Liver-directed gene transfer vectors

The ultimate goal of liver-directed gene therapy for genetic diseases is the stable expression of a therapeutic transgene in a significant proportion of hepatocytes. This article considers the various liver-directed gene transfer procedures studied so far. Performances and limitations of currently available vector systems are discussed with respect to their clinical relevance. Although some improvements have been reported, naked DNA and nonviral gene transfer vectors induce transient expression in only a limited number of cells. Clinical applications of retrovirus-mediated gene transfer are hampered by the need to induce hepatocyte division. First-generation adenovirus vectors are highly efficient; however, they induce an immune response leading to the rapid rejection of transduced cells. Promising new vector systems have emerged, including gutless adenovirus vectors, adeno-associated vectors, and lentivirus vectors. However, these systems are still poorly documented and their relevance to liver-directed gene therapy must be confirmed.

[Gene therapy of cerebral glioblastoma by adenovirus vector. Experimental model in the rat]

Our aim was to test the therapeutic effects of adenovirus-mediated gene therapy in an animal brain tumor model which was obtained by stereotactic injection of 9L gliosarcoma cells into the caudate nucleus of rat brains. Seven days after the implantation of tumor cells, adenovirus vectors bearing the Escherichia coli beta-galactosidase gene (ADVbgal) or the herpes simplex virus thymidine kinase gene (ADVtk) were stereotactically injected into the tumor. Injection of the ADVbgal resulted in the expression of the marker gene in 11 animals. Transfer of the ADVtk was followed, 3 days later, by intraperitoneal injection of ganciclovir (GCV) for 10 days. A control group was treated with saline instead of GCV. We observed a significant regression of the tumors in the rats treated with ADVtk and GCV as compared with control animals. In four cases the tumor completely disappeared after treatment. These results demonstrate the potential efficacy of adenovirus-mediated transfer of the HSVtk gene following by GCV administration for the treatment of glioblastomas.

[Gene therapy of a model of glioblastoma in rats using adenovirus vector encoding the HSVtk gene]

Our aim was to test the therapeutic effects of adenovirus-mediated gene therapy in an animal model of brain tumor which was obtained by injection of 9L gliosarcoma cells into the caudate nucleus of rat brains. Seven days after the implantation of tumor cells, adenovirus vectors bearing the Escherichia coli beta galactosidase gene (ADV beta-gal) or the herpes simplex virus thymidine kinase gene (ADVtk) were stereotactically injected in the tumor. Injection of the ADV beta gal resulted in the expression of the marker gene in 61% of the animals. Transfer of the ADVtk was followed, 3 days later, by intraperitoneal injection of ganciclovir (GCV) for 10 days. A control group was treated with saline instead of GCV. We observed a significant regression of the tumors in 50% of the rats treated with ADVtk and GCV as compared with control animals. In 4 cases out of 6, the tumor completely disappeared after treatment. These results demonstrate the potential efficacy of adenovirus-mediated transfer of the HSVtk gene following by GCV administration for the treatment of glioblastomas.

Highly efficient retrovirus-mediated gene transfer into rat hepatocytes in vivo

We have used high-titer (10(8) ffu/ml) recombinant retroviral vectors to transfer the beta-galactosidase (beta-Gal) gene to rat hepatocytes in vivo. In animals injected twice in the portal blood stream the next day after partial hepatectomy, half of the hepatocytes (46 +/- 17%) expressed the marker at the end of liver regeneration. The number of positive cells closely correlated with the viral titer as well as with beta-Gal enzymatic activity present in the whole liver. Because genes transferred via retroviral vectors in the liver are known to be expressed permanently, our present results open new possibilities for the development of gene therapy protocols for hereditary liver diseases using recombinant retroviral vectors.

[Gene therapy of primary cancers of the liver: hopes and realities]

Many efforts have been devoted to the development of gene therapy for primary liver tumors. This has been hampered by the absence of efficient gene transfer vectors for delivering genes into hepatoma cells in vivo. Also it remains to determine which type of gene has to be used to achieve complete tumor regression. Recent studies have documented improvements obtained using recombinant adenoviral vectors carrying the herpes simplex virus thymidine kinase gene as well as the ability to specifically target gene expression into the tumor cells by using the alpha-fetoprotein gene regulatory sequence. Therefore it seems reasonable to expect the development of clinical protocols in the near future.

