Nanotherapeutics shielded with a pH responsive polymeric layer

Efficient intravenous delivery is the greatest single hurdle, with most nanotherapeutics frequently found to be unstable in the harsh conditions of the bloodstream. In the case of nanotherapeutics for gene delivery, viral vectors are often avidly recognized by both the innate and the adaptive immune systems. So, most modern delivery systems have benefited from being coated with hydrophilic polymers. Self-assembling delivery systems can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly, gene delivery viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Polymers that start degrading under acidic conditions are increasingly investigated as a pathway to trigger the release of drugs or genes once the carrier reaches a slightly acidic tumor environment or after the carrier has been taken up by cells, resulting in the localization of the polymer in acidic endosomes and lysosomes. Advances in the design of acid-degradable drug and gene delivery systems have been focused and discussed in this article with stress placed on HPMA-based copolymers. We designed a system that is able to "throw away" the polymer coat after successful transport of the vector into a target cell. Initial biological studies were performed and it was demonstrated that this principle is applicable for real adenoviral vectors. It was shown that the transfection ability of coated virus at pH 7.4 is 75 times lower then transfection at pH 5.4.

Comparison of molecular strategies for breast cancer virotherapy using oncolytic adenovirus

Oncolytic viruses are regulated by the tumor phenotype to replicate and lyse cancer cells selectively. To identify optimal strategies for breast cancer we compared five adenoviruses with distinct regulatory mechanisms: Ad-dl922-947 (targets G1-S checkpoint); Ad-Onyx-015 and Ad-Onyx-017 (target p53/mRNA export); Ad-vKH1 (targets Wnt pathway), and AdEHE2F (targets estrogen receptor/G1-S checkpoint/hypoxic signaling). The quantity of virus required to kill 50% of breast cancer cells after 6 days (EC(50), plaque-forming units per cell) was measured. The most potent virus was Ad-dl922-947 (EC(50), 0.01-5.4 in SkBr3, MDA-231, MDA-468, MCF7, and ZR75.1 cells), followed by wild-type (Ad-WT; EC(50), 0.3-5.5) and AdEHE2F (EC(50), 1.4-3.9). Ad-vKH1 (EC(50), 7.2-72.1), Ad-Onyx-017 (EC(50), 8.4-167), and Ad-Onyx-015 (EC(50), 17.7-377) showed less activity. Most viruses showed limited cytotoxicity in normal human cells, including breast epithelium MCF10A (EC(50), >722) and fibroblasts (EC(50), >192) and only moderate cytotoxicity in normal microvascular endothelial cells (HMVECs; EC(50), 42.8-149), except Ad-dl922-947, which was active in HMVECs (EC(50), 1.6). After injection into MDA-231 xenografts, Ad-WT, AdEHE2F, and Ad-dl922-947 showed replication, assessed by hexon staining and quantitative polymerase chain reaction measurement of viral DNA, and significantly inhibited tumor growth, leading to extended survival. After intravenous injection Ad-dl922-947 showed DNA replication (233% of the injected dose was measured in liver after 3 days) whereas AdEHE2F did not. Overall, AdEHE2F showed the best combination of low toxicity in normal cells and high activity in breast cancer in vitro and in vivo, suggesting that molecular targeting using estrogen response elements, hypoxia response elements, and a dysregulated G1-S checkpoint is a promising strategy for virotherapy of breast cancer.

Factors influencing retention of adenovirus within tumours following direct intratumoural injection

Direct intratumoural (IT) administration of adenovirus is widely used, however little is known about the resulting distribution of virus particles. Here we have evaluated the influence of tumour size, volume of injectate and occlusion of injection sites (to prevent retrograde seepage) on particle biodistribution and transgene expression. In subcutaneous MDA-231 xenografts, IT injection of relatively large volumes (4 x 20% (vol/vol) injections) resulted in just 40% of the administered dose being retained in tumour tissue after 30 min, with 15% in the liver thought to reflect systemic 'overflow'. Occlusion of the injection sites using surgical adhesive increased retention of the vector to 80% in the tumour with no increase in liver levels. Spread of expression was enhanced using multiple injection sites, but not by using larger injectate volumes. In ZR75.1 breast carcinoma xenografts virus distribution was different, with no evidence of systemic overflow leading to hepatic transduction following IT injection. Typically, clinical doses employ up to 30% vol/vol IT injections. Depending on the tumour, this may give considerable systemic overflow and might account for the high frequency of fevers observed. Virus performance might be improved by tailoring volumes and frequency of IT injection for tumour biology or histotype.

Incorporation of a laminin-derived peptide (SIKVAV) on polymer-modified adenovirus permits tumor-specific targeting via alpha6-integrins

Effective gene therapy for disseminated metastatic cancer is currently impossible because of poor delivery of vector to target sites. Modification of viral vectors to target advanced cancer has long been a challenge. In this study, we aimed to redirect adenovirus tropism to infect prostate cancer cells via alpha6beta1 integrins, whose expression is upregulated during prostate cancer progression. To ablate normal mechanisms of infection and provide a framework for attachment of targeting ligands, viruses were non-genetically modified with pHPMA-ONp polymer. Addition of polymer-coated virus to prostate cells showed significantly reduced transgene expression compared with unmodified virus. To restore infectivity, an alpha6-integrin binding peptide (-SIKVAV-) derived from laminin was incorporated onto the surface of the polymer-coated viruses. Photon correlation spectroscopic analysis revealed a small increase in the mean diameter of the particles following retargeting. Addition of -SIKVAV- peptide restored virus infectivity of PC-3 cells in a ligand concentration-dependent manner that was significantly improved following removal of unincorporated polymer and peptide. Competition assays using cells preincubated with Ad5 fiber protein or free -SIKVAV- peptide confirmed that entry of retargeted viruses was mediated via the incorporated ligand. Application of retargeted viruses to a panel of human cell lines revealed varying levels of transduction efficiency. Flow cytometric analysis of cells using anti-alpha6 integrin and anti-beta1 integrin antibodies demonstrated that for prostate cells, greater transduction efficiency correlated with higher levels of expression of both integrin subunits. Furthermore with the exception of LNCaP cells, increased alpha6beta1 integrin expression correlated with advanced disease. Intravenous administration of retargeted viruses to tumor-bearing mice resulted in slower plasma clearance and greatly reduced liver tropism, and hence toxicity compared with unmodified virus, while maintaining reporter gene expression in the tumor. The data suggest that YESIKVAVS-retargeted viruses have potential for systemic delivery for the treatment of metastatic disease.

Gene therapy targeting to tumor endothelium

Tumor-associated vasculature is a relatively accessible component of solid cancers that is essential for tumor survival and growth, providing a vulnerable target for cancer gene therapy administered by intravenous injection. Several features of tumor-associated vasculature are different from normal vasculature, including overexpression of receptors for angiogenic growth factors, markers of vasculogenesis, upregulation of coagulation cascades, aberrant expression of adhesion molecules and molecular consequences of hypoxia. Many of these differences provide candidate targets for tumor-selective 'transductional targeting' of genetically- or chemically modified vectors and upregulated gene expression can also enable 'transcriptional targeting', regulating tumor endothelia-selective expression of transgenes following nonspecific gene delivery. Tumor vasculature also represents an important site of therapeutic action by the secreted products of antiangiogenic gene therapies that are expressed in non-endothelial cells. In this review we assess the challenges faced and the vectors that may be suitable for gene delivery to exploit these targets. We also overview some of the strategies that have been developed to date and highlight the most promising areas of research.

