Therapeutic effect of adriamycin encapsulated in long-circulating liposomes on Meth-A-sarcoma-bearing mice

Innovative cancer nanomedicine based on immunology, gene editing, intracellular trafficking control

The recent rapid progress in the area of drug delivery systems (DDS) has opened a new era in medicine with a strong linkage to understanding the molecular mechanisms associated with cancer survival. In this review, we summarize new cancer strategies that have recently been developed based on our DDS technology. Cancer immunotherapy will be improved based on the concept of the cancer immunity cycle, which focuses on dynamic interactions between various types of cancer and immune cells in our body. The new technology of genome editing will also be discussed with reference to how these new DDS technologies can be used to introduce therapeutic cargoes into our body. Lastly, a new organelle, mitochondria will be the focus of creating a new cancer treatment strategy by a MITO-Porter which can deliver macromolecules directly to mitochondria of cancer cells via a membrane fusion approach and the impact of controlled intracellular trafficking will be discussed.

Photosensitization of pancreatic cancer cells by cationic alkyl-porphyrins in free form or engrafted into POPC liposomes: The relationship between delivery mode and mechanism of cell death

Cationic porphyrins bearing an alkyl side chain of 14 (2b) or 18 (2d) carbons dramatically inhibit proliferation of pancreatic cancer cells following treatment with light. We have compared two different ways of delivering porphyrin 2d: either in free form or engrafted into palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine liposomes (L-2d). Cell cytometry shows that while free 2d is taken up by pancreatic cancer cells by active (endocytosis) and passive (membrane fusion) transports, L-2d is internalized solely by endocytosis. Confocal microscopy showed that free 2d co-localizes with the cell membrane and lysosomes, whereas L-2d partly co-localizes with lysosomes and ER. It is found that free 2d inhibits the KRAS-Nrf2-GPX4 axis and strongly triggers lipid peroxidation, resulting in cell death by ferroptosis. By contrast, L-2d does not affect the KRAS-Nrf2-GPX4 axis and activates cell death mainly through apoptosis. Overall, our study demonstrates for the first time that cationic alkyl porphyrins, which have a IC50 ~ 23 nM, activate a dual mechanism of cell death, ferroptosis and apoptosis, where the predominant form depends on the delivery mode.

Liposome technologies towards colorectal cancer therapeutics

Colorectal cancer (CRC) is the third most common cancer and the fourth most common deadly cancer worldwide. After treatment with curative intent recurrence rates vary with staging 0-13% in Stage 1, 11-61% in S2 and 28-73% in Stage 3. The toxicity to healthy tissues from chemotherapy and radiotherapy and drug resistance severely affect the quality of life and cancer specific outcomes of CRC patients. To overcome some of these limitations, many efforts have been made to develop nanomaterial-based drug delivery systems. Among these nanocarriers, liposomes represented one of the most successful candidates in delivering targeted oncological treatment, improving safety profile and therapeutic efficacy of encapsulated drugs. In this review we will discuss liposome design with a particular focus on the targeting feature and triggering functions. We will also summarise the recent advances in liposomal delivery system for CRC treatment in both the preclinical and clinical studies. We will finally provide our perspectives on the liposome technology development for the future clinical translation. STATEMENT OF SIGNIFICANCE: Conventional treatments for colorectal cancer (CRC) severely affect the therapeutic effects for advanced patients. With the development of nanomedicines, liposomal delivery system appears to be one of the most promising nanocarriers for CRC treatment. In last three years several reviews in this area have been published focusing on the preclinical research and drug delivery function, which is a fairly narrow focus in the field of liposome technology for CRC therapy. Our review presented the most recent advances of the liposome technology (both clinical and preclinical applications) for CRC with strong potential for further clinical translation. We believe it will attract lots of attention from various audiences, including researchers, clinicians and the industry.

Mitochondrial Delivery of an Anticancer Drug Via Systemic Administration Using a Mitochondrial Delivery System That Inhibits the Growth of Drug-Resistant Cancer Engrafted on Mice

Mitochondrial delivery of an anticancer drug targeting cancer cells would eventually result in cell death. To achieve this, a drug delivery system targeting mitochondria is needed. We recently developed a MITO-Porter, a liposome that delivers its cargo to mitochondria. We reported that such a MITO-Porter could deliver doxorubicin (DOX), an anticancer drug, to mitochondria in OS-RC-2 cells, a drug resistant cancer cell, resulting in inhibiting the cell growth, based in in vitro experiments. Herein, we report on validating the benefit of such a therapeutic strategy for treating drug resistant cancers by the in vivo targeting of mitochondria. We prepared a DOX-MITO-Porter, in which DOX was encapsulated in the MITO-Porter and optimized its retention in blood circulation. When the DOX-MITO-Porter was administered to mice bearing OS-RC-2 cells via tail vein injection, tumor size was significantly decreased, compared to DOX itself and to the DOX-encapsulated polyethylene glycol-modified liposome (DOX-PEG-LP). Intracellular observation confirmed that the DOX-MITO-Porter had accumulated in tumor mitochondria. It was also found a relationship between anti-tumor effect and the mitochondrial function, as indicated by the depolarization of mitochondrial membrane potential. This study provides support for the utility of an in vivo mitochondrial delivery system in drug resistant cancer therapies.

MITO-Porter for Mitochondrial Delivery and Mitochondrial Functional Analysis

Mitochondria are attractive organelles that have the potential to contribute greatly to medical therapy, the maintenance of beauty and health, and the development of the life sciences. Therefore, it would be expected that the further development of mitochondrial drug delivery systems (DDSs) would exert a significant impact on the medical and life sciences. To achieve such an innovative objective, it will be necessary to deliver various cargoes to mitochondria in living cells. However, only a limited number of approaches are available for accomplishing this. We recently proposed a new concept for mitochondrial delivery, a MITO-Porter, a liposome-based carrier that introduces macromolecular cargoes into mitochondria via membrane fusion. To date, we have demonstrated the utility of mitochondrial therapeutic strategy by MITO-Porter using animal models of diseases. We also showed that the mitochondrial delivery of antisense oligo-RNA by the MITO-Porter results in mitochondrial RNA knockdown and has a functional impact on mitochondria. Here, we summarize the current state of mitochondrial DDS focusing on our research and show some examples of mitochondrial functional regulations using mitochondrial DDS.