[Principles and stakes of gene therapy]

As the human genome sequencing expands and the molecular bases of diseases are better understood, the tools that allow gene packaging and transfer are available. Transferring a therapeutical gene becomes a reality and indeed more than 100 clinical protocols are currently exploring a variety of applications, from the inherited genetic diseases such as cystic fibrosis to the acquired ones such as cancer. Herein, we describe the different gene transfer strategies applied to animals and humans and we present the advantages and limitations of the currently available vectors which, today, represent the limiting factor for efficient gene therapy.

In situ retrovirus-mediated gene transfer into the liver

Gene transfer into hepatocytes is a promising approach for the treatment of genetic liver diseases. Candidate diseases for human trials are life-threatening disorders resulting from a single genetic defect that do not compromise other liver functions and the organization of the hepatic tissue. Orthotopic liver transplantation has been successfully performed in patients with genetic liver disease, but then use is limited by the high mortality risk, the need for chronic immunosuppression, and the availability of organs. Gene therapy would pro vide an alternative to transplantation by restoring the expression of the defective gene in an organ that is otherwise structurally and functionally normal.

Creatinine determination in peritoneal dialysis: what method should be used?

The accuracy of methods for measurement of creatinine in plasma, urine and dialysate is of great importance in continuous ambulatory peritoneal dialysis (CAPD) patients, to assess the adequacy of CAPD (creatinine clearance) and to monitor the nutritional status (creatinine kinetic lean body mass). The methods most widely employed for creatinine determination are Jaffe's reaction and the enzymatic method, however these techniques may suffer from glucose interference, particularly for dialysate. We compared creatinine values obtained by Jaffe's reaction, the enzymatic method and high pressure liquid chromatography (HPLC) for three creatinine calibration curves prepared in three dialysis solutions with various concentrations of glucose and for plasma, urine and dialysate of 40 CAPD patients. High values of intercept of creatinine calibration curves were observed only with Jaffe's reaction and the enzymatic method in dialysis solutions. In plasma, urine and dialysate, creatinine values obtained by HPLC were always found to be lower than those measured by the other two methods. Concerning creatinine measurement in plasma and urine, Jaffe's reaction and the enzymatic method appeared equivalent. However it must be noted that, in dialysates, the enzymatic method may have glucose interference, and the use of a correcting factor for glucose with Jaffe's reaction is convenient. Nevertheless HPLC remains a method of reference. It is concluded that, for the CAPD patient, follow-up by creatinine kinetic lean body mass or creatinine clearance is possible provided that the same creatinine assay method is used in all biological fluids.

In vivo retroviral-mediated transfer of a marker-gene in ornithine transcarbamylase-deficient Spf(ash) mice

Gene therapy is a new therapeutic approach for inherited metabolic hepatopathies. The authors studied the potential application of such a strategy to the correction of ornithine transcarbamylase (OTC) deficiency by in vivo protocol of retroviral-mediated gene transfer to the liver. A partial hepatectomy was followed (24 to 48 hours later) by asanguinous perfusion of the regenerating liver with beta-galactosidase (beta-gal) recombinant retrovirus. This protocol allowed beta-gal gene transfer in normal C57B6 mice liver with 60 +/- 52 positive cells per square centimeter. This proportion never exceeded 20 cells per square centimeter in OTC-deficient spf(ash) mice. The high mortality rate for spf(ash) mice was explained by an important sensitivity of those mice to the protein catabolism rather than by technical difficulties during intraportal perfusion. This first in vivo retroviral-mediated gene transfer study in animals with a life-threatening metabolic inherited hepatopathy showed that, despite efficiency of gene therapy in normal animal models, several experimental difficulties should be overcome before human application of this protocol is considered.

In vitro and in vivo hepatoma cell-specific expression of a gene transferred with an adenoviral vector

Recombinant adenoviruses are widely used for the transfer of foreign genes into various mammalian cells. However, the utilization of these vectors for cancer gene therapy requires the specific and efficient expression of the transferred gene in tumor cells. To obtain targeted expression in hepatoma cells, we constructed recombinant adenoviral vectors containing transcriptional elements from either the rat alpha-fetoprotein (AFP) or the human insulin-like growth factor II (IGFII) genes driving expression of the nuclear beta-galactosidase gene (nls lacZ). In vitro infection revealed that the AFP but not the IGFII transcriptional regulatory sequence controlled nls lacZ expression specifically in hepatoma cells. The same specificity was obtained in vivo in subcutaneous human hepatic tumors generated by engraftment of Huh7 hepatoma cells in nude mice as well as in primary liver tumors developed in rats and mice. No marker gene expression was detectable after AFP-nls lacZ gene transfer to normal rat liver parenchyma despite evidence for the presence of DNA encoding the nls lacZ gene. However, in vivo experiments with primary liver tumors in rats and mice also revealed that primary hepatoma cells were poorly infected by adenoviral vectors. Peritumoral and normal tissues were infected efficiently by adenoviral vectors. We conclude that hepatoma cell-specific expression of a transgene can be achieved with AFP regulatory sequences but that adenoviral vectors may not be the preferable vector for transferring genes in vivo in primary liver tumors.

