Delivery of contrast agents for positron emission tomography imaging by liposomes

Quantitative Pharmacokinetics Reveal Impact of Lipid Composition on Microbubble and Nanoprogeny Shell Fate

Microbubble-enabled focused ultrasound (MB-FUS) has revolutionized nano and molecular drug delivery capabilities. Yet, the absence of longitudinal, systematic, quantitative studies of microbubble shell pharmacokinetics hinders progress within the MB-FUS field. Microbubble radiolabeling challenges contribute to this void. This barrier is overcome by developing a one-pot, purification-free copper chelation protocol able to stably radiolabel diverse porphyrin-lipid-containing Definity® analogues (pDefs) with >95% efficiency while maintaining microbubble physicochemical properties. Five tri-modal (ultrasound-, positron emission tomography (PET)-, and fluorescent-active) [64 Cu]Cu-pDefs are created with varying lipid acyl chain length and charge, representing the most prevalently studied microbubble compositions. In vitro, C16 chain length microbubbles yield 2-3x smaller nanoprogeny than C18 microbubbles post FUS. In vivo, [64 Cu]Cu-pDefs are tracked in healthy and 4T1 tumor-bearing mice ± FUS over 48 h qualitatively through fluorescence imaging (to characterize particle disruption) and quantitatively through PET and γ-counting. These studies reveal the impact of microbubble composition and FUS on microbubble dissolution rates, shell circulation, off-target tissue retention (predominantly the liver and spleen), and FUS enhancement of tumor delivery. These findings yield pharmacokinetic microbubble structure-activity relationships that disrupt conventional knowledge, the implications of which on MB-FUS platform design, safety, and nanomedicine delivery are discussed.

From Conventional to Stealth Liposomes a new Frontier in Cancer Chemotherapy

Many attempts have been made to achieve good selectivity to targeted tumor cells by preparing specialized carrier agents that are therapeutically profitable for anticancer therapy. Among these, liposomes are the most studied colloidal particles thus far applied in medicine and in particular in antitumor therapy. Although they were first described in the 1960s, only at the beginning of 1990s did the first therapeutic liposomes appear on the market. The first-generation liposomes (conventional liposomes) comprised a liposome-containing amphotericin B, Ambisome (Nexstar, Boulder, CO, USA), used as an antifungal drug, and Myocet (Elan Pharma Int, Princeton, NJ, USA), a doxorubicin-containing liposome, used in clinical trials to treat metastatic breast cancer. The second-generation liposomes (“pure lipid approach”) were long-circulating liposomes, such as Daunoxome, a daunorubicin-containing liposome approved in the US and Europe to treat AIDS-related Kaposi's sarcoma. The third-generation liposomes were surface-modified liposomes with gangliosides or sialic acid, which can evade the immune system responsible for removing liposomes from circulation. The fourth-generation liposomes, pegylated liposomal doxorubicin, were called “stealth liposomes” because of their ability to evade interception by the immune system, in the same way as the stealth bomber was able to evade radar. Actually, the only stealth liposome on the market is Caelyx/Doxil (Schering-Plough, Madison NJ, USA), used to cure AIDS-related Kaposi's sarcoma, resistant ovarian cancer and metastatic breast cancer. Pegylated liposomal doxorubicin is characterized by a very long-circulation half-life, favorable pharmacokinetic behavior and specific accumulation in tumor tissues. These features account for the much lower toxicity shown by Caelyx in comparison to free doxorubicin, in terms of cardiotoxicity, vesicant effects, nausea, vomiting and alopecia. Pegylated liposomal doxorubicin also appeared to be less myelotoxic than doxorubicin. Typical forms of toxicity associated to it are acute infusion reaction, mucositis and palmar plantar erythrodysesthesia, which occur especially at high doses or short dosing intervals. Active and cell targeted liposomes can be obtained by attaching some antigen-directed monoclonal antibodies (Moab or Moab fragments) or small proteins and molecules (folate, epidermal growth factor, transferrin) to the distal end of polyethylene glycol in pegylated liposomal doxorubicin. The most promising therapeutic application of liposomes is as non-viral vector agents in gene therapy, characterized by the use of cationic phospholipids complexed with the negatively charged DNA plasmid. The use of liposome formulations in local-regional anticancer therapy is also discussed. Finally, pegylated liposomal doxorubicin containing radionuclides are used in clinical trials as tumor-imaging agents or in positron emission tomography.

