Gene therapy with angiogenic factors: a new potential approach to the treatment of ischemic diseases

A new signaling mechanism of hepatocyte growth factor-induced endothelial proliferation

BACKGROUND

The hepatocyte growth factor (HGF) has been shown to promote endothelial cell proliferation. In this study, the signaling cascade responsible for the HGF-induced proliferation was examined.

METHODS

The proliferation of human umbilical cord vein endothelial cells (HUCVEC) was determined using cell counts. Changes of the membrane potential were analyzed using the fluorescence dye DiBAC. Intracellular cGMP-levels were measured by means of [3H]-cGMP-radioimmunoassay. Phosphorylation of the p42/p44 MAP-kinase (MAPK) and the endothelial nitric oxide synthase (eNOS) was analyzed by immunocytochemistry.

RESULTS

A dose-dependent (1-30 ng mL(-1)) increase of HUCVEC proliferation with a maximum at a concentration of 15 ng mL(-1) was induced by HGF. This effect was significantly reduced by the addition of the K+ channel blocker iberiotoxin (100 nmol L(-1)), eNOS inhibitor L-NMMA (300 micromol L(-1)), or the MEK inhibitor PD 98059 (20 micromol L(-1)). A HGF-induced hyperpolarization that was blocked by iberiotoxin was observed. In addition, HGF-induced activation of the eNOS was blocked by the K+ channel inhibitor. An increase of +101% MAPK phosphorylation was induced by HGF, which was blocked, if the cells were treated with L-NMMA (n = 20; P < 0.05), whereas HGF-induced phosphorylation of the eNOS was not affected by MEK inhibition.

CONCLUSIONS

Hepatocyte growth factor modulates endothelial K+ channels causing an activation of the eNOS; the increase of nitric oxide is necessary for the phosphorylation of the MAPK inducing the proliferation of HUCVEC.

Vascular Endothelial Growth Factor Immobilized on Platinum Microcoils for the Treatment of Intracranial Aneurysms: Experimental Rat Model Study

Platinum microcoils coated with immobilized recombinant human vascular endothelial growth factor (rhVEGF) were prepared and the effectiveness for the embolization of aneurysms was investigated using a rat model. Platinum coils were prepared by successive deposition of cationic polyethyleneimine and anionic heparin, and VEGF was immobilized through affinity interaction with heparin. Unmodified, heparin-coated, or rhVEGF-immobilized platinum coil segments were inserted into the ligated external carotid arteries at the bifurcation of the common carotid artery (CCA) of adult female rats. The bifurcation segments of the CCA were harvested 2 weeks after the coil placement. rhVEGF-immobilized coils showed significantly greater endothelial formation at the aneurysm orifice and cell infiltration in the aneurysm body compared with the unmodified and heparin-coated coils. The percentage of sac occlusion was significantly greater in the rhVEGF-immobilized group (77.53 +/- 27.58%) than in the heparin-coated group (44.81 +/- 38.30%) and unmodified group (34.99 +/- 28.15%). Scanning electron microscopy showed a tendency for more fibrotic and cellular collections on the coil surface and more tissue mass filling in the coil lumen in the rhVEGF-immobilized group. Platinum microcoils coated with immobilized rhVEGF may be effective for the obliteration of aneurysms.

Efficient gene regulation by PPAR gamma and thiazolidinediones in skeletal muscle and heart

We have developed a new gene regulation system for gene therapy. This system consists of two expression cassettes; one expresses the human peroxisome proliferator-activated receptor gamma(PPAR gamma), and the other expresses the therapeutic gene under the control of multiple peroxisome proliferator-activated receptor (PPAR) response elements (PPREs) linked to a basal promoter. Using direct injection of plasmid DNA into skeletal muscle or myocardium of rodents and oral administration of clinically approved PPAR gamma activators, we demonstrate that reporter gene expression can be induced more than 25-fold. We show that oral administration of PPAR gamma activator at intervals separated by several months results in repeated pulses of high-level reporter gene expression. We also document a PPAR gamma activator dose-response effect on reporter gene expression. This is the first report of a gene regulation system that makes use of a human transcription factor and that may be safer than chimeric transcription factors for human gene therapy.

