Dendrimers for use in targeted delivery

Abstract

The present invention provides cationic dendrimers for delivering bioactive molecules, such as polynucleotide molecules, peptides and polypeptides and/or pharmaceutical agents, to a mammalian body. The dendrimers disclosed herein are suitable for targeting the delivery of the bioactive molecules to, for example, the liver, spleen, lung, kidney or heart.

Description

The present invention relates to the targeted delivery of bioactive molecules in a mammalian body. In particular, the present invention relates to the use of cationic dendrimers for delivering polynucleotide molecules, peptides and polypeptides and/or pharmaceutical agents to a mammalian body, in particular, human.

The possibility of using genes as medicines to correct genetic disorders or treat cancers is hampered by the inability to efficiently deliver genetic material to diseased sites¹. A variety of viral and non-viral systems are being used experimentally each with distinct advantages and disadvantages. Viral systems² have been studied extensively and include a wide variety of viral types such as, retroviruses, adenoviruses, adeno-associated viruses, herpes simplex virus and the HIV based lentivirus. All have various inherent disadvantages³ such as safety concerns and scale-up difficulties. Non-viral systems such as cationic liposomes^4-6, cationic polymers^7,8, cationic polymeric vesicles^9,10 and dendrimers^11-14 have thus been studied as gene delivery agents in an effort to circumvent some of the safety and production problems associated with viruses. As well as applications in human health, suitable gene transfer systems are commercially attractive as in vitro molecular biology and in vivo transfection reagents for laboratory use.

Dendrimers are synthetic 3-dimensional macromolecules that are prepared in a step-wise fashion from simple branched monomer units, the nature and functionality of which can be easily controlled and varied. Dendrimers are synthesised from the repeated addition of building blocks to a multifunctional core (divergent approach to synthesis), or towards a multifunctional core (convergent approach to synthesis) and each addition of a 3-dimensional shell of building blocks leads to the formation of a higher generation of the dendrimers⁵¹. Polypropylenimine dendrimers start from a diaminobutane core to which is added twice the number of amino groups by a double Michael addition of acrylonitrile to the primary amines followed by the hydrogenation of the nitriles⁵². This results in a doubling of the amino groups⁵².

Polypropylenimine dendrimers contain 100% protonable nitrogens¹⁷ and up to 64 terminal amino groups (generation 5, DAB 64)^15,16. Protonable groups are usually amine groups which are able to accept protons at neutral pH. The use of dendrimers as gene delivery agents has largely focused on the use of the polyamidoamine^11-13,18-25 and phosphorous containing¹⁴ compounds with a mixture of amine/amide or N—P(O₂)S as the conjugating units respectively with no work being reported on the use of the lower generation polypropylenimine dendrimers for gene delivery. Polypropylenimine dendrimers have also been studied as pH sensitive controlled release systems for drug delivery^26,27 and for their encapsulation of guest molecules when chemically modified by peripheral amino acid groups²⁸. The cytotoxicity²⁹ and interaction of polypropylenimine dendrimers with DNA³⁰ as well as the transfection efficacy of DAB 64 has also been studied³¹.

Kabanov and others report that polypropylenimine dendrimers interact with DNA via the surface primary amines only with no involvement of the internal amine groups³⁰ while Gebhart and Kabanov report very low gene transfer activity with the 5^th generation polypropylenimine dendrimers DAB 64 in the easy to transfect COS cell line³¹. These workers also report that DAB 64 is far too toxic above a dendrimer, DNA weight ratio of 0.62:1 (nitrogen to phosphate ratio of 4:1). Additionally Malik and others conclude that the cationic dendrimers as opposed to the anionic dendrimers are too toxic for parenteral use without further derivatisation with biocompatible groups such as polyethylene glycol units²⁹.

The present invention is based upon the observation that, contrary to earlier reports, cationic dendrimers, such as polypropylenimine dendrimers, display suitable properties, such as specific targeting and low toxicity, for use in the targeted delivery of bioactive molecules, such as genetic material. In addition, derivatives of the cationic dendrimer also display suitable properties for the targeted delivery of bioactive molecules.

The chemical modification (derivatisation) of polypropylenimine dendrimers has been extensive with reports on the conjugation of amino acid^28,32, carboxylate^33,34, acetyl³⁵, 2-(hydroxy)propyltrimethylammonium²⁷, dimethyldodecylammoniumm³⁶, 3,4,5-(ologoethylenoxy) benzoyl³⁷, alkanoyl thioglucose³⁸, thiolactosyl³⁹ groups as well as the conjugation of hydrophobic 3,4-bis(decyloxy)benzoyl⁴⁰, palmitoyl⁴¹, pentafluorphenyl 11-[4-(4-hexyloxyphenylazo)phenyloxy]undecanoyl⁴¹, adamantine carboxyl⁴¹, decanoyl⁴², dodecyl⁴², polyisobutylene⁴³, stearoyl⁴⁴, ω-(4′cyanobiphenyloxy)alkyl⁴⁵, and oligo(p-phenylene vinylene)⁴⁶ groups to the primary amino groups on the surface of polypropylenimine dendrimers.

In addition to the targeted delivery of genetic material, selective targeting of other bioactive agents, such as peptides/polypeptides and pharmaceutical agents, is sought.

It is thus one of the objectives of the present invention to provide cationic dendrimers capable of targeted delivery of bioactive molecules to a particular location in a mammalian body.

Accordingly, the present invention provides a composition for the delivery of bioactive molecules to a target location in the body of a recipient, wherein said composition comprises a cationic dendrimer, and/or derivatives thereof, admixed with said bioactive molecule.

The term “cationic dendrimer” refers to a dendrimer molecule which possesses a positive charge at physiological pH. However, the dendrimer derivatives of the present invention may not in themselves be cationic as a result of the derivatisation.

The cationic dendrimers, or derivatives thereof, of the composition of the present invention may be derived from a core molecule comprising 2 to 10 carbon atoms, such as 3 or 4 carbon atoms, and in particular 4 carbon atoms with one or more functional groups which may, for example, be amine groups. It will be appreciated that, for example, the cationic dendrimers, or derivatives thereof, may be derived from a core molecule such as diaminoethane, diaminopropane or diaminobutane, and in particular, diaminobutane.

The groups attached to the core molecule may, for example, include propylamines Thus, the dendrimers may be polypropylenimine dendrimers, or derivatives thereof, and may possess a diaminobutane core.

The term “polypropylenimine dendrimer” is intended to refer to dendrimers comprising a diaminobutane core with 1, 2, 3, 4 or 5 generations of propylenimine molecules attached. The term encompasses DAB 4, DAB 8, 16, 32 and 64, DSAM 4, DSAM8, 16, 32 and 64, and QDAB4, 8, 16, 32 and 64, HDAB4, 8, 16, 32, 64 and bolamphiphilic polypropylenimine dendrimers BDAB4, BDAB8, BDAB16, BDAB32, BDAB64. Although all generations of the compounds DSAM, QDAB, HDAB and BDAB comprise a diaminobutane core with propylenimine groups attached thereto, the term “DAB” as generally used herein is intended to refer to the underivatised DAB8, 16, 32 and 64 compounds, unless otherwise indicated.

The term “generation” refers to the number of iterative reaction steps that are necessary to produce the compound. The number which follows the name or abbreviated name of the dendrimer, for example, 8, 16, 32 or 64 refers to the number of surface groups on the dendrimer molecule itself, which amino groups may or may not be derivatised.