Innovations in Liposomal DDS Technology and Its Application for the Treatment of Various Diseases

Liposomes have been widely used as drug carriers in the field of drug delivery systems (DDS), and they are thought to be ideal nano-capsules for targeting DDS after being injected into the bloodstream. In general, DDS drugs meet the needs of aged and super-aged societies, since the administration route of drugs can be changed, the medication frequency reduced, the adverse effects of drugs suppressed, and so on. In fact, a number of liposomal drugs have been launched and used worldwide including liposomal anticancer drugs, and these drugs have appeared on the market owing to various innovations in liposomal DDS technologies. The accumulation of long-circulating liposomes in cancer tissue is driven by the enhanced permeability and retention (EPR) effect. In this review, liposome-based targeting DDS for cancer therapy is briefly discussed. Since cancer angiogenic vessels are the ideal target of drug carriers after their injection and are critical for cancer growth, damaging of these neovessels has been an approach for eradicating cancer cells. Also, the usage of liposomal DDS for the treatment of ischemic stroke is possible, since we observed that PEGylated liposomes accumulate in the site of cerebral ischemia in transient middle cerebral artery occlusion (t-MCAO) model rats. Interestingly, liposomes carrying neuroprotectants partly suppress ischemia/reperfusion injury of these model rats, suggesting that the EPR effect also works in ischemic diseases by causing an increase in the permeability of the blood vessel endothelium. The potential of liposomal DDS against life-threatening diseases might thus be attractive for supporting long-lived societies.

Longitudinal investigation of permeability and distribution of macromolecules in mouse malignant transformation using PET

PURPOSE

We apply positron emission tomography (PET) to elucidate changes in nanocarrier extravasation during the transition from premalignant to malignant cancer, providing insight into the use of imaging to characterize early cancerous lesions and the utility of nanoparticles in early disease.

EXPERIMENTAL DESIGN

Albumin and liposomes were labeled with (64)Cu (half-life 12.7 hours), and longitudinal PET and CT imaging studies were conducted in a mouse model of ductal carcinoma in situ. A pharmacokinetic model was applied to estimate the tumor vascular volume and permeability.

RESULTS

From early time points characterized by disseminated hyperproliferation, the enhanced vascular permeability facilitated lesion detection. During disease progression, the vascular volume fraction increased 1.6-fold and the apparent vascular permeability to albumin and liposomes increased ∼2.5-fold to 6.6 × 10(-8) and 1.3 × 10(-8) cm/s, respectively, with the accumulation of albumin increasing earlier in the disease process. In the malignant tumor, both tracers reached similar mean intratumoral concentrations of ∼6% ID/cc but the distribution of liposomes was more heterogeneous, ranging from 1% to 18% ID/cc compared with 1% to 9% ID/cc for albumin. The tumor-to-muscle ratio was 17.9 ± 8.1 and 7.1 ± 0.5 for liposomes and albumin, respectively, indicating a more specific delivery of liposomes than with albumin.

CONCLUSIONS

PET imaging of radiolabeled particles, validated by confocal imaging and histology, detected the transition from premalignant to malignant lesions and effectively quantified the associated changes in vascular permeability.

Liposomal Cu-64 labeling method using bifunctional chelators: poly(ethylene glycol) spacer and chelator effects

Two bifunctional Cu-64 chelators (BFCs), (6-(6-(3-(2-pyridyldithio)propionamido)hexanamido)benzyl)-1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid (TETA-PDP) and 4-(2-(2-pyridyldithioethyl)ethanamido)-11-carboxymethyl-1,4,8,11-tetraazabicyclo(6.6.2)hexadecane (CB-TE2A-PDEA), were synthesized and conjugated to long-circulating liposomes (LCLs) via attachment to a maleimide lipid. An in vitro stability assay of (64)Cu-TETA, (64)Cu-TETA-PEG2k, and (64)Cu-CB-TE2A-PEG2k liposomes showed that more than 86% of the radioactivity remains associated with the liposomal fraction after 48 h of incubation with mouse serum. The in vivo time activity curves (TAC) for the three liposomal formulations showed that approximately 50% of the radioactivity cleared from the blood pool in 16-18 h. As expected, the in vivo biodistribution and TAC data obtained at 48 h demonstrate that the clearance of radioactivity from the liver slows with the incorporation of a poly(ethylene glycol)-2k (PEG2k) brush. Our data suggest that (64)Cu-TETA and (64)Cu-CB-TE2A are similarly stable in the blood pool and accumulation of radioactivity in the liver and spleen is not related to the stability of Cu-64 chelator complex; however, clearance of Cu-64 from the liver and spleen are faster when injected as (64)Cu-TETA-chelated liposomes rather than (64)Cu-CB-TE2A-chelated liposomes.

