N-(2-hydroxypropyl)methacrylamide copolymers targeted to the hepatocyte galactose-receptor: pharmacokinetics in DBA2 mice

Active transport nanochelators for the reduction of liver iron burden in iron overload

Liver dysfunction and failure account for a major portion of premature deaths in patients suffering from various iron associated pathogeneses, particularly primary and secondary iron overload disorders, despite intensive treatment. The liver is a central player in iron homeostasis and a major iron storage organ, and currently, there are no active approaches for the excretion of excess liver iron. Herein, we report a new method for the rapid reduction of iron burden in iron overload diseases by developing a new class of liver targeted nanochelators with favorable pharmacokinetics and biodistribution. The new nanochelators bypass the reticuloendothelial system and specifically target hepatocytes without non-specific accumulation in other organs. The targeted nanochelators bound and neutralized excess iron in the liver and from the vasculature and, eventually leading to rapid hepatobiliary excretion of labile iron. Further, these rapidly excreted nanochelators did not induce toxicity in the liver, were highly cytocompatible in both iron overload and non-loaded conditions, and were promising in mitigating iron triggered free radical oxidative damage. These studies provide key insights into the development of organ targeted nanochelating systems and the rapid reduction of iron burden in vivo. This methodology allows for further development of nanotherapeutics for specific iron overload diseases.

Self-Assemble Amphiphilic PEO-PPO-PEO Tri-Block Co-Polymeric Methotrexate Nanomicelles to Combat MCF7 Cancer Cells

BACKGROUND

Methotrexate (MTX) is a water-insoluble, anti-tumor agent that causes adverse effects like bone marrow suppression, chronic interstitial obstructive pulmonary disease, hepatotoxicity, leukopenia, interstitial pneumonitis and nephrotoxicity with slow drug release rate.

OBJECTIVE

The present study aimed to successfully incorporate MTX into novel-targeted Pluronic (PEOPPO- PEO tri-block co-polymer) F127 polymeric micelles intended for intravenous administration with improved drug loading and sustained release behavior necessary to achieve better efficacy of MTX.

METHODS

MTX-loaded Pluronic F127 micelles were characterized for critical micelle concentration, particle size and zeta potential,¹H NMR, drug loading, encapsulation efficiency characterization, cell uptake, in vitro release study along with partition coefficient and solubilization thermodynamics.

RESULTS

The micellar formulation resulted in nano size 27.32±1.43nm of PF127/SDS, as compared to Pluronic F127 micelles or PF127/Phosphatidyl choline which were 30.52±1.18nm and 154.35±5.5nm in size, respectively. The uptake of PF127/SDS micellar formulation incorporating Rhodamine 123 in MCF7 cancer cells was found to be higher (84.25%) than PF127/PC, PF127 and MTX i.e. 66.26%, 73.59% and 53% respectively. The in vitro MTX release from PF127, PF127/SDS and PF127/PC polymeric micelles formulations was observed to be 69%, 69.5% and 66% at 12 h whereas 80.89%, 77.67% and 78.54% after 24 h, respectively and revealed a sustained release. MTX-loaded PF127/SDS micelles showed high partition coefficient and negative free energy of solubilization compared to PF127 and PF127/PC which signify self-assembly behavior and thermodynamic stability towards higher dissociation.

CONCLUSION

It was finally concluded that MTX-loaded PF127/SDS micelles act as a potential anticancer delivery system in comparison to PF127/PC and PF127 to combat tumor cells by enhancing their cellular uptake targeting with sustained release pattern and reducing the thermodynamic instability. Thus, PF127/SDS micellar formulation can provide a useful alternative dosage form for intravenous administration of MTX.

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

Nanoparticles in Gastrooncology

BACKGROUND

Gastrointestinal malignancies have the greatest incidence and cancer-associated death rates worldwide. Routine therapeutic modalities include surgery, chemotherapy and radiation but they often fail to reach the goal of cancer-free survival.

SUMMARY

In the light of this urgent medical need for the treatment of GI tumors, nanotech-nology-based approaches, i.e. nanomedicine, promise new therapeutic options. Using nanoparticles instead of classically designed drugs, targeting anticancer agents directly to the tumor site may revolutionize both diagnostic and therapeutic tools thereby facilitating the identification and elimination of malignant cells. Importantly, diagnostic insight and therapeutic effects can be achieved simultaneously through the same nanoparticle. Additionally, a nanoparticle may be loaded with more than one agent, thereby further increasing the value and power of the nanotechnology approach in oncologic therapeutic concepts. Although most insight into mechanisms of nanomedicine has been gained from in vitro and preclinical in vivo models, few clinical trials have been conducted, and nanomedicine-based concepts are already part of standard treatment algorithms. However, despite substantial progress it remains a challenge to design nanoparticles that feature all desirable characteristics at the same time.

KEY MESSAGES

This review seeks to provide substantial insight into the current status of nanomedicine-based approaches employed for diagnostic and/or therapeutic purposes in the field of gastrointestinal cancers by highlighting achievements and pointing out unresolved issues that need to be further addressed by future research attempts.

Nanomedicine as a putative approach for active targeting of hepatocellular carcinoma

The effectiveness of chemotherapy in hepatocellular carcinoma (HCC) is restricted by chemo-resistance and systemic side effects. To improve the efficacy and safety of chemotherapeutics in HCC management, scientists have attempted to deliver these drugs to malignant tissues using targeted carriers as nanoparticles (NPs). Among the three types of NPs targeting (active, passive, and stimuli-responsive), active targeting is the most commonly investigated in HCC treatment. Despite the observed promising results so far, clinical research on nanomedicine targeting for HCC treatment still faces many challenges.These include batch-to-batch physicochemical properties' variations, limiting large scale production and insufficient data on human and environmental toxicities. This review summarized the characteristics of different nanocarriers, ligands, targeted receptors on HCC cells and provided recommendations to overcome the challenges, facing this novel line of treatment for HCC.

