Synthesis and pharmacokinetics of a new liver-specific carrier, glycosylated carboxymethyl-dextran, and its application to drug targeting

Targeting Tumor-Associated Macrophages with the Immune-Activating Nanomedicine for Achieving Strong Antitumor Activity with Rapid Clearance from the Body

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) crucial for the detection of infections and activation of downstream signaling pathways that lead to the production of pro-inflammatory cytokines and interferons. The TLR pathway is an attractive actively studied target pathway. Because of their strong immunostimulatory activity, TLRs are thought to be a "double-edged sword" for systemic treatment, even in the cancer field. To solve this, we have developed dextran-based TAM targeting activating conjugate (D-TAC) technology, which successfully uses tumor-associated macrophages (TAMs) to deliver the TLR7 agonist DSP-0509. We used low molecular weight dextran to target CD206 high M2-type macrophages, activate them, and induce a change in phenotype to antitumor M1-type macrophages with rapid clearance from the body and astonishing antitumor activity. We also demonstrated that the antitumor effect of our best drug candidate 5DEX-0509R is dependent on the abundance of TAMs, which is consistent with their mechanism of action. We believe that 5DEX-0509R generated by D-TAC technology can be a clinically applicable immunotherapy targeting the TLR signaling pathway.

Role of pharmacokinetic consideration for the development of drug delivery systems: A historical overview

Drug delivery system is defined as a system or technology to achieve optimum therapeutic effects of drugs through precise control of their movements in the body. In order to optimize function of drug delivery systems aiming at targeting, their whole-body distribution profiles should be systematically evaluated and analyzed, where pharmacokinetic analysis based on the clearance concepts plays important role. Organ perfusion experiments combined with statistical moment analysis further supply detailed information on drug disposition at organ and cellular levels. Based on general relationship between physicochemical properties and distribution profile, macromolecular prodrugs or polymer conjugates of proteins are rationally designed and further introduction of ligand structure brings cell-specific delivery for them. These approaches are also applicable for particulate carriers such as liposomes and offer various opportunities for biological drugs such as nucleic acid drugs for their delivery. Mechanistic approach for dermal absorption analysis based on physiological skin model offers another opportunity in rational design of drug delivery. Potential of drug delivery technology in future medicines such as cell therapy and nanomaterial platform application is further discussed in relation to pharmacokinetic consideration.

Designing the new generation of intelligent biocompatible carriers for protein and peptide delivery

Therapeutic proteins and peptides have revolutionized treatment for a number of diseases, and the expected increase in macromolecule-based therapies brings a new set of challenges for the pharmaceutics field. Due to their poor stability, large molecular weight, and poor transport properties, therapeutic proteins and peptides are predominantly limited to parenteral administration. The short serum half-lives typically require frequent injections to maintain an effective dose, and patient compliance is a growing issue as therapeutic protein treatments become more widely available. A number of studies have underscored the relationship of subcutaneous injections with patient non-adherence, estimating that over half of insulin-dependent adults intentionally skip injections. The development of oral formulations has the potential to address some issues associated with non-adherence including the interference with daily activities, embarrassment, and injection pain. Oral delivery can also help to eliminate the adverse effects and scar tissue buildup associated with repeated injections. However, there are several major challenges associated with oral delivery of proteins and peptides, such as the instability in the gastrointestinal (GI) tract, low permeability, and a narrow absorption window in the intestine. This review provides a detailed overview of the oral delivery route and associated challenges. Recent advances in formulation and drug delivery technologies to enhance bioavailability are discussed, including the co-administration of compounds to alter conditions in the GI tract, the modification of the macromolecule physicochemical properties, and the use of improved targeted and controlled release carriers.

Efficient Targeting of Adipose Tissue Macrophages in Obesity with Polysaccharide Nanocarriers

Obesity leads to an increased risk for type 2 diabetes, heart disease, stroke, and cancer. The causal link between obesity and these pathologies has recently been identified as chronic low-grade systemic inflammation initiated by pro-inflammatory macrophages in visceral adipose tissue. Current medications based on small-molecule drugs yield significant off-target side effects with long-term use, and therefore there is a major need for targeted therapies. Here we report that nanoscale polysaccharides based on biocompatible glucose polymers can efficiently target adipose macrophages in obese mice. We synthesized a series of dextran conjugates with tunable size linked to contrast agents for positron emission tomography, fluorophores for optical microscopy, and anti-inflammatory drugs for therapeutic modulation of macrophage phenotype. We observed that larger conjugates efficiently distribute to visceral adipose tissue and selectively associate with macrophages after regional peritoneal administration. Up to 63% of the injected dose remained in visceral adipose tissue 24 h after administration, resulting in >2-fold higher local concentration compared to liver, the dominant site of uptake for most nanomedicines. Furthermore, a single-dose treatment of anti-inflammatory conjugates significantly reduced pro-inflammatory markers in adipose tissue of obese mice. Importantly, all components of these therapeutic agents are approved for clinical use. This work provides a promising nanomaterials-based delivery strategy to inhibit critical factors leading to obesity comorbidities and demonstrates a unique transport mechanism for drug delivery to visceral tissues. This approach may be further applied for high-efficiency targeting of other inflammatory diseases of visceral organs.