Use of synthetic vectors for neutralising antibody resistant delivery of replicating adenovirus DNA

Use of synthetic vectors to deliver genomes of conditionally replicating lytic viruses combines the strengths of viral and non-viral approaches by enabling neutralising antibody resistant deployment of cancer virotherapy. Adenovirus is particularly suitable for this application since all proteins essential for replication can be expressed from the input DNA, although the presence of terminal protein (TP) covalently linked to the 5' termini of the input virus genomes both improves expression of transgenes encoded in the input DNA and also enhances replication. These roles of TP were distinguished in experiments where E1-deleted Ad(GFP)DNA bearing TP (Ad(GFP)DNA-TP), delivered with DOTAP, gave a two-fold greater frequency of transduction than Ad(GFP)DNA(without TP) in non-complementing A549 cells, while in 293 cells (which support replication of E1-deleted viruses) the presence of TP mediated a much greater differential transgene expression, commensurate with its ability to promote replication. Subsequent studies using AdDNA for virotherapy, therefore, included covalently linked TP. AdDNA-TP delivered to A549 cells using a synthetic polyplex vector was shown to be resistant to levels of neutralising antisera that completely ablated infection by wild-type adenovirus, enabling polyplex/Ad(wild type)DNA-TP to mediate a powerful cytopathic effect. Similarly in vivo, direct injection of a polyplex/Ad(wild type)DNA-TP into A549 tumours was neutralising antibody-resistant and enabled virus replication, whereas intact virus was neutralised by the antibody and failed to infect. The delivery of adenovirus genomes-TP using synthetic vectors should provide a strategy to bypass neutralising antibodies and facilitate clinical application of replicating adenovirus for cancer virotherapy.

Extended plasma circulation time and decreased toxicity of polymer-coated adenovirus

Systemic delivery of adenoviral vectors is a major goal in cancer gene therapy, but is currently prohibited by rapid hepatic uptake of virus following intravenous injection with levels of viable virus in the murine plasma typically falling to less than 0.1% after 30 min. We have used a surface-masking technique based on multivalent copolymers of poly(N-(2-hydroxypropyl)methacrylamide) to ablate all pathways of receptor-mediated infection, combined with dose modulation to achieve partial saturation of nonspecific uptake pathways. Polymer coating gave at least 100-fold decreased hepatic transgene expression at all doses and even high doses of coated virus (pc-virus) showed no weight loss or stimulation of serum transaminases. Low doses of virus and pc-virus (10(9) viral particles (vp)/mouse) were mainly captured by the liver (assessed by quantitative PCR), although higher doses led to greater fractional persistence in the plasma (measured after 30 min). Coated virus at a dose of 6 x 10(11) vp/mouse showed nearly 50% plasma circulation, representing a 3.5-fold greater area under the concentration-time curve (0-30 min) compared to unmodified virus. Such an increase in the bioavailability of adenovirus, coupled with substantial decreases in toxicity and unwanted transgene expression is an important step towards producing systemically available tumour-targeted viruses.

CTb targeted non-viral cDNA delivery enhances transgene expression in neurons

BACKGROUND

Efficient neuronal gene therapy is a goal for the long-term repair and regeneration of the injured central nervous system (CNS). We investigated whether targeting cDNA to neurons with cholera toxin b chain conjugated non-viral polyplexes led to increased efficiency of non-viral gene transfer in the CNS. Here, we illustrate the potential for this strategy by demonstrating enhanced transfection of a differentiated neuronal cell type, PC12.

METHODS

In vitro transfection efficiency of a cholera toxin b chain-poly(D-lysine) molecular conjugate (CTb-K(100)) was compared by fluorescence-activated cell sorting (FACS) analysis of green fluorescent protein (GFP) expression and luminometric measurement of beta-galactosidase (beta-gal) expression, to untargeted poly(D-lysine) (K(100)) in undifferentiated and NGF-differentiated PC12 cells.

RESULTS

Transfection of undifferentiated PC12 cells with CTb-K(100) polyplexes resulted in a 36-fold increase in levels of pCMV-DNA(LacZ) expression and a 20-fold increase in the frequency of transduction with pCMV-DNA(GFP), compared with untargeted K(100) polyplexes. Treatment of PC12 cells with 50 ng/ml/day of NGF for 14 days led to differentiation to a neuronal phenotype. Transfection of NGF-differentiated cells with CTb-K(100) polyplexes resulted in a 133-fold increase in levels of pCMV-DNA(LacZ) expression and a 11-fold increase in the percentage of cells transduced with pCMV-DNA(GFP), compared with untargeted K(100) polyplexes. Transfection was dependent on CTb, with CTb-K(100)-mediated transfections competitively inhibited with free CTb in both PC12 phenotypes.

CONCLUSIONS

Non-viral systems for gene transfer in damaged CNS show superior toxicological profiles to most viruses but are limited by inefficient and non-selective gene expression in target tissue. Cholera toxin is known to interact preferentially with neuronal cells of the central and peripheral nervous systems, mediating binding through the b subunit, CTb, and the pentasaccharide moiety of the gangliosaccharide, GM1, which is present at high levels on the neuronal cell surface. Here, we show that a molecular conjugate of the CTb subunit, covalently linked to poly(D-lysine), is able to successfully target and significantly enhance transfection of a neuronal cell type, NGF-differentiated rat PC12 pheochromocytoma cells. This observation encourages the further development of non-viral strategies for the delivery of therapeutic genes to neurons.

Gene therapy for colorectal cancer

Colorectal cancer is an important public health problem worldwide. Gene therapy has therapeutic potential for patients with advanced or recurrent colorectal cancer, incurable by conventional treatments. To date, many strategies of gene therapy have been explored, including mutant gene correction, prodrug activation, immune stimulation and genetically-modified oncolytic viruses. Although the preclinical results of gene therapy for colorectal cancer have shown promise, gene therapy is still at an early stage of clinical development and has not yet shown a significant therapeutic benefit for patients. The main obstacles for introduction of gene therapy to patients are poor targeting selectivity of the vectors and inefficient gene transfer. As the science supporting tumour-selective vectors evolves, gene therapy may expand rapidly in the clinical practice of colorectal cancer treatment.

Melittin enables efficient vesicular escape and enhanced nuclear access of nonviral gene delivery vectors

Entry of exogenously applied DNA into the cytoplasm and subsequent transport into the nucleus are major cellular barriers for nonviral gene delivery vectors. To overcome these barriers, we have covalently attached the cationic peptide melittin to poly(ethylenimine) (PEI). This conjugate condensed DNA into small, discrete particles (<100 nm in diameter), and the membrane lytic activity of melittin enabled efficient release of the DNA into the cytoplasm, as monitored by fluorescence microscopy and flow cytometry. Compared with PEI, the transfection activity was strongly increased within a broad range of cell lines and types tested, including different tumor cell lines but also primary hepatocytes and human umbilical vein endothelial cells. The early onset of gene expression (within 4 h, reaching maximal values after 12 h) and the high reporter gene expression achieved in slowly dividing or confluent cells suggested a further role of melittin after releasing the DNA into the cytoplasm. Intracytoplasmic microinjection of melittin-containing PEI.DNA complexes into fibroblasts produced 40% cellular frequency of reporter gene expression that was inhibitable by co-injection of wheat germ agglutinin, whereas simple PEI.DNA complexes showed only 10%. These data suggest that melittin enables release of nonviral gene transfer particles into the cytoplasm and also enhances their transport into the nucleus, possibly via the cationic cluster KRKR near the C terminus of the peptide.