Development of a multifunctional envelope-type nano device and its application to nanomedicine

Successful nanomedicines should be based on sound drug delivery systems (DDS) the permit intracellular trafficking as well as the biodistribution of cargos to be controlled. We have been developing new types of DDS that are multifunctional envelope-type nano devices referred to as MENDs. First, we will focus the in vivo delivery of siRNA to hepatocytes using a YSK-MEND which is composed of pH-responsive cationic lipids. The YSK-MEND is capable of inducing efficient silencing activity in hepatocytes and can be used to cure mice that are infected with hepatitis C or B. The YSK-MEND can also be applied to cancer immunotherapy through the activation of immune cells by delivering different compounds such as cyclic-di-GMP, siRNA or alpha-galactosylceramide as a lipid antigen. The findings indicate that, as predicted, these compounds, when encapsulated in the YSK-MEND, can be delivered to the site of action and induced immune activation through different mechanisms. Finally, a MITO-Porter, a membrane fusion-based delivery system to mitochondria, is introduced as an organelle targeting DDS and a new strategy for cancer therapy is proposed by delivering gentamicin to mitochondria of cancer cells. These new technologies are expected to extend the therapeutic area of Nanomedicine by increasing the power of DDS, especially from the view point of controlled intracellular trafficking.

Heterogeneity of tumor vasculature and antiangiogenic intervention: insights from MR angiography and DCE-MRI

PURPOSE

Solid tumor vasculature is highly heterogeneous, which presents challenges to antiangiogenic intervention as well as the evaluation of its therapeutic efficacy. The aim of this study is to evaluate the spatial tumor vascular changes due to bevacizumab/paclitaxel therapy using a combination approach of MR angiography and DCE-MRI method.

EXPERIMENTAL DESIGN

Tumor vasculature of MCF-7 breast tumor mouse xenografts was studied by a combination of MR angiography and DCE-MRI with albumin-Gd-DTPA. Tumor macroscopic vasculature was extracted from the early enhanced images. Tumor microvascular parameters were obtained from the pharmacokinetic modeling of the DCE-MRI data. A spatial analysis of the microvascular parameters based on the macroscopic vasculature was used to evaluate the changes of the heterogeneous vasculature induced by a 12 day bevacizumab/paclitaxel treatment in mice bearing MCF-7 breast tumor.

RESULTS

Macroscopic vessels that feed the tumors were not affected by the bevacizumab/paclitaxel combination therapy. A higher portion of the tumors was within close proximity of these macroscopic vessels after the treatment, concomitant with tumor growth retardation. There was a significant decrease in microvascular permeability and vascular volume in the tumor regions near these vessels.

CONCLUSION

Bevacizumab/paclitaxel combination therapy did not block the blood supply to the MCF-7 breast tumor. Such finding is consistent with the modest survival benefits of adding bevacizumab to current treatment regimens for some types of cancers.

Water exchange-minimizing DCE-MRI protocol to detect changes in tumor vascular parameters: effect of bevacizumab/paclitaxel combination therapy

OBJECTIVE

The purpose of this study was to assess changes in the tumor microvasculature induced by combination antiangiogenic therapy in MCF-7 breast tumor mouse models, using a noninvasive DCE-MRI method that minimizes the effect of water exchange.

MATERIALS AND METHODS

3D quantitative DCE-MRI images were acquired with a heavily T1-weighted saturation recovery gradient echo sequence with a recovery delay of 20 ms. Tumor vascular volume (VV) and vascular permeability-surface area product (PS) were obtained through a linear regression of the albumin-Gd-DTPA-enhanced dynamic image intensity on MCF-7 breast tumor mouse models treated with combination bevacizumab/paclitaxel therapy.

RESULTS

Measured tumor VV values were significantly higher than the values that have been reported previously using quantitative T1 mapping, and are in good agreement with micro-CT (computed tomography) results reported earlier from other tumor models. A trend of decreasing tumor PS was detected in the group of MCF-7 tumor bearing mice treated with the bevacizumab/paclitaxel combination regimen.

CONCLUSION

VV and PS maps obtained by a heavily T1-weighted acquisition protocol revealed the large peripheral blood vessels as well as the permeable areas within the tumor. A 12-day/three-dose combination treatment of bevacizumab and paclitaxel resulted in delayed tumor growth and a trend of decreasing tumor vascular permeability surface area product.

Preparation, characterization, and in vitro release study of albendazole-encapsulated nanosize liposomes

The purpose of the present study was to formulate effective and controlled release albendazole liposomal formulations. Albendazole, a hydrophobic drug used for the treatment of hydatid cysts, was encapsulated in nanosize liposomes. Rapid evaporation method was used for the preparation of albendazole-encapsulated conventional and PEGylated liposomes consisting of egg phosphatidylcholine (PC) and cholesterol (CH) in the molar ratios of (6:4) and PC:CH: polyethylene glycol (PEG) (5:4:1), respectively. In this study, PEGylated and conventional liposomes containing albendazole were prepared and their characteristics, such as particle size, encapsulation efficiency, and in vitro drug release were investigated. The drug encapsulation efficiency of PEGylated and conventional liposomes was 81% and 72%, respectively. The biophysical characterization of both conventional and PEG-coated liposomes were done by transmission electron microscopy and UV-vis spectrophotometry. Efforts were made to study in vitro release of albendazole. The drug release rate showed decrease in albendazole release in descending order: free albendazole, albendazole-loaded conventional liposomes, and least with albendazole-loaded PEG-liposomes. Biologically relevant vesicles were prepared and in vitro release of liposome-entrapped albendazole was determined.