The cationic dendrimers of the composition of the present invention may be modified by covalently binding derivatising groups, such as hydrophobic, hydrophilic or amphiphilic groups to the surface of the dendrimer or by attaching two dendrimer molecules to either end of a hydrocarbon chain with a carbon length of 8, 12, 14, 16 or 18 carbons to give bolamphiphilic dendrimers (said modified dendrimers referred to herein as “derivatives”). The number of derivatising groups may vary from one derivatising group per dendrimer molecule up to and including derivatising all available surface or terminal groups on the dendrimer molecule, for example, derivatising all 16 surface groups of the DAB16 molecule.

The amphiphilic derivative comprises a hydrophilic and a hydrophobic segment. The hydrophilic segment may be derived from a phosphoglycerate molecule, for example, glycerol 3-phosphate. The hydrophobic segment is covalently bound to the hydrophilic segment, for example, via an ester linkage. The hydrophobic segment is selected from any suitable hydrophobic group, for example, alkyl, alkenyl or alkynyl groups of 8-24 carbons in length. Therefore, the hydrophobic segment plus ester linkage can be defined as an acyl group. The amphiphilic derivative is attached to the dendrimer by a linker molecule, such as polyethylene glycol (PEG) or a sugar unit such as muramic acid bound to the hydrophilic segment. The length of the PEG linker molecule may for example be in the range of 1 to 120 ethylene glycol units, for example 50-100 and, for example, 70-80, for example, 77. In particular the linker molecule may be polyethylene glycol with a Mw of approximately 3,500. Alternatively, the linker molecule may be an ester, amine or ether linkage for ordinary hydrophobic modifications or a sugar molecule such as muramic acid. In particular, the derivative may be a phosphoglyceride such as a phosphatidyl ethanolamine, for example, distearoylphosphatidylethanolamine. The number of amphiphilic derivatives per dendrimer molecule may range from 1 derivatising group per dendrimer molecule to derivatising all of the groups of the dendrimer (the generation of the dendrimer will determine the total number of surface groups available for derivatising), and may be, in particular, one group per dendrimer. Thus, the dendrimers of the present invention include generations 1, 2, 3, 4 and 5 of the amphiphilic-derivatised diaminobutane dendrimer referred to herein as 1,2-diacyl-SN-glycero-3-phosphoethanolamine-N-[(polyethyleneglycol)-N-diaminobutanepolypropylenimine dendrimer-(NH₂)_x], where x=4, 8, 16, 32 or 64 (conveniently referred to as DSAM4, 8, 16, 32 or 64, respectively).

The hydrophobic derivative may be an alkyl, acyl, alkenyl, alkynyl or aryl group of 8-24 carbons in length. It is to be understood that the term “hydrophobic” can encompass acyl groups when the chain length of such acyl groups is 8 carbons or more and may, for example, be a hexadecanoyl group. The number of hydrophobic groups per dendrimer molecule may range from 1 derivatising group per dendrimer molecule to derivatising all of the groups of the dendrimer (the generation of the dendrimer will determine the total number of surface groups available for derivatising), and may be, in particular, one group per dendrimer. Thus, the dendrimers of the present invention include generations 1, 2, 3, 4 and 5 of the hydrophobic-derivatised diaminobutane dendrimer referred to herein as HDAB4, HDAB8, HDAB16, HDAB32, HDAB64.

The bolamphiphiles may consist of two molecules of any of the dendrimers DAB4, DAB8, DAB 16, DAB 32, DAB 64 linked to either end of an alkyl, acyl, alkenyl, alkynyl hydrophobic unit of 8 to 24 carbon chains in length or alternatively linked by an aryl group and may be a C12 bolamphiphile of DAB 4 or DAB 8. The term “bolamphiphiles” is understood to refer to an amphiphilic molecule wherein the hydrophilic groups are separated by the hydrophobic groups. Thus, the dendrimers of the present invention include C8-C16alkyl bolamphiphiles of dendrimers of generations 1, 2, 3, 4 and 5 herein referred to as B8DAB4, 8, 16, 32 or 64; B10DAB4, 8, 16, 32 or 64; B12DAB4, 8, 16, 32 or 64, B14DAB4, 8, 16, 32 or 64 and B16DAB4, 8, 16, 32 or 64. The amino derivative may, for example, be a tertiary amine or quaternary ammonium derivative, and in particular a quaternary derivative comprising C1-C4 alkyl groups, such as 3 methyl groups, covalently bound to a nitrogen atom on the surface of the dendrimer. The number of ammonium derivatives per dendrimer molecule may range from 1 derivatising group per dendrimer molecule to derivatising all groups of the dendrimer (the generation of the dendrimer will determine the total number of surface groups available for derivatising), and may be, in particular, all groups available for derivatising. Thus, the dendrimers of the present invention include generations 1, 2, 3, 4 and 5 of the quaternary ammonium-derivatised diaminobutane dendrimer referred to herein as quaternary ammonium diaminobutanepolypropylenimine dendrimer-[NH₂(CH₃)₃]_x, where x=4, 8, 16, 32 or 64 (conveniently referred to as QDAB4, 8, 16, 32 or 64, respectively).

The dendrimers in the present invention may also be derivatised with hydrophilic groups such as sugars, mono and oligohydroxy C1-C6 alkyl, mono and oligohydroxy C2-C6 acyl, C1-C2 alkoxy alkyl optionally having one or more hydroxy groups substituted on the alkoxy or alkylene groups, amino acids, peptides of 1-200 amino acids in length and oligo or poly-(oxa C1-C3 alkylene) such as polyoxyethylene comprising 1-120 ethylene oxide units.

Target locations for the delivery of bioactive molecules include the liver, spleen, lung, kidney and heart. In particular, two of the dendrimers of the present invention studied, DAB16 and DSAM16, have displayed organ-specific targeting to the liver and spleen, respectively.

Therefore, the present invention also provides a composition for the delivery of a bioactive molecule to the liver of a recipient, wherein said composition comprises the polypropylenimine dendrimer DAB16 admixed with a said bioactive molecule. Additionally, the present invention provides a composition for the delivery of bioactive molecules to the spleen of a recipient, wherein said composition comprises the polypropylenimine dendrimer DSAM16 admixed with a said bioactive molecule.

The recipient may be a mammal, such as a human.

The terms “bioactive molecules” and “biologically active molecules” are intended to encompass polynucleotides, peptides/polypeptides and/or pharmaceutical agents. The term “polynucleotides” generally refers to DNA unless otherwise indicated but may include RNA, cDNA, oligonucleotides, plasmids etc. The term may also be used interchangeably herein with the terms “polynucleotide”, “gene”, “genetic material” and “genetic sequence”. Such genes intended for expression are common to the field of gene therapy and include, but are not limited to, sense DNA or RNA for expressing a product in the target organ, or antisense DNA or RNA for reducing or eliminating expression of a native or introduced gene in the target organ. The term “peptide” refers to a chain of 4 to 600 amino acids long, such as 4 to 200 amino acids long and therefore encompasses polypeptides and proteins, and includes enzymes and polypeptide hormones. Furthermore, peptides modified by, for example, glycosylation, are also included in the present invention, as is a protein comprising two or more polypeptide chains each of length of 4 to 600 amino acids long cross-linked by, for example, disulphide bonds, for example, insulin and immunoglobulins. The term “pharmaceutical agent” is intended to include any natural or synthetic compound administered to a recipient in order to induce a physiological or pharmacological effect. Examples of such agents are anti-tumour drugs, antibiotics, hormones, anti-inflammatory agents, antiparasitic agents, DNA vaccines, etc

The cationic dendrimers are admixed with the bioactive agents in preparing the compositions of the present invention for delivery. The term “admixed” generally refers to the bioactive agent being associated with but not covalently bound to the dendrimer. The term is however also intended to encompass covalently binding the bioactive agent to the dendrimer via any suitable reactive group on the dendrimer and the agent.

