Inhibition of smooth muscle cell proliferation and migration in vitro by antisense oligonucleotide to c-myb

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

Myb overexpression overrides androgen depletion-induced cell cycle arrest and apoptosis in prostate cancer cells, and confers aggressive malignant traits: potential role in castration resistance

Myb, a cellular progenitor of v-Myb oncogenes, is amplified in prostate cancer and exhibits greater amplification frequency in hormone-refractory disease. Here, we have investigated the functional significance of Myb in prostate cancer. Our studies demonstrate Myb expression in all prostate cancer cell lines (LNCaP, C4-2, PC3 and DU145) examined, whereas it is negligibly expressed in normal/benign prostate epithelial cells (RWPE1 and RWPE2). Notably, Myb is significantly upregulated, both at transcript (>60-fold) and protein (>15-fold) levels, in castration-resistant (C4-2) cells as compared with androgen-dependent (LNCaP) prostate cancer cells of the same genotypic lineage. Using loss and gain of function approaches, we demonstrate that Myb promotes and sustains cell cycle progression and survival under androgen-supplemented and -deprived conditions, respectively, through induction of cyclins (A1, D1 and E1), Bcl-xL and Bcl2 and downregulation of p27 and Bax. Interestingly, Myb overexpression is also associated with enhanced prostate-specific antigen expression. Furthermore, our data show a role of Myb in enhanced motility and invasion and decreased homotypic interactions of prostate cancer cells. Myb overexpression is also associated with actin reorganization leading to the formation of filopodia-like cellular protrusions. Immunoblot analyses demonstrate gain of mesenchymal and loss of epithelial markers and vice versa, in Myb-overexpressing LNCaP and -silenced C4-2 cells, respectively, indicating a role of Myb in epithelial to mesenchymal transition. Altogether, our studies provide first experimental evidence for a functional role of Myb in growth and malignant behavior of prostate cancer cells and suggest a novel mechanism for castration resistance.

Suppression of growth factor expression and human vascular smooth muscle cell growth by small interfering RNA targeting EGR-1

Smooth muscle cell (SMC) proliferation and migration are key processes that occur in the reparative response to injury after percutaneous coronary intervention and in failed bypass grafts for the treatment of atherosclerosis. In the present study, we generated novel synthetic small interfering RNA (siRNA) molecules targeting the coding region of human early growth response-1 (EGR-1) mRNA that attenuate the expression of EGR-1 and that of fibroblast growth factor-2 (FGF-2) and granulocyte-colony stimulating factor (G-CSF). These agents suppressed SMC proliferation in a dose-dependent and non-toxic manner and blocked SMC regrowth from the wound edge following mechanical injury in vitro. In contrast, the scrambled counterpart did not inhibit SMC proliferation, EGR-1 protein expression or SMC regrowth after injury. These findings demonstrate that EGR-1 siRNA can serve as inhibitors of SMC proliferation and wound repair suggesting that these agents may potentially be useful in the control of vascular proliferative disorders.

Engineering of muscle tissue

The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Tissue engineering and regenerative medicine is an emerging interdisciplinary field that applies the principles of biology and engineering to the development of viable substitutes that restore, maintain, or improve the function of human tissues and organs. Tissue engineering science has provided critical new knowledge that will deepen our understanding of the phenotype of an important category of cell types-the muscle cells-and this knowledge may enable meaningful advances in musculoskeletal tissue engineering. There are two principle strategies for the replacement of impaired muscle tissues. One approach uses the application of isolated and differentiated cells (in vivo tissue engineering), using a transport matrix for the cell delivery; the other uses in vitro-designed and pre-fabricated tissue equivalents (in vitro tissue engineering). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and differentiation, the three-dimensional environment, the architecture of the cells, and gene expression of the developmental process and the survival of the cells and integration in the host in in vivo experiments. As the techniques of tissue engineering become more sophisticated and as issues such as vascularization and innervation are addressed, the usefulness of these methods for reconstructive surgery may grow significantly.

Arterial wall strength after endovascular photodynamic therapy

BACKGROUND AND OBJECTIVES

Vascular photodynamic therapy (PDT) inhibits intimal hyperplasia (IH) induced by angioplasty in rat iliac arteries by eradicating the proliferating smooth muscle cells. This process may jeopardise the structure and strength of the arterial wall, reflected by a decreased bursting pressure.

STUDY DESIGN/MATERIALS AND METHODS

Thirty male Wistar rats of 250-300 g were subdivided into 3 groups (n = 10). In all groups, IH was induced by balloon injury (BI). One experimental group received PDT at 50 J/cm diffuser length, the other group at 100 J/cm diffuser length. The third group served as control group and received no PDT. In half of each group the bursting pressure was analyzed after 2 hours (n = 5), in the other half after 1 year.

