ratios were not statistically different between the PEGylated and non-PEGylated liposomes. While PEGylation is a well-established strategy for increasing the blood circulation of nanostructures, in our study, the use of polymer coating did not result in a better in vivo profile. Further studies must be carried out to confirm the feasibility of the non-PEGylated pH-sensitive liposomes for tumor treatment.

Physicochemical Characterization and Skin Permeation of Cationic Transfersomes Containing the Synthetic Peptide PnPP-19.

BACKGROUND: PnPP-19 is a 19-amino-acid synthetic peptide previously described as a novel drug for the treatment of erectile dysfunction. OBJECTIVE: The aim of this work was to evaluate the physicochemical properties of cationic transfersomes containing PnPP-19 and the skin permeation of free PnPP-19 and PnPP-19-loaded transfersomes. METHODS: Three different liposomal preparation methods were evaluated. Cationic transfersomes contained egg phosphatidyl choline: stearylamine (9:1 w/w) and Tween 20 (84.6:15.4 lipid:Tween, w/w). Lipid concentration varied from 20 to 40 mM. We evaluated the entrapment percentage, mean diameter, zeta potential and stability at 4 °C of the formulations. The skin permeation assays were performed with abdominal human skin using Franz diffusion cell with 3 cm2 diffusion area at 32 °C and a fluorescent derivative of the peptide, containing 5-TAMRA, bound to PnPP-19 C-terminal region, where an extra lysine was inserted. RESULTS: Our results showed variable entrapment efficiencies, from 6% to 30%, depending on the preparation method and the lipid concentration used. The reverse phase evaporation method using a total lipid concentration equal to 40 mM led to the best entrapment percentage (30.2 + 4.5%). Free PnPP-19 was able to permeate skin at a rate of 10.8 ng/cm2/h. However, PnPP-19 was specifically hydrolyzed by skin proteases, generating a fragment of 15 amino acid residues. Encapsulated PnPP-19 permeated the skin at a rate of 19.8 ng/cm2/h. CONCLUSION: The encapsulation of PnPP-19 in cationic transfersomes protected the peptide from degradation, favoring its topical administration.

Nanostructured Lipid Carrier Co-loaded with Doxorubicin and Docosahexaenoic Acid as a Theranostic Agent: Evaluation of Biodistribution and Antitumor Activity in Experimental Model.

PURPOSE: Nanotheranostic platforms, i.e., the combination of both therapeutic and diagnostic agents on a single platform, are emerging as an interesting tool for the personalized cancer medicine. Therefore, the aim of this work was to evaluate the in vivo properties of a Tc-99m-labeled nanostructured lipid carrier (NLC) formulation, co-loaded with doxorubicin (DOX) and docosahexaenoic acid (DHA), for theranostic applications. PROCEDURES: NLC-DHA-DOX were prepared busing the hot melting homogenization method using an emulsification-ultrasound and were radiolabeled with Tc-99m. Biodistribution studies, scintigraphic images, and antitumor activity were performed in 4T1 tumor-bearing mice. RESULTS: NCL was successfully radiolabeled with Tc-99m. Blood clearance showed a relatively long half-life, with blood levels decaying in a biphasic manner (T1/2 α = 38.7 min; T1/2 ß = 516.5 min). The biodistribution profile and scintigraphic images showed higher tumor uptake compared to contralateral muscle in all time-points investigated. Antitumor activity studies showed a substantial tumor growth inhibition ratio for NLC-DHA-DOX formulation. In addition, the formulation showed more favorable toxicity profiles when compared to equivalent doses of free administered drugs, being able to reduce heart and liver damage. CONCLUSIONS: Therefore, NLC-DHA-DOX formulation demonstrated feasibility in breast cancer treatment and diagnosis/monitoring, leading to a new possibility of a theranostic platform.

Paclitaxel-loaded folate-coated long circulating and pH-sensitive liposomes as a potential drug delivery system: A biodistribution study.