Adenovirus hexon protein enhances nuclear delivery and increases transgene expression of polyethylenimine/plasmid DNA vectors

Inefficient nuclear delivery restricts transgene expression using polyelectrolyte DNA vectors. To increase transfer from the cytoplasm to the nucleus, we have covalently linked adenovirus hexon protein to polyethylenimine (PEI, 800 kDa). Activity of the conjugate was compared with PEI and PEI linked to albumin. Hexon-containing complexes gave 10-fold greater transgene expression in HepG2 cells than PEI/DNA or complexes containing albumin, without increasing cell uptake. Following cytoplasmic injection into Xenopus laevis oocytes, hexon-containing complexes showed reporter gene expression to be elevated by 10-fold compared with PEI/DNA. The ability of hexon to promote nuclear delivery of PEI/DNA nanoparticles was compared with that of classical nuclear localization sequences (NLS) by measuring transgene expression following intracytoplasmic microinjection of hexon-PEI/DNA complexes and NLS-albumin-PEI/DNA complexes in rat-1 fibroblasts. The resulting nuclear transfer efficiency was in the following order: hexon-PEI/DNA>NLS-albumin-PEI/DNA>PEI/DNA>DNA alone>albumin-PEI/DNA. The activities of both NLS-albumin-PEI and hexon-PEI were abolished by co-injection of wheat germ agglutinin, suggesting that both act by means of the nuclear pore complex (NPC); in contrast, excess free NLS-albumin abolished transgene expression with NLS-albumin-PEI/DNA, but only partially inhibited hexon-PEI/DNA. Nuclear transfer efficiency following cytoplasmic injection was dependent on DNA concentration for all materials, although hexon conjugates showed much better activity than NLS-albumin at low DNA doses (500-1000 plasmids/cell). Our data are consistent with hexon mediating nuclear delivery of plasmid complexes by means of the NPC, using mechanisms that are only partially dependent on the classical NLS import pathway. The hexon-mediated mechanism of nuclear import enables substantially better transgene expression, particularly when DNA concentrations in the cytoplasm are limiting.

Peptide-mediated RNA delivery: a novel approach for enhanced transfection of primary and post-mitotic cells

Synthetic vectors were evaluated for their ability to mediate efficient mRNA transfection. Initial results indicated that lipoplexes, but not polyplexes based on polyethylenimine (PEI, 25 and 22 kDa), poly(L-lysine) (PLL, 54 kDa) or dendrimers, mediated efficient translation of mRNA in B16-F10 cells. Significant mRNA transfection was achieved by lipoplex delivery in quiescent (passage 0) human umbilical vein endothelial cells (HUVEC), and by passage 4, 10.7% of HUVEC were transfected compared to 0.84% with DNA. Lack of expression with PEI 25 kDa/mRNA or PLL 54 kDa/mRNA in a cell-free translation assay and following cytoplasmic injection into Rat1 cells indicated that these polyplexes were too stable to release mRNA. In contrast, polyplexes formed using smaller PEI 2 kDa and PLL 3.4 kDa gave 5-fold greater expression in B16-F10 cells compared to DOTAP, but were dependent on chloroquine for transfection activity. Endosomolytic activity was incorporated by conjugating PEI 2 kDa to melittin and resulting PEI 2 kDa-melittin/mRNA polyplexes mediated high transfection levels in HeLa cells (31.1 +/- 4.1%) and HUVEC (58.5 +/- 2.9%) in the absence of chloroquine, that was potentiated to 52.2 +/- 2.7 and 71.6 +/- 1.7%, respectively, in the presence of chloroquine. These results demonstrate that mRNA polyplexes based on peptide-modified low molecular weight polycations can possess versatile properties including endosomolysis that should enable efficient non-viral mRNA transfection of quiescent and post-mitotic cells.

Conjugation of folate via gelonin carbohydrate residues retains ribosomal-inactivating properties of the toxin and permits targeting to folate receptor positive cells

Conjugation of folate to proteins permits receptor-mediated endocytosis via the folate receptor (FR) and delivery of the conjugate into the cytoplasm of cells. Since many cancers up-regulate the FR it has enabled the targeting of toxins to tumor cells resulting in specific cell death. However, current conjugation methods rely on chemistries that can affect certain catalytic subunits, such as the A-chain of the plant toxin gelonin. As a result many folate-targeted toxins are a compromise between receptor/ligand interaction and toxin activity. We describe the first example of folate conjugated to a protein via carbohydrate residues, using a novel SH-folate intermediate. The folate-gelonin conjugate retains over 99% of toxin activity in a cell-free translational assay compared with unmodified gelonin and is able to bind the FR at the same affinity as free folic acid (10(-10) m). Additionally, the conjugate exhibits prolonged inhibition of protein synthesis in FR positive cell lines in vitro. Folate linked to gelonin via amino conjugation exhibits the same affinity for FR as free folic acid but the toxin is 225-fold less active in a cell-free translational assay. The effect of different conjugation methods on toxin activity and the implications for folate targeting of other glycoproteins are discussed.

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.

Systemic circulation of poly(L-lysine)/DNA vectors is influenced by polycation molecular weight and type of DNA: differential circulation in mice and rats and the implications for human gene therapy

Effective gene therapy for diseases of the circulation requires vectors capable of systemic delivery. The molecular weight of poly(L-lysine) (pLL) has a significant effect on the circulation of pLL/DNA complexes in mice, with pLL(211)/DNA complexes displaying up to 20 times greater levels in the blood after 30 minutes compared with pLL(20)/DNA. It is shown that pLL(20)/DNA complexes fix mouse complement C3 in vitro, independent of immunoglobulin binding; are less soluble in the blood in vivo; bind erythrocytes; are rapidly removed by the liver, where they associate predominantly with Kupffer cells; and result in a rapid increase in hepatic leukocytes expressing high levels of complement receptor 3 (CR3). The circulation properties of these complexes are also dependent on the type of DNA used, with circular plasmid DNA complexes exhibiting increased circulation compared with linear DNA. PLL(211)/DNA complexes bind erythrocytes and associate with Kupffer cells but, in contrast, do not fix mouse complement in vitro and are unaffected by the type of DNA used. In rats, both types of complexes produce hematuria and are rapidly removed from the circulation. Correlation of in vivo and in vitro results suggests that the solubility of complexes in physiological saline and species-matched complement fixation and erythrocyte lysis may correlate with systemic circulation. Analysis using human blood in vitro shows no hemolysis, but both types of complexes fix complement and bind IgG, suggesting that pLL/DNA complexes may be rapidly cleared from the human circulation.

Harnessing nuclear localization pathways for transgene delivery

Inefficient transport of DNA from the cytoplasm into the nucleus remains a limiting step in the development of non-viral gene delivery systems. This is particularly acute in non-dividing cells, where entry to the nucleus is thought to occur only through the nuclear pore complex. Active import of physiological proteins is mediated by nuclear localization sequences (NLSs) within cargo proteins such as transcription factors. Here we review current knowledge of this import machinery and consider its exploitation by mammalian viruses. Significant research effort has been directed at incorporating NLSs into synthetic gene delivery systems to take advantage of this physiological pathway. Both non-covalent and covalent methods of conjugation are evaluated, with NLS linkage to both DNA and carrier, and compared with activities of simple cationic polymers. Finally, progress in the field of DNA sequence-specific nuclear import is examined and the current state of the technology assessed.

Key issues in non-viral gene delivery

The future of non-viral gene therapy depends on a detailed understanding of the barriers to delivery of polynucleotides. These include physicomechanical barriers, which limit the design of delivery devices, physicochemical barriers that influence self-assembly of colloidal particulate formulations, and biological barriers that compromise delivery of the DNA to its target site. It is important that realistic delivery strategies are adopted for early clinical trials in non-viral gene therapy. In the longer term, it should be possible to improve the efficiency of gene delivery by learning from the attributes which viruses have evolved; attributes that enable translocation of viral components across biological membranes. Assembly of stable, organized virus-like particles will require a higher level of control than current practice. Here, we summarize present knowledge of the biodistribution and cellular interactions of gene delivery systems and consider how improvements in gene delivery will be accomplished in the future.