Naked plasmid DNA encoding fibroblast growth factor type 1 for the treatment of end-stage unreconstructible lower extremity ischemia: preliminary results of a phase I trial

OBJECTIVE

The objective of this study was to evaluate the safety and tolerance of increasing single and repeated (n = 2) doses of intramuscular naked plasmid DNA encoding for fibroblast growth factor (FGF) type 1 (NV1FGF) administered to patients with unreconstructible end-stage peripheral arterial occlusive disease (PAD). The secondary objectives were to determine the biologic activity of NV1FGF on hemodynamic and clinical parameters associated with improved perfusion.

METHODS

Fifty-one patients with unreconstructible peripheral arterial occlusive disease with rest pain or tissue necrosis underwent treatment with intramuscular NV1FGF. Increasing single (500, 1000, 2000, 4000, 8000, and 16,000 microg) and repeated (2 x 500, 2 x 1000, 2 x 2000, 2 x 4000, and 2 x 8000 microg) doses of NV1FGF were injected into the ischemic thigh and calf. Arteriography was performed before treatment and was repeated 12 weeks after treatment. Side effects and serious adverse events were monitored. Measurements of plasma and urine levels were performed to evaluate NV1FGF plasmid distribution. Serum FGF-1 was measured as an analysis of gene expression at the protein level. Transcutaneous oxygen pressure, ankle brachial index, toe brachial index, pain assessment with visual analog scale, and ulcer healing also were assessed. The safety results are presented for 51 patients, and the clinical outcomes are presented for the first 15 patients (500 to 4000 microg) who completed the 6-month follow-up study.

RESULTS

NV1FGF was well tolerated. Sixty-six serious adverse events were reported; however, none were considered to be related to NV1FGF. Four patients had adverse events that were possibly or probably related to the study treatment: injection site pain, pain, peripheral edema, myasthenia, and paresthesia. No laboratory adverse events were related to the study treatment. Two deaths remote from the treatment were considered not related. Biodistribution of plasmid was limited and transient in plasma and absent in urine. No increase in the FGF-1 serum level was detected. A significant reduction in pain (P <.001) and aggregate ulcer size (P <.01) was associated with an increased transcutaneous oxygen pressure (P <.01) as compared with baseline pretreatment values. A significant increase in ankle brachial index (P <.01) was seen.

CONCLUSION

NV1FGF is well tolerated and potentially could be effective for the treatment of patients with end-stage limb ischemia. Biologic parameters indicate improved perfusion after NV1FGF administration. Dose response is not yet evident. The safety of NV1FGF and the magnitude of improvement observed in this study encourage further investigation with a placebo-controlled, double-blind clinical trial.

Biodegradable Polyglycolide Endovascular Coils Promote Wall Thickening and Drug Delivery in a Rat Aneurysm Model

OBJECTIVE

We designed biodegradable polyglycolide coils (BPCs) and compared the histopathological response to the coils with that to platinum Guglielmi detachable coils (GDCs), after insertion into ligated common carotid arteries (CCAs) of adult rats. BPCs were also tested for use in local drug delivery.

METHODS

Segments (4-mm) of unmodified BPCs, unmodified GDCs, or BPCs coated with Type I bovine collagen and recombinant human vascular endothelial growth factor-165 (500 μg/ml) were inserted into ligated CCAs of adult rats for 14 days, and specimens were compared with contralateral CCA control specimens.

RESULTS

Arterial segments with BPCs exhibited substantially increased wall thickening, compared with GDCs (0.33 mm versus 0.10 mm, P &lt; 0.005), which reduced the luminal diameter by 40%, relative to untreated contralateral control specimens (P &lt; 0.05, n = 6). Arterial segments with BPCs also exhibited a marked reduction (P &lt; 0.05, n = 6) in luminal area (0.72 ± 0.93 mm2), with marked cellular proliferation within the coil diameter, indicating coil integration. Arterial segments with collagen/recombinant human vascular endothelial growth factor-coated BPCs also exhibited a marked 2.9-fold increase (P &lt; 0.005, n = 5) in wall thickness (0.29 ± 0.11 mm) and a 34% reduction in luminal diameter, compared with contralateral control vessels. There was marked proliferation of cells within the coil lumen of vessels treated with BPCs with collagen/recombinant human vascular endothelial growth factor.