A range of antitumor agents for cancer treatment is available; however, they show low specificity, which often limit their use. Recently, we have reported the preparation of folate-coated long-circulating and pH-sensitive liposomes (SpHL-folate-PTX) loaded with paclitaxel (PTX), an effective drug for the treatment of solid tumors, including breast cancer. The purpose of this study was to prepare and characterize SpHL-PTX and SpHL-folate-PTX radiolabeled with technetium-99m (99mTc). Biodistribution studies and scintigraphic images were performed after intravenous administration of 99mTc-PTX, 99mTc-SpHL-PTX and 99mTc-SpHL-folate-PTX into healthy and tumor-bearing mice. High radiochemical purity (>98%) and in vitro stability (>90%) were achieved for both liposome formulations. The pharmacokinetic properties of 99mTc-SpHL-DTPA-PTX and 99mTc-SpHL-folate-DTPA-PTX decreased in a monophasic manner showing half-life of 400.1 and 541.8min, respectively. Scintigraphic images and biodistribution studies showed a significant uptake in liver, spleen and kidneys, demonstrating these routes as way for excretion. At 8h post-injection, the liposomal tumor uptake was higher than 99mTc-PTX. Interesting, 4h after administration, the liposome folate coated showed higher tumor-to-muscle ratio than 99mTc-SpHL-DTPA-PTX and 99mTc-PTX. In conclusion, the liposomal systems, showed high tumor uptake by scintigraphic images, especially the 99mTc-SpHL-folate-DTPA-PTX that showed a sustained and higher tumor-to-muscle ratio than non-functionalized liposome, which indicate its feasibility as a PTX delivery system to folate positive tumors.

Synthesis, characterization and radiolabeling of polymeric nano-micelles as a platform for tumor delivering.

The use of nanoparticles for diagnostic approaches leads to higher accumulation in the targeting tissue promoting a better signal-to-noise ratio and consequently, early tumor detection through scintigraphic techniques. Such approaches have inherent advantages, including the possibility of association with a variety of gamma-emitting radionuclides available, among them, Tecnethium-99m (99mTc). 99mTc is readily conjugated with nanoparticles using chelating agents, such as diethylenetriaminepentaacetic acid (DTPA). Leveraging this approach, we synthesized polymeric micelles (PM) consisting of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] (DSPE-mPEG2000) functionalized with DTPA for radiolabeling with 99mTc. Micelles made up of DSPE-mPEG2000 and DSPE-PEG2000-DTPA had a mean diameter of ∼10nm, as measured by DLS and SAXS techniques, and a zeta potential of -2.7±1.1mV. Radiolabeled micelles exhibited high radiochemical yields and stability. In vivo assays indicated long blood circulation time (456.3min). High uptake in liver, spleen and kidneys was observed in the biodistribution and imaging studies on healthy and tumor-bearing mice. In addition, a high tumor-to-muscle ratio was detected, which increased over time, showing accumulation of the PM in the tumor region. These findings indicate that this system is a promising platform for simultaneous delivery of therapeutic agents and diagnostic probes.

Development of a bone-targeted pH-sensitive liposomal formulation containing doxorubicin: physicochemical characterization, cytotoxicity, and biodistribution evaluation in a mouse model of bone metastasis.