Enhanced antitumor effect of novel dual-targeted paclitaxel liposomes

A novel dual-targeted peptide containing an alpha V integrins specific ligand and a neuropilin-1 specific motif was developed which showed an increased specific targeting affinity to tumors. Active dual-targeted liposomes were then produced with this peptide and exhibited greater binding activity than single-targeted liposomes in vitro. Paclitaxel entrapped in this formulation greatly increased the uptake of paclitaxel in the targeting cells and significantly suppressed the growth of HUVEC and A549 cells compared with general paclitaxel injections (Taxol) and single-targeted paclitaxel liposomes. The treatment of tumor xenograft models with dual-targeted paclitaxel liposomes also resulted in better tumor growth inhibition than any other treatment groups. Therefore, the dual-targeted paclitaxel liposomes prepared in the present study might be a more promising drug for cancer treatment. Furthermore, the dual-targeting approach may produce synergistic effects that can be applied in the development of new targeted drug delivery systems.

Nanotargeted radionuclides for cancer nuclear imaging and internal radiotherapy

Current progress in nanomedicine has exploited the possibility of designing tumor-targeted nanocarriers being able to deliver radionuclide payloads in a site or molecular selective manner to improve the efficacy and safety of cancer imaging and therapy. Radionuclides of auger electron-, α-, β-, and γ-radiation emitters have been surface-bioconjugated or after-loaded in nanoparticles to improve the efficacy and reduce the toxicity of cancer imaging and therapy in preclinical and clinical studies. This article provides a brief overview of current status of applications, advantages, problems, up-to-date research and development, and future prospects of nanotargeted radionuclides in cancer nuclear imaging and radiotherapy. Passive and active nanotargeting delivery of radionuclides with illustrating examples for tumor imaging and therapy are reviewed and summarized. Research on combing different modes of selective delivery of radionuclides through nanocarriers targeted delivery for tumor imaging and therapy offers the new possibility of large increases in cancer diagnostic efficacy and therapeutic index. However, further efforts and challenges in preclinical and clinical efficacy and toxicity studies are required to translate those advanced technologies to the clinical applications for cancer patients.

Towards new functional nanostructures for medical imaging

Nanostructures represent a promising new type of contrast agent for clinical medical imaging modalities, including magnetic resonance imaging, x-ray computed tomography, ultrasound, and nuclear imaging. Currently, most nanostructures are simple, single-purpose imaging agents based on spherical constructs (e.g., liposomes, micelles, nanoemulsions, macromolecules, dendrimers, and solid nanoparticle structures). In the next decade, new clinical imaging nanostructures will be designed as multi-functional constructs, to both amplify imaging signals at disease sites and deliver localized therapy. Proposals for nanostructures to fulfill these new functions will be outlined. New functional nanostructures are expected to develop in five main directions: Modular nanostructures with additive functionality; cooperative nanostructures with synergistic functionality; nanostructures activated by their in vivo environment; nanostructures activated by sources outside the patient; and novel, nonspherical nanostructures and components. The development and clinical translation of next-generation nanostructures will be facilitated by a combination of improved clarity of the in vivo imaging and biological challenges and the requirements to successfully overcome them; development of standardized characterization and validation systems tailored for the preclinical assessment of nanostructure agents; and development of streamlined commercialization strategies and pipelines tailored for nanostructure-based agents for their efficient translation to the clinic.

Radionuclides delivery systems for nuclear imaging and radiotherapy of cancer

The recent developments of nuclear medicine in oncology have involved numerous investigations of novel specific tumor-targeting radiopharmaceuticals as a major area of interest for both cancer imaging and therapy. The current progress in pharmaceutical nanotechnology field has been exploited in the design of tumor-targeting nanoscale and microscale carriers being able to deliver radionuclides in a selective manner to improve the outcome of cancer diagnosis and treatment. These carriers include chiefly, among others, liposomes, microparticles, nanoparticles, micelles, dendrimers and hydrogels. Furthermore, combining the more recent nuclear imaging multimodalities which provide high sensitivity and anatomical resolution such as PET/CT (positron emission tomography/computed tomography) and SPECT/CT (combined single photon emission computed tomography/computed tomography system) with the use of these specific tumor-targeting carriers constitutes a promising rally which will, hopefully in the near future, allow for earlier tumor detection, better treatment planning and more powerful therapy. In this review, we highlight the use, limitations, advantages and possible improvements of different nano- and microcarriers as potential vehicles for radionuclides delivery in cancer nuclear imaging and radiotherapy.