Where the bioactive agent is a polynucleotide molecule, the molecule is usually associated with, that is, not covalently bound to, the dendrimer to allow the polynucleotide to be expressed. However, it may also be possible that expression of a covalently bound polynucleotide molecule can occur, and therefore, these covalently bound polynucleotide molecules are intended to be encompassed by the present invention.

In a yet further aspect, the present invention provides a pharmaceutical formulation comprising a composition of the present invention, and a pharmaceutically acceptable carrier.

Pharmaceutically acceptable carriers are well known to those skilled in the art and include, but are not limited to, 0.1 M and preferably 0.05M phosphate buffer or 0.8% (w/v) saline. Additionally, such pharmaceutically acceptable carriers may be aqueous or non-aqueous solutions, suspensions, and emulsions. Examples of non-aqueous solutions are propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride, lactated Ringer's or fixed oils. Intravenous vehicles include fluid and nutrient replenishers, electrolyte replenishers such as those based on Ringer's dextrose, and the like. Preservatives and other additives may also be present, such as, for example, antimicrobials, antioxidants, chelating agents, inert gases and the like.

Conveniently, the composition or pharmaceutical formulation of the present invention may include an agent which assists in forming a colloidal suspension, for example, 5% dextrose solution. Other agents which may be included are viscosity enhancing polymers such as alginates and polyethyleneglycol polymers, buffering agents and mixtures of aqueous and non-aqueous solvents in emulsions.

The present invention also provides the use of the composition or pharmaceutical formulation of the present invention for the delivery of bioactive molecules to a target location in the body of a recipient.

In a further aspect, the present invention provides a method of delivering a bioactive molecule to a target location in the body of a recipient, which method comprises preparing a composition comprising a cationic dendrimer, or derivative thereof, admixed with a said bioactive molecule, and subsequently administering the composition to said recipient.

Although the dendrimers of the present invention display suitable properties for the delivery of bioactive molecules in vivo, they are also useful for transfecting mammalian cells in vitro. Thus, the present invention also provides a composition of the present invention for transfecting mammalian cells with a bioactive molecule in vitro. The mammalian cells may, for example, be human cells.

The present invention still further provides 1,2-diacyl-SN-glycero-3-phosphoethanolamine-N-[(polyethyleneglycol)-N-diaminobutanepolypropylenimine dendrimer-(NH₂)_x], where x=4, 8, 16, 32 or 64 (DSAM), and quaternary ammonium diaminobutanepolypropylenimine dendrimer-[NH₂(CH₃)₃]_x, where x=4, 8, 16, 32 or 64 (QDAB). The DSAM or QDAB dendrimers may, for example, be second, third, fourth or fifth generation dendrimers referred to herein as DSAM4, 8, 16, 32 and 64, and QDAB4, 8, 16, 32 and 64.

The present invention also provides a method of preparing a composition as described above, said method comprising admixing a cationic dendrimer, and/or derivatives thereof, and a bioactive molecule.

These and other aspects of the present invention will now be described by way of example only, in conjunction with the accompanying Figures, in which:

FIG. 1 illustrates DAB 16 generation 3 polypropylenimine dendrimer, DAB 64 contains 2 more generations of propylamines attached to this molecule;

FIG. 2 illustrates DSAM 16, an amphiphilic derivative of DAB 16 (DSPE-PEG-NHS+DAB16);

FIG. 3 illustrates BnDAB4, a bolamphiphile derivative of DAB4 (n=8, 10 or 12 to give B8DAB4, B10DAB4, B12DAB4 respectively);

FIG. 4 illustrates QDAB 16, a quaternary ammonium derivative of DAB 16 (CH₃₁+DAB16);

FIG. 5 illustrates Luciferase gene expression in vivo;

FIG. 6 illustrates liver targeting of gene expression by the polypropylenimine dendrimers; and

FIG. 7 illustrates tumour gene expression after the intravenous administration of DNA, PEI-DNA=the Exgen 500 formulation.

EXAMPLE 1

Methods

Synthesis of Modified Dendrimers

DSAM

To DAB 16 (Sigma Aldrich, Dorset, UK—3.52 g, 1.32 mmoles) dissolved in absolute ethanol (70 ml) was added triethylamine (27 ml, 6.6 mmoles) and to this solution was added dropwise DSPE-PEG-NHS (distearoylphosphatdylethanolamine polyethylene glycol N-hydroxysuccinimide—500 mg, 0.11 mmoles, Shearwater Polymers) dissolved in chloroform (25 mL) over 60 minutes. The reaction was left stirring protected from light for 72 h. At the end of this time the reaction mixture was evaporated to dryness by rotary evaporation under reduced pressure at 50° C. The residue was redissolved in absolute ethanol (40 ml), filtered and the filtrate evaporated to dryness. This latter residue was dissolved in water (80 ml) and dialysed against 5 l of water over 24 h with 6 changes. The dialysate was freeze-dried and the structure confirmed by ¹H and ¹³C NMR.

QDAB

DAB 16, 32 or 64 (500 mg) was dispersed in methyl-2-pyrolidone (50 ml) for 16 h at room temperature with stirring. To the DAB dispersion was added sodium hydroxide (120 mg), methyl iodide (3 g) and sodium iodide (150 mg). The reaction mixture was stirred under a stream of nitrogen for 3 h at 36° C. The quaternary ammonium product was recovered by precipitation in diethyl ether followed by filtration. The solid was washed with copious amounts of absolute ethanol (1 l) followed by copious amounts of diethyl ether (500 ml). The washed solid was then dissolved in water (150 ml) and passed over an ion exchange column (1×6 cm packed with 30 ml Amberlite IRA-93 Cl⁻ and subsequently washed with HCl—90 ml, 1 M followed by distilled water—500 ml until the eluate gives a neutral pH). The eluate obtained was freeze-dried and the structure confirmed by both ¹H and ¹³C NMR.

DNA Condensation

Plasmid (pCMVsport β-gal or pCMV luciferase, Life Technologies, UK) was grown in E. coli and plasmid purification carried out using a QIAGEN Endo-toxin free Giga Plasmid Kit (QIAGEN, Hilden, Germany) according to the manufacturer's instructions. Purity was confirmed by agarose gel electrophoresis⁴⁷. The reduced fluorescence of ethidium bromide (EthBr) was used to probe for DNA condensation by the polymers. EthBr fluorescence increases significantly (factor 40 compared to unbound EthBr) on intercalation with double stranded DNA⁴⁸. The electrostatic interaction between the anionic DNA and cationic groups of the carrier on formation of the DNA—vesicle complex reduces the number of EthBr binding sites, a process termed condensation, ultimately reducing the fluorescence intensity of the EthBr solution.