BACKGROUND: Despite recent advances in cancer therapy, the treatment of bone tumors remains a major challenge. A possible underlying hypothesis, limitation, and unmet need may be the inability of therapeutics to penetrate into dense bone mineral, which can lead to poor efficacy and high toxicity, due to drug uptake in healthy organs. The development of nanostructured formulations with high affinity for bone could be an interesting approach to overcome these challenges. PURPOSE: To develop a liposomal formulation with high affinity for hydroxyapatite and the ability to release doxorubicin (DOX) in an acidic environment for future application as a tool for treatment of bone metastases. MATERIALS AND METHODS: Liposomes were prepared by thin-film lipid hydration, followed by extrusion and the sulfate gradient-encapsulation method. Liposomes were characterized by average diameter, ζ-potential, encapsulation percentage, X-ray diffraction, and differential scanning calorimetry. Release studies in buffer (pH 7.4 or 5), plasma, and serum, as well as hydroxyapatite-affinity in vitro analysis were performed. Cytotoxicity was evaluated by MTT assay against the MDA-MB-231 cell line, and biodistribution was assessed in bone metastasis-bearing animals. RESULTS: Liposomes presented suitable diameter (~170 nm), DOX encapsulation (~2 mg/mL), controlled release, and good plasma and serum stability. The existence of interactions between DOX and the lipid bilayer was proved through differential scanning calorimetry and small-angle X-ray scattering. DOX release was faster when the pH was in the range of a tumor than at physiological pH. The bone-targeted formulation showed a strong affinity for hydroxyapatite. The encapsulation of DOX did not interfere in its intrinsic cytotoxicity against the MDA-MB-231 cell line. Biodistribution studies demonstrated high affinity of this formulation for tumors and reduction of uptake in the heart. CONCLUSION: These results suggest that bone-targeted pH-sensitive liposomes containing DOX can be an interesting strategy for selectively delivering this drug into bone-tumor sites, increasing its activity, and reducing DOX-related toxicity.

Pentyl Gallate Nanoemulsions as Potential Topical Treatment of Herpes Labialis.

Previous studies have demonstrated the antiherpes activity of pentyl gallate (PG), suggesting that it could be a promising candidate for the topical treatment of human herpes labialis. PG low aqueous solubility represents a major drawback to its incorporation in topical dosage forms. Hence, the feasibility of incorporating PG into nanoemulsions, the ability to penetrate the skin, to inhibit herpes simplex virus (HSV)-1 replication, and to cause dermal sensitization or toxicity were evaluated. Oil/water nanoemulsions containing 0.5% PG were prepared by spontaneous emulsification. The in vitro PG distribution into porcine ear skin after topical application of nanoemulsions was assessed, and the in vitro antiviral activity against HSV-1 replication was evaluated. Acute dermal toxicity and risk of dermal sensitization were evaluated in rat model. Nanoemulsions presented nanometric particle size (from 124.8 to 143.7 nm), high zeta potential (from -50.1 to -66.1 mV), loading efficiency above 99%, and adequate stability during 12 months. All formulations presented anti-HSV-1 activity. PG was able to reach deeper into the dermis more efficiently from the nanoemulsion F4. This formulation as well as PG were considered safe for topical use. Nanoemulsions seem to be a safe and effective approach for topically delivering PG in the treatment of human herpes labialis infection.

Evaluation of Antitumor Activity of Long-Circulating and pH-Sensitive Liposomes Containing Ursolic Acid in Animal Models of Breast Tumor and Gliosarcoma.

Background Ursolic acid (UA) is a triterpene found in different plant species, possessing antitumor activity, which may be a result of its antiangiogenic effect. However, UA has low water solubility, which limits its use because the bioavailability is impaired. To overcome this inconvenience, we developed long-circulating and pH-sensitive liposomes containing ursolic acid (SpHL-UA). We investigated the antiangiogenic effect of free UA and SpHL-UA in murine brain cancer and human breast tumor models by means of determination of the relative tumor volume, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and histopathological analysis. Methods The animals were treated with dimethyl sulfoxide in 0.9% (w/v) NaCl, free UA, long-circulating and pH-sensitive liposomes without drug (SpHL), or SpHL-UA. The animals were submitted to each treatment by intraperitoneal injection for 5 days. The dose of free UA or SpHL-UA was equal to 23 mg/kg. Results Tumor growth inhibition was not observed in human breast tumor-bearing animals. For murine gliosarcoma-bearing animals, a slight tumor growth inhibition was observed in the groups treated with free UA or SpHL-UA (9% and 15%, respectively). No significant change in any of the parameters evaluated by DCE-MRI for both experimental models could be observed. Nevertheless, the evaluation of the mean values of magnetic resonance parameters of human breast tumor-bearing animals showed evidence of a possible antiangiogenic effect induced by SpHL-UA. Histopathological analysis did not present significant change for any treatment. Conclusion SpHL-UA did not show antiangiogenic activity in a gliosarcoma model and seemed to induce an antiangiogenic effect in the human breast tumor model.

pH-Sensitive, Long-Circulating Liposomes as an Alternative Tool to Deliver Doxorubicin into Tumors: a Feasibility Animal Study.