Angiogenic vessel-targeting DDS by liposomalized oligopeptides

Liposomal oligopeptides are one of the promising nanocarriers to deliver a drug, DNA or siRNA to target tissues. In this chapter, we describe our methodology to develop liposomal oligopeptides targeting to tumor angiogenic vessels. At first, we introduce our strategies to identify objective peptides. We performed in vivo biopanning using a phage-displayed peptide library and identified Ala-Pro-Arg-Pro-Gly (APRPG) peptide as a ligand for angiogenic vessels. To modify APRPG peptide on the surface of PEGylated liposomes, we synthesized a novel lipid derivative of the peptide, distearoylphosphatidylethanolamine-polyethyleneglycol-APRPG (DSPE-PEG-APRPG). The lipid derivative of APRPG peptide is expected to be readily incorporated into liposomal membrane and enables to present the peptides on the surface of PEGylated liposomes. We next describe how to evaluate the advantages of liposomal oligopeptides using specific examples; (1) Intratumoral distribution of APRPG-PEG-modified liposomes, (2) Therapeutic efficacy of adriamycin encapsulated in APRPG-PEG-modified liposomes, (3) Preparation of 5'-O-dipalmitoylphosphatidyl 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (DPP-CNDAC) liposomes modified with APRPG-PEG, and (4) Therapeutic experiment with APRPG-PEG-modified liposomal DPP-CNDAC.

A novel DDS strategy, "dual-targeting", and its application for antineovascular therapy

Dual-targeting liposomes modified with Ala-Pro-Arg-Pro-Gly (APRPG) and Gly-Asn-Gly-Arg-Gly (GNGRG) peptides were developed. They remarkably associated to growing human umbilical vein endothelial cells (HUVECs) compared with single-targeting liposomes modified with APRPG or GNGRG. Doxorubicin (DOX) encapsulated in the dual-targeting liposomes significantly suppressed the growth of HUVECs compared with that in single-targeting liposomes. The dual-targeting liposomes containing DOX strongly suppressed tumor growth in Colon26 NL-17 carcinoma-bearing mice. Confocal microscopic data indicated that this anticancer effect was brought by the association of these liposomes to angiogenic vessels in the tumor. These findings suggest that "dual-targeting" would be a hopeful method for targeting therapies.

Preparation of pegylated nano-liposomal formulation containing SN-38: In vitro characterization and in vivo biodistribution in mice

7-Ethyl-10-hydroxy-camptothecin (SN-38), a metabolite of irinotecan x HCl, is poorly soluble in aqueous solutions and practically insoluble in most physiologically compatible and pharmaceutically acceptable solvents. Formulation of SN-38 in concentrated pharmaceutical delivery systems for parenteral administration is thus very difficult. Due to their biocompatibility and low toxicity, liposomes were considered for the delivery of SN-38. In this study, pegylated liposomes with distearoylphosphatidylcholine, distearoylphosphatidylethanolamine containing SN-38 were prepared and their characteristics, such as particle size, encapsulation efficiency, in vitro drug release and biodistribution, were investigated. The particle size of liposomes was in the range of 150--200 nm. The encapsulation efficiency and in vitro release rate of pegylated liposomes was higher than those of non-pegylated liposomes. As expected, the distribution of pegylated liposomes in body organs such as liver, kidney, spleen and lung was considerably lower than that of non-pegylated liposomes. Also, their blood concentration was at least 50 % higher than that of non-pegylated liposomes.

Identification of mRNA splicing factors as the endothelial receptor for carbohydrate-dependent lung colonization of cancer cells

Cell surfaces of epithelial cancer are covered by complex carbohydrates, whose structures function in malignancy and metastasis. However, the mechanism underlying carbohydrate-dependent cancer metastasis has not been defined. Previously, we identified a carbohydrate-mimicry peptide designated I-peptide, which inhibits carbohydrate-dependent lung colonization of sialyl Lewis X-expressing B16-FTIII-M cells in E/P-selectin doubly-deficient mice. We hypothesized that lung endothelial cells express an unknown carbohydrate receptor, designated as I-peptide receptor (IPR), responsible for lung colonization of B16-FTIII-M cells. Here, we visualized IPR by in vivo biotinylation, which revealed that the major IPR is a group of 35-kDa proteins. IPR proteins isolated by I-peptide affinity chromatography were identified by proteomics as Ser/Arg-rich alternative pre-mRNA splicing factors or Sfrs1, Sfrs2, Sfrs5, and Sfrs7 gene products. Bacterially expressed Sfrs1 protein bound to B16-FTIII-M cells but not to parental B16 cells. Recombinant Sfrs1 protein bound to a series of fucosylated oligosaccharides in glycan array and plate-binding assays. When anti-Sfrs antibodies were injected intravenously into mice, antibodies labeled a subset of lung capillaries. Anti-Sfrs antibodies inhibited homing of I-peptide-displaying phage to the lung colonization of B16-FTIII-M cells in vivo in the mouse. These results strongly suggest that Sfrs proteins are responsible for fucosylated carbohydrate-dependent lung metastasis of epithelial cancers.

Mitochondrial drug delivery systems for macromolecule and their therapeutic application to mitochondrial diseases

Mitochondrial dysfunction has been implicated in a variety of human disorders--the so-called mitochondrial diseases. Therefore, the organelle is a promising therapeutic drug target. In this review, we describe the key role of mitochondria in living cells, a number of mitochondrial drug delivery systems and mitochondria-targeted therapeutic strategies. In particular, we discuss mitochondrial delivery of macromolecules, such as proteins and nucleic acids. The discussion of protein delivery is limited primarily to the mitochondrial import machinery. In the section on mitochondrial gene delivery and therapy, we discuss mitochondrial diseases caused by mutations in mitochondrial DNA, several gene delivery strategies and approaches to mitochondrial gene therapy. This review also summarizes our current efforts regarding liposome-based delivery system including use of a multifunctional envelope-type nano-device (MEND) and mitochondrial liposome-based delivery as anti-cancer therapies. Furthermore, we introduce the novel MITO-Porter--a liposome-based mitochondrial delivery system that functions using a membrane-fusion mechanism.