Complexes of DAB 16 and DSAM with DNA were prepared at various polymer, DNA weight ratios and at various time points the fluorescence intensity (λ_excitation=526 nm, λ_emission•=592 nm) of the complexes determined in the presence of EthBr (40 μg ml⁻¹). The DNA concentration in the cuvette was kept constant (100 μg ml⁻¹) and the polymer solutions in PBS (phosphate buffered saline, pH=7) and a solution of DNA in PBS served as controls. The reduced fluorescence (F_t/F₀), was determined for each of the samples, where F_t=the fluorescence of the DNA, polymer complexes and F₀=the fluorescence of DNA alone.

In Vitro Cytotoxicity Assay

A human epidermoid carcinoma cell line (A431, ATCC CRL-1555) was maintained in Dulbecco's minimum essential medium (DMEM) supplemented with 10% foetal calf serum (FCS) and 2 mM glutamine (GibcoBRL, UK) at 10% CO₂ and 37° C.

Polypropylenimine dendrimer/dendrimer derivative formulation cytotoxicity was assessed by the measurement of the IC50 in a standard MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide thiazolyl blue—indicator dye) assay. Briefly, 96 well microtitre plates were seeded with 5000 cells per well and incubated for 24 hrs. Dilutions of the dendrimer/dendrimer—DNA formulations (100 μl) in tissue culture medium (Opti-Mem) were incubated with the cells for 4 h. The samples were then replaced with fresh DMEM daily and incubated for 72 h. After this period the indicator dye (50 μl, 50 mg ml⁻¹) was added to each well and incubated with the cells for 4 h in the dark. The medium and indicator dye were then removed and the cells lysed with dimethylsulphoxide (200 μl). After addition of Sorensen's glycine buffer (25 μl) the absorption was measured at 570 nm. Values were expressed as a percentage of the control to which no vesicles were added.

In Vitro Transfection

DNA Polymer Formulations

DAB and QDAB dendrimer—DNA (pCMVSport P-galactosidase) formulations were made by mixing DNA and dendrimers in a 5% dextrose solution and allowing to stand for no longer than 15 minutes before use. The resulting colloidal dispersion was sized by photon correlation spectroscopy (Malvern Instruments, UK).

Cell Culture

A431 cells (human epidermoid carcinoma cell line, ATCC, CRL-1555), maintained in Dulbecco's Minimal Essential Medium (DMEM, Life Technologies, UK) supplemented with foetal calf serum and L-glutamine (2 mM) were seeded at a density of 10⁴ cells ml⁻¹ and 200 μL of the cell suspension placed in 96 well flat bottomed plates. Cells were incubated for 24 h at 37° C. in 10% CO₂. Polymer—DNA complexes containing 200 μg ml⁻¹ DNA (100 μl) and serum free medium (100 μl, OPTIMEM, Life technologies, UK) were incubated with the cells for 4 h at 37° C. in 10% CO₂. Naked DNA served as the negative control while a formulation comprising N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulphate (DOTAP), DNA (5:1) served as the positive control. Both the negative and positive controls were dosed at a level of 20 μg DNA per well while the level of DNA dosed with the dendrimers varied as indicated. After this time the incubation medium was replaced with DMEM culture media containing penicillin (100 U ml⁻¹) and streptomycin (0.1 mg ml⁻¹) and once again incubated at 37° C. in 10% CO₂ for 48 h. The cells were then washed in phosphate buffered saline (200 μl) and lysed with 1×Passive Lysis Buffer (80 μL, Promega, UK) for 30 min. The cell lysates were subsequently analysed for β-galactosidase expression as described below.

β-Galactosidase Expression

To the assay buffer [50 μl (sodium phosphate buffer—200 mM, pH=7.3, magnesium chloride—2 mM, mercaptoethanol—100 mM, o-nitrophenol-β-galactopyranoside—1.33 mg ml⁻¹)] was added an equal volume of the cell lysate from above within 96 well flat-bottomed plates. Samples were incubated for 1 h and the visible absorbance read at 405 nm on an automatic plate reader.

In Vivo Transfection

DNA-Polymer Formulations

Exgen 500 (linear polyethylenimine 22 kD, Euromedex, France) was formulated with the luciferase reporter gene (pCMV luciferase) as described by the manufacturers. Both DAB 16 and DSAM were dissolved in 5% w/v dextrose by probe sonication (5 minutes with the instrument set at 15% of its maximum output) and mixed in a 5:1 weight ratio with DNA 15 minutes prior to intravenous injection.

Animal Experiments

Groups of Balb/C mice (n=3) were injected via the tail vein with either the DAB 16, DSAM, Exgen 500 or naked DNA formulations each containing 100 μg of DNA in an injection volume of 200-400 μl. Exgen 500 and naked DNA served as the positive and negative controls respectively. Organs were harvested 24 h later and quickly frozen in liquid nitrogen and stored at −80° C. until analysis could be performed on them.

Analysis for Luciferase

To the liver samples were added 5 μl of tissue lysis buffer (25 mM Tris HCl—pH=8.0, 2 mM DTT, 2 mM EDTA—pH 8.0, 10% w/v glycerol, 1% w/v Triton X-100, 1 Complete® protein inhibitor cocktail tablet per 50 ml of buffer) per mg of liver tissue. To the other organs was added 4 μl of tissue lysis buffer per mg of tissue. Organs were homogenised on ice in the lysis buffer to form a slurry and the slurry incubated on ice for 15 mins. The resulting slurry was centrifuged at 13,000 rpm to pellet tissue debris and the supernatant removed to a fresh tube. To the pellet was added another 50 μl of lysis buffer. The pellet was resuspended by homogenisation and centrifuged once more at 13,000 rpm and the supernatant removed and added to the previous supernatant sample. Supernatant samples were diluted 1:10 with the tissue lysis buffer and 80 μl of this solution sampled and used for the luciferase assay which was carried out according to the protocol provided by Promega, UK. Protein estimation was carried out using the Sigma (Sigma-Aldrich, UK) bicinchoninic acid system (BC-1).

Results and Discussion

DNA binds electrostatically with the nitrogen rich dendrimers DAB 16, DAB 32 and DAB 64 (Table 2) and presumably with DAB 8. These compounds begin to condense DNA at a nitrogen to phosphate ratio of 1.47, 1.49 and 1.45 respectively (Table 1) and a surface nitrogen to phosphate ratio of 0.78, 0.77 and 0.74 respectively.

