No abstract

We have developed a system for targeting foreign DNA to hepatocytes in vitro using a soluble DNA carrier that takes advantage of receptor-mediated endocytosis to achieve internalization. The idea is based on the fact that hepatocytes possess a unique receptor that binds and internalizes galactose-terminal (asialo)glycoproteins. To create a targetable carrier system that could bind DNA in a nondeforming manner, we used poly(L-lysine) to bind DNA in a strong but noncovalent interaction. An asialoglycoprotein, asialoorosomucoid (AsOR), was chemically coupled to poly(L-lysine) to form an asialoorosomucoid-poly(L-lysine) conjugate. Various proportions of conjugate to DNA were tested to determine conditions that maximized DNA content in a soluble complex and that limited solubility of complexes. To test the targetable gene delivery system, AsOR-poly(L-lysine) conjugate was complexed to the plasmid pSV2 CAT containing the gene for chloramphenicol acetyltransferase (CAT) driven by an SV-40 promoter. We tested this complex using a model system consisting of human hepatoma cell line Hep G2 [asialoglycoprotein receptor (+)], hepatoma SK-Hep 1, IMR-90 fibroblasts, and uterine smooth muscle [receptor (-)] cells. Each cell line was incubated with 0.2 micron filtered AsOR-poly(L-lysine)-DNA complex or controls consisting of DNA plus AsOR, DNA plus poly(L-lysine), or DNA alone. Cells were assayed for the presence of CAT activity as a measure of gene transformation. SK-Hep 1, IMR-90, and smooth muscle [receptor (-)] cells produced no detectable acetylated chloramphenicol derivatives under any of these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Targeting therapeutic genes to the liver is essential to improve gene therapy protocols of hepatic diseases and of some hereditary disorders. Transcriptional targeting can be achieved using liver-specific promoters. In this study we have made chimeric constructs combining promoter and enhancer regions of the albumin, alpha 1-antitrypsin, hepatitis B virus core protein, and hemopexin genes. Tissue specificity, activity, and length of gene expression driven from these chimeric regulatory sequences have been analyzed in cultured cells from hepatic and nonhepatic origin as well as in mice livers and other organs. We have identified a collection of liver-specific promoters whose activities range from twofold to less than 1% of the CMV promoter in human hepatoma cells. We found that the best liver specificity was attained when both enhancer and promoter sequences of hepatic genes were combined. In vivo studies were performed to analyze promoter function during a period of 50 days after gene transfer to the mouse liver. We found that among the various chimeric constructs tested in this work, the alpha1-antitrypsin promoter alone or linked to the albumin or hepatitis B enhancers is the most potent in directing stable gene expression in liver cells.

The 3-terminal sequences of hepatitis C virus (HCV) positive-and negative-strand RNAs contribute cis-acting functions essential for viral replication. The secondary structure and protein-binding properties of these highly conserved regions are of interest not only for the further elucidation of HCV molecular biology, but also for the design of antisense therapeutic constructs. The RNA structure of the positive-strand 3 untranslated region has been shown previously to influence binding by various host and viral proteins and is thus thought to promote HCV RNA synthesis and genome stability. Recent studies have attributed analogous functions to the negative-strand 3 terminus. We evaluated the HCV negative-strand secondary structure by enzymatic probing with single-strand-specific RNases and thermodynamic modeling of RNA folding. The accessibility of both 3-terminal sequences to hybridization by antisense constructs was evaluated by RNase H cleavage mapping in the presence of combinatorial oligodeoxynucleotide libraries. The mapping results facilitated identification of antisense oligodeoxynucleotides and a 10-23 deoxyribozyme active against the positivestrand 3-X region RNA in vitro.The untranslated regions (UTRs) of the hepatitis C virus (HCV) positive-strand genome and negative-strand intermediate contain cis-acting sequences essential for viral translation and RNA replication. The 341-nucleotide (nt) 5Ј-UTR of the positive strand acts as an internal ribosome entry site (IRES) to direct cap-independent translation of the single ϳ3,000-codon-long HCV open reading frame (38, 40). The tripartite 3Ј-UTR consists of a short upstream variable region, a central poly(U)-polypyrimidine stretch of variable length, and a terminal highly conserved 98-nt sequence (38). With the exception of the variable region, all sequence elements in the 3Ј-UTR are necessary for intracellular replication of HCV RNA (16,29,56).A number of in vitro studies (26,35,36,39,58) have established that the terminal 98-nt X region sequence can serve as a minimal template for de novo initiation of negative-strand synthesis by the viral RNA-dependent RNA polymerase, NS5B. The 3Ј terminus of the HCV negative strand reportedly plays an analogous role in positive-strand RNA synthesis (25,36,39). The binding of HCV 3Ј termini to various host proteins may exert subtle effects on IRES-mediated translation (16,23,34,55) or protect viral transcripts from degradation by cytoplasmic RNases (15,48,49).The replicative and protein-binding functions of heteropolymeric regions in the HCV 3Ј termini are, in many instances, dependent on the ability of the primary sequence to fold into higher-order RNA structure. In vitro, the X region sequence is capable of adopting a three-stem-loop structure, with the 3Ј-terminal 46 nt forming a thermodynamically stable stem-loop, SL I (6). Mutational analysis indicates that the duplex structure forming the base of SL I influences both the site and efficiency of de novo initiation by NS5B (26,35). Preservation of the interior stem-loo...

We have previously shown targeting of DNA to hepatocytes using an asialoorosomucoid-polylysine (AsOR-PL) carrier system. The AsOR-PL conjugate condenses DNA and facilitates entry via specific receptor-ligand interactions. In these studies, our objective was to determine if AsOR-PL conjugates protect bound DNA from nuclease attack. Double-stranded plasmid or single-stranded oligonucleotide DNA, alone or bound to conjugate, was incubated under conditions mimicking those encountered during in vitro and in vivo transfections. The results showed that complexed DNA was effectively protected from degradation by serum nucleases. Degradation of single-stranded oligonucleotides was inhibited 3- to 6-fold in serum during 5 hours of incubation. For complexed plasmids, greater than 90% remained full-length during 1.5 and 3 hour incubations in serum or culture medium containing 10% serum, respectively. Uncomplexed plasmid was completely degraded after 15 minutes in serum or 60 minutes in medium. In cell lysates, the conjugate was not effective in inhibiting endonuclease activity; plasmids were readily converted from supercoiled to open circular and linear forms. However, the resultant nicked forms were substantially protected from further degradation during one hour of incubation compared to plasmid alone. Under all conditions complexed DNA did not readily dissociate from the conjugate. Overall, for both single and double-stranded DNA, AsOR-PL conjugates conferred substantial protection from nuclease degradation.