Galactosylated manganese ferrite nanoparticles for targeted MR imaging of asialoglycoprotein receptor

Cancer cells can express specific biomarkers, such as cell membrane proteins and signaling factors. Thus, finding biomarkers and delivering diagnostic agents are important in the diagnosis of cancer. In this study, we investigated a biomarker imaging agent for the diagnosis of hepatic cancers. The asialoglycoprotein receptor (ASGPr) was selected as a biomarker for hepatoma cells and the ASGPr-targetable imaging agent bearing a galactosyl group was prepared using manganese ferrite nanoparticles (MFNP) and galactosylgluconic acid. The utility of the ASGPr-targetable imaging agent, galactosylated MFNP (G-MFNP) was assessed by several methods in ASGPr-expressing HepG2 cells as target cells and ASGPr-deficient MCF7 cells. Physical and chemical properties of G-MFNP were examined using Fourier-transform infrared spectroscopy, dynamic light scattering, zeta potential analysis, and transmission electron microscopy. No significant cytotoxicity was observed in either cell line. Targeting ability was assessed using flow cytometry, magnetic resonance imaging, inductively coupled plasma atomic emission spectroscopy, absorbance analysis, dark-field microscopy, Prussian blue staining, and transmission electron microscopy. We demonstrated that G-MFNP target successfully and bind to ASGPr-expressing HepG2 cells specifically. We suggest that these results will be useful in strategies for cancer diagnoses based on magnetic resonance imaging.

Development of Time-Programmed, Dual-Release System Using Multilayered Fiber Mesh Sheet by Sequential Electrospinning

In general clinical pharmacotherapy, multidrug therapy is performed with a view to enhancing drug efficacy or reducing drug’s side effects. It is essential that a Drug Delivery System (DDS) for plural drugs be developed to make multidrug therapy more functional and effective. In this review, we summarize prior DDS research and recent developmental efforts for multi-DDS, as well as of the electrospinning (ELSP) method, which has recently attracted great attention as preparation technique of fine polymer fiber in various fields. We also describe a time-programmed dual-drug controlled-release system using multilayered fiber mesh sheets that have been fabricated by a sequential ELSP method we developed. In addition, we address developmental approaches for DDS devices using micromachining technologies (MEMS) as well as issues and future expectations for robotics in DDS research.

Drug delivery systems and liver targeting for the improved pharmacotherapy of the hepatitis B virus (HBV) infection

In spite of the progress made in vaccine and antiviral therapy development, hepatitis B virus (HBV) infection is still the most common cause of liver cirrhosis and hepatocellular carcinoma, with more than 400 million people chronically infected worldwide. Antiviral therapy with nucleos(t)ide analogues and/or immunomodulating peptides is the only option to control and prevent the progression of the disease in chronic hepatitis B (CHB)-infected patients. So far, the current antiviral monotherapy remains unsatisfactory because of the low efficacy and the development of drug resistance mutants. Moreover, viral rebound is frequently observed following therapy cessation, since covalent closed circular DNA (cccDNA) is not removed from hepatocytes by antiviral therapy. First, this review describes the current pharmacotherapy for the management of CHB and the new drug candidates being investigated. Then, the challenges in the development of drug delivery systems for the targeting of antiviral drugs to the liver parenchyma are discussed. Finally, perspectives in the design of a more efficient pharmacotherapy to eradicate the virus from the host are addressed.

Nanoparticles for human liver-specific drug and gene delivery systems: in vitro and in vivo advances

A wide variety of nanoparticles (NPs) that can deliver incorporated therapeutic materials such as compounds, proteins, genes and siRNAs to the human liver have been developed to treat liver-related diseases. This review describes NP-based drug and gene delivery systems such as liposomes (including lipoplex), polymer micelles, polymers (including polyplex) and viral vectors. It focuses upon the modification of these NPs to enhance liver specificity or delivery efficiency in vitro and in vivo. We discuss recent advances in drug and gene delivery systems specific to the human liver utilizing bio-nanocapsules comprising hepatitis B virus (HBV) envelope L protein, which has a pivotal role in HBV infection. These NP-based medicines may offer novel strategies for the treatment of liver-related diseases and contribute to the development of nanomedicines targeting other tissues.

Synthesis, analysis, in vitro characterization, and in vivo disposition of a lamivudine-dextran conjugate for selective antiviral delivery to the liver

A liver-selective prodrug (3TCSD) of the antiviral drug lamivudine (3TC) was developed and characterized. 3TC was coupled to dextran ( approximately 25 kDa) using a succinate linker, and the in vitro and in vivo behavior of the conjugate was studied using newly developed size-exclusion and reversed-phase analytical methods. Synthesized 3TCSD had a purity of >99% with a degree of substitution of 6.5 mg of 3TC per 100 mg of the conjugate. Furthermore, the developed assays were precise and accurate in the concentration ranges of 0.125-20, 0.36-18, and 1-50 microg/mL for 3TC, 3TC succinate (3TCS), and 3TCSD, respectively. In vitro, the conjugate slowly released 3TC in the presence of rat liver lysosomes, whereas it was stable in the corresponding buffer. In vivo in rats, conjugation of 3TC to dextran resulted in 40- and 7-fold decreases in the clearance and volume of distribution of the drug, respectively. However, the accumulation of the conjugated 3TC in the liver was 50-fold higher than that of the parent drug. The high accumulation of the conjugate in the liver was associated with a gradual and sustained release of 3TC in the liver. These studies indicate the feasibility of the synthesis of 3TCS-dextran and its potential use for the selective delivery of 3TC to the liver.

