Title:  Methods of forming protein-linked lipidic microparticles, and compositions thereof

United States Patent:  6,210,707

Assignee:  The Regents of the University of California (Oakland, CA)

Filed:  May 12, 1998

The present invention provides for lipid:nucleic acid complexes that have increased shelf life and high transfection activity in vivo following intravenous injection, and methods of preparing such complexes. The methods generally involve contacting a nucleic acid with an organic polycation to produce a condensed nucleic acid, and then combining the condensed nucleic acid with a lipid comprising an amphiphilic cationic lipid to produce the lipid:nucleic acid complex. This complex can be further stabilized by the addition of a hydrophilic polymer attached to hydrophobic side chains. The complex can also be made specific for specific cells, by incorporating a targeting moiety such as an Fab' fragment attached to a hydrophilic polymer. The present invention further relates to lipidic microparticles with attached proteins which have been first conjugated to linker molecules having a hydrophilic polymer domain and a hydrophobic domain capable of stable association with the microparticle, or proteins which have been engineered to contain a hydrophilic domain and a lipid moiety permitting stable association with the microparticle.

SUMMARY OF THE INVENTION

The present invention provides a novel method of preparing cationic lipid:nucleic acid complexes that have increased shelf life. In one embodiment, these complexes are prepared by contacting a nucleic acid with an organic polycation, to produce a condensed or partially condensed nucleic acid. The condensed nucleic acid is then combined with an amphiphilic cationic lipid plus a neutral helper lipid such as cholesterol in a molar ratio from about 2:1 to about 1:2, producing the lipid:nucleic acid complex. Optionally, a hydrophilic polymer is subsequently added to the lipid:nucleic acid complex. Alternatively, the hydrophilic polymer is added to a lipid:nucleic acid complex comprising nucleic acid that has not been not condensed. These lipid:nucleic acid complexes have an increased shelf life, e.g., when stored at 22^oC. or below, as compared to an identical lipid:nucleic acid complex in which the nucleic acid component has not been contacted with the organic polycation and/or in which the lipid:nucleic acid complex has not been contacted with a hydrophilic polymer.

In a particularly preferred embodiment, the polycation is a polyamine, more preferably a polyamine such as spermidine or spermine.

In another preferred embodiment, the lipid:nucleic acid complexes are prepared by combining a nucleic acid with an amphiphilic cationic lipid and then combining the complex thus formed with a hydrophilic polymer. This lipid:nucleic acid complex has an increased shelf life, e.g., when stored at 22^oC. or below as compared to an identical complex that has not been combined with the hydrophilic polymer.

In one embodiment, the hydrophilic polymer is selected from the group consisting of polyethylene glycol (PEG), polyethylene glycol derivatized with phosphatidyl ethanolamine (PEG-PE), polyethylene glycol derivatized with tween, polyethylene glycol derivatized with distearoylphosphatidylethanolamine (PEG-DSPE), ganglioside G_M1 and synthetic polymers.

In one embodiment, the lipid:nucleic acid complex is lyophilized.

In any of the methods and compositions of this invention, the nucleic acid can be virtually any nucleic acid, e.g., a deoxyribonucleic acid (DNA) or a ribonucleic acid (RNA), and peptide nucleic acid (PNA) etc., and is most preferably a DNA. In a particularly preferred embodiment, the DNA is an expression cassette capable of expressing a polypeptide in a cell transfected with the lipid:nucleic acid complex.

In one embodiment the lipid:nucleic acid complexes are formed by first forming a liposome, and then combining the formed liposome with condensed or partially condensed nucleic acid to form a lipid:nucleic acid complex. Optionally, the lipid:nucleic acid complex is subsequently contacted with a hydrophilic polymer. The liposomes can alternatively be combined with an uncondensed nucleic acid to form a lipid:nucleic acid complex to which a hydrophilic polymer (e.g., PEG-PE) is later added. A lipid:nucleic acid complex prepared by the combination of nucleic acid and a liposome contacted with a hydrophilic polymer can be subsequently combined with additional hydrophilic polymer. In a preferred embodiment, the lipid and nucleic acid are combined in a ratio ranging from about 1 to about 20, more preferably from about 4 to about 16, and most preferably from about 8 to about 12 nmole lipid:.mu.g nucleic acid. The lipid and hydrophilic polymer are combined in a molar ratio ranging from about 0.1 to about 10%, more preferably from about 0.3 to about 5% and most preferably from about 0.5% to about 2.0% (molar ratio of hydrophilic polymer to cationic lipid of the complex).