Antineovascular therapy with angiogenic vessel-targeted polyethyleneglycol-shielded liposomal DPP-CNDAC

Causing damage to angiogenic vessels is a promising approach for cancer chemotherapy. The present study is a codification of a designed liposomal drug delivery system (DDS) for antineovascular therapy (ANET) with 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC). The authors have previously reported that liposomalized 5'-O-dipalmitoylphosphatidyl CNDAC (DPP-CNDAC), a phospholipid derivative of the novel antitumor nucleoside CNDAC, is quite useful for ANET. DPP-CNDAC liposomes modified with APRPG, a peptide having affinity toward angiogenic vessels, efficiently suppressed tumor growth by damaging angiogenic endothelial cells. In the present study, the authors masked the hydrophilic moiety of DPP-CNDAC, namely, CNDAC, on the liposomal surface with APRPG-polyethyleneglycol (PEG) conjugate to improve the availability of DPP-CNDAC liposomes. The use of the APRPG-PEG conjugate attenuated the negative zeta-potential of the DPP-CNDAC liposomes and reduced the agglutinability of them in the presence of serum. These effects improved the blood level of DPP-CNDAC liposomes in colon 26 NL-17 tumor-bearing BALB/c male mice, resulting in enhanced accumulation of them in the tumor. Laser scanning microscopic observations indicated that APRPG-PEG-modified DPP-CNDAC liposomes (LipCNDAC/APRPG-PEG) colocalized with angiogenic vessels and strongly induced apoptosis of tumor cells, whereas PEG-modified DPP-CNDAC liposomes (LipCNDAC/PEG) did not. In fact, LipCNDAC/APRPG-PEG suppressed the tumor growth more strongly compared to LipCNDAC/PEG and increased significantly the life span of the mice. The present study is a good example of an effective liposomal DDS for ANET that is characterized by: (i) phospholipid derivatization of a certain anticancer drug to suit the liposomal formulation; (ii) PEG-shielding for masking undesirable properties of the drug on the liposomal surface; and (iii) active targeting to angiogenic endothelial cells using a specific probe.

Efficient cytoplasmic protein delivery by means of a multifunctional envelope-type nano device

The potential for protein therapy, such as the use of antibodies, and vaccines is now well accepted. However, it is difficult to enhance efficiency in protein therapy without a suitable delivery system for delivering proteins to target sites. Here we describe the development of protein delivery system, which is capable of cytoplasmic delivery as well as efficient packaging. The multifunctional envelope-type nano device (MEND), which was originally developed for the delivery of nucleic acids such as plasmid DNA and oligodeoxynucleotides, can also be applied to protein delivery. In this study, the green fluorescent protein (GFP), a model protein, was condensed with stearyl octaarginine (stearyl R8) to form a nano particle, which was then coated with a lipid membrane, thus permitting R8 to be introduced for efficient cellular uptake and controlled intracellular trafficking. The packaging efficiency of the MEND was significantly higher than that of conventional liposomes, because the GFP can be encapsulated a condensed form. According to confocal laser scanning microscopy, the MEND is internalized efficiently and escapes from the acidic compartment to efficiently release GFP into the cytosol. These results indicate that the MEND can serve as a useful cytoplasmic delivery system for protein therapy.

Mitochondrial drug delivery and mitochondrial disease therapy--an approach to liposome-based delivery targeted to mitochondria

Recent progress in genetics and molecular biology has provided useful information regarding the molecular mechanisms associated with the mitochondrial diseases. Genetic approaches were initiated in the late 1980s to clarify the gene responsible for various mitochondrial diseases, and information concerning genetic mutations is currently used in the diagnosis of mitochondrial diseases. Moreover, it was also revealed that mitochondria play a central role in apoptosis, or programmed cell death, which is closely related to the loss of physiological functions of tissues. Therefore, drug therapies targeted to the mitochondria would be highly desirable. In spite of the huge amount of mechanism-based studies of mitochondrial diseases, effective therapies have not yet been established mainly because of the lack of an adequate delivery system. To date, numerous investigators have attempted to establish a mitochondrial drug delivery system. However, many problems remain to be overcome before a clinical application can be achieved. To fulfill a drug delivery targeted to mitochondria, we first need to establish a method to encapsulate various drugs, proteins, peptides, and genes into a drug carrier depending on their physical characteristics. Second, we need to target it to a specific cell. Finally, multi-processes of intracellular trafficking should be sophisticatedly regulated so as to release a drug carrier from the endosome to the cytosol, and thereafter to deliver to the mitochondria. In this review, we describe the current state of the development of mitochondrial drug delivery systems, and discuss the advantage and disadvantage of each system. Our current efforts to develop an efficient method for the packaging of macromolecules and regulating intracellular trafficking are also summarized. Furthermore, novel concept of "Regulation of intramitochondrial trafficking" is proposed herein as a future challenge to the development of a mitochondrial drug delivery system.

Identification of oligopeptides binding to peritoneal tumors of gastric cancer

This is a report of in vivo intraperitoneal biopanning, and we successfully identified a novel peptide to target the multiple peritoneal tumors of gastric cancer. A phage display library was injected directly into the abdominal cavity of mice bearing peritoneal tumors of human gastric cancer, and phages associated with the tumors were subsequently reclaimed from isolated samples. The tumor-associated phages were amplified and the biopanning cycle was repeated five times to enrich for high affinity tumor-selective binding peptides. Finally, a tri-peptide motif, KLP, which showed homology with laminin 5 (a ligand for alpha3beta1 integrin), was identified as a binding peptide for peritoneal tumors of gastric cancer. Phage clones displaying the sequence KLP showed 64-fold higher binding to peritoneal tumors than control phage and were preferentially distributed in tumors rather than in normal organs after intraperitoneal injection into mice. In addition, the KLP phages were more likely to bind to cancer cells in malignant ascites derived from a patient with recurrent gastric cancer. Synthesized peptide containing the motif KLP (SWKLPPS) also showed a strong binding activity to peritoneal tumors without cancer growth effect. Liposomes conjugated with SWKLPPS peptide appeared significantly more often in tumors than control liposomes after intraperitoneal injection into mice. Furthermore, modification of liposomes with SWKLPPS peptide enhanced the antitumor activity of adriamycin on gastric cancer cells. The peptide motif KLP seems a potential targeting ligand for the treatment of peritoneal metastasis of gastric cancer.