Dynamic microPET imaging of ultrasound contrast agents and lipid delivery

Interest in ultrasound contrast agents (lipid-shelled microbubbles) as delivery vehicles is increasing; however, the biodistribution of these agents remains uncharacterized, both with and without ultrasound. In this study, an (18)F-labeled lipid ([(18)F]fluorodipalmitin), incorporated in microbubble shells, was used as a dynamic microPET probe for quantitative 90-minute biodistribution measurements in male Fischer 344 rats (n=2). The spleen retained the highest concentration of radioactive lipid at approximately 2.6%-injected dose per cubic centimeter (% ID/cc) and the liver demonstrated the largest total accumulation (approximately 17% ID). The microbubble pharmacokinetic profile differed from free lipid, which is rapidly cleared from blood, and liposomes, which remain in circulation. Additionally, region of interest (ROI) analysis over 60 minutes (post-ultrasound treatment) quantified the delivery of lipid by therapeutic ultrasound from microbubbles to kidney tissue (n=8). The ultrasound sequence consisted of a 200 kPa, 5.3 MHz radiation force pulse followed by a 1.6 MPa, 1.4 MHz fragmentation pulse and was applied to one kidney, while the contralateral kidney served as a control. ROI-estimated activity in treated kidneys was slightly but significantly greater at 0 and 60 min than in untreated kidneys (p=0.0012 and 0.0035, respectively). This effect increased with the number of microbubbles injected (p=0.006). In summary, [(18)F]fluorodipalmitin was used to characterize the biodistribution of contrast microbubble shells and the deposition of lipid was shown to be locally increased after insonation.

Long-circulating liposomes radiolabeled with [18F]fluorodipalmitin ([18F]FDP)

Synthesis of a radiolabeled diglyceride, 3-[(18)F]fluoro-1,2-dipalmitoylglycerol [[(18)F]fluorodipalmitin ([(18)F]FDP)], and its potential as a reagent for radiolabeling long-circulating liposomes were investigated. The incorporation of (18)F into the lipid molecule was accomplished by nucleophilic substitution of the p-toluenesulfonyl moiety with a decay-corrected yield of 43+/-10% (n=12). Radiolabeled, long-circulating polyethylene-glycol-coated liposomes were prepared using a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, cholesterol, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] ammonium salt (61:30:9) and [(18)F]FDP with a decay-corrected yield of 70+/-8% (n=4). PET imaging and biodistribution studies were performed with free [(18)F]FDP and liposome-incorporated [(18)F]FDP. Freely injected [(18)F]FDP had the highest uptake in the liver, spleen and lungs. Liposomal [(18)F]FDP remained in blood circulation at near-constant levels for at least 90 min, with a peak concentration near 2.5%ID/cc. Since [(18)F]FDP was incorporated into the phospholipid bilayer, it could potentially be used for radiolabeling a variety of lipid-based drug carriers.

Enhancement of anticancer activity in antineovascular therapy is based on the intratumoral distribution of the active targeting carrier for anticancer drugs

We previously observed the enhanced anticancer efficacy of anticancer drugs encapsulated in Ala-Pro-Arg-Pro-Gly-polyethyleneglycol-modified liposome (APRPG-PEG-Lip) in tumor-bearing mice, since APRPG peptide was used as an active targeting tool to angiogenic endothelium. This modality, antineovascular therapy (ANET), aims to eradicate tumor cells indirectly through damaging angiogenic vessels. In the present study, we examined the in vivo trafficking of APRPG-PEG-Lip labeled with [2-(18)F]2-fluoro-2-deoxy-D-glucose ([2-(18)F]FDG) by use of positron emission tomography (PET), and observed that the trafficking of this liposome was quite similar to that of non-targeted long-circulating liposome (PEG-Lip). Then, histochemical analysis of intratumoral distribution of both liposomes was performed by use of fluorescence-labeled liposomes. In contrast to in vivo trafficking, intratumoral distribution of both types of liposomes was quite different: APRPG-PEG-Lip was colocalized with angiogenic endothelial cells that were immunohistochemically stained for CD31, although PEG-Lip was localized around the angiogenic vessels. These results strongly suggest that intratumoral distribution of drug carrier is much more important for therapeutic efficacy than the total accumulation of the anticancer drug in the tumor, and that active delivery of anticancer drugs to angiogenic vessels is useful for cancer treatment.