Nanomedicines for Malaria Chemotherapy: Encapsulation vs. Polymer Therapeutics

Malaria is one of the oldest infectious diseases that afflict humans and its history extends back for millennia. It was once prevalent throughout the globe but today it is mainly endemic to tropical regions like sub-Saharan Africa and South-east Asia. Ironically, treatment for malaria has existed for centuries yet it still exerts an enormous death toll. This contradiction is attributed in part to the rapid development of resistance by the malaria parasite to chemotherapeutic drugs. In turn, resistance has been fuelled by poor patient compliance to the relatively toxic antimalarial drugs. While drug toxicity and poor pharmacological potentials have been addressed or ameliorated with various nanomedicine drug delivery systems in diseases like cancer, no clinically significant success story has been reported for malaria. There have been several reviews on the application of nanomedicine technologies, especially drug encapsulation, to malaria treatment. Here we extend the scope of the collation of the nanomedicine research literature to polymer therapeutics technology. We first discuss the history of the disease and how a flurry of scientific breakthroughs in the latter part of the nineteenth century provided scientific understanding of the disease. This is followed by a review of the disease biology and the major antimalarial chemotherapy. The achievements of nanomedicine in cancer and other infectious diseases are discussed to draw parallels with malaria. A review of the current state of the research into malaria nanomedicines, both encapsulation and polymer therapeutics polymer-drug conjugation technologies, is covered and we conclude with a consideration of the opportunities and challenges offered by both technologies.

New molecular targets for functionalized nanosized drug delivery systems in personalized therapy for hepatocellular carcinoma

Hepatocellular carcinoma, the most frequent solid tumor of the liver, has a very poor prognosis, being the second most common cause of death from cancer worldwide. The incidence and mortality of this liver tumor are increasing in most areas of the world as a consequence of aging and the emerging of new risk factors such as the metabolic syndrome, beside the recognized role of hepatitis B and C viral infections and alcohol abuse. Despite the increasing knowledge on the molecular mechanisms underlying hepatic carcinogenesis, effective therapeutic strategies are still an unmet clinical need. Efforts have been made to develop selective drugs as well as effective targeted drug delivery systems. The development of novel drug carriers for therapeutic molecules can indeed offer a valuable strategy to ameliorate the efficacy of HCC treatment. In this review, we discuss recent drug delivery strategies for HCC treatment based on the exploitation of targeted nanoparticles (NPs). Indeed, a few of these platforms have achieved an advanced stage of preclinical development. Here, we review the most promising drug nanovehicles based on both synthetic and natural polymers, including polysaccharides that have emerged for their biocompatibility and biodegradability. To maximize site-selectivity and therapeutic efficacy, drug delivery systems should be functionalized with ligands which can specifically recognize and bind targets expressed by HCC, namely cell membrane associated antigens, receptors or biotransporters. Cell surface and intracellular molecular targets are exploited either to selectively deliver drug-loaded nanovehicles or to design novel selective therapeutics. In conclusion, the combination of novel and safe drug delivery strategies based on site-specific targeted drug nanovehicles with therapeutic molecular targets may significantly improve the pharmacological efficacy for the treatment of HCC.

Angiogenesis regulation by nanocarriers bearing RNA interference

Since the approval of bevacizumab as anti-angiogenic therapy in 2004 by the FDA, an array of angiogenesis inhibitors have been developed and approved. However, results were disappointing with regard to their therapeutic efficacy. RNA interference approaches offer the possibility of rational design with high specificity, lacking in many current drug treatments for various diseases including cancer. However, in vivo delivery issues still represent a significant obstacle for widespread clinical applications. In the current review, we summarize the advances in the last decade in the field of angiogenesis-targeted RNA interference approaches, with special emphasis on oncology applications. We present pro-angiogenic and anti-angiogenic factors as potential targets, experimental evidence and clinical trials data on angiogenesis regulation by RNA interference. Consequent challenges and opportunities are discussed.

Carbohydrate-based amphiphilic nano delivery systems for cancer therapy

Nanoparticles (NPs) are novel drug delivery systems that have been attracting more and more attention in recent years, and have been used for the treatment of cancer, infection, inflammation and other diseases. Among the numerous classes of materials employed for constructing NPs, organic polymers are outstanding due to the flexibility of design and synthesis and the ease of modification and functionalization. In particular, NP based amphiphilic polymers make a great contribution to the delivery of poorly-water soluble drugs. For example, natural, biocompatible and biodegradable products like polysaccharides are widely used as building blocks for the preparation of such drug delivery vehicles. This review will detail carbohydrate based amphiphilic polymeric systems for cancer therapy. Specifically, it focuses on the nature of the polymer employed for the preparation of targeted nanocarriers, the synthetic methods, as well as strategies for the application and evaluation of biological activity. Applications of the amphiphilic polymer systems include drug delivery, gene delivery, photosensitizer delivery, diagnostic imaging and specific ligand-assisted cellular uptake. As a result, a thorough understanding of the relationship between chemical structure and biological properties facilitate the optimal design and rational clinical application of the resulting carbohydrate based nano delivery systems for cancer therapy.