Efficient transfer of regulated genes in adipocytes and hepatoma cells by the combination of liposomes and replication-deficient adenovirus

Efficient transfer of genes maintaining a correct hormonal control in transfected cells is the prerequisite for gene regulation studies and for gene therapy. Differentiated cells, like adipocytes or hepatocytes, are difficult to transfect. In an attempt to improve gene transfer, we first transiently transfected cultured 3T3-F442A adipocytes with a construct containing the simian virus 40 (SV40) promoter fused to the chloramphenicol acetyltransferase (CAT) gene (pSV2-CAT), using various cationic liposomes. Among these, only lipofectAMINE was five times more efficient than the standard calcium phosphate procedure. To further augment efficiency, we transfected 3T3-F442A adipocytes and FAO hepatoma cells with the lipofectAMINE/pSV2-CAT complex in the presence of replication-deficient recombinant type-5 adenovirus at 200 pfu/cell. CAT activity of transiently transfected cells was increased about 50-fold when compared to the calcium phosphate procedure. To determine whether this methodology would be useful for obtaining stable transfectants and would not interfere with correct gene regulation, we used a construct containing -2100 to +69 bp of the phosphoenolpyruvate carboxykinase gene fused to the CAT gene (pPL1-CAT). This construct was shown previously to be cAMP-responsive after calcium-phosphate-mediated transfection of adipocytes and hepatoma cells. 3T3-F442A or FAO cells in which pPL1-CAT was either transiently or stably transferred by lipofectAMINE and adenovirus responded to isoproterenol or cAMP, respectively, with a 2-3-fold increase in CAT activity. Therefore the association of liposomes and adenovirus is an efficient method for transient or stable transfer of regulated genes in adipocytes and hepatoma cells.

In vivo cell lineage analysis during chemical hepatocarcinogenesis using retroviral-mediated gene transfer

We have studied the proliferation of cells in two models of chemical hepatocarcinogenesis. The cells were genetically labeled in vivo using retrovirally mediated transfer of the Escherichia coli beta-galactosidase marker gene coupled to a nuclear localization signal (nls-lacZ gene). In the first carcinogenic model, rats were fed a choline-deficient diet containing 2-acetylaminofluorene, and their livers were perfused with recombinant retrovirus at the onset of oval cell proliferation. The second model was based on the administration of diethylnitrosamine coupled with a partial hepatectomy and is thought to induce cancer with no involvement of oval cells. Analysis of beta-galactosidase expression in the liver at various times after gene transfer revealed the presence of large clusters of positive cells in both models. Moreover, the beta-galactosidase-positive cells displayed morphologic, antigenic, and enzymatic profiles consistent with a hepatocyte phenotype. Our results, therefore, provide evidence for a strikingly similar clonal proliferation of apparently normal hepatocytes during the course of 2-acetylaminofluorene- as well as diethylnitrosamine-induced liver carcinogenesis.

Hepatoma cell-specific expression of a retrovirally transferred gene is achieved by alpha-fetoprotein but not insulinlike growth factor II regulatory sequences

To target gene expression to malignant hepatic cells, we have constructed recombinant retroviral vectors containing a reporter gene encoding nuclear beta-galactosidase (nls-LacZ) under transcriptional control of regulatory sequences from the rat alpha-fetoprotein (AFP) or human insulinlike growth factor II (IGFII) genes. The AFP and IGFII P3 promoters activate transcription during fetal development and are often reactivated in hepatocellular carcinoma (HCC). Infection of several cultured cell types with the retroviral vector containing the IGFII P3 sequence resulted in expression of the reporter gene in all cell lines tested, including those that do not produce IGFII. In contrast, selective expression was achieved by vectors containing the AFP transcriptional regulatory sequence. Nuclear beta-galactosidase activity was detectable in cells from lines that produce AFP, and not in cells that do not express the AFP gene. In most infected cell lines, retroviral RNA synthesis from the 5' LTR was inhibited, and deletion of the retroviral LTR enhancer did not change expression from either the IGFII P3-nls-LacZ or the AFP-nls-LacZ cassettes. After treatment of cells with 12-O-tetradecanoylphorbol-13-acetate and epidermal growth factor (EGF), the decrease in concentrations of endogenous AFP messenger RNA (mRNA) and nls-LacZ mRNA transcribed from the transferred AFP regulatory sequence were similar. In the context of an integrated provirus, the AFP transcriptional regulatory sequence is therefore subject to similar regulatory control as that of the endogenous gene. These data show that the AFP sequence, and not the IGFII P3 promoter we used, is suitable for targeting gene expression to malignant hepatic cells.