It will be appreciated that a targeting moiety (e.g., an antibody or an antibody fragment) can be attached to the lipid and/or liposome before or after formation of the lipid:nucleic acid complex. In a preferred embodiment, the targeting moiety is coupled to the hydrophilic polymer (e.g., PEG), where the targeting moiety/hydrophilic polymer is subsequently added to the lipid:nucleic acid complex. This provides a convenient means for modifying the targeting specificity of an otherwise generic lipid:nucleic acid complex.

In a particularly preferred embodiment, the method of increasing the shelf life of the lipid:nucleic acid complex includes the steps of combining an expression cassette with spermidine or spermine with an amphiphilic cationic lipid plus a helper lipid such as cholesterol, and a Fab' fragment of an antibody attached to a spacer, e.g., polyethylene glycol, so that the complex has increased shelf life when stored at about 4^oC.

In one particularly preferred embodiment, the method of increasing the shelf life of the lipid:nucleic acid complex includes the steps of combining an expression cassette with spermidine or spermine with an amphiphilic cationic lipid, and a Fab' fragment of an antibody attached to a polyethylene glycol derivative. In another particularly preferred embodiment, includes the steps of combining an expression cassette with an amphiphilic cationic lipid, and a Fab' fragment of an antibody attached to a polyethylene glycol derivative so that the complex has increased shelf life when stored at about 4^oC.

This invention also provides for a method of transfecting a nucleic acid into a mammalian cell, the method comprising contacting the cell with any one of the lipid:nucleic acid complexes prepared as described above. In one embodiment, the method uses systemic administration of a lipid:nucleic acid complex into a mammal. In a preferred embodiment, the method of transfecting uses intravenous administration of the lipid:nucleic acid complex into a mammal. In a particularly preferred embodiment, the method comprises contacting a specific cell that expresses a ligand that recognizes the Fab' fragment.

In yet another embodiment, this invention also provides for pharmaceutical composition comprising the lipid:condensed nucleic acid complex described above. The pharmaceutical compositions comprise a therapeutically effective dose of the lipid:nucleic acid complex and a pharmaceutically acceptable carrier or excipient.

In yet another embodiment, the invention also provides a kit for preparing a lipid:nucleic acid complex, the kit comprising a container with a liposome; a container with a nucleic acid; and a container with a hydrophilic polymer, wherein the liposome and the nucleic acid are mixed to form the lipid:nucleic acid complex and wherein the lipid:nucleic acid complex is contacted with the hydrophilic polymer. In a preferred embodiment, the hydrophilic polymer is derivatized with a targeting moiety, preferably an Fab' fragment. In another preferred embodiment, the nucleic acid is condensed.

This invention also provides for a lipid:condensed nucleic acid complex prepared using the method of increasing shelf life using nucleic acid condensed with an organic polycation, as summarized above.

The invention further provides a method for making lipidic microparticles bearing attached proteins. The method employs proteins which have been conjugated to linker molecules which will stably associate with lipidic microparticles. The invention therefore permits the attachment of proteins to the surface, for example, of lipidic microparticles which have been preformed.

Claim 1 of 46 Claims

What is claimed is:

1. A method for preparing a lipidic microparticle attached to a protein by means of a linker molecule, said method comprising the step of:

incubating a lipidic microparticle with a protein conjugated to a linker molecule comprising a hydrophobic domain, a hydrophilic polymer chain terminally attached to the hydrophobic domain, and a chemical group reactive to one or more functional groups on a protein molecule and attached to the hydrophilic polymer chain at a terminus contralateral to the hydrophobic domain, for a time sufficient to permit the hydrophobic domain to become stably associated with the lipidic microparticle.

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