Use of New Aminosugar Derivatives as Comonomers for the Synthesis of Glycosylated Poly(Amido-Amines)

New sugar functionalized poly(amido-amines) (PAA) polymers were synthesized. The PAA made by the addition polymerization of 2-methylpiperazine-2,2-bisacrylamidoacetic acid (ISA) was chosen for its potential applications in the biomedical field and the sugar monomers were obtained by chemical and enzymatic synthetic strategies. Specifically, the 2-aminoethyl fi-D-galactopyranosyl monomer was directly obtained by enzymatic catalysis, while the 2-aminoethyl amide and the 3-aminopropyl amide of lactobionic acid were obtained by ning-opening reactions of the corresponding lactone. The presence of sugar moieties in the polymer chains was confirmed by FT-IR, 'H NMR, 13C NMR analysis and calorimetric assay. The sugar content of polymer derivatives is sufficient for targeting purpose, making these compounds potential soluble drug carriers.

Carbohydrate-based materials for targeted delivery of drugs and genes to the liver

The insult to liver by toxic materials leads to cirrhosis, hepatitis and cancer. Upon administration, drugs accumulate in liver, which is systemically cleared by reticuloendothelial system. However, specific targeting of drugs to liver is a serious challenge. Specific delivery of molecules to hepatocytes is accomplished by targeting cell surface lectins, asialoglycoprotein receptors. Asialofetuin, N-acetyl glucosamine and galactose are high-affinity ligands of asialoglycoprotein receptors. The bioconjugation of drugs, fluorescent molecules and gene delivery vectors with lectin-targeting agents, and their delivery in liver hepatocytes, is discussed. Mannose and N-acetyl glucosamine conjugates are evaluated for their delivery to hepatic stellate and kupffer cells. The glycosylated gene and drug delivery vectors in clinical trials are outlined.

Prodrug applications for targeted cancer therapy

Prodrugs are widely used in the targeted delivery of cytotoxic compounds to cancer cells. To date, targeted prodrugs for cancer therapy have achieved great diversity in terms of target selection, activation chemistry, as well as size and physicochemical nature of the prodrug. Macromolecular prodrugs such as antibody-drug conjugates, targeted polymer-drug conjugates and other conjugates that self-assemble to form liposomal and micellar nanoparticles currently represent a major trend in prodrug development for cancer therapy. In this review, we explore a unified view of cancer-targeted prodrugs and highlight several examples from recombinant technology that exemplify the prodrug concept but are not identified as such. Recombinant "prodrugs" such as engineered anthrax toxin show promise in biological specificity through the conditionally targeting of multiple cellular markers. Conditional targeting is achieved by structural complementation, the spontaneous assembly of engineered inactive subunits or fragments to reconstitute functional activity. These complementing systems can be readily adapted to achieve conditionally bispecific targeting of enzymes that are used to activate low-molecular weight prodrugs. By leveraging strengths from medicinal chemistry, polymer science, and recombinant technology, prodrugs are poised to remain a core component of highly focused and tailored strategies aimed at conditionally attacking complex molecular phenotypes in clinically relevant cancer.

Albumin-drug conjugates in the treatment of hepatic disorders

INTRODUCTION

This review deals with the use of serum albumin (SA) as a carrier for the selective delivery of drugs to liver cells.

AREAS COVERED

The synthesis and properties of the SA conjugates prepared to enhance the performance of the drugs used in the treatment of viral hepatitis, hepatocellular carcinoma (HCC), liver micrometastases and hepatic fibrosis are reported.

EXPERT OPINION

Studies in humans and laboratory animals demonstrated the capacity of SA conjugates to accomplish a liver targeting of the drugs, but at the same time underscored their limits and drawbacks, which can explain why to date these complexes did not reach a practical application. The major drawback is the need of administration by intravenous route, which prevents long-term daily treatments as required by some liver pathologies, such as chronic virus hepatitis and fibrosis. At present, only a conjugate carrying doxorubicin and addressed to the treatment of HCC showed in laboratory animals a solid potentiality to improve the value of the coupled drug. In the future, conjugation to SA could remain a successful strategy to permit the administration of drugs with rapid resolutive effects inside liver cells without causing severe extrahepatic adverse reactions.

Cathepsin B-cleavable doxorubicin prodrugs for targeted cancer therapy (Review)

Doxorubicin (DOX) is one of the most effective cytotoxic anticancer drugs used for the treatment of hematological malignancies, as well as a broad range of solid tumors. However, the clinical applications of this drug have long been limited due to its severe dose-dependent toxicities. Therefore, DOX derivatives and analogs have been developed to address this issue. A type of DOX prodrug, cleaved by cathepsin B (Cat B), which is highly upregulated in malignant tumors and premalignant lesions, has been developed to achieve a higher DOX concentration in tumor tissue and a lower concentration in normal tissue, so as to enhance the efficacy and reduce toxicity to normal cells. In this review, we focused on Cat B-cleavable DOX prodrugs and discussed the efficacy of these prodrugs, demonstrated by preclinical and clinical developments.

Tropism ablation and stealthing of oncolytic adenovirus enhances systemic delivery to tumors and improves virotherapy of cancer

Intravenous delivery of therapeutic virus particles remains a major goal for virotherapy of metastatic cancer. Avoiding phagocytic capture and unwanted infection of nontarget cells is essential for extended plasma particle kinetics, and simply ablating one or the other does not give extended plasma circulation. Here we show that polymer coating of adenovirus type 5 (Ad5) can combine with predosing strategies or Kupffer cell ablation to achieve systemic kinetics with a half-life >60 min, allowing ready access to peripheral tumors. Accumulation of virus particles within tumor nodules is proportional to the area under the plasma concentration/time curve. Polymer coating wild-type Ad5 in this way is known to decrease hepatic toxicity, increasing the dose of virus particles that can be safely administered. Using polymer-coating technology to deliver a replicating Ad5 systemically, virus replication and transgene expression was almost totally confined to tumor tissues, giving a much improved therapeutic index compared with uncoated virus, and complete control of human HepG2 tumor xenografts.