Fluoro-substitution effects in deoxyfluoro-d-glucose derivatives: random conformational search and quantum chemical calculation

The effect of substitution by the fluorine atom at different positions of D-glucose was investigated by quantum chemical calculation of the low-energy conformers. These were obtained through the Random conformational search method. The geometries of conformers were optimized at the RHF/6-31(d) level, then reoptimization and vibrational analysis were performed at the B3LYP/6-31+G(d) level. Single-point energies were calculated at the B3LYP/6-311++G(2d,2p) level. The free energies of solvation in water were calculated utilizing the AM1-SM5.4 solvation model. For all substitution positions, the ring conformation does not change much, and the pyranoid 4C1 conformers are dominant, while variations in the substitution site result in different effects in the network of hydrogen bonds, anomeric effect, the solvation free energy, and the ratio of alpha- and beta-anomers.

Lipid-based nanoparticles for contrast-enhanced MRI and molecular imaging

In the field of MR imaging and especially in the emerging field of cellular and molecular MR imaging, flexible strategies to synthesize contrast agents that can be manipulated in terms of size and composition and that can be easily conjugated with targeting ligands are required. Furthermore, the relaxivity of the contrast agents, especially for molecular imaging applications, should be very high to deal with the low sensitivity of MRI. Lipid-based nanoparticles, such as liposomes or micelles, have been used extensively in recent decades as drug carrier vehicles. A relatively new and promising application of lipidic nanoparticles is their use as multimodal MR contrast agents. Lipids are amphiphilic molecules with both a hydrophobic and a hydrophilic part, which spontaneously assemble into aggregates in an aqueous environment. In these aggregates, the amphiphiles are arranged such that the hydrophobic parts cluster together and the hydrophilic parts face the water. In the low concentration regime, a wide variety of structures can be formed, ranging from spherical micelles to disks or liposomes. Furthermore, a monolayer of lipids can serve as a shell to enclose a hydrophobic core. Hydrophobic iron oxide particles, quantum dots or perfluorocarbon emulsions can be solubilized using this approach. MR-detectable and fluorescent amphiphilic molecules can easily be incorporated in lipidic nanoparticles. Furthermore, targeting ligands can be conjugated to lipidic particles by incorporating lipids with a functional moiety to allow a specific interaction with molecular markers and to achieve accumulation of the particles at disease sites. In this review, an overview of different lipidic nanoparticles for use in MRI is given, with the main emphasis on Gd-based contrast agents. The mechanisms of particle formation, conjugation strategies and applications in the field of contrast-enhanced, cellular and molecular MRI are discussed.

Novel biomimetic polymersomes as polymer therapeutics for drug delivery

Novel amphiphilic diblock copolymers, cholesterol-end-capped poly(2-methacryloyloxyethyl phosphorylcholine) (CMPC), which have poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) as hydrophilic segment and cholesterol as hydrophobic segment, was specially designed as drug delivery systems. Fluorescence probe technique and transmission electron microscope (TEM) characterizations indicated that this novel amphiphilic copolymer formed micelles structure in water and the critical micelle concentration (CMC) was determined to be 1.57 x 10(-7) mol/l. A commercial obtained polymeric amphiphiles, Cholesterol end capped PEO (CPEO), which had a similar structure with CMPC, was used as a control in the cytotoxicity test. While CPEO showed obvious cytotoxicity, cytotoxicity of this novel amphiphiles was not observed as indicated by cell culture. Anti-cancer drug adriamycin (ADR) was incorporated into the micelles by oil-in-water method. The size of the drug-containing micelles was less than 200 nm, and the size distribution of the drug-containing micelles showed a narrow and monodisperse unimodal pattern. The release rate of ADR from the nanosphere was slow and the release continued over 7 days and the release rate decreased with the increase of molecular weights of the copolymer and the amount of the drug entrapped. These experimental results suggested that the nanoparticles prepared from CMPC block copolymers could be a good candidate for injectable drug delivery carrier.

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.