Antitumor Activity of Liposomal Naphthoquinone Esters Isolated from Thai Medicinal Plant: Rhinacanthus nasutus KURZ

We previously observed that rhinacanthins-C, -N and -Q, three main naphthoquinone esters isolated from the roots of Thai medicinal plant; Rhinacanthus nasutus KURZ. (Acanthaceae) induced apoptosis of human cervical carcinoma HeLaS3 cells. Since these rhinacanthins showed limited solubility in aqueous medium, we attempted to entrap them into liposomal membrane: Liposomalization enabled injection of the drugs and the drugs were expected to transfer to lipoproteins in the bloodstream. Liposomal formulations of rhinacanthins-C, -N and -Q showed strong antiproliferative activity against HeLaS3 cells with the IC50 values of 32, 17, 70 microM; 19, 17, 52 microM and 2.7, 2.0 and 5.0 microM for the exposure time of 24, 48, and 72 h, respectively. These liposomes suppressed the tumor growth in Meth-A sarcoma-bearing BALB/c mice at the dose of 5.0 mg/kg/d for 10 d. Among rhinacanthins, liposomal rhinacanthin-N significantly suppressed solid tumor growth. Based on these results, our findings demonstrated that rhinacanthin-N suppressed tumor growth in vivo, and suggested that liposomes are useful for preparing injectable formulation of hydrophobic drugs.

Liposomalization of SN-38 as active metabolite of CPT-11

Although many drugs have been developed for the treatment of disease, some drugs have complications such as adverse effects, and antitumor agents should target tumors or cells more selectively. It is therefore necessary to develop drug delivery systems, and liposomes are reportedly useful as an effective drug carrier. An antitumor agent, CPT-11, inhibits DNA synthesis by the inhibition of topoisomerase1 and has a strong antitumor activity. SN-38 is converted from CPT-11 as an active metabolite by carboxylesterase in the liver. As SN-38 is insoluble, it has not been applied at the clinical stage as an injection. It is expected that SN-38 liposomalization may increase its usefulness in cancer chemotherapy. Our purpose is to have a clinical application of SN-38 by a novel method of liposomalization to expand the application for the other insolubility drugs. As SN-38 is hydrophobic, SN-38-trapped liposome preparation was attempted using the Bangham method, which is effective for general preparation. However, a high ratio of SN-38 trapped in liposome was not achieved, and this was not improved by the freezing-thawing method or the freeze-drying method. On the other hand, the ratio of SN-38 trapped in liposome by the modified remote loading method was about 4 times that by the Bangham method, and the ratio by the film loading method, novel method of liposomal preparation, reached 2 times and 8 times that by the modified remote loading method and Bangham method, respectively, showing a remarkable increase. In conclusion, it was suggested that the preparation of SN-38 liposome using the film loading method effectively entraps SN-38. Thus, it is expected that SN-38 liposome can be applied as an injection. This preparation method is useful if application is possible in the other insolubility drugs.

Liposomalized Oligopeptides in Cancer Therapy

Organ-specific delivery of biofunctional agents is thought to enhance their activity and to reduce their side effects. Liposomes have been used as drug carriers in cancer chemotherapy, since they accumulate passively in tumor tissues due to an enhanced permeability and retention (EPR) effect. In addition, modification of liposomes with specific ligands enables active targeting. A small peptide having a high affinity for a certain antigen is suitable for modification of liposomes, since it is biocompatible, biodegradable, and less antigenic compared with antibody and other modifiers. Oligopeptide-modified liposomes are prepared by using lipophilic derivatives of the peptide, which are synthesized easily and incorporated readily into the liposomal bilayer. We describe two examples of the use of liposomal oligopeptides: one for antimetastatic therapy and the other for antineovascular therapy. Arg-Gly-Asp (RGD)-related peptides are known to contribute various cellular functions such as adhesion and invasion and to inhibit tumor metastasis. However, peptide drugs are generally rapidly hydrolyzed and eliminated from the bloodstream. Liposomal RGD enables the half-lives and affinity to be improved, resulting in enhancement of antimetastatic activity. We then describe the usefulness of liposomal Ala-Pro-Arg-Pro-Gly (APRPG) for tumor treatment, which is specific for tumor angiogenic vessels. APRPG is originally isolated by use of a phage-displayed peptide library. Adriamycin encapsulated in APRPG-modified liposomes accumulated specifically in and damage tumor neovessels, resulting in notable antitumor efficacy.

Glucuronate-Modified, Long-Circulating Liposomes for the Delivery of Anticancer Agents

Liposomes are useful as drug carriers in drug delivery systems, especially for drugs with severe side effects such as antitumor agents. The conventional formulations of liposomes are opsonized by plasma proteins in the bloodstream and trapped in the reticuloendothelial system (RES). Therefore, liposomes with reduced opsonization are expected to have prolonged circulation and to accumulate in tumor tissue due to the leaky endothelium of the tissue. To avoid RES trapping of liposomes, two approaches have been considered. Liposomes may mimic cells circulating in the blood to escape host recognition as foreign substances, or liposomes may be covered with a hydrophilic barrier to escape recognition. For the latter purpose, poly(ethylene glycol) is widely used. For the former purpose, here we focus on the characteristics, in vivo trafficking, and usage in cancer therapy of glucuronate-modified liposomes. Glucuronate-modified liposomes bind to a lower extent to macrophage-like cells in vitro and passively accumulate in tumor tissue evaluated by a technique using positron emission tomography. Glucuronate-modified liposomes with extended circulation are useful for delivering anticancer agents to tumors and reducing the toxic side effects of the agents.