Recent advances in ligand targeted therapy

BACKGROUND

Ligand targeted therapy (LTT) is a powerful pharmaceutical strategy to achieve selective drug delivery to pathological cells, for both therapeutic and diagnostic purposes, with the advantage of limited side effects and toxicity. This active drug targeting approach is based on the discovery that there are receptors overexpressed on pathological cells, compared to their expression in normal tissues.

PURPOSE

The purpose of this article is to review recently published data on LTT with applications, both in the field of cancer therapy and other diseases. Moreover, data on LTT exploiting receptors overexpressed at cytoplasmatic level are also reviewed.

METHODS

Data were deduced from Medline (PubMed) and SciFinder and their selections were made with preference to papers where the most relevant receptors were involved.

RESULTS

Several groups have reported improved delivery of targeted nanocarriers, as compared to nontargeted ones, to pathological cells. LTT offers several advantages, but there are also limitations in the development of this strategy. Moreover, LTT have shown encouraging results in in vitro and in animal models in vivo; hence their clinical potential awaits investigation.

CONCLUSION

Recent studies highlight that the ligand density plays an important role in targeting efficacy. Furthermore, LTT applications in diseases different from cancer and those exploiting receptors overexpressed at cytoplasmatic level are growing.

Targeted delivery of low molecular drugs using chitosan and its derivatives

Chitosan has prompted the continuous impetus for the development of safe and effective drug delivery systems because of its unique physicochemical and biological characteristics. The primary hydroxyl and amine groups located on the backbone of chitosan allow for chemical modification to control its physical properties. When the hydrophobic moiety is conjugated to a chitosan molecule, the resulting amphiphile may form self-assembled nanoparticles that can encapsulate a quantity of drugs and deliver them to a specific site of action. Chemical attachment of the drug to the chitosan throughout the functional linker may produce useful prodrugs, exhibiting the appropriate biological activity at the target site. Mucoadhesive and absorption enhancement properties of chitosan increase the in vivo residence time of the dosage form in the gastrointestinal tract and improve the bioavailability of various drugs. The main objective of this review is to provide an insight into various target-specific carriers, based on chitosan and its derivatives, towards low molecular weight drug delivery. The first part of the review is concerned with the organ-specific delivery of low molecular drugs using chitosan and its derivatives. The subsequent section considers the recent developments of drug delivery carriers for cancer therapy with special focus on various targeting strategies.

Development of HPMA copolymer-anticancer conjugates: clinical experience and lessons learnt

The concept of polymer-drug conjugates was proposed more than 30 years ago, and an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugate of doxorubicin covalently bound to the polymer backbone by a Gly-Phe-Leu-Gly peptidyl linker (FCE28068) became the first synthetic polymer-based anticancer conjugate to enter clinical trial in 1994. This conjugate arose from rational design attempting to capitalise on passive tumour targeting by the enhanced permeability and retention effect and, at the cellular level, lysosomotropic drug delivery to improve therapeutic index. Early clinical results were promising, confirming activity in chemotherapy refractory patients and the safety of HPMA as a new polymer platform. Subsequent Phase I/II trials have investigated an HPMA copolymer-based conjugate containing a doxorubicin and additionally galactose as a targeting moiety to promote liver targeting (FCE28069), and also HPMA copolymer conjugates of paclitaxel (PNU 166945), camptothecin (PNU 166148) and two platinates (AP5280 and AP5346- ProLindac). The preclinical and clinical observations made in these, and clinical studies with other polymer conjugates, should shape the development of next generation anticancer polymer therapeutics.

HPMA Copolymer-1,5-Diazaanthraquinone Conjugates as Novel Anticancer Therapeutics

1,5-diazaanthraquinones (DAQs) are promising anticancer drugs, however, their clinical potential is limited due to poor solubility. Conjugation of anticancer agents to hydrophilic water-soluble polymers can overcome this problem and has already been used to generate conjugates with demonstrated clinical benefit. Here a library of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates containing a novel amino-functionalised 1,5-diazaanthraquinone derivative (amino-DAQ) have been synthesised. The conjugates were fully characterised by UV, HPLC, SEC, FT-Raman and NMR spectroscopy. Conjugation to HPMA copolymers improved amino-DAQ aqueous solubility (>7-fold). The HPMA copolymer-amino-DAQ conjugates were slightly less haemolytic than the parent compound (2% Hb released in 1 h for conjugate HPMA copolymer-GFLG (5 mol%)-amino-DAQ conjugate compared to 13% obtained with amino-DAQ). When conjugates were incubated with isolated rat liver lysosomal enzymes (Tritosomes) the rate of amino-DAQ release was influenced by both drug loading and the composition of the peptidyl side chain used to link the drug to the carrier. The higher the drug loading the lower the rate of drug release. Whereas the GG linker did not release amino-DAQ, up to 26% of the amino-DAQ was released from a GFLG linker over 24 h. The in vitro cytotoxicity of these conjugates was evaluated against two different cell lines, B16F10 murine melanoma and MCF-7 human breast cancer cells. HPMA copolymer-amino-DAQ conjugates, which are internalised by cells by the endocytic pathway, showed much lower in vitro cytotoxicity (IC50 for HPMA copolymer-GFLG (5 mol%)-amino-DAQ conjugate>397 microM drug-equiv.) than the free drug (the IC50 for amino-DAQ was 12.6 and 2.8 microM against the B16F10 murine melanoma and the MCF-7 breast cancer cell line, respectively). Nonetheless, the observed lysosomal activation of the HPMA copolymer-GFLG-amino-DAQ conjugates, suggests that evaluation of the antitumour potential in vivo is warranted.

