Encapsulation of cisplatin in long-circulating and pH-sensitive liposomes improves its antitumor effect and reduces acute toxicity

pH-Responsive Liposomes of Dioleoyl Phosphatidylethanolamine and Cholesteryl Hemisuccinate for the Enhanced Anticancer Efficacy of Cisplatin

The current study aimed to develop pH-responsive cisplatin-loaded liposomes (CDDP@PLs) via the thin film hydration method. Formulations with varied ratios of dioleoyl phosphatidylethanolamine (DOPE) to cholesteryl hemisuccinate (CHEMS) were investigated to obtain the optimal particle size, zeta potential, entrapment efficiency, in vitro release profile, and stability. The particle size of the CDDP@PLs was in the range of 153.2 ± 3.08–206.4 ± 2.26 nm, zeta potential was −17.8 ± 1.26 to −24.6 ± 1.72, and PDI displayed an acceptable size distribution. Transmission electron microscopy revealed a spherical shape with ~200 nm size. Fourier transform infrared spectroscopic analysis showed the physicochemical stability of CDDP@PLs, and differential scanning calorimetry analysis showed the loss of the crystalline nature of cisplatin in liposomes. In vitro release study of CDDP@PLs at pH 7.4 depicted the lower release rate of cisplatin (less than 40%), and at a pH of 6.5, an almost 65% release rate was achieved compared to the release rate at pH 5.5 (more than 80%) showing the tumor-specific drug release. The cytotoxicity study showed the improved cytotoxicity of CDDP@PLs compared to cisplatin solution in MDA-MB-231 and SK-OV-3 cell lines, and fluorescence microscopy also showed enhanced cellular internalization. The acute toxicity study showed the safety and biocompatibility of the developed carrier system for the potential delivery of chemotherapeutic agents. These studies suggest that CDDP@PLs could be utilized as an efficient delivery system for the enhancement of therapeutic efficacy and to minimize the side effects of chemotherapy by releasing cisplatin at the tumor site.

Folate-coated, long-circulating and pH-sensitive liposomes enhance doxorubicin antitumor effect in a breast cancer animal model

Long circulating pH-sensitive liposomes have been shown to effectively deliver doxorubicin (DOX) to tumors and reduce its toxic effects. Folic acid receptors are upregulated in a wide variety of solid, epithelial tumors, including breast cancer. In order to improve liposomal endocytosis and antitumor activity, folic acid has been added to nanoparticles surfaces to exploit overexpression of folate receptors in tumor cells. The purpose of this study was to evaluate the antitumor activity in vitro and in vivo of long circulating pH-sensitive folate-coated DOX-loaded liposomes (SpHL-DOX-Fol) in a 4T1 breast cancer model system in vitro and in vivo. Biodistribution studies were performed and in vivo electrocardiographic parameters were evaluated. A higher tumor uptake for radiolabeled SpHL-Fol (^99mTc-SpHL-Fol) 4 h after intravenous administration was observed in comparision with non-folate-coated liposomes (^99mTc-SpHL). Antitumor activity showed that SpHL-DOX-Fol treatment led to a 68% growth arrest and drastically reduce pulmonary metastasis foci. Additionally, eletrocardiographic parameters analysis revealed no dispersion in the QT and QTc interval was observed in liposomal treated mice. In summary, this novel multifunctional nanoplatform deomonstrated higher tumor uptake and antitumor activity. SpHL-DOX-Fol represents a drug delivery platform to improve DOX tumor delivery and reduce dose-limiting toxicity.