CONCLUSION

In this feasibility study, BPCs enhanced the vascular response of CCA segments, compared with GDCs, and were also suitable for local protein delivery to the vessel lumen, under conditions of stasis and arterial pressurization of vascular cells.

Gene Therapy for Cardiovascular Disease

During the past decade, gene therapy for the treatment of many inherited and acquired medical problems has become the subject of increasing focus in both the scientific litera ture and the lay press. This review examines the history and current status of gene therapy for advanced chronic periph eral and myocardial ischemia.

Evaluation of the effects of intramyocardial injection of DNA expressing vascular endothelial growth factor (VEGF) in a myocardial infarction model in the rat--angiogenesis and angioma formation

OBJECTIVES

The effects of direct intramyocardial injection of the plasmid encoding vascular endothelial growth factor (phVEGF165) in the border zone of myocardial infarct tissue in rat hearts were investigated.

BACKGROUND

Controversy exists concerning the ability of VEGF to induce angiogenesis and enhance coronary flow in the myocardium.

METHODS

Sprague-Dawley rats received a ligation of the left coronary artery to induce myocardial infarction (MI). At 33.1 +/- 6.5 days, the rats were injected with phVEGF165 at one location and control plasmid at a second location (500 microg DNA, n = 24) or saline (n = 16). After 33.1 +/- 5.7 days, the hearts were excised for macroscopic and histologic analysis. Regional blood flow ratios were measured in 18 rats by radioactive microspheres.

RESULTS

phVEGF165-treated sites showed macroscopic angioma-like structures at the injection site while control DNA and saline injection sites did not. By histology, 21/24 phVEGF165-treated hearts showed increased focal epicardial blood vessel density and angioma-like formation. Quantitative morphometric evaluation in 20 phVEGF165-treated hearts revealed 44.4 +/- 10.5 vascular structures per field in phVEGF165-treated hearts versus 21.4 +/- 4.7 in control DNA injection sites (p < 0.05). Regional myocardial blood flow ratios between the injection site and noninfarcted area did not demonstrate any difference between phVEGF,165-treated hearts (0.9 +/- 0.2) and saline-treated hearts (0.7 +/- 0.1).

CONCLUSIONS

Injection of DNA for VEGF in the border zone of MI in rat hearts induced angiogenesis. Angioma formation at the injection sites did not appear to contribute to regional myocardial blood flow, which may be a limitation of gene therapy for this application.

Fibroblast growth factor-2

Fibroblast growth factor-2 (FGF-2) is a heparin-binding growth factor which occurs in several isoforms resulting from alternative initiations of translation: an 18 kD cytoplasmic isoform and four larger molecular weight nuclear isoforms (22, 22.5, 24 and 34 kD). FGF-2 has pleiotropic roles in many cell types and tissues; it is a motogenic, angiogenic and survival factor which is involved in cell migration, cell differentiation and in a variety of developmental processes. Although devoid of signal peptide, it could be secreted. It acts mainly through a paracrine/autocrine mechanism involving high affinity transmembrane receptors and heparan sulfate proteoglycan low affinity receptors, but also through still unknown intracrine process(es) on intracellular targets. FGF-2 has many biological functions which are probably isoform-specific. Nevertheless, FGF-2 is not essential for embryonic development as knock-out mice for the growth factor are viable and fertile although they exhibit abnormalities in neuronal differentiation. Use of FGF-2 as therapeutic agent for the treatment of ischemic cardiovascular disease is promising and clinical trials are in progress.