Glycosilated Macromolecular Conjugates of Antiviral Drugs with a Polyaspartamide

Two new polymeric conjugates for specific liver targeting were prepared by conjugation of sugar moieties and antiviral drugs to alpha, beta-poly[N-2-(hydroxyethyl)-DL-aspartamide] (PHEA). PHEA-galactopyranosylphenylthiocarbamide-mono-O-succinylganciclovir (conjugate 7) and PHEA-mannopyranosylphenylthiocarbamide-O-succinylacyclovir (conjugate 8) were synthesized according to a multi-step procedure which allowed for obtaining high product yield and process standardization. Conjugate 7 contained 7.5 and 8.5% of galactose and ganciclovir (substituent/repeating unit, mol/mol), respectively, and conjugate 8 contained 14.2 and 10.8% of mannose and acyclovir, respectively. In vitro studies demonstrated that both acyclovir and ganciclovir are released from the polymeric adducts at a release rate, which depended on the incubation medium. Though a detailed study evidenced that the two bioconjugates undergo different hydrolysis pathways, in both cases high drug release rate was found in plasma, while the glycosidic moiety was not released. Pharmacokinetic studies carried out by intravenous administration of the bioconjugates to Balb/c mice demonstrated that the conjugation of glycosidic moieties promotes the disappearance of the polymer from the bloodstream. The two derivatives displayed a different pharmacokinetic profile. In particular, the mannosyl conjugation promoted the rapid disposition of the macromolecule in the kidneys and in the liver, while prevented the accumulation in the spleen. On the contrary, the galactosyl derivative was found to dispose in the liver at the same extent of the naked polymer. Few considerations on the different behavior of the conjugates were reported.

Establishment of subcellular fractionation techniques to monitor the intracellular fate of polymer therapeutics II. Identification of endosomal and lysosomal compartments in HepG2 cells combining single-step subcellular fractionation with fluorescent imaging

As they are often designed for lysosomotropic, endosomotropic and/or transcellular delivery, an understanding of intracellular trafficking pathways is essential to enable optimised design of novel polymer therapeutics. Here, we describe a single-step density gradient subcellular fractionation method combined with fluorescent detection analysis that provides a new tool for characterisation of endocytic traffic of polymer therapeutics. Hepatoma (HepG2) cells were used as a model and cell breakage was optimised using a cell cracker to ensure assay of the whole cell population. After removal of unbroken cells and nuclei, the cell lysate as a post-nuclear supernatant (PNS) was layered onto an iodixanol (OptiPrep) density gradient optimised to 5-20%. Early endosomes, late endosomes and lysosomes were identified from gradient fractions by immunoblotting for marker proteins early endosome antigen 1 (EEA 1) and lysosomal associated membrane protein 1 (LAMP 1) using horseradish peroxidase or fluorescently-labelled secondary antibodies. Lysosomes were also detected using N-acetyl-beta-glucosamindase (Hex A) activity. In addition, cells were incubated with Texas-red labelled transferrin (TxR-Tf) for 5 min to specifically label early endosomes and this was directly detected from SDS-PAGE gels. Internalised macromolecules and colloidal particles can potentially alter vesicle buoyant density. To see if typical macromolecules of interest would alter vesicle density or perturb vesicle traffic, HepG2 cells were incubated with dextran or a polyethyleneglycol (PEG)-polyester dendron G4 (1 mg/ml for 24 h). The PEG-polyester dendron G4 caused a slight redistribution of endocytic structures to lower density fractions but immunofluorescence microscopy showed no obvious dendron effects. In conclusion, the combined subcellular fractionation with fluorescent imaging approach described here can be used as a tool for both fundamental cell biology research and/or the quantitative localisation of polymer therapeutics in the endocytic pathway.

N-(2-Hydroxypropyl)methacrylamide Copolymers of a Glutathione (GSH)-Activated Glyoxalase I Inhibitor and DNA Alkylating Agent: Synthesis, Reaction Kinetics with GSH, and in Vitro Antitumor Activities

The incorporation of anticancer prodrugs into polyacrylamide conjugates has been shown to improve tumor targeting via the so-called "enhanced permeability and retention" effect. This strategy has now been expanded to include two different classes of glutathione (GSH)-activated antitumor agents prepared by radical polymerization of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-methacryloyloxy-methyl-2-cyclohexenone (7) and/or with S-(N-4-chlorophenyl-N-hydroxycarbamoyl-thioethyl)methacrylamide (8), followed by treatment with 3-chloroperoxybenzoic acid, to give the HPMA copolymers of 7 and the 8-sulfoxide, respectively. In aqueous-buffered solution at pH 6.5, GSH reacts rapidly with poly-HPMA-8-sulfoxide (k approximately 2.3 mM(-1) min(-1)) to give S-(N-4-chlorophenyl-N-hydroxycarbamoyl)glutathione (1), a tight-binding transition state analogue inhibitor of the antitumor target enzyme glyoxalase I (K(i) = 46 nM), or with poly-HPMA-7 (k approximately 0.02 mM(-1) min(-1)) to give the electrophilic antitumor agent 3-glutathio-2-methylenecyclohexenone (4). Indeed, B16 melanotic melanoma in culture is inhibited by poly-HPMA-8-sulfoxide and by poly-HPMA-7 with IC(50) values of 168 +/- 8 and 284 +/- 5 microM, respectively. These values are significantly greater than those of the unpolymerized prodrugs suggesting that the cytotoxicity of the polymer prodrugs might be limited by slow cellular uptake via pinocytosis. This prodrug strategy should be applicable to a range of different GSH-based antitumor agents.