Polymer-coated adenovirus permits efficient retargeting and evades neutralising antibodies

Adenovirus is a widely used vector for cancer gene therapy because of its high infection efficiency and capacity for transgene expression in both dividing and nondividing cells. However, neutralisation of adenovirus by pre-existing antibodies can lead to inefficient delivery, and the wide tissue distribution of the coxsackie and adenovirus receptor (CAR, the primary receptor for adenovirus type 5) precludes target selectivity. These limitations have largely restricted therapeutic use of adenovirus to local or direct administration. A successful viral gene therapy vector would be protected from neutralising antibodies and exhibit a preferential tropism for target cells. We report here the development of a covalent coating and retargeting strategy using a multivalent hydrophilic polymer based on poly-[N-(2-hydroxypropyl)methacrylamide] (pHPMA). Incorporation of targeting ligands such as basic fibroblast growth factor and vascular endothelial growth factor on to the polymer-coated virus produces ligand-mediated, CAR-independent binding and uptake into cells bearing appropriate receptors. Retargeted virus is resistant to antibody neutralisation and can infect receptor-positive target cells selectively in mixed culture, and also in xenografts in vivo. Multivalent polymeric modification of adenovirus is an effective way of changing its tropism and interaction with the immune system. As a non-genetic one-step process, the technology is simple, versatile and should yield vectors with an improved safety profile.

Pre-clinical and clinical study of QC12, a water-soluble, pro-drug of quercetin

BACKGROUND

Quercetin is a naturally occurring flavonoid with many biological activities including inhibition of a number of tyrosine kinases. A phase I, dose-escalation trial of quercetin defined the maximum tolerated dose (MTD) as 1700 mg/m2 three weekly, but the vehicle, dimethyl sulphoxide (DMSO) is unsuitable for further clinical development of quercetin.

PATIENTS AND METHODS

A water-soluble, pro-drug of quercetin (3'(N-carboxymethyl)carbomyl-3,4',5,7-tetrahydroxyflavone), QC12 has been synthesised. Six cancer patients received 400 mg of QC12 (equivalent to 298 mg of quercetin), orally on day 1 and intravenously (i.v.) in normal saline on day 14.

RESULTS

Following oral administration of QC12 we were unable to detect QC12 or quercetin in plasma. After i.v. administration, we detected peak plasma concentrations of QC12 of 108.7 +/- 41.67 microMolar (microM). A two-compartment model with mean t(1/2)alpha of 0.31 +/- 0.27 hours and mean t(1/2)beta of 0.86 +/- 0.78 hours best described the concentration-time curves for QC12. The mean AUC was 44.54 +/- 13.0 microM.hour and mean volume of distribution (Vd) of 10.0 +/- 6.2 litres (l). Quercetin was found in all patients following i.v. infusion of QC12, with peak levels of quercetin 19.9 +/- 11.8 microM. The relative bioavailability of quercetin was estimated to be 20%-25% quercetin released from QC12.

CONCLUSIONS

QC12 is not orally bioavailable. This water-soluble pro-drug warrants further clinical investigation; starting with a formal phase I, IV, dose-escalation study.

Folic acid targeting of protein conjugates into ascites tumour cells from ovarian cancer patients

Despite a wealth of in vitro data describing the use of folic acid for drug and DNA delivery into ovarian cancer cell lines, there have been no reports describing the targeting of such compounds to freshly isolated tumour cells. We have carried out a study to determine the usefulness of folic acid as a targeting ligand for ovarian cancer by measuring the uptake of folic acid-BSA-FITC in tumour cells isolated from the ascitic fluid of ovarian cancer patients. In 7 out of 7 patients we have found folic acid mediated uptake of the fluorescently labelled albumin, with the accumulation (average cell fluorescence) and differential uptake (ratio between receptor mediated and fluid phase uptake) varying between patients. Accumulation of folic acid-albumin FITC occurs in ascites tumour cells expressing the epithelial cell marker EMA, with a significant proportion of EMA negative cells also accumulating the conjugate. There is no correlation between cell cycle and uptake of folic acid-BSA-FITC. These results suggest that folic acid-targeting of therapeutics is a promising approach for the treatment of ovarian cancer.

A versatile system for receptor-mediated gene delivery permits increased entry of DNA into target cells, enhanced delivery to the nucleus and elevated rates of transgene expression

We have developed a method for stabilisation of polyelectrolyte gene delivery vectors by crosslinking their surfaces with biodegradable multivalent copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA). The resulting nanoparticulate vectors resist attack by serum proteins and can be modified for cell-specific delivery by incorporation of targeting ligands onto the polymer coating. Here we show that vascular endothelial growth factor (VEGF), transferrin and basic fibroblast growth factor (bFGF) can each be linked to polyHPMA-coated poly(L-lysine)/DNA complexes. All ligand-targeted complexes demonstrated increased uptake into receptor-positive cells (measured using plasmids containing 32P-dCTP), that could be antagonised with excess free ligand. Targeted complexes also showed increased transfection, resistant to inhibition by serum, suggesting the possibility of effective application in vivo. Analysis using fluorescence microscopy confirmed enhanced uptake of ligand-targeted complexes (using Texas Red-labelled plasmid DNA), although VEGF- and transferrin-targeted complexes were restricted to cytoplasmic or perinuclear distributions. In contrast, bFGF-targeted complexes showed efficient delivery into the nucleus, with accumulation of more than 100000 plasmids per cell within distinct intranuclear compartments. This method permits versatile targeting of genes to selected cells and may also permit manipulation of intracellular trafficking. It should find several important applications in gene delivery systems both in vitro and in vivo.

Influence of hydrophilicity of cationic polymers on the biophysical properties of polyelectrolyte complexes formed by self-assembly with DNA

To investigate the possibility of producing charge-neutral gene delivery complexes with extended, non-particulate structures, DNA was allowed to self-assemble with a series of hydrophilic cationic polymers containing quaternary charged trimethylammonio ethylmethacrylate (TMAEM, 5, 15, 50, 100 mol%) copolymerised with hydrophilic N-(2-hydroxypropyl)methacrylamide (HPMA, 95, 85, 50, 0 mol%, respectively). Copolymers were all able to bind DNA, assessed using ethidium bromide fluorescence, although copolymers with low TMAEM content did not expel ethidium bromide. Increasing TMAEM content of the copolymers changed the morphology of the complexes from extended (5-15 mol% TMAEM), through partially condensed particles (50 mol%) to discrete nanoparticles (100 mol% TMAEM). Complexes based on copolymers with low TMAEM content (5-50 mol%) showed less resistance to degradation by nucleases and lower surface charge (21.2+/-5.9-45.1+/-3.9 mV) than those formed using 100 mol% TMAEM (57.8+/-8.2 mV). They also showed significantly less association with phagocytic cells in vitro (human leucocytes, uptake decreased by up to 92.3%; murine peritoneal macrophages, uptake decreased by up to 69.6%), although in vivo their hepatic accumulation was only slightly decreased (maximum decrease 27.6%). Finding the appropriate balance of hydrophilicity and stability is key to development of effective vectors for gene delivery.