Reduced sinoatrial cAMP content plays a role in postnatal heart rate slowing in the rabbit

1. Decreasing heart rate during development is known to be the result of parasympathetic nervous system maturation that depresses the pacemaker current (If) by acetylcholine (ACh). However, a direct effect of ACh on If has been ruled out and the involvement of other secondary messengers, such as cAMP, was verified in previous studies. Therefore, we hypothesized that reduced basal cAMP production in sinoatrial (SA) nodal cells may contribute to the slowing of heart rate after birth. 2. The electrocardiogram and heart rate variability (HRV) were documented and measured in vivo and in vitro (in isolated perfused Langendorff preparations) for rabbits aged 2, 4, 6, 8 and 12 weeks. Sinoatrial node action potential (AP) recording and perforated patch-clamp analyses were used to investigate the spontaneous depolarization rate and pacemaker If currents. Concentrations of cAMP in SA nodal tissues were determined by radioimmunoassay. Relative expression of adenylate cyclases (ADCY1, 5) and phosphodiesterases (PDE1A, 4A and 8A) were quantified by real-time reverse transcription-polymerase chain reaction. 3. Significantly reduced heart rate, but unchanged HRV, was observed in perfused hearts in the older age groups, accompanied with a slowed phase 4 spontaneous depolarization rate (90.5 +/- 4.7 vs 49.6 +/- 2.6 mV/s for 2 week vs 4 week hearts, respectively; n = 5; P < 0.05), a negative shift of the If threshold potential (-45.5 +/- 3.0 vs -51.1 +/- 6.0 mV for 2 week vs 4 week hearts, respectively; n = 9; P < 0.05) and decreasing basal levels of SA nodal cAMP (0.31 +/- 0.05 vs 0.025 +/- 0.002 micromol/L for 2 week vs 4 week hearts, respectively; n = 6; P < 0.05). Gene expression levels of PDE1A, 4A and 8A were increased in the 12 week group compared with the 2 week group 1.5-, 2- and 1.8-fold, respectively (P < 0.05), with little change in ADCY1 and 5. 4. These data suggest that, in addition to autonomic innervation, slowing of heart rate during postnatal maturation can be attributed to a negative shift of the If activation caused by diminished baseline cAMP content in SA nodal cells.

Bio-nanocapsules for In vivo Pinpoint Drug Delivery

To maximize the beneficial effects and minimize the side effect of drugs, DDS (drug delivery system) has been attracted many researchers in the recent drug development. Especially, the in vivo pinpoint delivery system for drugs is very important and key technology for developing the next generations of anti-cancer drugs and gene therapies. Bio-nanocapsule (BNC) is recombinant yeast-derived hepatitis B virus surface antigen particle, which has been used as a recombinant hepatitis B vaccine for the last 20 years in the world. BNC can incorporate various materials (chemical compounds, proteins, genes, siRNA, etc) by the fusion with liposome, and deliver them to the organs and tissues in vivo specifically by the action of bio-recognition molecules on the BNC's surface. The transfection efficiency is significantly higher than that of liposome, because BNC harbors the complete set of hepatitis B virus infection machinery. Recently, we succeeded in the in vivo retargeting of BNC by displaying either antibody or homing peptide, less than 10 amino acid residues for in vivo targeting. BNC is a hybrid of liposome and virus, and very flexible system for in vivo retargeting. BNC might be very promising carriers in the next generation of DDS.

Uptake characteristics of mannosylated and fucosylated bovine serum albumin in primary cultured rat sinusoidal endothelial cells and Kupffer cells

The purpose of this study is to delineate uptake characteristics of mannosylated and fucosylated proteins in primary cultured sinusoidal endothelial cells and Kupffer cells. In cultured sinusoidal endothelial cells, uptake of mannosylated and fucosylated bovine serum albumin (BSA) was significantly inhibited by excess mannosylated and fucosylated BSAs but not by galactosylated BSA, suggesting that both glycosylated proteins might be primarily taken up via mannose receptors. In cultured Kupffer cells, uptake of fucosylated BSA was significantly inhibited by excess galactosylated BSA as well as mannosylated and fucosylated BSAs, although that of mannosylated BSA was inhibited only by mannosylated and fucosylated BSAs. This suggests that uptake of fucosylated BSA by Kupffer cells might be mediated by both Kupffer cell lectin (fucose receptor) and mannose receptor. On the other hand, in vivo hepatic uptake of fucosylated BSA was inhibited to a greater extent by GdCl3 pretreatment than that of mannosylated BSA. Based on in vitro and in vivo experiments, it was concluded that fucosylated BSA is more Kupffer cell-selective because it exhibited a lower sinusoidal endothelial cell uptake than mannosylated BSA.

Development of cell-specific targeting systems for drugs and genes

Cell-specific targeting systems for drugs and genes have been developed by using glycosylated macromolecule as a vehicle that can be selectively recognized by carbohydrate receptors. Pharmacokinetic analyses of the tissue distribution of glycosylated proteins came to the conclusion that the surface density of the sugar moiety on the protein derivative largely determines the binding affinity for the receptors and plasma lectin. Many glycosylated delivery systems have been developed and their usefulness investigated in various settings. Galactosylated polymers, when properly designed, were found to be effective in delivering prostaglandin E1 and other low-molecular-weight drugs selectively to hepatocytes. In addition, glycosylated superoxide dismutase and catalase were successfully developed with minimal loss of enzymatic activity. A simultaneous targeting of these two enzymes to liver nonparenchymal cells significantly prevented hepatic ischemia/reperfusion injury. On the other hand, galactosylated catalase, a derivative selectively delivered to hepatocytes, effectively inhibited hepatic metastasis of colon carcinoma cells in mice. Finally, hepatocyte-targeted in vivo gene transfer was achieved by synthesizing a multi-functional carrier molecule, which condenses plasmid DNA, delivering DNA to hepatocytes through recognition by asialoglycoprotein receptors, and releasing DNA from endosomes/lysosomes into cytoplasm.