Anti-neovascular therapy by use of tumor neovasculature-targeted long-circulating liposome

For the purpose of cancer anti-neovascular therapy (ANET), we previously isolated 5-mer peptide Ala-Pro-Arg-Pro-Gly (APRPG) that specifically bound to the tumor angiogenic site and observed that APRPG-modified liposomes encapsulating adriamycin were effective for the suppression of tumor in tumor-bearing mice. Since polyethylene glycol (PEG) modification of liposomes endows them with a future of long circulation, we modified liposomes with PEG and APRPG-conjugated distearoylphosphatidylethanolamine (DSPE-PEG-APRPG) and examined the applicability of the liposomes on ANET. Liposomes containing DSPE-PEG-APRPG not only specifically bound to vascular endothelial growth factor-stimulated human umbilical vein endothelial cells in vitro, but also showed long-circulating characteristic and enhanced accumulation in tumor in vivo. Furthermore, adriamycin-encapsulated liposomes modified with APRPG-PEG caused more efficient tumor growth suppression than adriamycin-encapsulated liposomes modified with PEG alone in Colon 26 NL-17 carcinoma-bearing mice, despite not so much different accumulation of both liposomes in the tumor. These data suggest that tumor neovasculature-targeted long-circulating liposomes encapsulating anti-cancer drugs effectively eradicate cancerous cells through damaging of angiogenic endothelial cells. ANET promises no drug resistance and is expected to be effective against essentially any kind of solid tumors. The present results demonstrate the beneficial usage of APRPG-PEG for the active-targeting of drug carriers to angiogenic site in the novel modality of tumor treatment, namely ANET.

Antiangiogenic photodynamic therapy (PDT) using Visudyne causes effective suppression of tumor growth

We previously observed that antiangiogenic photodynamic therapy (PDT), namely, laser irradiation at 15 min after administration of photosensitizer, by using stable liposomal benzoporphyrin derivative monoacid ring A (BPD-MA), in which the liposomes were composed of dipalmitoylphosphatidylcholine, palmitoyloleoylphosphatidylcholine, cholesterol, and dipalmitoylphosphatidylglycerol (10:10:10:2.5 as a molar ratio), was quite effective for cancer treatment. On the other hand, Visudyne, a commercialized liposomal formulation of BPD-MA, is based on more fluid lipids, namely, dimyristoylphosphatidylcholine and egg yolk phosphatidylglycerol, and is thought to be less stable in the presence of serum. The data of spin column chromatography indicated a little faster transfer of BPD-MA from Visudyne to lipoprotein fraction when Visudyne was incubated with serum than when the stable liposomal BPD-MA was used. The phototoxicity of Visudyne against a human endothelial cell line, ECV304, was almost the same as that of stable liposomal BPD-MA after PDT treatment. Therefore, we examined the antiangiogenic scheduling of PDT with Visudyne. Tumor growth of Meth-A sarcoma-bearing mice was strongly suppressed when the antiangiogenic scheduling was performed with Visudyne, namely, irradiation at 15 min after injection of the drug, in comparison with the conventional scheduling in which laser irradiation is done at 3 h post-injection. This greater effectiveness of PDT at 15 min was suggested to be caused by hemostasis, based on observations made in a dorsal air sac angiogenesis model. Visudyne-mediated antiangiogenic PDT cured 40 or 60% of Meth-A-bearing mice completely when 0.25 or 0.5 mg/kg BPD-MA, respectively, was used. These data suggest that the antiangiogenic scheduling is effective in Visudyne-mediated cancer PDT despite the transferring of BPD-MA from the liposomal fraction to lipoproteins in the bloodstream.

Acute and subchronic (28-day) oral toxicity study in rats fed with novel surfactants

The toxicity of 2 new synthetic lipids, 1,2-dioleoyl-rac-glycerol-3-dodecaethylene glycol, GDO-12 (lipid 1) and 1,2-distearoyl-rac-glycerol-3-dodecaethylene glycol, GDS-12 (lipid 2) has been evaluated in acute and subchronic toxicity studies. Acute oral toxicity studies in male and female rats documented no deaths or treatment-related signs at high doses. The lipids were individually administered (by gavage) to male and female Sprague-Dawley rats at concentrations of 250, 500, and 1000 mg/Kg bodyweight for 28 days. All animals survived the duration of the study, with no significant changes in clinical signs, hematological parameters, organ weights, ophthalmology evaluations, or histopathological findings. These studies establish that both GDO-12 (lipid 1) and GDS-12 (lipid 2) are nontoxic in rats following oral administration. The no-observed-adverse-effect level ranged between 250 mg/Kg and 1000 mg/Kg following oral administration.

Polycation liposome enhances the endocytic uptake of photosensitizer into cells in the presence of serum

To construct a novel drug delivery carrier that possesses high therapeutic efficacy with low dosage, we designed polyethylenimine-modified liposome (polycation liposome, PCL) and examined the entrapment of photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA), for antiangiogenic photodynamic therapy (PDT). Photosensitizer entrapped in PCLs showed enhanced phototoxicity for a human vascular endothelial cell line, ECV304, in comparison with that for nonmodified control liposome. Interestingly, phototoxicity of control liposomal BPD-MA was suppressed in the presence of serum, but PCL maintained the phototoxicity in the presence of serum following PCL-mediated PDT treatment due to the stability of PCL and the reduced detachment of encapsulated photosensitizer from liposome to serum. In fact, PCL enhanced the uptake level of BPD-MA to ECV304 cells despite the presence or absence of serum. Since polycation modification enhances bioavailability of the liposomal photosensitizer and this property is maintained in the presence of serum, PCL would be useful for antiangiogenic PDT.

[Chemotherapy with hybrid liposomes without any drug in vivo]

Prolonged survival was seen in a carcinoma model in mice intraperitoneally inoculated with B-16 melanoma cells after the intraperitoneal treatment with hybrid liposomes composed of L-alpha-dimyristoylphosphatidylcholine (DMPC) and polyoxyethylenedodecyl ether (C12(EO)n, n = 10 and 23 respectivery) which had a uniform and stable structure. No drug was administered. The therapeutic effects of the single-component liposomes composed of lipids with a variety of hydrophilic head groups and different hydrophobic alkyl chains were investigated. Markedly prolonged survival (248%) of mice was achieved after treatment with DMPC liposomes. However, DMPC liposomes have the disadvantage of an unstable structure, requiring daily sonication. On the other hand, no life-prolonging effects or toxicity occurred with the administration of the other single-component liposome employed in this study. Next, we successfully prepared stable, uniform liposomes composed of 90 mol% DMPC and 10 mol% C12(EO)n (n = 10 and 23, respectively), which have diameters of 70 nm and 100 nm, respectively. Interestingly, prolonged survival (173-186%) of mice was achieved after treatment with hybrid liposomes of 90 mol% DMPC/10 mol% C12(EO)n (n = 10 and 23). Finally, we conducted toxicity tests using normal rats to determine hybrid liposome stability. There were no abnormal findings in blood chemistry or relative organ weights at autopsy of normal rats after hybrid liposome administration. In addition, hybrid liposomes were metabolized in the liver after intravenous administration to normal mice. These results suggest that hybrid liposomes could be used as a new single chemotherapeutic agent in the treatment of carcinoma with no side effects.