PURPOSE: Therapeutic agents used in chemotherapy have low specificity leading to undesired severe side effects. Hence, the development of drug delivery systems that improve drug specificity, such as liposome moieties, is an alternative to overcome chemotherapy limitations and increase antitumor efficacy. In this study, the biodistribution profile evaluation of pH-sensitive long-circulating liposomes (SpHL) containing [99mTc]DOX in 4T1 tumor-bearing BALB/c mice is described. PROCEDURES: [99mTc]DOX was radiolabeled by direct method. Liposomes were prepared and characterized. [99mTc]DOX was encapsulated into liposomes by freezing and thawing. Circulation time for SpHL-[99mTc]DOX was determined by measuring the blood activity from healthy animals. Biodistribution studies were carried out in tumor-bearing mice at 1, 4, and 24 h after injection. RESULTS: Blood levels of the SpHL-[99mTc]DOX declined in a biphasic manner, with an α half-life of 14.1 min and ß half-life of 129.0 min. High uptake was achieved in the liver and spleen, due to the macrophages captured. Moreover, tumor uptake was higher than control tissue, resulting in high tumor-to-muscle ratios, indicating higher specificity for the tumor area. CONCLUSION: [99mTc]DOX was successfully encapsulated in liposomes. Biodistribution indicated high tumor-to-muscle ratios in breast tumor-bearing BALB/c mice. In summary, these results showed the higher accumulation of SpHL-[99mTc]DOX in the tumor area, suggesting selective delivery of doxorubicin into tumor.

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.

Technetium-99m-labeled doxorubicin as an imaging probe for murine breast tumor (4T1 cell line) identification.

OBJECTIVE: Early diagnosis of malignant tumors is essential to successfully plan a radical and curative approach. In this study we describe the direct radiolabeling of doxorubicin (DOX) at physiological pH to identify murine breast tumor (4T1 cells)-bearing BALB/c mice. MATERIALS AND METHODS: Technetium-99m (99mTc) DOX was prepared by adding 99mTc-pertechnetate to a PBS (pH 7.4) solution containing DOX in the presence of stannous chloride. Radiochemical purity and in-vitro stability were determined. The circulation time of 99mTc-DOX was determined by measuring blood radioactivity in healthy animals. Scintigraphic images and biodistribution studies were carried out in tumor-bearing mice at 1, 4, and 8 h after injection. RESULTS: The 99mTc-DOX complex showed high radiochemical purity (99.27 ± 0.34%) and in-vitro stability until 8 h. Tc-DOX levels in blood declined in a biphasic manner, with an α half-life of 4.5 min and a ß half-life of 277.2 min. High uptake was achieved in kidneys, liver, and spleen, because of the drug elimination routes. Moreover, tumor uptake was higher than that of control tissue, resulting in high tumor-to-muscle ratios. CONCLUSION: DOX was successfully labeled with 99mTc-pertechnetate and showed high stability. Biodistribution and scintigraphic studies indicated high tumor-to-muscle ratios in breast tumor-bearing BALB/c mice. These results suggested the feasibility of 99mTc-DOX as a functional agent in tumor diagnosis.

Feasibility study with 99mTc-HYNIC-ßAla-Bombesin(7-14) as an agent to early visualization of lung tumour cells in nude mice.

AIM: More sensitive and accurate imaging approaches for early detection and therapy monitoring of lung tumours are needed to ameliorate prognosis and outcome. Lung tumours are known to overexpress receptors for bombesin-like peptides. However, thus far, no study has demonstrated the potential role of bombesin-like peptides in identifying A549 lung tumour cells in xenograft animal models. Thus, we evaluate the feasibility of Tc-HYNIC-ßAla-Bombesin(7-14) as an imaging probe in lung cancer. METHODS AND RESULTS: Xenograft lung tumours were implanted in nude mice and evaluated by histopathological analysis. Tumours were easily visualized by Tc-HYNIC-ßAla-Bombesin(7-14) within 30 days after inoculation of the A549 cell line into mice. Scintigraphic images showed high tumour-to-background ratio. DISCUSSION: The data obtained in this study indicate that Tc-HYNIC-ßAla-Bombesin(7-14) may be useful as an imaging probe to detect A549 lung cancer cells. To our knowledge, this is the first time that this specific radiocompound has been used to visualize non-small-cell lung cancer A549 in mice. Further translational research in humans is required to establish the potential role of this radiocompound in clinical practice.