Steric stabilization of poly-L-Lysine/DNA complexes by the covalent attachment of semitelechelic poly[N-(2-hydroxypropyl)methacrylamide]

The concept of steric stabilization was utilized for self-assembling polyelectrolyte poly-L-lysine/DNA (pLL/DNA) complexes using covalent attachment of semitelechelic poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA). We have examined the effect of coating of the complexes with pHPMA on their physicochemical stability, phagocytic uptake in vitro, and biodistribution in vivo. The coated complexes showed stability against aggregation in 0.15 M NaCl and reduced binding of albumin, chosen as a model for the study of the interactions of the complexes with plasma proteins. The presence of coating pHPMA had no effect on the morphology of the complexes as shown by transmission electron microscopy. However, results of the study of polyelectrolyte exchange reactions with heparin and pLL suggested decreased stability of the coated complexes in these types of reactions compared to uncoated pLL/DNA complexes. Coated complexes showed decreased phagocytic capture by mouse peritoneal macrophages in vitro. Decreased phagocytosis in vitro, however, did not correlate with results of in vivo study in mice showing no reduction in the liver uptake and no increase in the circulation times in the blood. We propose that the rapid plasma elimination of coated pLL/DNA complexes is a result of binding serum proteins and also of their low stability toward polyelectrolyte exchange reactions as a consequence of their equilibrium nature.

Physicochemical and biological characterisation of an antisense oligonucleotide targeted against the bcl-2 mRNA complexed with cationic-hydrophilic copolymers

The aim of this study was to evaluate the use of cationic-hydrophilic copolymers for self-assembly with antisense oligonucleotides targeted to the bcl-2 mRNA in order to improve their biocompatibility and modulation of their pharmacokinetics for greater therapeutic usefulness. Examination of the ability of poly(trimethylammonioethyl methacrylate chloride)-poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA-b-pTMAEM) block copolymers to condense the oligonucleotide by fluorescence and electrophoresis techniques showed that complexes were formed more efficiently than with copolymers containing poly(ethylene glycol) blocks grafted onto the backbone of poly(L-lysine) (pLL-g-pEG). In addition, the copolymer pTMAEM-b-pHPMA produced oligonucleotide complexes with the most favourable physicochemical properties appropriate for in vivo applications. The complexes were small (approximately 36 nm in diameter), with low surface charge as measured by zeta potential, relatively stable to physiological salt conditions and could be formed at a DNA concentration of 500 microg/ml. Complex formation with the copolymer pTMAEM-b-pHPMA or pLL-g-pEG reduced the urinary clearance of the oligonucleotide after intravenous injection into mice. However after 30 min, the oligonucleotide complexes were cleared from the bloodstream. These results indicate that for the systemic delivery of oligonucleotides the polymer-derived complexes are not stable enough for prolonged circulation. Instead, these complexes may be more suitable for localised in vivo applications.

DNA delivery systems based on complexes of DNA with synthetic polycations and their copolymers

Block and graft copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with 2-(trimethylammonio)ethyl methacrylate were synthesised and used for preparation of polyelectrolyte complexes with calf thymus DNA intended for targeted delivery of genes in vivo. In this study the effects of the speed of component mixing, total concentration of polymers, ionic strength of solvents, copolymer structure and content of HPMA in the copolymers on parameters of the polyelectrolyte complexes was investigated. Static and dynamic light scattering methods were used as a main tool for characterising these complexes. The presence of HPMA units in the polycation had no significant effect on its ability to form complexes with DNA, but did affect molecular parameters and aggregation (precipitation) of the complexes. The size of the complexes increases whereas their molecular weight decreases with increasing content of HPMA units. The density of the complexes decreases with increasing HPMA content independently of the copolymer structure. In order to prepare stable DNA complexes containing single DNA molecule, the following rules should be observed: (1) copolymers should have a content of HPMA units higher than 40%; (2) the DNA concentrations in solutions should be kept below 4 x 10(-5) g/ml and (3) both components should be mixed together in deionized water. The stability of the complexes against precipitation in 0.15 M NaCl and the resistance of the complexed DNA to the action of nucleases was also studied. Whereas DNA complexes of all copolymers showed very good nuclease stability, the presence of a sufficiently high content of HPMA is necessary for their good stability in 0.15 M NaCl. The investigation of the stability and the interaction of DNA complexes in aqueous solutions of serum albumin and dilute human blood serum revealed adsorption of biomacromolecules on DNA complexes accompanied by significant changes in the zeta-potential which finally resulted in formation of a "protein layer" and in undesirable precipitation of DNA complexes. In in vitro transfection experiments, the transfection efficiency of DNA complexes with copolymers was always higher than that of the cationic homopolymer slightly increasing with increasing content of HPMA in the copolymers but being about 10-100-times lower than the complexes DNA-poly(L-lysine. In the cytoplasmic injections, it was observed that DNA complexes produced greater gene expression than a direct microinjection of free DNA. The block copolymer complexes were also found to be more efficient than the corresponding simple polycation complexes. In the nuclear microinjection, precisely the opposite behaviour was observed.

Poly-L-glutamic acid derivatives as vectors for gene therapy

This paper describes the synthesis and evaluation of biodegradable derivatives of poly-L-glutamic acid as suitable vectors for gene therapy. When mixed with DNA the new polymers self assemble and form polyelectrolyte complexes. The formation of the complexes and determination of their stability towards disruption by serum albumin was monitored by Ethidium bromide (EtBr) fluorescence spectroscopy. All polymers were able to form complexes and their size, determined by photon correlation spectroscopy, was between 84.5+/-2 nm and 96. 7+/-1.6 nm, depending on the type of polymer and the charge ratio. All complexes were stable towards serum albumin. The results from the biodegradability tests, using tritosomes, show that the polymers are biodegradable and the rate of degradation is influenced by the number of charged groups in the side chains. Haemolysis and red blood cell (RBC) agglutination were assessed and compared to poly(L-lysine) (pLL) and polyethyleneimine (pEI). RBC agglutination was monitored with optical microscopy. Results show that the new polymers are less toxic than pLL and pEI. Preliminary transfection studies show that the polymers are suitable vectors for gene delivery.

Poly(ethylene glycol) multiblock copolymer as a carrier of anti-cancer drug doxorubicin

The synthesis of a novel water-soluble polymer drug carrier system based on biodegradable poly(ethylene glycol) block copolymer is described in this paper. The copolymer consisting of PEG blocks of molecular weight 2000 linked by means of an oligopeptide with amino end groups was prepared by interfacial polycondensation of the diamine and PEG bis(succinimidyl carbonate). The structure of the oligopeptide diamine consisting of glutamic acid and lysine residues was designed as a substrate for cathepsin B, a lysosomal enzyme, which was assumed to be one of the enzymes responsible for the degradation of the polymer carrier in vivo. Each of the oligopeptide blocks incorporated in the carrier contained three carboxylic groups of which some were used for attachment of an anti-cancer drug, doxorubicin (Dox), via a tetrapeptide spacer Gly-Phe-Leu-Gly. This tetrapeptide spacer is susceptible to enzymatic hydrolysis. In vitro release of Dox and the degradation of the polymer chain by cathepsin B as well as preliminary evaluation of in vivo anti-cancer activity of the conjugate are also demonstrated.