RESULTS

Two hours after the procedure the bursting pressure was 3.37 +/- 0.58 (+/-SEM) bar in the BI + PDT 50 and 3.96 +/- 0.43 bar in the BI + PDT 100 group, compared to 2.20 +/- 0.27 bar in the BI group (P < 0.05). After 1 year these values were 3.18 +/- 0.87 bar in the BI + PDT 50 (P < 0.05) and 2.02 +/- 0.31 bar in the BI + PDT 100 group, compared to 2.10 +/- 0.30 bar in the BI group (NS). In the BI + PDT 100 group, 3 out of 5 rats appeared to have aneurysmal dilatation after 1 year.

CONCLUSIONS

Endovascular PDT increases the arterial wall strength as measured by the bursting pressure at short-term. After 1 year, wall strength is not diminished as measured by bursting pressure, but aneurysmal dilatation nevertheless developed with 100 J/cm. dl. This may limit the use of high energy PDT.

Conditional expression of a dominant-negative c-Myb in vascular smooth muscle cells inhibits arterial remodeling after injury

Inhibiting activity of the c-Myb transcription factor attenuates G1 to S phase cell cycle transitions in vascular smooth muscle cells (SMCs) in vitro. To determine the effects of arterial SMC-specific expression of a dominant-negative c-Myb molecule (Myb-Engrailed) on vascular remodeling in vivo, we performed carotid artery wire-denudation in 2 independent lines of binary transgenic mice with SM22alpha promoter-defined Doxycycline-suppressible expression of Myb-Engrailed. Adult mice with arterial SMC-specific expression of Myb-Engrailed were overtly normal in appearance and did not display any changes in cardiovascular structure or physiology. However, bromodeoxyuridine-defined arterial SMC proliferation, neointima formation, medial hyperplasia, and arterial remodeling were markedly decreased in mice expressing arterial SMC-restricted Myb-Engrailed after arterial injury. These data suggest that c-Myb activity in arterial SMCs is not essential for arterial structure or function during development, but is involved in the proliferation of arterial SMCs as occurs in vascular pathology, and that the expression of a dominant-negative c-Myb can dramatically reduce adverse arterial remodeling in an in vivo model of restenosis. As such, this model represents a novel tissue-specific strategy for the potential gene therapy of diseases characterized by arterial SMC proliferation.

Local delivery of mithramycin restores vascular reactivity and inhibits neointimal formation in injured arteries and vascular grafts

Arterial restenosis is responsible for the high failure rates of vascular reconstruction procedures. Local sustained drug delivery has shown promise in the prevention of restenosis. The drug release rate from mithramycin-loaded EVA matrices (0.1%) was evaluated, and their antirestenotic effect was studied in the rat carotid model and rabbit model of vascular grafts. The modulation of c-myc expression by mithramycin treatment was examined by immunohistochemistry in the rat carotid model. The proliferative response of injured rat arteries was studied by bromdeoxyuridine (BrdU) immunostaining. The impact of mithramycin treatment on vasomotor responses of the venous segments grafted into arterial circulation was studied ex vivo using vasoreactive compounds. Mithramycin was released exponentially from EVA matrices in PBS. Matrices co-formulated with PEG-4600 revealed enhanced release kinetics. The perivascular implantation of drug-loaded EVA-PEG matrices led to 50% reduction of neointimal formation, and reduced the c-myc expression and BrdU labeling in comparison to control implants. Decreased sensitivity of mithramycin-treated grafts to serotonin-induced vasoconstriction was observed. Local perivascular mithramycin treatment limits the functional alteration caused by the grafting of venous segments in high-pressure arterial environment, and potently inhibits stenosis secondary to grafting and angioplasty injury. The antirestenotic effect is associated with reduced c-myc expression and with subsequent decrease in SMC proliferation.

The migratory response to platelet-derived growth factor of smooth muscle cells isolated from synthetic vascular grafts in a canine model

OBJECTIVE

Previous studies on smooth muscle cells (SMCs) harvested from implanted synthetic grafts demonstrate increased production of platelet-derived growth factor (PDGF) but decreased proliferative response compared with aortic SMCs. The purpose of this study was to determine the migratory response of graft versus aortic SMCs.

METHODS

Thoracoabdominal grafts were implanted in beagles. The SMCs were harvested from the graft and infrarenal aorta. Migration was determined with the use of a razor-scrape assay and computerized image analysis.

RESULTS

The mean distance migrated and the number of cells that migrated were greater in graft SMCs at baseline (185 +/- 18 micrometer and 108 +/- 17 cells) compared with aortic cells (110 +/- 10 micrometer and 42 +/- 5 cells)(P <.05). Baseline differences persisted after treatment with antibodies to PDGF. The addition of PDGF (10 ng/mL) resulted in increased migration in both graft (229 +/- 23 micrometer and 146 +/- 20 cells) and aortic SMCs (130 +/- 9 micrometer and 70 +/- 5 cells) compared with baseline (P <.05). The relative increase in response to PDGF was similar between the two groups (P = not significant).

CONCLUSIONS

Graft SMCs differ phenotypically from aortic SMCs; they exhibit increased basal migration that is independent of autocrine stimulation by PDGF. In contrast to their blunted proliferative response, graft SMCs have a similar migratory response to PDGF compared with aortic SMCs.