TABLE 1
% Condensation of DNA by DAB Dendrimers
	Dendrimer,
Dendrimer	DNA weight ratio	% DNA condensation after 30 min
DAB 16	5.00	90.3
	2.00	93.9
	1.00	96.2
	0.50	96.0
	0.25	94.1
	0.13	42.8
QDAB 16	5.00	96.2
	2.00	95.3
	1.00	95.7
	0.50	94.6
	0.25	33.6
	0.13	19.2
DAB 32	5.00	94.4
	2.00	96.9
	1.00	96.7
	0.50	96.1
	0.25	87.2
	0.13	21.8
QDAB 32	5.00	96.7
	2.00	96.9
	1.00	96.4
	0.50	43.9
	0.25	12.6
	0.13	7.5
DAB 64	5.00	93.4
	2.00	95.4
	1.00	93.1
	0.50	96.2
	0.25	87.9
	0.13	26.3
QDAB 64	5.00	96.0
	2.00	96.2
	1.00	95.4
	0.50	46.0
	0.25	15.3
	0.13	11.9
DSAM 16	5	85.1
	10	85.0
	15	85.9
	20	85.7

It appears as if DNA does not bind only to the surface nitrogens of polypropylenimine dendrimers as reported³⁰ but also to nitrogens possibly in the second shell of the dendrimer also. Condensation of DNA with the polyamidoamine dendrimers has also been found to occur by electrostatic means¹⁹. We propose that the polypropylenimine dendrimers have advantages over the polyamidoamine polymers for gene delivery applications simply due to the increased content of protonable nitrogens on the polypropylenimine polymers. There are also advantages associated with the polymer shape over linear polymers as DNA appears to interact with the surface primary amines only, leaving the internal tertiary amines available for the neutralization of the acid pH⁵⁰ within the endosomal/lysosomal compartment. The release of polyamidoamine carried genes by the endosome has been attributed to the protonation of the internal tertiary nitrogens by endosomal protons which then results in a swelling of the endosome and the release of the DNA to the cytoplasm¹². Also the hydrolytic degradation of polyamidoamine dendrimer amide bonds in water or ethanol^{12, 13} increases transfection efficacy up to 50 fold which the authors attribute to the increased flexibility of the polymer on heat degradation. This increased flexibility is said to be crucial to the swelling of the endosome¹². However we propose that simply increasing the level of tertiary amines in the polymer available for neutralization of the endosomal/lysosomal pH improves transfection irrespective of the flexibility of the polymer.

In vitro transfection efficacy with the polypropylenimine dendrimers reveals that protein expression obtained by using 20 μg of DNA in the DOTAP formulation is obtained using just 5 μg of DNA in the DAB 16 formulation and there is no significant difference between the use of 15 μg DNA in the QDAB 16 formulation and 20 μg DNA in the DOTAP formulation (Table 2).

TABLE 2
The in vitro transfection of DAB dendrimers in the A431 cell line
		β-galactosidase
Formulation	DNA dose per well (μg)	expression*
DAB 8, DNA (3:1 g g−1)	20	101.3
	15	102.6
	10	80.1
	5	45.1
DAB 8, DNA (5:1 g g−1)	20	108.7
	15	96.5
	10	73.1
	5	59.2
DAB 8, DNA (10:1 g g−1)	20	82.0
	15	76.4
	10	78.6
	5	71.7
DAB 16, DNA (1:1 g g−1)	20	54.2
	15	40.0
	10	38.3
	5	33.7
DAB 16, DNA (3:1 g g−1)	20	23.9
	15	40.7
	10	57.7
	5	56.5
DAB 16, DNA (5:1 g g−1)	20	18.3
	15	24.1
	10	88.4
	5	100.8
QDAB 16, DNA (1:1 g g−1)	20	54.2
	15	40.0
	10	38.3
	5	33.7
QDAB 16, DNA (3:1 g g−1)	20	76.4
	15	70.4
	10	45.3
	5	13.8
QDAB 16, DNA (5:1 g g−1)	20	42.3
	15	50.8
	10	48.5
	5	45.5
DSAM 16, DNA (5:1 g g−1)	20	28.6
	15	35.2
	10	25.1
	5	26.7
DSAM 16, DNA (10:1 g g−1)	20	26.1
	15	22.2
	10	22.3
	5	24.3
DSAM 16, DNA (15:1 g g−1)	20	21.1
	15	21.6
	10	21.4
	5	21.9
DAB 32, DNA (3:1 g g−1)	20	12.2
	15	16.3
	10	17.6
	5	16.6
QDAB 32, DNA (3:1 g g−1)	20	13.8
	15	23.2
	10	33.1
	5	21.3
*% Expression relative to expression obtained for optimum DOTAP (DOTAP, β-galactosidase reporter DNA ratio = 5:1) formulation on dosing cells with 20 μg DNA. % protein expression relative to DOTAP formulation obtained with 20 μg naked DNA alone = 25.15%

Transfection with DAB 8 is also slightly superior to that obtained with DOTAP (Table 2). This indicates a superior gene transfer activity for the DAB 8 and DAB 16 dendrimers. DAB 4 is currently being tested in our laboratories. For the DAB 16 formulation, transfection appears to be optimum when using DAB 16 complexes with DNA at a nitrogen to phosphate ratio of 30:1, forming complexes of 150 nm in size. Transfection with DAB 8 is also optimum at a nitrogen to phosphate ratio of 30:1. Transfection with polyamidoamine dendrimers is optimum when low-density soluble material is formed at a nitrogen to phosphate ratio of 20:1¹⁹.

DAB 8 the most transfection efficient molecule studied to date in the polypropylenimine dendrimer class is also the least toxic, exhibiting an IC50 almost 6× higher than DOTAP (Table 3).

TABLE 3
In vitro cytotoxicity against the A431 cell line
Formulation              IC50 (μg ml−1)
DAB 8                    352.4
DAB 8, DNA (5:1 g g−1)   669.4
DAB 16                   38.9
DAB 16, DNA (5:1 g g−1)  36.0
QDAB 16                  44.6
QDAB 16, DNA (3:1 g g−1) 129
DAB 32                   5.7
DAB 32, DNA (3:1 g g−1)  5.8
QDAB 32                  11.2
QDAB 32 (3:1 g g−1)      33
DOTAP                    62

The data in Table 3 indicate that the complex formed by DNA and the quaternised molecule (QDAB 32 and QDAB 16) is less toxic than that formed by DNA and the unquaternised molecule. The quartenised molecule QDAB 16 is as active as DOTAP at the 20 μg DNA dose and QDAB 32 shows slight activity as a gene transfer agent at the 10 μg dose level (Table 2) while DAB 32 is inactive. It is envisaged that QDAB 8 will produce a gene transfer formulation with good biocompatibility and also with no loss of activity when compared to the unquaternised parent polymer.

DAB 16 and DSAM are efficient deliverers of DNA to tissues in vivo comparing favourably to the commercial product Exgen 500 and with the added ability of being able to target the liver (DAB 16) and spleen (DSAM 16) more effectively than Exgen 500 (Table 4, FIG. 5).

TABLE 4
In vivo luciferase expression obtained in the mouse model
	% Luciferase expression
	relative to Exgen 500*
	Formulation	Lung	Liver	Kidney	Heart	Spleen
	DAB 16	48.9	762.6	28.6	73.2	100
	DSAM 16	25.8	264.3	11.3	58.2	599.2
	DNA Alone	9.2	43.6	10.6	33.0	97.0
	*% luciferase expression relative to that obtained with linear PEI (Mw = 22 kD, Exgen 500 ®) on intravenous injection of 50 μg DNA DAB 16 (DAB 16, DNA weight ratio = 5:1) and DSAM 16 (DSAM 16, DNA weight ratio = 5:1) formulations. Exgen 500 formulation consists of linear PEI, DNA weight ratio = 6:1.

CONCLUSIONS

In summary the lower generation polypropylenimine dendrimers (DAB 8 and DAB 16) show improved biocompatibility when compared to DOTAP and transfection activity which is at some dose levels superior to that obtained with DOTAP. Additionally DAB 16 may be used to target the liver, and DSAM 16 used to target the spleen in vivo.