A novel liposome radiolabeling method using 99mTc-"SNS/S" complexes: in vitro and in vivo evaluation

Liposomes are important carriers for controlled drug release, for gene or antisense therapy, and for immunization. Radiolabeled liposomes can be used to evaluate the in vivo behavior of different liposome formulations, as well as for diagnostic imaging and radionuclide therapy. A novel method for radiolabeling liposomes with (99m)Tc-"SNS/S" complexes is introduced. This labeling method can be applied to liposome radiolabeling with not only (99m)Tc but also two therapeutic radionuclides, (186)Re and (188)Re. Liposomes encapsulating glutathione (GSH) were studied for (99m)Tc labeling. N,N-bis(2-mercaptoethyl)-N',N'-diethyl-ethylenediamine (BMEDA), N,N-bis(2-mercaptoethyl)-1-butylamine (BMBuA), and benzene thiol (BT) were investigated to make (99m)Tc-"BMEDA", (99m)Tc-"BMEDA + BT", (99m)Tc-"BMBuA", and (99m)Tc-"BMBuA + BT", for liposome labeling. The labeling efficiencies of (99m)Tc-GSH liposomes were from 36.9 to 69.2%. After incubation in serum, (99m)Tc-GSH liposomes labeled with (99m)Tc-"BMEDA" or (99m)Tc-"BMEDA + BT" had the best labeling stability of the formulations tested. Distribution studies after intravenous injection of (99m)Tc-liposomes composed of distearoyl phosphatidylcholine (DSPC) and cholesterol had a slow blood clearance and a high spleen accumulation demonstrating the in vivo labeling stability of the radiolabeled liposomes. The (99m)Tc-liposomes have great potential as a radiopharmaceutical system for evaluating various kinds of liposomes with different lipid composition, for evaluating in advance a subsequent radionuclide therapy using (186)Re or (188)Re labeled liposomes and for diagnostic imaging.

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.

The Use of Scintigraphic Imaging During Liposome Drug Development

Liposomes, spherical lipid bilayers enclosing an aqueous space, have become an important class of drug carriers. This review describes the usefulness of scintigraphic imaging during the development of liposome-based drugs. This imaging modality is particularly helpful for tracking the distribution of liposomes in the body, monitoring the therapeutic responses following administration of liposome-based drugs, and investigating the physiological responses associated with liposome administration. Scintigraphy also can be used to monitor the therapeutic responses of patients given approved liposomal drugs. Several examples describing the potential of this imaging modality during both the preclinical formulation and clinical trial stages of liposomal drug development are included. Techniques for radiolabeling liposomes as well as methods for producing scintigraphic images are also described.

Targeting and anti-tumor efficacy of liposomal 5'-O-dipalmitoylphosphatidyl 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine in mice lung bearing B16BL6 melanoma

2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC) is a potent anti-cancer agent, and we previously observed that liposomal formulation of 5'-O-dipalmitoylphosphatidyl derivative of CNDAC (DPP-CNDAC) is desirable for targeting. For targeting to pulmonary cancer, we investigated the in vivo behavior of liposomes containing DPP-CNDAC by a non-invasive method using positron emission tomography. Liposomes composed of DPP-CNDAC and cholesterol (DPP-CNDAC/CH liposomes) were markedly accumulated in mice lung bearing B16BL6 melanoma. In metastatic pulmonary cancer model, DPP-CNDAC/CH liposomes significantly reduced the lung colonization in a dose-dependent manner. The activity was significantly superior to conventional liposomal formulation or soluble CNDAC. These results suggest that DPP-CNDAC/CH liposomes are useful for metastatic pulmonary cancer.

Suppression of GD1alpha ganglioside-mediated tumor metastasis by liposomalized WHW-peptide

GD1alpha ganglioside-replica peptides were recently isolated from a phage-displayed random pentadecapeptide library by assaying for inhibition of adhesion of RAW117-H10 lymphosarcoma cells to hepatic sinusoidal microvessel endothelial (HSE) cells. We show here that the Trp-His-Trp (WHW) peptide was identified as a minimal sequence of the GD1alpha-replica peptide WHWRHRIPLQLAAGR. The addition of WHW peptide-attached liposomes displayed efficient inhibition of liver metastasis of RAW117-H10 cells as well as of GD1alpha-mediated adhesion of RAW117-H10 cells to HSE cells in vitro. These results suggest that engineered liposomes for peptide delivery are applicable to treatment for metastasis.