Correction of fumarylacetoacetate hydrolase deficiency (type I tyrosinemia) in cultured human fibroblasts by retroviral-mediated gene transfer

Type I hereditary tyrosinemia results from an inherited deficiency in fumarylacetoacetate hydrolase, the enzyme involved in the last step in tyrosine catabolic pathway. The cloning of the cDNA encoding FAH in human has opened the way to genetic treatment of HT 1. We have constructed recombinant retroviral vectors carrying the cDNA encoding human FAH. In the present report we show that these vectors are able to restore FAH activity stably in primary fibroblasts from HT 1 patients and at high level. The possibility to express FAH stably in deficient patients represents a first step towards future gene therapy for type I hereditary tyrosinemia and may help to decipher the pathogenesis of the disease at the molecular level.

Influence of hepatic impairment on the pharmacokinetics of nefazodone and two of its metabolites after single and multiple oral doses

The pharmacokinetics of nefazodone, a new antidepressant, and two of its active metabolites, hydroxy-nefazodone and m-chlorophenylpiperazine, were determined after single and repeated oral escalating doses of 50, 100 and 200 mg, in healthy volunteers (n = 13) and patients with mild (n = 13) or severe (n = 6) hepatic impairment. All subjects were classified according to their dextromethorphan oxidation capacity. In healthy volunteers, nefazodone was rapidly absorbed after which the plasma concentrations declined with an apparent elimination half-life ranging from 2.7 +/- 1.7 h to 10.2 +/- 4.4 h according to the dosage. Hydroxy-nefazodone appeared rapidly in plasma and its time-course (half-life ranging 1.4 +/- 0.9 h to 6.5 +/- 1.6 h) paralleled that of nefazodone, while mCPP showed low and variable concentrations. The disproportionately longer half-life and more markedly increased Cmax and AUC0-48 which was observed with dosage and treatment duration, and moreover AUC0-12 at steady state significantly higher (P < 0.05) than AUC0-infinity after single dose demonstrated the non-linearity of the pharmacokinetics of nefazodone and hydroxy-nefazodone. The constant molar AUC0-48 hydroxy-nefazodone/nefazodone ratio (0.32 +/- 0.04) and the close correlation (r2 = 0.95) between kinetic parameters of nefazodone and hydroxy-nefazodone suggest that nefazodone hydroxylation is not a saturable process. The kinetics of nefazodone and metabolites were significantly affected by severe but not by mild liver insufficiency. As a consequence, on a pharmacokinetic basis nefazodone should be used with caution in severely hepatic impaired patients.

Factors influencing retroviral-mediated gene transfer into hepatocytes in vivo

Direct gene transfer into hepatocytes represents an attractive alternative to organ transplantation for the treatment of genetic liver diseases. This approach is hampered either by the difficulty to obtain, cultivate, and reimplant hepatocytes or by the poor stability of the expression of the transgene. In the present report, we show that direct in vivo infection of hepatocytes with a retroviral vector following partial hepatectomy results in a life-long expression of the transgene in adult rats and mice. We demonstrate that the kinetics of hepatocyte susceptibility to infection is closely associated with the kinetics of cell division. We also present evidence that a complete vascular exclusion of the organ allows better gene transfer as compared to simple portal infusion of the viral particles, presumably through a higher volume of retrovirus-containing medium delivered to the liver.

Cell lineage study in the liver using retroviral mediated gene transfer. Evidence against the streaming of hepatocytes in normal liver

The fate of normal hepatocytes in adult rat liver was studied after genetic labeling using the Escherichia coli beta-galactosidase gene coupled to a nuclear localization signal. The marker gene was introduced by direct in vivo retroviral-mediated gene transfer into hepatocytes 24 hours after partial hepatectomy. Analysis of beta-galactosidase expression in the liver at various time after gene transfer revealed that labeled hepatocytes were distributed throughout the entire lobule with a predominance in the periportal and mediolobular regions. Long-term experiments demonstrated that division of hepatocytes did occur as was revealed by the increasing number of beta-galactosidase-positive cells in isolated clusters. There was no evidence for the participation of stem cells in this process. Moreover, we found that after more than 1 year, the pattern of distribution of positive cells within the lobule was not modified. This suggests that hepatocytes do not migrate from the portal space to the perivenous region, as has been previously hypothesized.