Ursolic acid incorporation does not prevent the formation of a non-lamellar phase in pH-sensitive and long-circulating liposomes.

Ursolic acid (UA) is a triterpene found in different plant species that has been shown to possess significant antitumor activity. However, UA presents a low water solubility, which limits its biological applications. In this context, our research group has proposed the incorporation of UA in long-circulating and pH-sensitive liposomes (SpHL-UA).These liposomes, composed of dioleylphosphatidylethanolamine (DOPE), cholesteryl hemisuccinate (CHEMS), and distearoylphosphatidylethanolamine-polyethylene glycol2000 (DSPE-PEG2000), were shown to be very promising carriers for UA. Considering that the release of UA from SpHL-UA and its antitumor activity depend upon the occurrence of the lamellar to non-lamellar phase transition of DOPE, in the present work, the interactions of UA with the components of the liposomes were evaluated, aiming to clarify their role in the structural organization of DOPE. The study was carried out by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) under low hydration conditions. DSC studies revealed that DOPE phase transition temperatures did not shift significantly upon UA addition. On the other hand, in SAXS studies, a different pattern of DOPE phase organization was observed in the presence of UA, with the occurrence of the cubic phase Im3m at 20 °C and the cubic phase Pn3m at 60 °C. These findings suggest that UA interacts with the lipids and changes their self-assembly. However, these interactions between the lipids and UA were unable to eliminate the lamellar to non-lamellar phase transition, which is essential for the cytoplasmic delivery of UA molecules from SpHL-UA.

pH-sensitive liposomes for drug delivery in cancer treatment.

In recent years, liposomes have been employed with growing success as pharmaceutical carriers for antineoplastic drugs. One specific strategy used to enhance in vivo liposome-mediated drug delivery is the improvement of intracytoplasmic delivery. In this context, pH-sensitive liposomes (pHSLip) have been designed to explore the endosomal acidification process, which may lead to a destabilization of the liposomes, followed by a release of their contents into the cell cytoplasm. This review considers the current status of pHSLip development and its applicability in cancer treatment, focusing on the mechanisms of pH sensitivity and liposomal composition of pHSLip. The final section will discuss the application of these formulations in both in vitro and in vivo studies of antitumor efficacy.

Preparation, physicochemical characterization, and cell viability evaluation of long-circulating and pH-sensitive liposomes containing ursolic acid.

Cancer is one of the leading causes of death worldwide. Although several drugs are used clinically, some tumors either do not respond or are resistant to the existing pharmacotherapy, thus justifying the search for new drugs. Ursolic acid (UA) is a triterpene found in different plant species that has been shown to possess significant antitumor activity. However, UA presents a low solubility in aqueous medium, which presents a barrier to its biological applications. In this context, the use of liposomes presents a promising strategy to deliver UA and allow for its intravenous administration. In this work, long-circulating and pH-sensitive liposomes containing UA (SpHL-UA) were developed, and their chemical and physicochemical properties were evaluated. SpHL-UA presented adequate properties, including a mean diameter of 191.1 ± 6.4 nm, a zeta potential of 1.2 ± 1.4 mV, and a UA entrapment of 0.77 ± 0.01 mg/mL. Moreover, this formulation showed a good stability after having been stored for 2 months at 4 °C. The viability studies on breast (MDA-MB-231) and prostate (LNCaP) cancer cell lines demonstrated that SpHL-UA treatment significantly inhibited cancer cell proliferation. Therefore, the results of the present work suggest the applicability of SpHL-UA as a new and promising anticancer formulation.