Targeting angiogenesis with a conjugate of HPMA copolymer and TNP-470

Angiogenesis is crucial for tumor growth. Angiogenesis inhibitors, such as O-(chloracetyl-carbamoyl) fumagillol (TNP-470), are thus emerging as a new class of anticancer drugs. In clinical trials, TNP-470 slowed tumor growth in patients with metastatic cancer. However, at higher doses necessary for tumor regression, many patients experienced neurotoxicity. We therefore synthesized and characterized a water-soluble conjugate of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer, Gly-Phe-Leu-Gly linker and TNP-470. This conjugate accumulated selectively in tumor vessels because of the enhanced permeability and retention (EPR) effect. HPMA copolymer-TNP-470 substantially enhanced and prolonged the activity of TNP-470 in vivo in tumor and hepatectomy models. Polymer conjugation prevented TNP-470 from crossing the blood-brain barrier (BBB) and decreased its accumulation in normal organs, thereby avoiding drug-related toxicities. Treatment with TNP-470 caused weight loss and neurotoxic effects in mice, whereas treatment with the conjugate did not. This new approach for targeting angiogenesis inhibitors specifically to the tumor vasculature may provide a new strategy for the rational design of cancer therapies.

Design of a multivalent galactoside ligand for selective targeting of HPMA copolymer–doxorubicin conjugates to human colon cancer cells

N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymers have been shown to be efficient carriers for anticancer drugs because of their versatile chemistry and good biocompatibility. As demonstrated with hepatocytes, targeting efficacy of anticancer drugs could be further improved when the drug (doxorubicin) was conjugated to HPMA copolymers with biorecognisable groups, such as simple carbohydrates. The present study was devised to learn whether the cluster (multivalent) construction of carbohydrate residues could improve the targeting capability of HPMA copolymer-doxorubicin (DOX) conjugates towards human colon adenocarcinoma cells. DOX was linked via a lysosomally degradable tetrapeptide sequence to HPMA copolymers bearing galactosamine (GalN), lactose (Lac), or multivalent galactose residues (TriGal) to produce targetable polymeric drug carriers. The effect of the type of sugar moiety and its three-dimensional cluster arrangement on biorecognition by three human colon-adenocarcinoma cell lines was studied. The role of galectin-3 in the biorecognition of HPMA copolymer conjugates was explored. Biorecognition of the targetable (glycoside-bearing) conjugates decreased their IC(50) doses in comparison to the non-targetable (non-glycosylated) conjugates. The biorecognition of the TriGal-containing HPMA copolymer-doxorubicin conjugate by the cells was superior with concomitant decrease of its IC(50) doses. It is suggested that the increased cytotoxicity of the glycosylated HPMA-copolymer-DOX conjugates toward human colon-adenocarcinoma cells was caused by their biorecognition and effective internalisation via receptor-mediated endocytosis. All three human colon adenocarcinoma cell lines tested, Colo-205, SW-480 and SW-620, expressed the galectin-3 protein and the galectin-3-specific RNA. However, contrary to expectation, Colo-205 cells did not express a detectable amount of galectin-3 on the cell surface. This suggests that the binding of the glycoside-bearing HPMA copolymer-DOX conjugates to the cells was mediated not only by galectin-3. We conclude that targeting of the anticancer agent, doxorubicin, using HPMA copolymer conjugates bearing multivalent galactoside residues can improve their cytotoxicity.

HPMA copolymer-bound doxorubicin targeted to tumor-specific antigen of BCL1 mouse B cell leukemia

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer carrier containing the anticancer drug doxorubicin and targeted with B1 monoclonal antibody (mAb) to BCL1 leukemia cells was synthesised and tested in vitro and in vivo. BCL1 leukemia growing in syngenic Balb/c mice was selected as a tumor model system. B1 mAb recognising the idiotype of surface IgM on BCL1 cells was used as a targeting moiety. Both B1 mAb and doxorubicin were conjugated to HPMA copolymer carrier by aminolysis through a tetrapeptidic Gly-Phe(D,L)-Leu-Gly spacer to ensure the intracellular delivery and controlled release of the drug. B1 mAb-targeted conjugate was shown to possess strictly tumor-specific binding capacity to target BCL1 cells in vitro. A similar conjugate, but containing human nonspecific Ig (HuIg) instead of B1 mAb, failed to bind to BCL1 cells. In vitro, B1 mAb-targeted conjugate demonstrated 40-fold higher cytotoxic effect than nontargeted or human nonspecific Ig-containing HPMA copolymer-bound doxorubicin. Conjugate targeted with B1 mAb was also shown to bind to target BCL1 cells in vivo. B1 mAb-targeted conjugate was shown to be more efficient in the treatment of established BCL1 leukemia than free doxorubicin, nontargeted and human nonspecific Ig-containing conjugate. Antibody-targeted polymeric drugs are thus promising conjugates for cancer treatment.