Nanoparticles as Carriers of Proteins, Peptides and Other Therapeutic Molecules

Nanoparticles have many applications both in industry and medicine. Depending upon their physical and chemical properties, they can be used as carriers of therapeutic molecules or as therapeutics. Nanoparticles are made of synthetic or natural polymers, lipids or metals. Their use allows for faster transport to the place of action, thus prolonging its presence in the body and limiting side effects. In addition, the use of such a drug delivery system protects the drug from rapid disintegration and elimination from the body. In recent years, the use of proteins and peptides as therapeutic molecules has grown significantly. Unfortunately, proteins are subject to enzymatic digestion and can cause unwanted immune response beyond therapeutic action. The use of drug carriers can minimize undesirable side effects and reduce the dose of medication needed to achieve the therapeutic effect. The current study presents the use of several selected drug delivery systems for the delivery of proteins, peptides and other therapeutic molecules.

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.

Stimulus-responsive liposomes as smart nanoplatforms for drug delivery applications

Liposomes are known to be promising nanoparticles (NPs) for drug delivery applications. Among different types of self-assembled NPs, liposomes stand out for their non-toxic nature, and their possession of dual hydrophilic-hydrophobic domains. Advantages of liposomes include the ability to solubilize hydrophobic drugs, the ability to incorporate different hydrophilic and lipophilic drugs at the same time, lessening the exposure of host organs to potentially toxic drugs and allowing modification of the surface by a variety of different chemical groups. This modification of the surface, or of the individual constituents, may be used to achieve two important goals. Firstly, ligands for active targeting can be attached that are recognized by cognate receptors over-expressed on the target cells of tissues. Secondly, modification can be used to impart a stimulus-responsive or "smart" character to the liposomes, whereby the cargo is released on demand only when certain internal stimuli (pH, reducing agents, specific enzymes) or external stimuli (light, magnetic field or ultrasound) are present. Here, we review the field of smart liposomes for drug delivery applications.

Diminishing the side effect of mitomycin C by using pH-sensitive liposomes: in vitro characterization and in vivo pharmacokinetics

Introduction

Mitomycin C is an anticancer antibiotic agent that has the potential for broad-spectrum use against several cancers, including mammary cancers. Because its half-life is 17 min after a 30 mg intravenous bolus administration, the suitability of mitomycin C for wide use in the clinical setting is limited. Based on tumor pathophysiology, pH-sensitive liposomes could provide better tumor-targeted effects. The aim of this study was to investigate the possibility of diminishing the side effect of mitomycin C by using pH-sensitive liposomes.

Materials and methods

pH-sensitive liposomes was employed to deliver mitomycin C and evaluate the characterization, release behaviors, cytotoxicity, in vivo pharmacokinetics and biochemical assay.

Results

The results demonstrated that mitomycin C-loaded pH-sensitive liposomes had a particle diameter of 144.5±2.8 nm and an entrapment efficiency of 66.5%. The in vitro release study showed that the pH-sensitive liposome release percentages at pH 7.4 and pH 5.5 were approximately 47% and 93%, respectively. The cell viability of MCF-7 cells showed that both the solution and liposome group exhibited a concentration-dependent effect on cell viability. The MCF-7 cell uptake of pH-sensitive liposomes with a folate modification was higher which was indicated by an increased fluorescence intensity compared to that without a folate modification. The area under the concentration-time curve of mitomycin C-loaded pH-sensitive liposomes (18.82±0.51 µg·h/L) was significantly higher than that of the mitomycin C solution group (10.07±0.31 µg·h/L). The mean residence times of the mitomycin C-loaded and mitomycin C solution groups were 1.53±0.16 and 0.05 h, respectively. In addition, there was no significant difference in terms of V_ss (p>0.05). Moreover, the half-life of pH-sensitive liposomes and the mitomycin C solution was 1.35±0.15 and 1.60±0.04 h, respectively. In terms of safety, mitomycin C-loaded pH-sensitive liposomes did not affect the platelet count and the levels of blood urea nitrogen and aspartate aminotransferase.

Conclusion

The positive results of pH-sensitive liposomes demonstrated maintained the cytotoxicity and decrease the side effect.

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.

Development of Long-Circulating pH-Sensitive Liposomes to Circumvent Gemcitabine Resistance in Pancreatic Cancer Cells

PURPOSES

To develop pH-sensitive liposomes (PSL) containing a high content of gemcitabine; and to investigate whether drug loading (DL) would alter the in vitro and pharmacokinetic properties.