Decreased binding to proteins and cells of polymeric gene delivery vectors surface modified with a multivalent hydrophilic polymer and retargeting through attachment of transferrin

Binding of serum proteins to polyelectrolyte gene delivery complexes is thought to be an important factor limiting bloodstream circulation and restricting access to target tissues. Protein binding can also inhibit transfection activity in vitro. In this study a multivalent reactive hydrophilic polymer has been used to inhibit protein binding. This polymer is based on poly-[N-(2-hydroxypropyl)methacrylamide] (pHPMA) bearing pendent oligopeptide (Gly-Phe-Leu-Gly) side chains terminated in reactive 4-nitrophenoxy groups (8.6 mol%). The polymer reacts with the primary amino groups of poly(L-lysine) (pLL) and produces a hydrophilic coating on the surface of pLL.DNA complexes (as measured by fluorescamine). The resulting pHPMA-coated complexes show a decreased surface charge (from +14 mV for pLL.DNA complexes to -25 mV for pHPMA-modified complexes) as measured by zeta potential analysis. The pHPMA-coated complexes also show a slightly increased average diameter (approximately 90 nm compared with 60 nm for pLL. DNA complexes) as viewed by atomic force and transmission electron microscopy and around 100 nm as viewed by photon correlation spectroscopy. They are completely resistant to protein interaction, as determined by turbidometry and SDS-polyacrylamide gel electrophoresis analysis of complexes isolated from plasma, and show significantly decreased nonspecific uptake into cells in vitro. Spare reactive ester groups can be used to conjugate targeting ligands (e.g. transferrin) on to the surface of the complex to provide a means of tissue-specific targeting and transfection. The properties of these complexes therefore make them promising candidates for targeted gene delivery, both in vitro and potentially in vivo.

Characterisation of the binding interaction between poly(L-lysine) and DNA using the fluorescamine assay in the preparation of non-viral gene delivery vectors

A major factor limiting the development of non-viral gene delivery systems is the poor characterisation of polyelectrolyte complexes formed between cationic polymers and DNA. The present study uses the fluorescamine reagent to improve characterisation of poly(L-lysine) (pLL)/DNA complexes post-modified with a multivalent hydrophilic polymer by determining the availability of free amino groups. The results show that the fluorescamine reagent can be used to monitor the self-assembly reaction between pLL and DNA and the degree of surface modification of the resultant complexes with a hydrophilic polymer. This experimental approach should enable the preparation of fully defined complexes whose properties can be better related to their biological activity.

Polyelectrolyte vectors for gene delivery: influence of cationic polymer on biophysical properties of complexes formed with DNA

Cationic polymer/DNA complexes are widely used for gene delivery, although the influence of the cationic polymer on the biophysical properties of the resulting complex is poorly understood. Here, several series of cationic polymers have been used to evaluate the influence of structural parameters on properties of DNA complexes. Parameters studied included the length of side chain, charge type (primary versus tertiary and quaternary), polymer molecular weight, and charge spacing along the polymer backbone. Cationic polymers with short side chains (such as polyvinylamine) formed small complexes, resistant to destabilization by polyanions, with low surface charge, limited transfection activity, and efficient intranuclear transcription. Conversely, cationic polymers with long side chains (e.g., poly[methacryloyl-Gly-Gly-NH-(CH(2))(6)-NH(2))] showed inefficient complex formation, high positive surface charge, and better transfection activity. The effects of molecular weight varied between polymers, for example, low molecular weight poly(L-lysine) produced relatively small complexes, whereas low molecular weight poly[2-(trimethylammonio)ethyl methacrylate chloride] produced large aggregates. Polymers containing quaternary ammonium groups showed efficient complex formation but poor transfection. Finally, spreading charges widely on the polymer structure inhibited their ability to condense DNA. In summary, to achieve small, stable complexes, the use of cationic polymers with short side chains bearing primary amino groups is suggested.

Effect of albumin and polyanion on the structure of DNA complexes with polycation containing hydrophilic nonionic block

Self-assembling systems based on ionic complexes of DNA with block copolymer of N-(2-hydroxypropyl)methacrylamide with 2-(trimethylammonio)ethyl methacrylate were studied as systems suitable for gene delivery. In this study, the influence of albumin and polyanion on parameters of the DNA polyelectrolyte complexes in aqueous solutions was investigated. Static and dynamic light-scattering methods were used as a main tool for characterizing these interactions. It was found that albumin is not able to release free DNA, but it can rather bind to the complexes forming ternary DNA-polycation-albumin complexes with increased hydrodynamic radii of about 10 nm. Polyanion tested, sodium poly(styrenesulfonate), was able to release free DNA in the presence of a low-molecular-weight electrolyte. In the absence of a low-molecular-weight electrolyte, only formation of ternary complexes and no DNA release was observed. The in vivo biodistribution analysis of DNA complexes showed no effect of the presence of hydrophilic nonionic poly(HPMA) on the circulatory time or organ distribution. The interaction of DNA complexes with albumin and other plasma proteins was suggested to be a major reason for the short circulatory times.

High-performance liquid chromatographic method for sensitive determination of the alkylating agent CB1954 in human plasma

A high-performance liquid chromatography (HPLC) method is described for the measurement of the weak alkylating agent CB1954 in human plasma. CB1954 can be used as an innocuous prodrug designed for activation by bacterial nitroreductases in strategies of gene-directed enzyme-prodrug therapy, and becomes activated to a potent bifunctional alkylating agent. The HPLC method involves precipitation and solvent extraction and uses Mitomycin C (MMC) as an internal standard, with a retention time for MMC of 5.85 +/- 0.015 min, and for CB1954 of 10.72 +/- 0.063 min. The limit of detection for CB1954 is 2.9 ng/ml, and this compares favourably with systems involving direct analysis of plasma (limit of detection 600 ng/ml, approximately). The method is now being used for pharmacokinetic measurements in plasma samples from cancer patients entering phase I clinical trials of CB1954. Results using serial plasma samples from one patient are presented. The patient was treated intravenously with CB1954 (6 mg/m2), and plasma clearance of the drug showed biphasic kinetics with alpha half-life 14.6 min, and beta half-life 170.5 min.

Factors affecting blood clearance and in vivo distribution of polyelectrolyte complexes for gene delivery

Self-assembling polycation/DNA complexes represent a promising synthetic vector for gene delivery. However, despite considerable versatility and transfectional activity in vitro, such materials are quickly eliminated from the bloodstream following intravenous injection (plasma alpha half-life typically less than 5 min). For targeted systemic delivery a more prolonged plasma circulation of the vector is essential. Here we have examined factors contributing to rapid elimination of poly(L-lysine) (pLL)/DNA complexes from the bloodstream, and implicate the binding of proteins to the polyelectrolyte complexes as a likely cause for their blood clearance. pLL/DNA complexes reisolated from serum associate with several proteins, depending on their net charge, although the major band on SDS-PAGE co-migrates with albumin. Serum albumin binds to pLL/DNA complexes in vitro, forming a ternary pLL/DNA/albumin complex which regains some ethidium bromide fluorescence and fails to move during agarose electrophoresis. Albumin also causes increased turbidity of complexes, and reduces their zeta potential to the same level (-16 mV) as is measured in serum. We propose that rapid plasma elimination of polycation/DNA complexes results from their binding serum albumin and other proteins, perhaps due to aggregation and phagocytic capture or accumulation of the ternary complexes in fine capillary beds.

Preliminary clinical study of the distribution of HPMA copolymers bearing doxorubicin and galactosamine

Galactose-targeted delivery of macromolecules and drug conjugates to asialoglycoprotein receptor (ASGPR) positive cells has been widely documented in animals, although targeting in humans has never been demonstrated. In this study we report the pharmacokinetics and imaging determined in the first patient enrolled in a phase I clinical study of the poly[N-(2-hydroxypropyl)methacrylamide] copolymer bearing doxorubicin and galactosamine, known as PK2. Gradient high performance liquid chromatography (HPLC) evaluation of plasma and urine has been combined with 123I-based imaging to show biphasic clearance of the drug from the plasma (half-lives of 78+/-1 and 990+/-15), and approximately 30% delivery of the drug to the hepatic region, as determined by planar whole body imaging at 24 h. This patient has a multifocal hepatoma, and single photon emission computed tomography (SPECT) analysis showed a ratio of tumour tissue to normal liver uptake of approximately 1:3, at 24 h. On the basis of this patient, effective hepatic targeting can be achieved following an intravenous dose of 20 mg/m2 doxorubicin as PK2, however the therapeutic usefulness of this targeted drug has yet to be established.