Synthesis and in vitro evaluation of potential anti-leishmanial targeted drugs of pyrimethamine

Pyrimethamine, an antimalarial drug, was found to be able to inhibit both enzymes (DHFR-TS and PTR1) of the leishmanial folate pathway, although this effect in vivo appears only in relatively high concentrations. To reach the parasites inside macrophage cells, where they are sheltered, targeted drugs of pyrimethamine, carboxymethyldextran-thiomannopyranoside-pyrimethamine (CMD-P), and succinyldextran-thiomannopyranoside-pyrimethamine (SD-P), were synthesized and assayed against L.(L.) amazonensis amastigotes. CMD-P has 2.43% and SD-P has 2.58% of pyrimethamine attached. At a CMD-P dose of 200 microg/mL (4.86 microg/mL pyrimethamine), the results were very promising, with a destruction of approximately 50% of the intracellular amastigotes, with no detectable toxicity to macrophage cells. SD-P in similar doses did not show good results, probably due to different patterns of drug release. These results open the possibility of treating leishmaniasis with a safe targeted drug of pyrimethamine released directly inside the macrophage cells, reducing the host systemic toxicity.

Synthesis and biological properties of antitumor-active conjugates of ADR with dextran

Three kinds of polymeric adriamycin (ADR) conjugates of dextran were synthesized, namely a dextran-Gly-Leu-Gly-ADR (DGLGA) conjugate with a lysosomally degradable tripeptide spacer group, a dextran-Gly-Leu-Gly-ADR-galactosamine (DGLGA-Ga) conjugate with a targeting moiety of galactosamine on DGLGA, and a dextran-C6H10-ADR (DC6A) conjugate with a hexamethylen spacer group. The content of the ADR moiety in the polymeric-drug conjugate was about 3 mol%. Enzyme hydrolysis of DGLGA and DC6A was carried out by incubation with papain. The total amount of ADR released after 48 h was 43 mol% for DGLGA and less than 1 mol% for DC6A. In an in vitro cytotoxicity experiment, the DGLGA-Ga conjugate has higher cytotoxic efficacy than the other conjugates for incubation with Hep-3B cells and consequently, the capability of targeting hepatoma cells of the galactosamine residue was determined. In contrast, for the incubation with SiHa cells of these conjugates, there was no significant cytotoxicity effect. The in vivo cytotoxic efficacy of each conjugate (20 mg ADR equiv./kg) against CT-26 mice colon cells implanted subcutaneously in Balb-C mice was studied. The DGLGA conjugate generated the best therapeutic effect with the presence of long-term survival (LTS) at day 50 (2/6).

Development of polymeric nanoparticulate drug delivery systems: evaluation of nanoparticles based on biotinylated poly(ethylene glycol) with sugar moiety

Liver specific polymeric nanoparticles were designed and synthesized from biotinylated poly(ethylene glycol) conjugated with lactobionic acid containing a galactose moiety (abbreviated as BEL). Synthesized BEL conjugate was identified by Fourier transform-infrared (FT-IR) and 1H-nuclear magnetic resonance (NMR) spectroscopy. The fluorescence spectroscopy data showed that BEL conjugate was self-assembled in water to form core-shell structure nanoparticles, and the critical association concentration (CAC) value was estimated as 0.028 g/l. From the transmission electron microscope (TEM) observation, the BEL nanoparticles were spherically shaped and ranged in size between 30 and 60 nm. The particle size distribution was measured by photon correlation spectroscopy (PCS), and the result was 41.2+/-11.7 nm. Anti-cancer drug all-trans-retinoic acid (ATRA) was loaded into the BEL nanoparticles for evaluating its efficacy as a drug delivery carrier. The crystallinities of ATRA and ATRA-loaded nanoparticles were examined by X-ray diffraction (XRD) patterns. The ATRA release kinetics from the BEL nanoparticles showed a pseudo zero-order pattern during 1-month period.

Synthesis of a poly(vinylpyrrolidone-co-dimethyl maleic anhydride) co-polymer and its application for renal drug targeting

We have synthesized a polymeric drug carrier, polyvinylpyrrolidone-co-dimethyl maleic anhydride [poly(VP-co-DMMAn)], for use in renal drug delivery. About 80% of the 10-kDa poly(VP-co-DMMAn) selectively accumulated in the kidneys 24 h after intravenous administration to mice. Although this accumulated poly(VP-co-DMMAn) was gradually excreted in the urine, about 40% remained in the kidneys 96 h after treatment. Poly(VP-co-DMMAn) was taken up by the renal proximal tubular epithelial cells and no cytotoxicity was noted. Higher doses did not produce toxicity in the kidneys or other tissues. In contrast, polyvinylpyrrolidone of the same molecular weight did not show any tissue-specific distribution. Poly(VP-co-DMMAn)-modified superoxide dismutase accumulated in the kidneys after intravenous administration and accelerated recovery from acute renal failure in a mouse model. In contrast, polyvinylpyrrolidone-modified superoxide dismutase and native superoxide dismutase were not as effective. Thus, poly(VP-co-DMMAn) is a useful candidate as a targeting carrier for renal drug delivery systems.

Anti-HBV effect of targeted lamivudy palmitate solid lipid nano-particles

AIM: To investigate the anti-HBV effect of targeted lamivudy palmitate solid lipid Nano-particles (LAP-SLN).

METHODS: The nano-particles modified by galactosides (LAP-GSLN) were prepared and delivered into 2.2.15 cells. HBsAg, HBeAg and HBVDNA of 2.2.15 cells were detected by ELISA and hepatitis B virus fluorescence polymerase chain reaction (PCR). The cytotoxicity of targeted LAP-GSLN on 2.2.15 cells were observed. Fifteen male mice (2 months old) were randomly divided into 3 groups: LAP-SLN group, LAP-GSLN group and LA group. Levels of lamivudine in serum, liver, kidney, lung and spleen tissue were detected by reversed-phase high performance liquid chromatography (RP-HPLC).