METHODS

PSL with a high DL were obtained using a modified small-volume incubation method. The DL effects on drug release rate and in vitro cytotoxicity of PSL were evaluated using MIA PaCa-2 pancreatic cancer cells and their pharmacokinetics investigated in rats.

RESULTS

The highest DL of 4.5 ± 0.1% was achieved for gemcitabine in PSL with 145 ± 5 nm diameter. DL did not alter the in vitro release rate from PSL. The IC50 (48 h) of PSL (DL 0.5 and 4.5%) and non pH-sensitive liposomes (NPSL, DL 4.2%) were 1.1 ± 0.1, 0.7 ± 0.1 and 37.0 ± 7.5 μM, respectively. The PSL resulted in a 4.2-fold increase in its elimination half-life (6.2 h) compared to gemcitabine solution (1.4 h) in rats. No significant difference in pharmacokinetic parameters was observed between the two PSL (DL 0.5 and 4.5%).

CONCLUSION

The PSL offered advantages over NPSL in restoring the sensitivity of pancreatic cancer cells to gemcitabine without requiring a high DL. DL in the PSL did not alter release rate, cytotoxicity or their long-circulating properties. Graphical Abstract ᅟ.

Enhanced pH-Responsiveness, Cellular Trafficking, Cytotoxicity and Long-circulation of PEGylated Liposomes with Post-insertion Technique Using Gemcitabine as a Model Drug

PURPOSE

The in vitro and in vivo properties of PEGylated pH-sensitive liposomes (PSL) prepared by pre- and post-insertion techniques were investigated.

METHODS

A pre-insertion or post-insertion technique was used for PSL PEGylation. For the first time, confocal laser scanning microscopy coupled with a modified calcein self-quench assay was applied to evaluate the endosome escape capability. PSL cellular uptake was evaluated using macrophages and the cytotoxicity using a gemcitabine (model drug)-resistant MIA PaCa-2 cells. The pharmacokinetics of PSL encapsulated gemcitabine was investigated in rats.

RESULTS

PEGylation reduced the pH-sensitivity in a concentration-dependent manner (0.5-5% mol). Both PEGylation methods reduced the uptake of PSL by macrophages by over 60%. Cytotoxicity was ranked in the order: post-inserted PSL ≥ pre-inserted PSL > non-PSL > gemcitabine solution, consistent with the confocal microscopic observation and pH-sensitivity. Both pre and post-inserted PSL resulted in significant reductions (p < 0.05) in plasma clearance (58.6 and 38.4 ml/h/kg), increases in the area-under-the-concentration-time curve (56.9 and 87.1 μM · h) and half-life (6.1 and 6.2 h) compared to gemcitabine solution (152.9 ml/h/kg, 22.2 μM · h and 1.4 h).

CONCLUSION

PEGylation by post-insertion offers advantages over pre-insertion to obtain PSL with enhanced pH-sensitivity, more effective intra-cytoplasmic delivery, and a superior pharmacokinetics.

pH-triggered echogenicity and contents release from liposomes

Liposomes are representative lipid nanoparticles widely used for delivering anticancer drugs, DNA fragments, or siRNA to cancer cells. Upon targeting, various internal and external triggers have been used to increase the rate for contents release from the liposomes. Among the internal triggers, decreased pH within the cellular lysosomes has been successfully used to enhance the rate for releasing contents. However, imparting pH sensitivity to liposomes requires the synthesis of specialized lipids with structures that are substantially modified at a reduced pH. Herein, we report an alternative strategy to render liposomes pH sensitive by encapsulating a precursor which generates gas bubbles in situ in response to acidic pH. The disturbance created by the escaping gas bubbles leads to the rapid release of the encapsulated contents from the liposomes. Atomic force microscopic studies indicate that the liposomal structure is destroyed at a reduced pH. The gas bubbles also render the liposomes echogenic, allowing ultrasound imaging. To demonstrate the applicability of this strategy, we have successfully targeted doxorubicin-encapsulated liposomes to the pancreatic ductal carcinoma cells that overexpress the folate receptor on the surface. In response to the decreased pH in the lysosomes, the encapsulated anticancer drug is efficiently released. Contents released from these liposomes are further enhanced by the application of continuous wave ultrasound (1 MHz), resulting in substantially reduced viability for the pancreatic cancer cells (14%).