New DNA enzyme targeting Egr-1 mRNA inhibits vascular smooth muscle proliferation and regrowth after injury

Early growth response factor-1 (Egr-1) binds to the promoters of many genes whose products influence cell movement and replication in the artery wall. Here we targeted Egr-1 using a new class of DNA-based enzyme that specifically cleaved Egr-1 mRNA, blocked induction of Egr-1 protein, and inhibited cell proliferation and wound repair in culture. The DNA enzyme also inhibited Egr-1 induction and neointima formation after balloon injury to the rat carotid artery wall. These findings demonstrate the utility of DNA enzymes as biological tools to delineate the specific functions of a given gene, and implicate catalytic nucleic acid molecules composed entirely of DNA as potential therapeutic agents.

Vascular smooth muscle cell proliferation and regrowth after mechanical injury in vitro are Egr-1/NGFI-A-dependent

Smooth muscle cell (SMC) proliferation is a key event in renarrowing of blood vessels after balloon angioplasty. Mechanical injury imparted to the arterial wall in experimental models induces the expression of the immediate-early gene, egr-1. Egr-1 binds to and activates expression from the proximal promoters of multiple genes whose products can, in turn, influence the vascular response to injury. Here, we used antisense strategies in vitro to inhibit rat vascular SMC proliferation by directly targeting Egr-1. A series of phosphorothioate antisense oligonucleotides of 15 base length and complementary to various theoretically accessible regions within Egr-1 mRNA were synthesized and assessed for their ability to selectively inhibit SMC proliferation in an Egr-1-dependent manner. Western blot analysis revealed that two oligonucleotides, AS2 and E11, inhibited Egr-1 synthesis in cells exposed to serum without affecting levels of the zinc finger protein Sp1. AS2 and E11 inhibited serum-inducible [(3)H]thymidine incorporation into DNA, as well as serum stimulation of total cell numbers. Size-matched phosphorothioate oligonucleotides with random, scrambled, sense or mismatch sequences failed to inhibit. Antisense Egr-1 inhibition was nontoxic and reversible. These oligonucleotides also inhibited SMC regrowth after mechanical injury in vitro. Egr-1 thus plays a key regulatory role in SMC proliferation and repair following injury.

Myb targeted therapeutics for the treatment of human malignancies

For the past several years, we have been engaged in developing a therapeutically effective strategy for disrupting gene function with reverse complementary, or so called 'antisense', oligodeoxynucleotides (ODN). This pursuit has focused on finding appropriate diseases in which to apply this approach, and suitable gene targets. Of the genes that we have targeted for disruption using the antisense ODN strategy (Clevenger et al., 1995; Gewirtz and Calabretta, 1988; Ratajczak et al., 1992c; Small et al., 1994) one that has been of particular interest, and one where therapeutically motivated disruptions are now in clinical trial, is the myb gene (reviewed in Lyon et al., 1994). These trials involve treatment of human leukemias. These diseases are a logical choice for developing oncogene targeted therapies because of easy access to tissues, and the abundance of knowledge about the cell and molecular biology of these diseases. Nevertheless, as will be touched on below, other malignancies have also been examined as models for Myb targeted therapy with some surprisingly encouraging results. Finally, while we have focused our efforts on the ODN strategy, I will allude briefly to other strategies for disrupting Myb function with therapeutic intent.

Cellular effects of beta-particle delivery on vascular smooth muscle cells and endothelial cells: a dose-response study

BACKGROUND

Although endovascular radiotherapy inhibits neointimal hyperplasia, the exact cellular alterations induced by beta irradiation remain to be elucidated.

METHODS AND RESULTS

We investigated in vitro the ability of 32P-labeled oligonucleotides to alter (1) proliferation of human and porcine vascular smooth muscle cells (VSMCs) and human coronary artery endothelial cells (ECs), (2) cell cycle progression, (3) cell viability and apoptosis, (4) cell migration, and (5) cell phenotype and morphological features. beta radiation significantly reduced proliferation of VSMCs (ED50 1.10 Gy) and ECs (ED50 2.15 Gy) in a dose-dependent manner. Exposure to beta emission interfered with cell cycle progression, with induction of G0/G1 arrest in VSMCs, without evidence of cell viability alteration, apoptosis, or ultrastructural changes. This strategy also proved to efficiently inhibit VSMC migration by 80% and induce contractile phenotype appearance, as shown by the predominance of alpha-actin immunostaining in beta-irradiated cells compared with control cells.

CONCLUSIONS

32P-labeled oligonucleotide was highly effective in inhibiting proliferation of both VSMCs and ECs in a dose-dependent fashion, with ECs showing a higher resistance to these effects. beta irradiation-induced G1 arrest was not associated with cytotoxicity and apoptosis, thus demonstrating a potent cytostatic effect of beta-based therapy. This effect, coupled to that on VSMC migration inhibition and the appearance of a contractile phenotype, reinforced the potential of ionizing radiation to prevent neointima formation after angioplasty.