RESULTS: LAP-GSLN could be targeted to the liver. Liver LAP-GSLN content in LAP-GSLN group was 3.3 times of that in the LA group. HBV DNA was inhibited on the 4th day. HBV DNA in LAP-GSLN group and LA group with concentration of lamivudine at 10 mg/L was less than 1.11×10⁷ /L and 5.06×10⁹/L, respectively. Inhibition of HBsAg and HBeAg showed on the 6th day, the inhibition rate of LAP-GSLN on HBsAg and HBeAg with concentration of lamivudine at 0.01 mg/L was 52.9%, 53.9%, respectively; while the inhibition rate of LA on HBsAg and HBeAg was 32.2%, 31.1%, respectively. When the concentration of lamivudine was 10 mg/L, the inhibition rate of LAP-GSLN on HBsAg and HBeAg was 67.2%, 69.0%, respectively; while the inhibition rate of LA on HBsAg and HBeAg was 45.1%, 41.0%, respectively. No cytotoxic effect on 2.2.15 cells was found.

CONCLUSION: LAP-GSLN can target liver effectively in vivo and inhibit HBV expression and DNA replication.

Development of a polymeric nanoparticulate drug delivery system

This paper reports the synthesis of polymeric nanoparticles from a sugar-containing conjugate for liver-specific drug delivery. The conjugate was composed of lactobionic acid, diamine-terminated poly(ethylene glycol) and cholic acid (abbreviated as LEC). The conjugate was characterized by (1)H NMR and FT-IR spectroscopy measurements. In aqueous media, the conjugate can self-assemble to form core-shell type nanoparticles, and the formation of a core-shell structure was observed by fluorescence spectroscopy. The critical association concentration (CAC) of the LEC conjugate nanoparticles was determined from fluorescence excitation spectra to be 0.05 g/l. The LEC nanoparticles were mostly spherical with sizes ranging from 10 to 30 nm. Clonazepam (CNZ) was used as a model hydrophobic drug, and was incorporated into the hydrophobic core of the nanoparticles. CNZ was released more slowly at a higher drug loading due to drug crystallization.

Clinical pharmacokinetics of cytarabine formulations

Cytarabine (cytosine arabinoside, Ara-C) is an effective chemotherapeutic agent for the treatment of acute myelogenous leukaemia and lymphocytic leukaemias. As cytarabine is an S-phase-specific drug, prolonged exposure of cells to cytotoxic concentrations is critical to achieve maximum cytotoxic activity. However, the activity of cytarabine is decreased by its rapid deamination to the biologically inactive metabolite uracil arabinoside. This rapid deamination is the reason for the ongoing search for effective formulations and derivatives of cytarabine that cannot be deaminated and exhibit better pharmacokinetic parameters. Protection of cytarabine from fast degradation and elimination has been investigated by encapsulating the drug into pharmaceutically acceptable carriers. Cytarabine derivatives have shown promise in vitro and in animal models. For example, ancitabine (cyclocytidine), enocitabine and cytarabine ocfosfate have been used clinically in Japan. Cytarabine encapsulated into multivesicular liposomes has been approved in several countries for the intrathecal treatment of lymphomatous meningitis. Although many compounds have been investigated, few cytarabine derivatives are currently available for clinical use. Further research is needed to improve the efficacy of cytarabine against haematological and solid tumours.

Pharmacokinetic analysis of lectin-dependent biodistribution of fucosylated bovine serum albumin: a possible carrier for Kupffer cells

To examine the potential utility of fucosylation of drug carriers for targeted drug delivery to Kupffer cells, the pharmacokinetics of (111)In-labeled fucosylated bovine serum albumin (Fuc-BSA) with different numbers of fucose residues (11, 16, 25, 31 or 41) was studied. After intravenous injection in mice, all (111)In-Fuc-BSAs were mainly delivered to the liver and their hepatic uptake became saturated when the dose was increased. Of these derivatives, only (111)In-Fuc41-BSA showed a slow plasma elimination at low doses, suggesting an interaction with blood components. Examination of binding conditions as well as electrophoretic analysis of the binding components indicated that the serum-type mannan binding protein (MBP) is responsible. Kupffer cells, which possess fucose receptors, showed the highest uptake of (111)In-Fuc41-BSA, followed by endothelial cells and hepatocytes. The hepatic uptake of (111)In-Fuc41-BSA was inhibited by co-injection of Gal42-BSA, but not by Man46-BSA. On the other hand, excess Fuc41-BSA inhibited the hepatic uptake of (111)In-Man46-BSA, while (111)In-Gal42-BSA did not: These findings suggest that not only the fucose receptors on Kupffer cells but also other lectins are involved in the biodistribution of Fuc-BSAs. To understand how the degree of fucose modification affects the binding affinity of Fuc-BSA with hepatic lectins and serum MBP, a pharmacokinetic analysis was performed based on a physiological model. The Michaelis constant of the hepatic uptake of (111)In-Fuc-BSA decreased with an increasing number of fucose units, and the intrinsic hepatic clearance of (111)In-Fuc25-, (111)In-Fuc31- and (111)In-Fuc41-BSAs was close to, or much greater than, the hepatic plasma flow rate, indicating efficient hepatic uptake of these derivatives. These results suggest that fucosylation is a potentially useful method making drug carriers selective for Kupffer cells, although extensive modification might result in retarded delivery due to binding to other lectins like MBP.