Macromolecular derivatives of N,N-di-(2-chloroethyl)-4-phenylene diamine mustard. 2. In vitro cytotoxicity and in vivo anticancer efficacy

Prodrugs of N,N-di-(2-chloroethyl)-4-phenylene diamine (PDM) based on soluble poly[N5-(2-hydroxyethyl)-l-glutamine] (PHEG) have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with systemic liberation of free PDM. Modification of PDM by coupling via oligopeptide spacers onto a polymeric carrier significantly reduced its cytotoxicity towards different cell types in vitro. On the other hand, incubation of the cells with the PHEG-Gly-Phe-Ala-Leu-PDM conjugate in the presence of collagenase IV led to the release of lethal amounts of free drug, resulting in higher cytotoxicity for this derivative. The PHEG-Gly-Phe-Ala-Leu-PDM conjugate, which is rapidly degraded by lysosomal and tumour-associated enzymes also showed a decreased systemic toxicity in vivo and could be administered at a dose of 8 mg PDM/kg body weight intravenously, compared with just 2 mg/kg for free PDM. Furthermore, this derivative also showed better antitumour activity against a C26 colorectal carcinoma tumour model, compared with no activity for the free drug. The results indicate that the PHEG-Gly-Phe-Ala-Leu-PDM conjugate is a promising candidate for cancer treatment.

A novel dosage approach for evaluation of SMANCS [poly-(styrene-co-maleyl-half-n-butylate) - neocarzinostatin] in the treatment of primary hepatocellular carcinoma

We report a Phase I/II clinical trial of poly-(styrene-co-maleyl-half-n-butylate)-neocarzinostatin (SMANCS) for intra-arterial treatment of hepatoma. Early patients received 4 or 8 mg SMANCS dissolved in Lipiodol; later patients were treated according to tumour size and degree of filling achieved. SMANCS/Lipiodol drained rapidly from normal liver but was retained within tumour interstitium. Tumour nodules filled with SMANCS/Lipiodol usually stabilised and often regressed. No UICC criteria-defined responses were achieved, partly due to difficulties of filling several lesions simultaneously. Signs of therapeutic activity suggest a more extensive clinical study is warranted.

Novel vectors for gene delivery formed by self-assembly of DNA with poly(L-lysine) grafted with hydrophilic polymers

Complexes formed between DNA and cationic polymers are attracting increasing attention as novel synthetic vectors for delivery of genes. We are trying to improve biological properties of such complexes by oriented self-assembly of DNA with cationic-hydrophilic block copolymers, designed to enshroud the complex within a protective hydrophilic polymer corona. Poly(L-lysine) (pLL) grafted with range of hydrophilic polymer blocks, including poly(ethylene glycol) (pEG), dextran and poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA), shows efficient binding to DNA and mediates particle self-assembly and inhibition of ethidium bromide/DNA fluorescence. The complexes formed are discrete and typically about 100 nm diameter, viewed by atomic force microscopy. Surface charges are slightly shielded by the presence of the hydrophilic polymer, and complexes generally show decreased cytotoxicity compared with simple pLL/DNA complexes. pEG-containing complexes show increased transfection activity against cells in vitro. Complexes formed with all polymer conjugates showed greater aqueous solubility than simple pLL/DNA complexes, particularly at charge neutrality. These materials appear to have the ability to regulate the physicochemical and biological properties of polycation/DNA complexes, and should find important applications in packaging of nucleic acids for specific biological applications.

Lipid-mediated enhancement of transfection by a nonviral integrin-targeting vector

Nonviral vectors consisting of integrin-targeting peptide/DNA (ID) complexes have the potential for widespread application in gene therapy. The transfection efficiency of this vector, however, has been limited by endosomal degradation. We now report that lipofectin (L) incorporated into the ID complexes enhances integrin-mediated transfection, increasing luciferase expression by more than 100-fold. The transfection efficiency of Lipofectin/Integrin-binding peptide/DNA (LID) complexes, assessed by beta-galactosidase reporter gene expression and X-gal staining, was improved from 1% to 10% to over 50% for three different cell lines, and from 0% to approximately 25% in corneal endothelium in vitro. Transfection complexes have been optimized with respect to their transfection efficiency and we have investigated their structure, function, and mode of transfection. Both ID and LID complexes formed particles, unlike the fibrous network formed by lipofectin/DNA complexes (LD). Integrin-mediated transfection by LID complexes was demonstrated by the substantially lower transfection efficiency of LKD complexes in which the integrin-biding peptide was substituted for K16 (K). Furthermore, the transfection efficiency of complexes was shown to be dependent on the amount of integrin-targeting ligand in the complex. Finally, a 34% reduction in integrin-mediated transfection efficiency by LID complexes was achieved with a competing monoclonal antibody. The role of lipofectin in LID complexes appears, therefore, to be that of a co-factor, enhancing the efficiency of integrin-mediated transfection. The mechanism of enhancement is likely to involve a reduction in the extent of endosomal degradation of DNA.

Chloroquine and amphipathic peptide helices show synergistic transfection in vitro

A pH-responsive peptide fragment modelled on the influenza virus haemagglutinin (INF7-SGSC) can promote the transfectional activity of poly(L)-lysine (pLL)/DNA complexes against 293 cells. Chloroquine also promotes transfection, but the combination of INF7-SGSC and chloroquine gives an increased, synergistic, transfectional activity. This was unexpected since the supposed modes of action of these two agents are expected to be incompatible. Microinjection of pLL/DNA complexes into the cytoplasm of Xenopus oocytes produced greater gene expression than microinjection of free DNA, possibly reflecting nuclear-homing or protection from degradation by cytoplasmic nucleases. However, pretreatment of complexes with INF7-SGSC (but not chloroquine) before cytoplasmic microinjection promoted gene expression still further. When pLL/DNA complexes were injected directly into the nucleus, INF7-SGSC again increased gene expression. The mechanism of post-endosomal action of INF7-SGSC is unknown, but could reflect its polyanionic nature, possibly enhancing intranuclear dissociation of the complexes. Whatever the mechanism, it appears that INF7-SGSC mediates two effects-one probably endosomal and the second post-endosomal, the latter showing a synergistic transfection interaction with chloroquine.

Simultaneous gas chromatographic-mass spectrophotometric determination of alpha-fluoro-beta-alanine and 5-fluorouracil in plasma

A gas chromatographic-mass spectrometric (GC-MS) method is reported for simultaneous determination of alpha-fluoro-beta-alanine (FBA), the major end metabolite of 5-fluorouracil (5-FU), and 5-FU in plasma samples isolated from cancer patients. 5-Chlorouracil (5-CIU, 1 micrograms/ml) is added to samples as an internal standard. The method relies on protein precipitation of the plasma sample followed by derivatisation with pentafluorobenzyl bromide. Following sample purification with Sep-pak C18 columns the derivatives are analysed by GC-MS, with FBA, 5-FU and 5-CIU being determined at 36.96-37.03, 46.91-46.98 and 51.99-52.13 min, respectively. The ions measured in each case had m/z of 390, 490 and 506, respectively. The method showed good reproducibility with coefficients of variation between 3 and 10%, with a detection limit of < 1 ng/ml for 5-FU and < 5 ng FBA/ml plasma. The possibility of sensitive determination of FBA without the use of radioisotopes should permit routine estimation of rates of 5-FU metabolism in individual patients.