Cardiovascular gene therapy

Vascular gene transfer potentially offers new treatments for cardiovascular diseases. It can be used to overexpress therapeutically important proteins and correct genetic defects, and to test experimentally the effects of various genes in a local vascular compartment. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers have improved blood flow and collateral development in ischaemic limb and myocardium. Promising therapeutic effects have been obtained in animal models of restenosis or vein-graft thickening with the transfer of genes coding for VEGF, nitric-oxide synthase, thymidine kinase, retinoblastoma, growth arrest homoeobox, tissue inhibitor of metalloproteinases, cyclin or cyclin-dependent kinase inhibitors, fas ligand and hirudin, and antisense oligonucleotides against transcription factors or cell-cycle regulatory proteins. First experiences of VEGF gene transfer and decoy oligonucleotides in human beings have been reported. However, further developments in gene-transfer vectors, gene-delivery techniques and identification of effective treatment genes will be required before the full therapeutic potential of gene therapy in cardiovascular disease can be assessed.

Adenovirus-mediated acidic fibroblast growth factor gene transfer induces angiogenesis in the nonischemic rabbit heart

Most patients with severe coronary artery disease have normal baseline myocardial blood flow. Therefore, interventions aimed at inducing therapeutic angiogenesis in these patients should cause new blood vessel growth in the heart in the absence of chronic ischemia. It was examined whether adenovirus-mediated gene transfer of recombinant, secreted acidic fibroblast growth factor (sp+aFGF(1-154)), next to a major epicardial artery, may induce neovascularization and reduce the risk region for myocardial infarction upon coronary ligation near the injection site. Fifteen days prior to coronary artery occlusion, rabbits were treated with intramyocardial injections of AdCMV.sp+aFGF(1-154), the control vector AdCMV.NLSbetagal (1 x 10(9) plaque-forming units), or saline. Messenger RNA transcripts for aFGF(1-154) were present up to 12 days after injection in the tissues exposed to AdCMV.aFGF(1-154). Following coronary artery occlusion rabbits treated with AdCMV. sp+aFGF(1-154) showed a 50% reduction of the risk region for myocardial infarction (P < 0.01 vs control). Histologic analysis showed a twofold increase in length density of intramural coronary arterioles (P < 0.01 vs control) and a 17% increase in length density of the capillary network (P < 0.001) in the myocardium exposed to AdCMV.sp+aFGF(1-154). Thus, gene therapy with AdCMV. sp+aFGF(1-154) can induce angiogenesis in the absence of chronic ischemia. The newly formed collateral blood vessels provide an anatomical basis for the reduction in the risk region for myocardial infarction upon subsequent occlusion of the coronary artery in proximity of the site where angiogenesis was induced.

Characterization of physiologically regulated vectors for the treatment of ischemic disease

A high therapeutic index is as important for gene-based therapies as it is for chemotherapy or radiotherapy. One approach has been transcriptional targeting through the use of tissue-specific regulatory elements. A more versatile approach would be to use a regulatory element that is controlled via a parameter common to a broad range of diseases. Ischemia is characteristic of a number of pathologies that range from vascular occlusion through to cancer. The state of low oxygen, hypoxia, triggers a transcriptional signaling pathway that is mediated by transcription factors binding to a specific enhancer, the hypoxia response element (HRE). These observations have therefore led to the use of HREs to drive gene expression in a number of target tissues from tumors to cardiac muscle. To translate these observations into a clinically useful vector system we have now assessed the potency of a number of naturally derived HREs in various configurations combined with minimal promoters. The optimal HRE has been introduced into a single transcription unit retroviral vector that can deliver regulated gene expression in response to hypoxia. An important feature of this new physiologically regulated vector is the combination of low basal expression and high-level activated expression that is on a par with that obtained with the cytomegalovirus immediate-early (CMV IE) promoter. The role of elements that stabilize mRNA in the presence of hypoxia has also been assessed. These hypoxia-regulated vectors may have utility for restricting the delivery of therapeutic proteins to tumors and ischemic sites.

Gene therapy as a therapeutic intervention for vascular disease

Gene therapy for the treatment of many medical problems, including vascular disease, has become the subject of increasing discussion in both the scientific literature and the national press over the past decade. This review will examine the history and current status of gene therapy for vascular proliferative disorders and advanced chronic peripheral and cardiac ischemia.