Adenoviral-mediated gene transfer to renal tubular cells in vivo

The efficient introduction of genetic material into quiescent renal cells is potentially important in the study of renal physiopathology and for gene therapy of kidney related disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding the nuclear beta-galactosidase was either selectively perfused into the renal artery or infused through a retrograde catheter into the pyelic cavity of the left kidney of adult rats. Highly efficient gene transfer was achieved by either route of administration, and nuclear beta-galactosidase activity was detected for two to four weeks following a progressive decline of expression. Genetically-modified cells were identified as proximal tubular cells when the adenoviral vector was selectively perfused via the renal artery, while tubular cells from the papilla and medulla were selectively transduced by retrograde infusion of the viral vector. No obvious cytopathic effect was observed. We conclude that: (i) efficient gene transfer in renal tubular cells can be achieved by adenoviral vectors; (ii) the targeted cell population can be chosen through the route of administration.

[Gene therapy of the liver: from the laboratory to the patient's bedside]

Gene transfer techniques have significantly improved during the last few years. A number of therapeutic protocols has now been advanced for use in animal models and some are now in the first phases of clinical trials. In the field of hepatology, gene therapy represents a new therapeutic approach in the treatment of inherited hepatic diseases as well as liver tumors. In the present paper, we will review some examples of gene therapy of such diseases in animal models. Regarding inherited pathologies, Watanabe rabbits, which constitute a model of familial hypercholesterolemia, have been successfully treated by ex vivo gene transfer into hepatocytes using retroviral vectors. The genetic defect in Gunn rats, a model of type 1 Crigler-Najjar disease, has been corrected by in vivo retroviral mediated gene transfer. Adenoviral vectors have also been used to restore enzyme activity in OTC deficient mice. Concerning liver tumors, retroviral mediated transfer of a suicide gene into experimental liver metastasis has proven efficient in reducing the size of the tumors in treated animals. Taken together, these results clearly demonstrate the feasibility of treating hepatic diseases by gene transfer and may be considered as a promising therapeutic tool in hepatology.

Pharmacokinetics of chlormezanone in elderly patients

The pharmacokinetics of Chlormezanone (CM) has been determined after a single oral dose of 400 mg CM in 5 young volunteers (28 y) and in 8 elderly patients (79 y). In the young subjects, CM was rapidly absorbed and distributed, and was slowly eliminated with a half-life of 38 h major metabolites were not detected in plasma or urine. Only 3% of CM was excreted unchanged in urine. In elderly patients absorption was delayed but not reduced; the Cmax and AUC did not differ from those in younger subjects, the elimination rate was reduced compared to the younger subjects (mean 54 h). The increase was in part related to the reduction in renal function and metabolism observed in aging. However, the change in pharmacokinetics was moderate and no adjustment in dosage seems necessary for treatments of limited duration in elderly patients.

Retroviral-mediated gene transfer into hepatocytes in vivo

Stable gene transfer into hepatocytes might be used to compensate for a genetic deficiency affecting liver function or to deliver diffusible factors into the blood stream. In rats, we have combined retroviral-mediated gene transfer with a surgical procedure in which the liver is temporarily excluded from the circulation and infected in vivo. Partial hepatectomy was performed 24-48 hr before perfusion with virus to induce hepatocyte division and facilitate viral integration. A helper-free recombinant retrovirus coding for beta-galactosidase with nuclear localization was used to score cells that expressed the transgene. For at least 3 months after gene transfer, up to 5% of hepatocytes expressed nuclear beta-galactosidase. Whereas in vitro reimplantation of genetically modified hepatocytes has proved to be inefficient in stably transferring genes into the liver, our approach provides a feasible alternative.

Increased serotonin platelet uptake after tianeptine administration in depressed patients

Tianeptine is a new antidepressant drug reported to enhance serotonin (5-hydroxytryptamine [5-HT]) uptake in rat brain. The effect of tianeptine on 5-HT platelet uptake was studied in 10 depressed patients treated for 28 days. Tianeptine increases Vmax of 5-HT platelet uptake during treatment without inducing any change in Km. As early as 2 hr after the first administration, Vmax increased significantly (+23%, alpha = 0.01). Although of a lesser magnitude, 5-HT platelet uptake remains increased after chronic administration (+14% on day 10 and +13% on day 28). This suggests that tianeptine affects 5-HT platelet uptake sites, either directly or via an action on modulators of 5-HT uptake. These results, in contrast with the action of other tricyclic antidepressants, confirm the original action of tianeptine on 5-HT platelet metabolism.