Characterization of vectors for gene therapy formed by self-assembly of DNA with synthetic block co-polymers

Cationic polymers can self-assemble with DNA to form polyelectrolyte complexes capable of gene delivery, although biocompatibility of the complexes is generally limited. Here we have used A-B type cationic-hydrophilic block co-polymers to introduce a protective surface hydrophilic shielding following oriented self-assembly with DNA. Block co-polymers of poly(ethylene glycol)-poly-L-lysine (pEG-pLL) and poly-N-(2-hydroxypropyl)methacrylamide-poly(trimethylammonioethyl methacrylate chloride) (pHPMA-pTMAEM) both show spontaneous formation of complexes with DNA. Surface charge measured by zeta potential is decreased compared with equivalent polycation-DNA complexes in each case. Atomic force microscopy shows that pHPMA-pTMAEM/DNA complexes are discrete spheres similar to those formed between DNA and simple polycations, whereas pEG-pLL/DNA complexes adopt an extended structure. Biological properties depend on the charge ratio of formation. At optimal charge ratio, pEG-pLL/DNA complexes show efficient transfection of 293 cells in vitro, while pHPMA-pTMAEM/DNA complexes are more inert. Both block co-polymer-DNA complexes show only limited cytotoxicity. Careful selection of block co-polymer structure can influence the physicochemical and biological properties of the complexes and should permit design of materials for specific applications, including targeted delivery of genes in vivo.

Vascular endothelial growth factor stimulates protein kinase C-dependent phospholipase D activity in endothelial cells

Many tumors produce vascular endothelial growth factor (VEGF), a paracrine factor acting selectively on endothelial cells. VEGF has many effects on cultured endothelial cells and mediates angiogenesis and enhanced vascular permeability in vivo. The endothelial signal transduction pathways of VEGF represent novel targets for cancer therapy because they are readily accessible to systemically administered drugs. We have examined VEGF-stimulated signals generated in HUVEC to identify potential targets for therapeutic intervention. The transphosphatidylation reaction has been used to monitor phospholipase D (PLD) activity; total inositol phosphates have been measured after prelabeling of cells with [3H]myoinositol; and intracellular free calcium has been measured using Fura-2 fluorescence. After HUVEC-stimulation with VEGF, there is an early influx of calcium (maximal by 100 seconds) followed by activation of PLD (half maximal by 100 seconds, EC50 70 pm). The PLD activity was inhibited by reducing extracellular calcium (150 nM, 50% inhibition), exposure to 12-O-tetradecanoylphorbol 13 acetate (200 nM, 24 hours, 100% inhibition), Roche 31,8220 (10 microM, 15 minutes, 72% inhibition), or genestein (100 microM, 30 minutes, 56% inhibition), which suggests a dependence on both protein kinase C and tyrosine phosphorylation. Activation of phospholipase C-catalyzed hydrolysis of phosphatidylinositol-4,5-bisphosphate was inferred from the production of inositol phosphates, although this response was slower (half maximal by 3 minutes). The phospholipase C activity was also dependent on influx of calcium and was partially inhibited by low (150 nM) extracellular calcium. PLD may be involved in mediating a number of endothelial responses to tumor-secreted VEGF, notably cytoskeleton-dependent effects such as the cell migration involved in angiogenesis. This signal transduction pathway could represent an accessible and vulnerable target for cancer therapeutic intervention and has the novelty of being located within normal cells rather than tumor cells.

Polymeric prodrugs of mitomycin C designed for tumour tropism and sustained activation

Prodrugs of mitomycin C (MMC) based on soluble poly-[N-(2-hydroxyethyl)-L-glutamine] (pHEG) polymers have been evaluated as tumour-targeted drugs. These materials are designed to exploit the enhanced permeability of tumour vasculature, combining a passive tumour tropism with decreased systemic liberation of free MMC. A tri- or tetrapeptide linkage (e.g. Gly-Phe-Ala-Leu) between pHEG and the aziridine nitrogen of MMC can combine good hydrolytic stability with rapid cleavage by lysosomal enzymes, releasing free MMC. The conjugates showed decreased systemic toxicity and could be administered to mice at a total MMC dose of 15 mg/kg i.v., compared with just 6 mg/kg for free MMC. Conjugates also showed better activity against animal models of established tumours, achieving up to 77% increased life span (ILS) against solid P388 leukaemia, compared with only 23% for free MMC, and up to 121% ILS against solid C26 colorectal carcinoma, compared with no activity for the free drug. Improving the therapeutic index of anticancer drugs by combining tumour tropism with decreased systemic toxicity is a versatile approach that should produce a new generation of improved anticancer agents.

Atomic force microscopic analysis of the influence of the molecular weight of poly(L)lysine on the size of polyelectrolyte complexes formed with DNA

We are developing self-assembling micellar vehicles based on multifunctional block copolymers as well-defined synthetic vehicles suitable for safe in vivo delivery of DNA. As a first stage, DNA expression vectors (6 kb) were condensed with poly(L)lysine of different molecular weights (3970-224 500) to form polyelectrolyte complexes and analysed by atomic force microscopy (AFM). Discrete complexes were formed in every case, although the highest molecular weight poly(L)lysine preparation (224 500) produced large complexes with significant polydispersity (diameters ranging from 120-300 nm), while the smallest poly(L)lysine (3970) produced more homogeneous complexes with diameters ranging from 20-30 nm. Poly (L)lysine preparations of molecular weight 53 700 and 23 800 produced complexes of intermediate size and poly-dispersity. The mean volumes of the complexes formed using poly(L)lysine 224 500 and 3970 were 606 000 nm3 and 3700 nm3, respectively. Polyelectrolyte complexes formed using low molecular weight poly(L)lysine also showed significantly decreased cytotoxicity. Given restrictions of access to many cellular targets and the need for good biocompatibility, synthetic vectors based on DNA condensed with low molecular weight polycations may be more appropriately developed for general use.

Melanoma cell lines express VEGF receptor KDR and respond to exogenously added VEGF

Tumour-secreted vascular endothelial growth factor (VEGF) exerts a number of effects which are important in tumour pathology, including stimulation of angiogenesis and permeabilisation of tumour-associated vasculature. In this study we have examined the possibility that VEGF may also play an autocrine role in tumour growth. Using reverse-transcriptase polymerase chain reaction (RT-PCR), the expression of VEGF was found in 15/15 human tumour cell lines examined, while the VEGF receptor KDR was detected only in three melanoma cell lines (MeWo and A375, both wild type and metastatic variant). Exogenously added VEGF (10ng/ml) was able to stimulate up to 40% increased proliferation of A375 M melanoma cells following a 48-h period of quiescence, suggesting that VEGF may indeed play a role in autocrine, as well as paracrine, stimulation of melanoma growth.

Determination of quercetin in human plasma using reversed-phase high-performance liquid chromatography

A method is reported for the measurement of quercetin in human plasma using reversed-phase high-performance liquid chromatography (HPLC). Quercetin and kaempferol (as internal standard) were spiked into plasma samples and extracted using C18 Sep-Pak Light cartridges (efficiency > 85%). Flavonoids were eluted with aqueous acetone (50% v/v, pH 3.5), dried down and redissolved in aqueous acetone (45% v/v, pH 3.5). The increased osmolarity promoted a phase separation and the water-saturated acetone layer, containing the flavonoids, was analysed by HPLC with aqueous acetone mobile phase (45% v/v acetone in 250 mM sodium dihydrogen sulphate. The mixture was adjusted to pH 3.5 with phosphoric acid and used at a flow-rate of 1.0 ml/min) and mu Bondapak C18 column (150 x 3.9 mm I.D., 10 microns particle size). The detection limit (A375 nm) for quercetin in plasma was 0.1 microgram/ml (300 nM). The method also detects metabolites of quercetin, although these are not yet identified.