Design and synthesis of pH-responsive polymeric carriers that target uptake and enhance the intracellular delivery of oligonucleotides

The delivery of biomolecular therapeutics that function intracellularly remains a significant challenge in the field of biotechnology. In this report, a new family of polymeric drug carriers that combine cell targeting, a pH-responsive membrane-disruptive component, and serum-stabilizing polyethylene glycol (PEG) grafts, is shown to direct the uptake and endosomal release of oligonucleotides in a primary hepatocyte cell line. These polymers are called encrypted polymers and are graft terpolymers that consist of a hydrophobic, membrane-disruptive backbone onto which hydrophilic PEG chains have been grafted through acid-degradable linker acetal linkages. In this report, the ability of the encrypted polymers to deliver rhodamine-labeled oligonucleotides or PEG-FITC (a model macromolecular drug) (5 kDa) into the cytoplasm of hepatocytes was investigated by fluorescence microscopy. Two new encrypted polymer derivatives (polymers E2 and E3) were synthesized that contained lactose for targeting to hepatocytes. Polymer E2 also has PEG-FITC conjugated to it, as a model macromolecular drug, and polymer E3 contains a pendant hexalysine moiety for complexing oligonucleotides. The results of the fluorescence microscopy experiments show that the encrypted polymers direct vesicular escape and efficiently deliver oligonucleotides and macromolecules into the cytoplasm of hepatocytes.

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.

The role of galactose, lactose, and galactose valency in the biorecognition of N-(2-hydroxypropyl)methacrylamide copolymers by human colon adenocarcinoma cells

PURPOSE

To examine the beta-galactoside and beta-lactoside binding capacity of three human colon-adenocarcinoma cell lines and their sugar specificity, using N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates of galactosamine, lactose, and triantennary galactose.

METHODS

Three types of HPMA copolymers containing the saccharide epitopes galactosamine (P-Gal), lactose (P-Lac), or triantennary galactose (P-TriGal) were synthesized. The relationship between the content of the saccharide moieties, the valency of the galactose residues, and their biorecognition by the cell lines (Colo-205, SW-480, and SW-620) was investigated using flow cytometry and confocal fluorescence microscopy analysis.

RESULTS

The binding of the glycoconjugates to the human colonadenocarcinoma cell lines was dependent on the type and the number of bound sugar residues per macromolecule. The higher the sugar contents in the HPMA copolymers, the higher the extent of binding. Although introduction of galactoside residues into the HPMA copolymer resulted in a significant increase in the binding of the copolymers to the cells, low biorecognition of the lactoside-containing HPMA copolymers by all cell lines used was observed. The trivalent galactoside-containing HPMA copolymers did not yield a notable glycoside cluster effect for the beta-galactoside-binding lectin expressed on human colon-adenocarcinoma cells. Among the various cell line little differences in the extent of binding of the glycopolymers to the cells were observed. The data on the internalization of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometry analysis of their biorecognition by target cells.

CONCLUSIONS

The lectin-mediated endocytosis of the HPMA glycoconjugates in human colon cancer cell lines suggests their potential use as targeting tools of cytotoxic drugs to colon adenocarcinoma.

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.

Hepatic drug targeting: phase I evaluation of polymer-bound doxorubicin

PURPOSE

Preclinical studies have shown good anticancer activity following targeting of a polymer bearing doxorubicin with galactosamine (PK2) to the liver. The present phase I study was devised to determine the toxicity, pharmacokinetic profile, and targeting capability of PK2.

PATIENTS AND METHODS

Doxorubicin was linked via a lysosomally degradable tetrapeptide sequence to N-(2-hydroxypropyl)methacrylamide copolymers bearing galactosamine. Targeting, toxicity, and efficacy were evaluated in 31 patients with primary (n = 25) or metastatic (n = 6) liver cancer. Body distribution of the radiolabelled polymer conjugate was assessed using gamma-camera imaging and single-photon emission computed tomography.

RESULTS

The polymer was administered by intravenous (i.v.) infusion over 1 hour, repeated every 3 weeks. Dose escalation proceeded from 20 to 160 mg/m(2) (doxorubicin equivalents), the maximum-tolerated dose, which was associated with severe fatigue, grade 4 neutropenia, and grade 3 mucositis. Twenty-four hours after administration, 16.9% +/- 3.9% of the administered dose of doxorubicin targeted to the liver and 3.3% +/- 5.6% of dose was delivered to tumor. Doxorubicin-polymer conjugate without galactosamine showed no targeting. Three hepatoma patients showed partial responses, with one in continuing partial remission 47 months after therapy.

CONCLUSION

The recommended PK2 dose is 120 mg/m(2), administered every 3 weeks by IV infusion. Liver-specific doxorubicin delivery is achievable using galactosamine-modified polymers, and targeting is also seen in primary hepatocellular tumors.

Enhanced biorecognition and internalization of HPMA copolymers containing multiple or multivalent carbohydrate side-chains by human hepatocarcinoma cells

N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing pendant saccharide moieties (galactosamine, lactose, and triantennary galactose) were synthesized. The relationship between the content of saccharide moieties and three-dimensional arrangement of galactose residues and their biorecognition and internalization by human hepatocarcinoma HepG2 cells was investigated. The results obtained clearly indicated preferential binding of the trivalent galactose and the lactose-containing copolymers to these cells. The higher the saccharide moieties content in HPMA copolymers, the higher the levels of binding. The biorecognition of the glycosylated HPMA copolymers by HepG2 cells was inhibited by free lactose. The data on the internalization and subcellular trafficking of HPMA copolymer conjugates obtained by confocal fluorescence microscopy correlated well with the flow cytometric analysis of their biorecognition by target cells. Structural features of the glycosides responsible for the specific recognition of the HPMA copolymers have been identified. The results underline the potential of glycosylated HPMA copolymers for delivery of pharmaceutical agents to hepatocarcinoma cells.