Synthesis and pharmacological activity of a novel water-soluble hepatocyte-specific polymeric prodrug of prostaglandin E(1) using lactosylated poly(L-glutamic hydrazide) as a carrier

A novel polymeric prodrug of prostaglandin E(1) (PGE(1)) was synthesized using lactosylated poly(L-glutamic hydrazide) (Lac-NH-PLGA) as a targetable carrier to hepatocytes. Poly(L-glutamic hydrazide) (PLGA-HZ) was prepared by reacting poly(gamma-benzyl-L-glutamate) with hydrazine monohydrate, followed by coupling with lactose via a hydrazone linkage. Then the lactosylated PLGA-HZ was reduced by sodium cyanoborohydride (NaBH(3)CN) in order to make the linkage irreversible (Lac-NH-PLGA). Finally, PGE(1) was bound to hydrazide moieties remaining in Lac-NH-PLGA without any condensing agent under weakly acidic conditions (pH 5) where PGE(1) would be chemically most stable at room temperature (PGE(1) conjugate). The PGE(1) conjugate prepared was sufficiently water-soluble in spite of the hydrophobic nature of its backbone (-NH-CH-CO-) and PGE(1) itself. After intravenous injection in mice, the [111In]PGE(1) conjugate rapidly accumulated in the liver, whereas [111In]PLGA-HZ did not, suggesting the involvement of a galactose-specific mechanism in the uptake of the [111In]PGE(1) conjugate. Fractionation of liver cells revealed that the [111In]PGE(1) conjugate was preferentially taken up by liver parenchymal cells. The pharmacological activity was examined in mice with fulminant hepatitis induced by intraperitoneal injection of carbon tetrachloride. Intravenous injection of the PGE(1) conjugate at a dose of 1 mg (0.065 mg PGE(1))/kg effectively inhibited the increase in plasma glutamic pyruvic transaminase (GPT) activity compared with that of free PGE(1) at a dose of 0.065 or 0.65 mg/kg. These results suggest that the PGE(1) conjugate is an excellent prodrug for the treatment of fulminant hepatitis.

Self-assembled hydrogel nanoparticles from curdlan derivatives: characterization, anti-cancer drug release and interaction with a hepatoma cell line (HepG2)

Self-assembled hydrogel nanoparticles were synthesized from carboxymethylated (CM)-curdlan, substituted with a sulfonylurea (SU) as a hydrophobic moiety for self-assembly. The degree of SU substitution was 2.4, 5.6, or 7.2 SU groups per hundred anhydroglucose units of curdlan. The physicochemical properties of the self-assembled hydrogel nanoparticles (DS 2.4, DS 5.6, and DS 7.2) in aqueous media were characterized by dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy. The mean diameter of all samples was less than 300 nm with a unimodal size distribution. The critical aggregation concentrations (CAC) of self-assembled hydrogel nanoparticles in distilled water were 4.2 x 10(-2), 3.1 x 10(-2) and 1.9 x 10(-2) mg/ml for DS 2.4, 5.6 and 7.2, respectively. The loading and release of all-trans retinoic acid (ATRA) was studied. The ATRA loading efficiencies and loading contents of CM-curdlan/SU nanoparticles increased as the degree of SU substitution increased. The ATRA release rate was controlled by the degree of substitution and drug-loading. For specific interaction with a hepatic carcinoma cell line (HepG2), CM-curdlan was additionally conjugated with lactobionic acid (LBA; galactose moiety) (5.5 LBA molecules per hundred glucose units). HepG2 was strongly luminated by ligand-receptor interactions with fluorescence-labeled LBA/CM-curdlan/SU hydrogel nanoparticles. The luminescence was not observed for other control cases. It is concluded that LBA/CM-curdlan/SU hydrogel nanoparticles are a useful drug carrier for the treatment of liver cancer, because of the potential immunological enhancement activities of CM-curdlan in the body, the ligand-receptor mediated specific interactions, and the controlled release of the anti-cancer drug.

Dextrans for targeted and sustained delivery of therapeutic and imaging agents

Dextrans are glucose polymers which have been used for more than 50 years as plasma volume expanders. Recently, however, dextrans have been investigated for delivery of drugs, proteins/enzymes, and imaging agents. These highly water soluble polymers are available commercially as different molecular weights (M(W)) with a relatively narrow M(W) distribution. Additionally, dextrans contain a large number of hydroxyl groups which can be easily conjugated to drugs and proteins by either direct attachment or through a linker. In terms of pharmacokinetics, the intact polymer is not absorbed to a significant degree after oral administration. Therefore, most of the applications of dextrans as macromolecular carriers are through injectable routes. However, a few studies have reported the potential of dextrans for site (colon)-specific delivery of drugs via the oral route. After the systemic administration, the pharmacokinetics of the conjugates of dextran with therapeutic/imaging agents are significantly affected by the kinetics of the dextran carrier. Animal and human studies have shown that both the distribution and elimination of dextrans are dependent on the M(W) and charge of these polymers. Pharmacodynamically, conjugation with dextrans has resulted in prolongation of the effect, alteration of toxicity profile, and a reduction in the immunogenicity of drugs and/or proteins. A substantial number of studies on dextran conjugates of therapeutic/imaging agents have reported favorable alteration of pharmacokinetics and pharmacodynamics of these agents. However, most of these studies have been carried out in animals, with only a few being extended to humans. Future studies should concentrate on barriers for the clinical use of dextrans as macromolecular carriers for delivery of drugs, proteins, and imaging agents.

Pharmacokinetics and in vivo gene transfer of plasmid DNA complexed with mannosylated poly(L-lysine) in mice

To achieve mannose receptor-mediated, cell-specific, in vivo gene transfer by intravenous injection of plasmid DNA, mannosylated poly(L-lysine) (Man-PLL) was synthesized as a carrier molecule, and mixed with a plasmid DNA encoding chloramphenicol acetyltransferase (CAT) gene to form DNA/Man-PLL complex. The particle size and zeta potential of DNA/Man-PLL (prepared at 1:0.7 on a weight basis) were determined to be 220 nm and +12 mV, respectively. The pharmacokinetics of the DNA/Man-PLL complex was assessed in mice using 32P-labeled DNA ([32P]DNA). After intravenous injection of [32P]DNA/Man-PLL, the radioactivity in plasma fell rapidly and was recovered mainly in the liver nonparenchymal cells. The amount in the liver reached more than 80% of the dose. Radioactivity observed in kidney, lung, and spleen was very low compared to that in the liver. Then, the in vivo gene expression after intravenous injection of DNA/Man-PLL was examined by a CAT assay. Highest CAT activity was detected in the liver, but no activity was detected in the lung, kidney, and spleen. These results clearly indicate that a cell-specific gene delivery system can be developed by regulating the biodistribution of DNA/carrier complex through the control of its physicochemical properties.