Anti-neovascular therapy by liposomal DPP-CNDAC targeted to angiogenic vessels

We previously reported that liposomalized 5'-O-dipalmitoylphosphatidyl 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (DPP-CNDAC), a hydrophobized derivative of the novel antitumor nucleoside CNDAC, is quite useful for cancer therapy. On the other hand, for anti-neovascular therapy, we recently isolated peptides homing to angiogenic vessels from a phage-displayed random peptide library, and observed that peptide-modified liposomal adriamycin strongly suppressed tumor growth, perhaps through damaging angiogenic endothelial cells. In the present study, we modified DPP-CNDAC-liposomes with one of the angiogenic homing peptides, APRPG, and examined their antitumor activity. Three doses of APRPG-modified DPP-CNDAC-liposomes (15 mg/kg as CNDAC) strongly inhibited tumor growth compared with the same number of doses of unmodified DPP-CNDAC-liposomes. The life span was increased 31.8%, with one completely cured mouse out of the six mice treated. Since the accumulation of liposomes in the tumor tissue was not so much different between APRPG-liposomes and non-modified liposomes, the enhanced therapeutic efficacy may be explained as the alteration of targets, i.e. APRPG-modified DPP-CNDAC-liposomes caused tumor growth suppression through damage of angiogenic endothelial cells. Anti-neovascular therapy promises no drug resistance, and should be effective against essentially any kind of solid tumor; and thus the present results demonstrate another benefit of the therapy, namely, high efficacy of cancer treatment.

Potential usage of liposomal 4beta-aminoalkyl-4'-O-demethyl-4-desoxypodophyllotoxin (TOP-53) for cancer chemotherapy

To enhance the therapeutic efficacy as well as to reduce the side effect, we attempted to liposomalize 4beta-aminoalkyl-4'-O-demethyl-4-desoxypodophyllotoxin (TOP-53), a novel and effective topoisomerase II inhibitor. More than 90% of TOP-53 was efficiently incorporated into the liposomes composed of dipalmitoylphosphatidylcholine and cholesterol by remote-loading method. Anti-tumor activity of liposomal TOP-53 against solid tumor was examined in vivo using colon26 NL-17 carcinoma model mice. Three doses of liposomal TOP-53 (12 mg/kg/dose) showed significant tumor growth suppression (97.5% reduction determined at day 25) and the increase in life span (33%) of tumor-bearing mice. Furthermore, one mouse out of 5 was completely cured after treatment. Since similar efficacy was observed in the free TOP-53 treated group, liposomalization does not contribute much to the enhancement of therapeutic efficacy. However, a slight but measurable damage at the injection site was observed when free TOP-53 was injected, and the damage was diminished by the liposomalization. Taken together, liposomalization reduces the side effect rather than enhancing the therapeutic efficacy when TOP-53 is used.

Anti-neovascular therapy using novel peptides homing to angiogenic vessels

Cancer chemotherapy targeted to angiogenic vessels is expected to cause indirect tumor regression through the damage of the neovasculature without the induction of drug resistance. To develop a tool for neovasculature-specific drug delivery, we isolated novel peptides homing to angiogenic vessels formed by a dorsal air sac method from a phage-displayed peptide library. Three distinct phage clones that markedly accumulated in murine tumor xenografts presented PRPGAPLAGSWPGTS-, DRWRPALPVVLFPLH- or ASSSYPLIHWRPWAR-peptide respectively. After the determination of the epitope sequences of these peptides, we modified liposomes with epitope penta-peptides. Liposome modified with APRPG-peptide showed high accumulation in murine tumor xenografts, and APRPG-modified liposome encapsulating adriamycin effectively suppressed experimental tumor growth. Finally, specific binding of APRPG-modified liposome to human umbilical endothelial cells, and that of PRP-containing peptide to angiogenic vessels in human tumors, i.e., islet cell tumor and glioblastoma, were demonstrated. The present study indicates the usefulness of APRPG-peptide as a tool for anti-neovascular therapy, a novel modality of cancer treatment.

Photodynamic therapy targeted to tumor-induced angiogenic vessels

Cancer photodynamic therapy (PDT) with benzoporphyrin derivative monoacid ring A (BPD-MA, verteporfin) may be effective not only by being directly cytotoxic to tumor cells, but also by being cytotoxic to the endothelium of tumor neovasculature. In the present study, we investigated the effect of PDT with an experimental liposomal formulation of BPD-MA on tumor-induced angiogenic vessels using a murine dorsal air sac model. First, hemostasis of neovasculature was examined by varying the regimen of PDT. Laser irradiation at 15 min after injection of 2 mg/kg liposomal BPD-MA (15 min PDT) caused complete blocking of blood flow in neovasculature. In contrast, PDT did not inhibit blood flow when the irradiation occurred 3 h after the injection of liposomal BPD-MA (3 h PDT). Next, the antitumor effect of PDT on Meth A sarcoma-bearing mice was investigated by using the hemostasis-inducing regimen. Tumor growth was strongly inhibited after the 15 min PDT with BPD-MA at a dose of 0.5-2 mg/kg. In contrast, 3 h PDT with BPD-MA at a dose of 2 mg/kg suppressed tumor growth only partially. The current study indicates that 15 min PDT causes strong suppression of tumor growth, perhaps through damaging endothelial cells in the tumor neovasculature rather than through a direct cytotoxic effect on tumor cells.