EXAMPLE 2

Materials

All polypropylenimine dendrimers, glucose, were obtained from Sigma-Aldrich, UK. Phenyl methyl sulphonyl fluoride (PMSF), protease Inhibitor cocktail and phosphate buffered saline tablets, isopropanol and maltose were all supplied by Sigma Aldrich, UK. 9H-(1,3-dichloro-9,9-dimethylacridin-2-one-7-yl)-D-galactopyranoside (DDAO) was purchased from Molecular Probes. Exgen 500 (linear polyethylenimine, Mw=22 kD) was obtained from Euromedex, France. Passive lysis buffer was supplied by Promega, UK. pCMV-beta gal DNA was obtained from Life Sciences/Invitrogen and propagated in E. Coli as previously described⁹.

Methods

Groups of healthy female Balb-C mice (n=3) were injected intravenously with either DAB8-DNA, quaternary ammonium DAB8 (Q8)-DNA, DAB16-DNA or DAB32-DNA or Exgen 500 (linear polyethylenimine)-DNA. Formulations of the Dendrimer or Exgen 500, DNA Complexes (200 μl) dispersed in glucose 5% w/v containing 100 μg DNA were injected into each mouse and the dendrimer, DNA weight ratios were as follows: DAB8, Q8 and DAB 16 were all administered at a dendrimer, DNA weight ratio of 5:1. DAB32 was administered at a dendrimer, DNA weight ratio of 3:1. Exgen 500 was administered in accordance with the manufacturers instructions.

Mice were killed after 24 h and their lungs and livers removed and frozen in liquid nitrogen until an assay for β-galactosidase could be performed. For the assay, 1 g of organ was made up to 2 mL with a protease lysis buffer. The protease lysis buffer consisted of a) Protease lysis buffer 5× (1 mL), b) Phenyl methyl sulphonyl fluoride (PMSF) (50 mM in methanol, 200 μL), c) Protease Inhibitor cocktail (100 μl) and water (3.7 mL).

1×10⁶ A431 cells dispersed in 0.1 ml phosphate buffered saline (pH=7.4, PBS) were implanted subcutaneously in each flank of CD-1 female nude mice. 4 days after the injection, the tumours were palpable (around 2 mm). 8 days after the injection, the size of the tumours increased (around 5 mm) and the blood vessels were more visible. The animals were dosed 11 days after tumour implantation. Mice (n=4) were injected intravenously with 50 □g DNA as naked DNA, DAB16-DNA, Exgen500-DNA all dispersed in 200 μL 5% w/v dextrose. Control animals were injected with 5% w/v dextrose. Animals were killed 24 h later and tumours were excised and immediately frozen in liquid nitrogen. For the assay each tumour was added to 0.3 mL of the Protease lysis buffer. Organs contained in the buffer were homogenised and 100 μl of the homogenised organ dispersion was added to 300 μl of the assay reagent. The assay reagent consisted of: a) DDAO 5 mg mL⁻¹ in DMSO (15 μL), b) PMSF 50 mM in methanol (20 μL), c) maltose 20% w/v in PBS (100 μl), d) Protease inhibitor cocktail (15 μL), e) PBS (150 μl). The samples were incubated for the appropriate time (45-90 min.) at 37° C. 200 μl of this mixture was warmed at 95° C. for 2 min, in order to stop the β-galactosidase reaction and to denaturate the proteins which could interfere with the assay. 800 μl isopropanol was then added to the dispersion. The mixture obtained was vortexed to homogeneity and shaken for 20 min in the dark. The dispersion was then centrifuged for 4 min, at 13000 rpm. 500 μl of the supernatant was then added to 500 μl distilled water and the fluorescence read on a Beckman LS-50B fluorimeter (λ_Exc: 630 nm, λ_Em: 658 nm, slit: 2.5 nm). The amount of enzyme was then quantified using a β-galactosidase standard.

Results and Discussion

DAB16, Q8 and DAB 32 all resulted in liver targeting when compared to the commercial formulation Exgen500 (FIG. 6). DAB 16 resulted in more gene expression in the tumours when compared to Exgen500 (FIG. 7).

This data provides further support that polypropylenimine dendrimers target the liver and produce higher gene expression in tumour tissue when compared to commercial formulations where, for example, non-viral gene delivery systems target the lung^8,53. Targeting the liver is likely to prove useful in the treatment of liver enzyme deficiencies and liver tumours. FIG. 7 illustrates that high expression in tumours may be obtained with the polypropylenimine dendrimers.