Liver-directed gene therapy: promises, problems and prospects at the turn of the century

Although liver-directed gene therapy arrived later than gene therapy directed at bone marrow cells, intrinsic advantages of the liver as a target organ make it likely that gene therapy for liver diseases will be among the first therapeutically relevant applications of this treatment modality at the onset of the 21st century. Vectorology for gene transfer to the liver is advancing rapidly, and it is safe to predict that gene therapy vehicles that will be in clinical use a decade from now, have not yet been developed. None of the currently available modes of gene transfer to the liver is optimal for all types of applications. Nonetheless, the concerted effort of many investigators has provided a wide choice of non-viral and viral vectors for gene transfer to the liver for use in specific situations. Original strategies for liver-directed gene therapy included substitution of missing gene products, overexpression of intrinsic or extrinsic genes and inhibition of expression of specific genes. To the list is now added the possibility of site-specific correction or generation of mutations within specific genes in somatic cells of living adult animals. Thus, despite some initial faux pas, liver-directed gene therapy is poised to make an important impact on health care in the year 2000 and beyond.

Structural requirements for alkylglycoside-type renal targeting vector

PURPOSE

We have previously shown Glc-S-C7-Me (octyl beta-D-thioglucoside) exhibits renal targeting potential in vivo in addition to its specific binding to the renal membrane fraction in vitro. Thus, "alkylglycoside" is considered to be a novel targeting vector for the kidney (1,2). The present study is designed to clarify the structural requirements for alkylglycoside as a renal targeting vector.

METHODS

Inhibitory effects of various sugars and glycosides on 3H-Glc-S-C7-Me binding to the kidney membrane fraction were evaluated by a centrifugation method.

RESULTS

As far as the sugar moiety is concerned, no other sugars except D-aldohexose and D-aldohexose derivatives (containing F, S, and N) showed greater inhibition than D-glucose. Therefore, octylthio derivatives of various D-aldohexose were prepared and their inhibitory effects were investigated. The following findings were obtained: Equatorial OH at 4 position is essential; OH at 2 position can have either orientation or be deleted. As far as the alkyl moiety is concerned, the length, branching and electrical environment in the region of the glycoside bond are important; aromatic structures can substitute for the alkyl portion; the preferred glycoside bonding atom is as follows: S > NH > O.

CONCLUSIONS

The structural requirements for the renal targeting vector have been identified to be as follows: a hydrophobic group (alkyl chain or aromatic ring) should be introduced to a sugar (D-glucose, D-mannose, or 2-deoxy-D-glucose) via a beta-glycoside binding atom (S > NH > O).

Pharmacokinetic evaluation of mannosylated bovine serum albumin as a liver cell-specific carrier: quantitative comparison with other hepatotropic ligands

To assess the feasibility of mannosylated macromolecules as a liver-specific carrier system, hepatic uptake characteristics of mannosylated bovine serum albumin (Man-BSA) were pharmacokinetically investigated. After intravenous injection, 111In-Man18-BSA accumulated in the liver up to 70% of dose at 2h; the endothelial cells and Kupffer cells contributed about 66% and 21% of the uptake, respectively. In single-pass perfusion experiments using rat liver at varying inflow concentrations (0.1-2.0 microg/ml), 111In-Man18-BSA and 111In-Man33-BSA were continuously extracted by the liver and their extraction ratios decreased with the increasing inflow concentrations. The outflow curves of each 111In-Man-BSA at three concentrations were simultaneously fitted to a pharmacokinetic model including a binding to the cell surface and an internalization, by using a nonlinear regression program MULTI(RUNGE). The binding constant augmented with the increase in the number of mannose per BSA, whereas the internalization rate constant was quite comparable for both derivatives. The pharmacokinetic analysis has demonstrated that the uptake process of 111In-Man-BSA is characterized to possess fewer binding sites and a greater internalization rate in comparison with other liver-specific carriers such as galactosylated, succinylated and cationized BSAs. These results will provide useful information in designing drug targeting systems to the liver nonparenchymal cells via mannose receptors.

Disposition characteristics of glycosylated poly(amino acids) as liver cell-specific drug carrier

Potentials of glycosylated poly(amino acids) as carriers of drugs and/or polynucleotides to the liver were studied in mice in detail. Poly-L-glutamic acid (PLGA) and poly-L-lysine (PLL) were selected as carrier backbones and modified with 2-imino-2-methoxyethyl 1-thiogalactoside or mannoside to obtain galactosylated and mannosylated derivatives. After intravenous injection in mice at a dose of 1 mg/kg, Gal-PLGA and Man-PLGA were selectively taken up by the liver parenchymal cells (PC) and liver nonparenchymal cells (NPC), respectively. Moreover, the uptake of Gal-PLGA and Man-PLGA by the liver were significantly inhibited by the presence of Gal-BSA and Man-BSA, respectively. On the other hand, PLL was targeted to the liver without glycosylation. However, Gal-PLL and Man-PLL showed higher accumulation in the liver than unmodified PLL. Although Gal-PLL and Man-PLL showed different distribution between PC and NPC from that of PLL, the effect of the modifications was less pronounced than the cases of PLGA derivatives. In addition, these glycosylated poly(amino acids) investigated, regardless of the type of amino acid or the sugar grafted, were rapidly degraded to be eluted in the low molecular weight fractions in a gel filtration chromatography. These results suggest that glycosylated PLGAs can be useful carriers of low molecular drugs to the liver cells through conjugation, while glycosylated PLLs could be targetable carriers to the cells after the reduction of their cationic charge by complex formation with polynucleotides.