Potential usage of thermosensitive liposomes for site-specific delivery of cytokines

Long-circulating liposomes reside long in the bloodstream, and transient swelling during phase transition of liposomes with hyper-osmotic internal aqueous phase causes release of macromolecules. Here we examined the applicability of long-circulating thermosensitive liposomes for delivery of tumor necrosis factor (TNF) by the heating of a local tumor-growing site after injection of TNF-loaded liposomes into tumor-bearing mice. Glucuronate modified thermosensitive liposomes with internal solution of two-fold higher osmotic pressure and sized through 200 nm-pore, released encapsulated [(131)I] human serum albumin at 42 degrees C in vitro and showed long-circulating character in vivo. Cytotoxic action of TNF encapsulated in long-circulating thermosensitive-liposomes (LCTS-liposomes) against L929 fibrosarcoma cells was enhanced at 42 degrees C in vitro. Furthermore, the tumor growth tended to be inhibited more by hyperthermia of mice bearing Meth A sarcoma than without heating after injection of TNF encapsulated in LCTS-liposomes. These results suggest that the cytokine can be released at the tumor site from the circulating CLTS-liposomes.

Anticancer therapy using glucuronate modified long-circulating liposomes

Since conventional liposomes tend to be trapped by the reticuroendothelial systems (RES), their use as drug carriers is limited when the targets are not RES cells. Therefore, many attempts have been made to avoid the RES-trapping of liposomes. Favorable results were obtained by a modification of liposomes with a glucuronic acid derivative, PGlcUA, and polyethyleneglycol. These liposomes have a long-circulating character, and showed the further advantage for passive targeting to tumor tissues, since the vasculature in tumor tissues is leaky enough for small-sized liposomes to extravasate. Thus long-circulating liposomes are useful for tumor imaging and treatment. PGlcUA-modified liposomes were actually found to accumulate effectively in tumor tissue, and showed enhanced efficacy of antitumor agents, such as adriamycin and vincristine when they were encapsulated into the liposomes. Usefulness of PGlcUA liposomes as drug carriers was also observed in photodynamic therapy and in treatment of cancer by amphiphilic novel antitumor agents.

The size of liposomes: a factor which affects their targeting efficiency to tumors and therapeutic activity of liposomal antitumor drugs

The size of liposomes has been shown to be an important factor in the efficient delivery of an antitumor agent to a tumor. In this paper, the effects of the size of liposomes on the pharmacokinetics of liposomes and liposome-encapsulated drugs are discussed with reference to: (1) the circulation amount and residence time of liposomes in the blood, (2) the accumulation of liposomes in the tumor, and (3) in vivo drug release from liposomes. In addition, the effect of size on therapeutic activity (antitumor efficacy and toxicity) of a liposomal anticancer preparation is discussed. Finally we discuss the importance of liposome size in the design of a more effective liposomal antitumor preparation.

Antitumor activity of vincristine encapsulated in glucuronide-modified long-circulating liposomes in mice bearing Meth A sarcoma

Liposomes modified with the uronic acid derivative palmityl-D-glucuronide (PGlcUA) have a long circulation time and tend to accumulate in the tumors of tumor-bearing mice. Taking advantage of this character, we investigated the therapeutic effect of vincristine (VCR) encapsulated in liposomes containing PGlcUA (dipalmitoylphosphatidylcholine/cholesterol/PGlcUA = 4:4:1 as a molar ratio) on tumor-bearing mice. VCR was loaded into liposomes by a remote loading method, and then free or liposomal VCR was injected intravenously into BALB/c mice bearing Meth A sarcoma implanted subcutaneously 5 days before hand. Single-dose administration of VCR (3.0 mg/kg) in PGlcUA-liposomes significantly suppressed tumor growth, and prolonged the survival time (T/C = 1.37). Furthermore, two-dose administration of the liposomes cured one third of the animals. The therapeutic effect of PGlcUA-liposomes was greater than that of control liposomes containing dipalmitoylphosphatidylglycerol instead of PGlcUA. PGlcUA-liposomes might thus be a useful tool for delivering antitumor agents to tumor tissues.

Recent advances in liposomal drug-delivery systems

Liposomal drug-delivery systems have come of age in recent years, with several liposomal drugs currently in advanced clinical trials or already on the market. It is clear from numerous pre-clinical and clinical studies that drugs, such as antitumor drugs, packaged in liposomes exhibit reduced toxicities, while retaining, or gaining enhanced, efficacy. This results, in part, from altered pharmacokinetics, which lead to drug accumulation at disease sites, such as tumors, and reduced distribution to sensitive tissues. Fusogenic liposomal systems that are under development have the potential to deliver drugs intracellularly, and this is expected to markedly enhance therapeutic activity. Advances in liposome design are leading to new applications for the delivery of new biotechnology products, such as recombinant proteins, antisense oligonucleotides and cloned genes.

Real-time analysis of liposomal trafficking in tumor-bearing mice by use of positron emission tomography

Long-circulating liposomes are known to accumulate passively in tumor tissues of tumor-bearing animals. To evaluate the in vivo behavior of such liposomes, we investigated the real-time liposomal trafficking by a non-invasive method using position emission tomography (PET). Liposomes composed of dipalmitoylphosphatidylcholine, cholesterol, and palmityl-D-glucuronide (PGlcUA) in a molar ratio of 4:4:1 were prepared in the presence of 2-[18F]fluoro-2-deoxyglucose ([2-18F]FDG). [2-18F]FDG-labeled liposomes sized by extrusion through a filter with various-sized pores were administered to mice bearing Meth A sarcoma, and a PET scan was performed for 120 min. Small-sized, long-circulating liposomes (100 nm in diameter) constructed with PGlcUA tended to accumulate in the tumor tissues. On the contrary, control liposomes (100 nm in diameter) containing dipalmitoylphosphatidylglycerol instead of PGlcUA accumulated in the liver. Large-sized PGlcUA-containing liposomes (> 300 nm) also accumulated in the liver, as well as in the spleen. Time-activity curves indicated that the small long-circulating liposomes (< 200 nm) transiently accumulated in the liver right after the injection but that the accumulation there decreased time-dependently. These data suggest that, although the majority of small long-circulating liposomes remain in the bloodstream, some extravasate once into the interstitial spaces in the liver re-enter the bloodstream again, and finally accumulate in the tumor tissues. This PET technique might be useful for studying real-time liposomal trafficking and for tumor imaging.