Preclinical evaluation of the cardiotoxicity of PK2: a novel HPMA copolymer-doxorubicin-galactosamine conjugate antitumour agent

PK2 is a polymeric anticancer conjugate composed of an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer backbone and pendant doxorubicin (DOX) linked via a Gly-Phe-Leu-Gly peptide spacer. Additionally galactose residues are present to facilitate liver targeting. To justify clinical evaluation of PK2 it was necessary to determine its late cardiotoxicity compared to that of free DOX. A well standardised Sprague-Dawley rat model was used with either intravenous (i.v.) administration (4, 8 and 12 mg/kg DOX equivalent) or intraperitoneal (i.p.) administration (12, 18, 24 and 36 mg/kg DOX equivalent) of PK2. This variation in the route was due to the limited solubility of PK2 at higher doses. PK2 showed two to three times less acute toxicity (assessed by the maximum reduction in body weight in the first 2 weeks) than free DOX, and both compounds were less toxic when given i.p.. No animals given PK2 i.v. showed clinical signs of cardiotoxicity, the only toxicity seen was abnormal tooth growth (approximately 50% of the animals receiving 12 mg/kg, DOX equivalent). In contrast, several animals receiving free DOX (1-4 mg/kg) i.v. died due to cardiotoxicity in an approximately dose-related manner. All animals receiving free DOX (4 mg/kg) died by 12 weeks. Following i.p. administration of PKZ there were only two late deaths related to cardiotoxicity and these were in the 24 mg/kg DOX equivalent group. All animals receiving PK2 at the highest dose (36 mg/kg DOX equivalent) died within 4 weeks, cardiotoxicity was not the main contributing factor. In this study, PK2 displayed a approximately 5-fold reduction in cardiotoxicity relative to free DOX and this supported the progression of PK2 into early clinical investigation.

N-(2-hydroxypropyl)methacrylamide copolymer-6-(3-aminopropyl)-ellipticine conjugates. Synthesis, in vitro, and preliminary in vivo evaluation

Ellipticine derivatives have potential as anticancer drugs. Their clinical use has been limited, however, by poor solubility and host toxicity. As N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-anticancer conjugates are showing promise in early clinical trials, a series of novel HPMA copolymer conjugates have been prepared containing the 6-(3-aminopropyl)-ellipticine derivative (APE, NSC176328). Drug was linked to the polymer via GFLG or GG peptide side chains. To optimize biological behavior, HPMA copolymer-GFLG-APE conjugates with different drug loading (total APE: 2.3-7% w/w; free APE: <0.1% w/w) were synthesized. Conjugation of APE to HPMA copolymers considerably increased its aqueous solubility (>10-fold). HPMA copolymer-GG-APE did not liberate drug in the presence of isolated lysosomal enzymes (tritosomes), but HPMA copolymer-GFLG-APE released APE to a maximum of 60% after 5 h. The rate of drug release was influenced by drug loading; lower loading led to greater release. Whereas free APE (35 microg/mL) caused significant hemolysis (50% after 1 h), HPMA copolymer-APE conjugates were not hemolytic up to 300 microg/mL (APE-equiv). As would be expected from its cellular pharmacokinetics, HPMA copolymer-GFLG-APE was >75 times less cytotoxic than free drug (IC(50) approximately 0.4 microg/mL) against B16F10 melanoma in vitro. However, in vivo when tested in mice bearing s.c. B16F10 melanoma, HPMA copolymer-GFLG-APE (1-10 mg/kg single dose, APE-equiv) given i.p. was somewhat more active (highest T/C value of 143%) than free APE (1 mg/kg) (T/C =127%). HPMA copolymer-APE conjugates warrant further evaluation as potential anticancer agents.

The role of pro-drug therapy in the treatment of cancer

The administration of anti-cancer agents is currently associated with significant toxicity and lack of tumour specificity. Prodrugs are being designed to favourably alter the therapeutic index of these agents by improving their efficacy and reducing toxicity. Progress in the development of prodrugs including the cytotoxic agents most commonly used in cancer treatments namely 5-fluorouracil (5-FU), the anthracyclines, paclitaxel and platinum will be described. Many of these agents are at an early stage of development: however, this article will also describe those which have already made an impact in the clinic. It is likely that future improvements in care will come from refinement of the drugs already well established in clinical practice. In addition, this technology could be applied to novel agents with alternative cellular targets such as those involved in angiogenesis or in conferring metastatic potential. Thus, lessons learned with standard drugs may be applicable across a wider spectrum of therapeutics.

Triggered intracellular activation of disulfide crosslinked polyelectrolyte gene delivery complexes with extended systemic circulation in vivo

We have developed polyelectrolyte gene delivery vectors that display good extracellular stability and are activated intracellularly to permit transgene expression. The strategy comprises covalent crosslinking of primary amines in poly-L-lysine/DNA complexes with a crosslinking agent that can later be cleaved by reduction. Crosslinked complexes maintained the same size and surface charge but showed increased stability against polyelectrolyte exchange with poly-L-aspartic acid. Surface modification with polyethyleneglycol improved solubility and masked their positive surface charge. Crosslinked complexes showed 10-fold increased plasma circulation following intravenous administration to Balb/c mice. In the absence of chloroquine, the levels of transgene expression in B16F10 murine melanoma cells were similar for crosslinked and non-crosslinked complexes, however, chloroquine selectively potentiated transgene expression by the non-crosslinked complexes. Cellular uptake of the complexes was the same, irrespective of crosslinking. Following microinjection into the cytoplasm of Xenopus oocytes, or the cytoplasm or nucleus of Rat-1 fibroblasts, crosslinked complexes mediated the same transgene expression as non-crosslinked complexes, indicating crosslinked complexes are rapidly reduced and activated intracellularly. We therefore hypothesize that the lower in vitro transfection activity of crosslinked complexes in the presence of chloroquine is due to reduced transfer from endosome to cytoplasm, mainly due to increased stability against destabilization by chloroquine. The extended systemic circulation together with triggered intracellular activation makes these complexes a promising system for targeted gene delivery in vivo.