REFERENCES

• 1. Anderson, W. F. (1998), Human gene therapy, Nature, 392, 25-30.
• 2. Verma, I. M. and Somia, N. (1997), Gene therapy—promises, problems and prospects, Nature, 389, 239-42.
• 3. Jolly, D., Viral vector systems for gene therapy, in The Internet Book of Gene Therapy, R. E. Sobol and K. J. Scanlon, Editors. 1996, Appleton & Lange. p. 3-25.
• 4. Felgner, P. L., Gadek, T. R., Holm, M., Roman, R., Chan, H. W., Wenz, M., Northrop, J. P., Ringold, G. M., and Danielsen, M. (1987), Lipofection—a Highly Efficient, Lipid-Mediated DNA-Transfection Procedure, Proc. Natl. Acad. Sci. USA, 84, 7413-7417.
• 5. Song, Y. K., Liu, F., Chu, S., and Liu, D. (1997), Characterization of cationic liposome-mediated gene transfer in vivo by intravenous administration, Human Gene Ther., 8, 1585-1594.
• 6. Song, Y. K., Liu, F., and Liu, D. (1998), Enhanced gene expression in mouse lung by prolonging the retention time of intravenously injected plasmid DNA, Gene Ther., 5, 1531-7.
• 7. Wagner, E., Zenke, M., Cotten, M., Beug, H., and Birnstiel, M. L. (1990), Transferrin-polycation conjugates as carriers for DNA uptake into cells, Proc. Natl. Acad. Sci. U.S.A., 87, 3410-4.
• 8. Ogris, M., Brunner, S., Schuller, S., Kircheis, R., and Wagner, E. (1999), Pegylated DNA/transferrin-PEI complexes: reduced interaction with blood components, extended circulation in blood and potential for systemic gene delivery, Gene Ther., 6, 595-605.
• 9. Brown, M. D., Schätzlein, A. G., Brownlie, A., Jack, V., Tetley, L., Gray, A. I., and Uchegbu, I. F. (2000), Preliminary characterisation of novel amino acid based polymeric vesicles as gene delivery agents, Bioconjug. Chem., 11, 880-891.
• 10. Brownlie, A., Gray, A. I., Schätzlein, A. G., Tetley, L., Tufail, U., and Uchegbu, I. F. (2000), Preliminary characterisation of modified polyethylenimine polymers for gene delivery, AAPS Pharm Sci, 2 (Suppl.), 2408.
• 11. Kukowska-Latallo, J. F., Bielinska, A. U., Johnson, J., Spindler, R., Tomalia, D. A., and Baker, J. R. (1996), Efficient Transfer of Genetic Material Into Mammalian-Cells Using Starburst Polyamidoamine Dendrimers, Proc. Natl. Acad. Sci. USA, 93, 4897-4902.
• 12. Tang, M. X., Redemann, C. T., and Szoka, F. C. (1996), In vitro gene delivery by degraded polyamidoamine dendrimers, Bioconjug. Chem., 7, 703-714.
• 13. Hudde, T., Rayner, S. A., Corner, R. M., Weber, M., Isaacs, J. D., Waldmann, H., Larkin, D. P. F., and George, A. J. T. (1999), Activated polyamidoamine dendrimers, a non-viral vector for gene transfer to the corneal endothelium, Gene Ther., 6, 939-943.
• 14. Loup, C., Zanta, M. A., Caminade, A. M., Majoral, J. P., and Meunier, B. (1999), Preparation of water-soluble cationic phosphorus-containing dendrimers as DNA transfecting agents, Chemistry-a Eur. J., 5, 3644-3650.
• 15. Debrabandervandenberg, E. M. M. and Meijer, E. W. (1993), Poly(Propylene Imine) Dendrimers—Large-Scale Synthesis by Hetereogeneously Catalyzed Hydrogenations, Angew. Chem. Intl. Ed. Engl., 32, 1308-1311.
• 16. Debrabandervandenberg, E. M. M., Nijenhuis, A., Mure, M., Keulen, J., Reintjens, R., Vandenbooren, F., Bosman, B., Deraat, R., Frijns, T., Vanderwal, S., Castelijns, M., Put, J., and Meijer, E. W. (1994), Large-Scale Production of Polypropylenimine Dendrimers, Macromolecul. Symp., 77, 51-62.
• 17. vanDuijvenbode, R. C., Borkovec, M., and Koper, G. J. M. (1998), Acid-base properties of poly(propylene imine) dendrimers, Polymer, 39, 2657-2664.
• 18. Bielinska, A. U., Yen, A., Wu, H. L., Zahos, K. M., Sun, R., Weiner, N. D., Baker, J. R., and Roessler, B. J. (2000), Application of membrane-based dendrimer/DNA complexes for solid phase transfection in vitro and in vivo, Biomaterials, 21, 877-887.
• 19. Bielinska, A. U., Chen, C. L., Johnson, J., and Baker, J. R. (1999), DNA complexing with polyamidoamine dendrimers: Implications for transfection, Bioconjug. Chem., 10, 843-850.
• 20. Toth, I., Sakthivel, T., Wilderspin, A. F., Bayele, H., Odonnell, M., Perry, D. J., Pasi, K. J., Lee, C. A., and Florence, A. T. (1999), Novel cationic lipidic peptide dendrimer vectors—In vitro gene delivery, STP Pharma Sci., 9, 93-99.
• 21. Du, B., Zhou, R. J., and Zhuo, R. X. (1998), Synthesis of cyclic core dendritic polymer and its usage as a vector for transferring foreign DNA into human cells, Chin. Chem. Lett., 9, 635-638.
• 22. Bielinska, A., Kukowskalatallo, J., Piehlero, L. T., Yin, R., Spindler, R., Tomalia, D. A., and Baker, J. R. (1995), Starburst(R) Pamam Dendrimers—a Novel Synthetic Vector for the Transfection of DNA into Mammalian-Cells, Abstr. Pap. Am. Chem. Soc., 210, 145-PMSE.
• 23. Bielinska, A., Johnson, J., Kukowskalatallo, J., Tomalia, D., Spindler, R., and Baker, J. (1995), Unique Characteristics of Starburst(Tm) Dendrimers in in-Vitro DNA Transfer, Faseb J., 9, A312.
• 24. Bielinska, A. U., KukowskaLatallo, J. F., and Baker, J. R. (1997), The interaction of plasmid DNA with polyamidoamine dendrimers: mechanism of complex formation and analysis of alterations induced in nuclease sensitivity and transcriptional activity of the complexed DNA, Biochim. Biophys. Acta, 1353, 180-190.
• 25. BenMamoun, C., Truong, R., Gluzman, I., Akopyants, N. S., Oksman, A., and Goldberg, D. E. (1999), Transfer of genes into Plasmodium falciparum by polyamidoamine dendrimers, Mol. Biochem. Parasitol., 103, 117-121.
• 26. Pistolis, G., Malliaris, A., Tsiourvas, D., and Paleos, C. M. (1999), Poly(propyleneimine) dendrimers as pH-sensitive controlled-release systems, Chemistry-a Eur. J., 5, 1440-1444.
• 27. Sideratou, Z., Tsiourvas, D., and Paleos, C. M. (2000), Quaternized poly(propylene imine) dendrimers as novel pH-sensitive controlled-release systems, Langmuir, 16, 1766-1769.
• 28. Jansen, J., Debrabandervandenberg, E. M. M., and Meijer, E. W. (1994), Encapsulation of Guest Molecules into a Dendritic Box, Science, 266, 1226-1229.
• 29. Malik, N., Wiwattanapatapee, R., Klopsch, R., Lorenz, K., Frey, H., Weener, J. W., Meijer, E. W., Paulus, W., and Duncan, R. (2000), Dendrimers: Relationship between structure and biocompatibility in vitro, and preliminary studies on the biodistribution of I-125-labelled polyamidoamine dendrimers in vivo Download Full Text of Article, J. Control. Rel. 65, 133-148.
• 30. Kabanov, V. A., Zezin, A. B., Rogacheva, V. B., Gulyaeva, Z. G., Zansochova, M. F., Joosten, J. G. H., and Brackman, J. (1999), Interaction of Astramol poly(propyleneimine) dendrimers with linear polyanions, Macromolecules, 32, 1904-1909.
• 31. Gebhart, C. L. and Kabanov, A. V. (2001), Evaluation of polyplexes as gene transfer agents, J. Control. Rel., 73, 401-406.
• 32. Zhang, X. Y., Wilhelm, M., Klein, J., Pfaadt, M., and Meijer, E. W. (2000), Modification of surface interactions and friction by adsorbed dendrimers: 1. Low surface-energy fifth-generation amino acid-modified poly(propyleneimine) dendrimers, Langmuir, 16, 3884-3892.
• 33. vanDuijvenbode, R. C., Rajanayagam, A., Koper, G. J. M., Baars, M., deWaal, B. F. M., Meijer, E. W., and Borkovec, M. (2000), Synthesis and protonation behavior of carboxylate-functionalized poly(propyleneimine) dendrimers, Macromolecules, 33, 46-52.
• 34. Roman, C., Fischer, H. R., and Meijer, E. W. (1999), Microphase separation of diblock copolymers consisting of polystyrene and acid-functionalized poly(propylene imine) dendrimers, Macromolecules, 32, 5525-5531.
• 35. Bodnar, I., Silva, A. S., Deitcher, R. W., Weisman, N. E., Kim, Y. H., and Wagner, N. J. (2000), Structure and rheology of hyperbranched and dendritic polymers. I. Modification and characterization of poly(propyleneimine) dendrimers with acetyl groups, J. Polymer Sci. Part B-Polymer Phys., 38, 857-873.
• 36. Chen, C. Z., Tan, N. C. B., and Cooper, S. L. (1999), Incorporation of dimethyldodecylammonium chloride functionalities onto poly(propylene imine) dendrimers significantly enhances their antibacterial properties, Chem. Commun., 1585-1586.
• 37. Baars, M., Kleppinger, R., Koch, M. H. J., Yeu, S. L., and Meijer, E. W. (2000), The localization of guests in water-soluble oligoethyleneoxy-modified poly(propylene imine) dendrimers, Angew. Chem.-Intl. Ed., 39, 1285-1290.
• 38. Peerlings, H. W. I., Nepogodiev, S. A., Stoddart, J. F., and Meijer, E. W. (1998), Synthesis of spacer-armed glucodendrimers based on the modification of poly(propylene imine) dendrimers, Eur. J. Org. Chem., 1879-1886.
• 39. Pavlov, G. M., Korneeva, E. V., Jumel, K., Harding, S. E., Meijer, E. W., Peerlings, H. W. I., Stoddart, J. F., and Nepogodiev, S. A. (1999), Hydrodynamic properties of carbohydrate-coated dendrimers, Carbohydrate Polymers, 38, 195-202.
• 40. Cameron, J. H., Facher, A., Lattermann, G., and Diele, S. (1997), Poly(propyleneimine) dendromesogens with hexagonal columnar mesophase, Advanced Materials, 9, 398-405.
• 41. Schenning, A., ElissenRoman, C., Weener, J. W., Baars, M., vanderGaast, S. J., and Meijer, E. W. (1998), Amphiphilic dendrimers as building blocks in supramolecular assemblies, J. Am. Chem. Soc., 120, 8199-8208.
• 42. Liu, M. J. and Frechet, J. M. J. (1999), Preparation, MALDI-TOF analysis, and micelle-like behavior of alkyl-modified poly(propylene imine) dendrimers, Polymer Bull., 43, 379-386.
• 43. Liu, M. J., Petro, M., Frechet, J. M. J., Haque, S. A., and Wang, H. C. (1999), Preparation of hydrophobic poly(isobutylene) star polymers with hydrophilic poly(propylene imine) dendritic cores, Polymer Bull., 43, 51-58.
• 44. Froehling, P. E. and Linssen, H. A. J. (1998), Positional and compositional heterogeneity of partially modified poly(propyleneimine) dendrimers, Macromolecul. Chem. Phys., 199, 1691-1695.
• 45. Yonetake, K., Masuko, T., Morishita, T., Suzuki, K., Ueda, M., and Nagahata, R. (1999), Poly(propyleneimine) dendrimers peripherally modified with mesogens, Macromolecules, 32, 6578-6586.
• 46. Schenning, A., Peeters, E., and Meijer, E. W. (2000), Energy transfer in supramolecular assemblies of oligo(p-phenylene vinylene)s terminated poly(propylene imine) dendrimers, J. Am. Chem. Soc., 122, 4489-4495.
• 47. Ausubel, F., Brent, R., Kingston, E., Moore, D., Seidman, J., Smith, J., and Struhl, K., eds. Current Protocols In Molecular Biology., ed. V. Chanda. Vol. I-III. 1998, John Wiley & Sons.
• 48. Pecq, J.-B. L. (1971), Use of ethidium bromide for separation and determination of nucleic acids of various conformational forms and measurement of their associated enzymes, Methods Biochem Anal, 20, 41-86.
• 49. Freshney, R. I., Culture of animal cells: a manual of basic technique. 3rd ed. 1994, New York: Wiley-Liss. xxiv, 486.
• 50. Lee, R. J., Wang, S., and Low, P. S. (1996), Measurement of endosome pH following folate receptor-mediated endocytosis, Biochim. Biophys. Acta, 1312, 237-242.
• 51. Bosman, A. W., Janssen, H. M., Meijer, E. W. (1999). About dendrimers: structure, physical properties, and applications. Chem. Rev. 99, 1665-1688.
• 52. De Brabander-van den Berg, E. M. M., Meijer, E. W. (1993). Poly(propylene imine) dendrimers: large scale synthesis by heterogenously catalyzed hydrogenations. Angew. Chem. Int. Ed. Engl. 32, 1308-1311.
• 53. M. D. Brown, A. Schätzlein, A. Brownlie, V. Jack, W. Wang, L. Tetley, A. I. Gray, I. F. Uchegbu, Preliminary characterization of novel amino acid based polymeric vesicles as gene and drug delivery agents, Bioconjugate Chemistry, 11 (2000), 880-91.