Cisplatin-incorporated nanoparticles of poly(acrylic acid-co-methyl methacrylate) copolymer

Background

Although cisplatin is extensively used in the clinical field, its intrinsic toxicity limits its clinical use. We investigated nanoparticle formations of poly(acrylic acid-co-methyl methacrylate) (PAA-MMA) incorporating cisplatin and their antitumor activity in vitro and in vivo.

Methods

Cisplatin-incorporated nanoparticles were prepared through the ion-complex formation between acrylic acid and cisplatin. The anticancer activity of cisplatin-incorporated nanoparticles was assessed with CT26 colorectal carcinoma cells.

Results

Cisplatin-incorporated nanoparticles have small particle sizes of less than 200 nm with spherical shapes. Drug content was increased according to the increase of the feeding amount of cisplatin and acrylic acid content in the copolymer. The higher acrylic acid content in the copolymer induced increase of particle size and decrease of zeta potential. Cisplatin-incorporated nanoparticles showed a similar growth-inhibitory effect against CT26 tumor cells in vitro. However, cisplatin-incorporated nanoparticles showed improved antitumor activity against an animal tumor xenograft model.

Conclusion

We suggest that PAA-MMA nanoparticles incorporating cisplatin are promising carriers for an antitumor drug-delivery system.

Recent trends in multifunctional liposomal nanocarriers for enhanced tumor targeting

Liposomes are delivery systems that have been used to formulate a vast variety of therapeutic and imaging agents for the past several decades. They have significant advantages over their free forms in terms of pharmacokinetics, sensitivity for cancer diagnosis and therapeutic efficacy. The multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers. Multifunctional liposomal nanocarriers should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor lesion relative to healthy tissues, remote-controlled or tumor stimuli-sensitive extravasation from blood at the tumor's vicinity, internalization motifs to move from tumor bounds and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing. This review will focus on current strategies used for cancer detection and therapy using liposomes with special attention to combination therapies.

Recombinant Immunotoxin Therapy of Solid Tumors: Challenges and Strategies

Immunotoxins are a group of protein-based therapeutics, basically comprising two functional moieties: one is the antibody or antibody Fv fragment that allows the immunotoxin to bind specifically to target cells; another is the plant or bacterial toxin that kills the cells upon internalization. Immunotoxins have several unique features which are superior to conventional chemotherapeutics, including high specificity, extraordinary potency, and no known drug resistance. Development of immunotoxins evolves with time and technology, but significant progress has been achieved in the past 20 years after introduction of recombinant DNA technique and generation of the first single-chain variable fragment of monoclonal antibodies. Since then, more than 1,000 recombinant immunotoxins have been generated against cancer. However, most success in immunotoxin therapy has been achieved against hematological malignancies, several issues persist to be significant barriers for effective therapy of human solid tumors. Further development of immunotoxins will largely focus on the improvement of penetration capability to solid tumor mass and elimination of immunogenicity occurred when given repeatedly to patients. Promising strategies may include construction of recombinant antibody fragments with higher binding affinity and stability, elimination of immunodominant T- and B-cell epitopes of toxins, modification of immunotoxins with macromolecules like poly(ethylene glycol) and liposomes, and generation of immunotoxins with humanized antibody fragments and human endogenous cytotoxic enzymes. In this paper, we briefly reviewed the evolution of immunotoxin development and then discussed the challenges of immunotoxin therapy for human solid tumors and the potential strategies we may seek to overcome the challenges.