Asialoglycoprotein receptor-mediated gene transfer using novel galactosylated cationic liposomes

We synthesized three novel galactosylated cholesterol derivatives, cholesten-5-yloxy-N-(4-((1-imino-c-beta-D-thiogalactosyl+ ++-ethyl)amino) butyl)formamide (Gal-C4-Chol) and its ethyl formamide and hexyl formamide analogues (Gal-C2-Chol, Gal-C6-Chol), to prepare liposomal gene carriers possessing the cationic charge necessary for plasmid DNA binding and galactose residues as a targetable ligand for liver parenchymal cells. Liposome/DNA complexes prepared with these lipids showed low cytotoxicity in human hepatoma HepG2 cells. Gal-C4-Chol/DC-Chol/DOPE(3:3:4) liposomes, consisting of 3:3:4 mixtures of Gal-C4-Chol, 3beta[N',N', N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol), and dioleoylphosphatidylethanolamine (DOPE), showed higher transfection activity and [32P]DNA uptake than DC-Chol/DOPE(6:4) liposomes. The presence of 20 mM galactose significantly inhibited both transfection efficiency and uptake of DNA of Gal-C4-Chol/DC-Chol/DOPE(3:3:4) and Gal-C4-Chol/DOPE(6:4) liposomes, but not those of DC-Chol/DOPE(6:4) liposomes. These results indicate that the liposome/DNA complexes prepared using novel galactosylated cholesterol derivatives are efficiently recognized by asialoglycoprotein receptors and internalized and lead to gene expression. In addition, we found that the galactosylated cholesterol derivative with a longer spacer showed higher transfection activity.

Extravasation of macromolecules

Macromolecules can extravasate across the normal endothelium by transcapillary pinocytosis as well as by passage through interendothelial cell junctions, gaps or fenestrae. The main biological factors that control extravasation of a solute include regional differences in the capillary structures, the disease state of the organ or tissue, and the rate of blood and lymph supply. Physicochemical properties that are of profound significance in the extravasation of macromolecules are molecular size, shape, charge and hydrophilic/lipophilic balance (HLB) characteristics. Extravasation of small drugs, proteins, oligonucleotides and genes can be controlled by conjugating or forming complexes with macromolecular carriers. This requires a thorough understanding of the relationship between the chemical structures, physicochemical properties and the pharmacokinetics of both carrier and active molecules. This review article discusses the extravasation of macromolecules from the view points of pharmacokinetics and drug delivery systems, with the main emphasis on the extravasation across the liver, kidney and tumor capillaries.

Targeted delivery of plasmid DNA complexed with galactosylated poly(L-lysine)

Galactose was introduced to poly(L-lysine) (PLL) with an average molecular weight of 13,000 to develop a hepatocyte-specific carrier for gene drugs. The pharmacokinetic characteristics of a model plasmid, pCAT (plasmid DNA encoding chloramphenicol acetyltransferase reporter gene), complexed with galactosylated PLL (Gal-PLL) was studied in mice in relation to its physicochemical properties. pCAT/Gal-PLL complex at a ratio of 1:0.6 (w/w) has a zeta potential of -20 mV and a mean particle size of about 180 nm. After intravenous injection, [32P]pCAT/Gal-PLL was rapidly eliminated from the circulation and preferentially taken up by the liver's parenchymal cells. The hepatic uptake of [32P]pCAT/Gal-PLL was significantly inhibited by prior administration of Gal-bovine serum albumin, suggesting that the uptake was mediated by the asialoglycoprotein receptors on hepatocytes. In vitro transfection experiments using a hepatoma cell line expressing the asialoglycoprotein receptor revealed that pCAT/Gal-PLL gave a high CAT gene expression whereas pCAT complexed with unmodified PLL failed to transfect the cells.

Design of macromolecular biological response modifier by immobilizing of D-glucose analogue of muramyl dipeptide on carboxymethyl-dextran having mannose branches

It is well known that muramyl dipeptide is a minimum required structure of bacterial peptidoglycan responsible for immunoadjuvant activity. Since mannose receptors exist on the surface of macrophages, polymers with branched mannose residues are expected to target moieties to macrophages. To achieve an efficient delivery of D-glucose analogue of muramyl dipeptide (GADP) via receptor-mediated endocytosis by mannose receptors on the surface of macrophages, GADP/carboxymethyl-dextran (CM-Dex)/Man conjugate was synthesized. Moreover, to study the effect of the introduction of mannose residues, we also synthesized GADP/CM-glucomannan (CM-GM) and GADP/CM-Dex conjugates. The immunological enhancement activities of their conjugates were evaluated by measurements of glucose consumption and beta-D-glucuronidase activity from macrophage-like cells. The GADP/CM-Dex/Man and GADP/CM-GM conjugates showed higher immunological enhancement activity than the GADP/CM-Dex conjugate. The immunological enhancement activity of GADP/CM-Dex/Man and GADP/CM-GM conjugates was decreased to the same level of immunological enhancement activity of GADP/CM-Dex conjugate under the presence of excess mannose. These results suggested that the introduction of mannose residues into GADP/CM-Dex conjugate could increase the affinity against macrophage and the immunological enhancement activity of GADP/CM-Dex conjugate itself.

Synthesis of lactosyl phosphate diester derivatives of nucleosides

Derivatives of the lactosyl phosphate diester and the lactosyl thiophosphate diester of 1-(beta-D-arabinofuranosyl)cytosine (Ara-C) and 9-(beta-D-arabinofuranosyl)adenine (Ara-A) were synthesized by condensation of 3-hydroxypropyl lactoside and a protected Ara-C or Ara-A via H-phosphonate methodology and phosphoramidite methodology, respectively.