Claims

1-33. (canceled).

34. A composition for the delivery of a bioactive molecule to a target location in the body of a recipient, said composition comprising a cationic polypropylenimine dendrimer comprising a diaminobutane core with 1, 2, or 3 generations of propylenimine molecules attached, admixed with the bioactive molecule.

35. The composition according to claim 34, wherein the cationic dendrimers are modified by covalently binding derivatising groups.

36. The composition according to claim 35, wherein the cationic dendrimers are derivatised using groups selected from the group consisting of hydrophobic, hydrophilic and amphiphilic groups.

37. The composition according to claim 35, wherein the cationic dendrimers are derivatised by binding two dendrimer molecules to either end of a hydrocarbon chain.

38. The composition according to claim 37, wherein the length of the hydrocarbon chain is selected from the group consisting of 8, 12, 14, 16 and 18 carbons.

39. The composition according to claim 37, wherein the derivatised cationic dendrimer is a bolamphiphilic dendrimer.

40. The composition according to claim 39, wherein the number of derivatising groups is from one derivatising group per dendrimer molecule up to and including derivatising all available surface or terminal groups on the dendrimer molecule.

41. The composition according to claim 36, wherein the amphiphilic derivative comprises a hydrophilic and a hydrophobic segment.

42. The composition according to claim 41, wherein the hydrophilic segment is derived from a phosphoglycerate molecule.

43. The composition according to claim 41, wherein the hydrophobic segment is covalently bound to the hydrophilic segment via an ester linkage.

44. The composition according to claim 41, wherein the hydrophobic segment is selected from the group consisting of alkyl, alkenyl and alkynyl groups of from 8 to 24 carbons in length.

45. The composition according to claim 41, wherein the amphiphilic derivative is attached to the dendrimer by a linker molecule selected from the group consisting of polyethylene glycol (PEG) and a sugar molecule.

46. The composition according to claim 45, wherein the length of the PEG linker molecule is from 1 to 120 ethylene glycol units.

47. The composition according to claim 45, wherein the linker molecule is a phosphoglyceride.

48. The composition according to claim 41, wherein the number of amphiphilic derivatives per dendrimer molecule is from 1 derivatising group per dendrimer molecule to derivatising all of the groups of the dendrimer.

49. The composition according to claim 34, wherein the bioactive molecule is selected from the group consisting of polynucleotides, peptides, polypeptides and pharmaceutically active agents.

50. In a method of transfecting mammalian cells in vitro with a composition, the improvement comprising transfecting said cells in vitro with a composition according to claim 34.

51. A pharmaceutical formulation comprising the composition of claim 34 and a pharmaceutically acceptable carrier.

52. A method of delivering a bioactive molecule to a target location in the body of a recipient, comprising administering the composition of claim 34 to said recipient.

53. The method according to claim 52, wherein the target location is selected from the group consisting of the liver, spleen, lung, kidney and heart.

54. The method according to claim 52, wherein the composition is for the delivery of a bioactive molecule to the liver of the recipient, and wherein said composition comprises the polypropylenimine dendrimer DAB16 admixed with said bioactive molecule.

55. The method according to claim 52, wherein the composition is for the delivery of a bioactive molecule to the spleen of the recipient, and wherein said composition comprises the polypropylenimine dendrimer DSAM16 admixed with said bioactive molecule.

56. The method according to claim 52, wherein the recipient is a human.

57. A method of preparing the composition of claim 34, comprising admixing a polypropropylenimine dendrimer comprising a diammobutane core with 1, 2 or 3 generations of propylenimine molecules attached, and/or derivatives thereof, and at least one bioactive molecule.