A prescreening system for potential antiproliferative agents: implications for local treatment strategies of postangioplasty restenosis

Nanoparticle drug- and gene-eluting stents for the prevention and treatment of coronary restenosis

Percutaneous coronary intervention (PCI) has become the most common revascularization procedure for coronary artery disease. The use of stents has reduced the rate of restenosis by preventing elastic recoil and negative remodeling. However, in-stent restenosis remains one of the major drawbacks of this procedure. Drug-eluting stents (DESs) have proven to be effective in reducing the risk of late restenosis, but the use of currently marketed DESs presents safety concerns, including the non-specificity of therapeutics, incomplete endothelialization leading to late thrombosis, the need for long-term anti-platelet agents, and local hypersensitivity to polymer delivery matrices. In addition, the current DESs lack the capacity for adjustment of the drug dose and release kinetics appropriate to the disease status of the treated vessel. The development of efficacious therapeutic strategies to prevent and inhibit restenosis after PCI is critical for the treatment of coronary artery disease. The administration of drugs using biodegradable polymer nanoparticles as carriers has generated immense interest due to their excellent biocompatibility and ability to facilitate prolonged drug release. Despite the potential benefits of nanoparticles as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of nanoparticle materials, as well as to their size and shape. This review describes the molecular mechanism of coronary restenosis, the use of DESs, and progress in nanoparticle drug- or gene-eluting stents for the prevention and treatment of coronary restenosis.

N-acetylcysteine potentiates doxorubicin-induced ATM and p53 activation in ovarian cancer cells

Doxorubicin has been used clinically to treat various types of cancer, and yet the molecular mode of actions of doxorubicin remains to be fully unraveled. In this study, we investigated the effect of doxorubicin on cultured ovarian cancer cells (CaOV3). MTT assay data showed that doxorubicin inhibits cell proliferation in a time- and dose-dependent manner. Phagokinetic cell motility assay data indicated that doxorubicin inhibits both basal level and EGF-induced cell migration in CaOV3 cells. Confocal microscopic data revealed that doxorubicin induces reorganization of cytoskeletal proteins including actin, tubulin and vimentin. Doxorubicin induces phosphorylation of p53 at Ser15 and 20, acetylation of p53 and ATM activation. Doxorubicin also induces phosphorylation of histone H2AX at Ser139. Interestingly, doxorubicin also inhibits mTOR activity, measured by phosphorylation of S6 ribosomal protein. Pretreatment of CaOV3 cells with antioxidant N-acetylcysteine (NAC), but not pyrrolidine dithiocarbamate (PDTC) potentiates doxorubicin-induced phosphorylation of p53 and ATM. Collectively, we conclude that doxorubicin induces ATM/p53 activation leading to reorganization of cytoskeletal networks, inhibition of mTOR activity, and inhibition of cell proliferation and migration. Our data also suggest that removal of oxidants by antioxidants such as NAC may enhance the efficacy of doxorubicin in vivo.

Sustained local drug delivery from a novel polymeric ring to inhibit intimal hyperplasia

The long-term clinical success of autologous vein and synthetic vascular grafts are limited because of the development of anastomotic intimal hyperplasia (IH). We have previously published data suggesting that cyclosporine (CyA) may reduce the development of IH in a canine model (Hirko et al., J Vasc Surg 1993;17:877-887). However, systemic administration of CyA could create serious adverse effects. Therefore, it is our long-term goal to test the hypothesis that the controlled local release of CyA from a polymeric vascular wrap would prevent the development of IH. To test this hypothesis, we developed a controlled release polymeric ring that could be placed around anastomotic sites to deliver therapeutic drugs locally. The ring is a composite polymeric device consisting of poly(DL-lactide-co-glycolide) (PLGA) microspheres embedded in a poly(ethylene glycol) hydrogel. Several in vitro studies were conducted to evaluate the effects of different sterilization procedures on the properties of the device. It was determined that gamma sterilization was the preferred sterilization method of choice for this device. In vivo studies were conducted on a swine model to evaluate the biocompatibility of the ring. The histological findings of the ring implants at 2 and 4 weeks demonstrate the biocompatibility of this device.

Colchicine Inhibits Intimal Hyperplasia and Leukocyte VEGF Expression in Dogs

BACKGROUND

Restenosis due to intimal hyperplasia following percutaneous transluminal angioplasty limits its long-term efficacy. We evaluated the effect of colchicine on the development of intimal hyperplasia following balloon angioplasty and on the vascular endothelial growth factor (VEGF) expression in leukocytes.

MATERIAL AND METHODS

Adult dogs underwent balloon angioplasty of the right iliofemoral artery. Group 1 served as control, while groups 2 and 3 (six animals per group) received 0.1 and 0.5 mg/kg/d of colchicine p.o., respectively, starting 2 d before angioplasty and continued for 14 d. Before angioplasty and at day 14, blood samples were collected for drug toxicity analysis and the determination of leukocyte expression of VEGF. Animals were euthanized and iliofemoral arteries were perfusion fixed in situ and processed for histological and morphometric analysis.

RESULTS

Balloon angioplasty without colchicine resulted in 446% (P < 0.001), 111% (P = 0.7), and 267% (P < 0.001) increase in intimal and medial thickness and intima/media ratio compared with contralateral uninjured iliofemoral arteries. Low-dose and high-dose colchicine resulted in 32% and 58% reduction in intima/media ratio, respectively (both P < 0.001). VEGF expression in leukocytes of control group was up-regulated (40%), but was down-regulated by 12% and 55%, respectively, in low-dose and high-dose colchicine groups at 2 wk after angioplasty compared with preangioplasty expression. The results of complete blood count and serum transaminases and creatinine were within normal range.

CONCLUSION

This study demonstrates that oral colchicine for 2 wk significantly reduces intimal hyperplasia following balloon angioplasty in dogs through down-regulation of leukocyte VEGF expression and without apparent toxicity.

Sirolimus inhibits key events of restenosis in vitro/ex vivo: evaluation of the clinical relevance of the data by SI/MPL- and SI/DES-ratios

Background

Sirolimus (SRL, Rapamycin) has been used successfully to inhibit restenosis both in drug eluting stents (DES) and after systemic application. The current study reports on the effects of SRL in various human in vitro/ex vivo models and evaluates the theoretical clinical relevance of the data by SI/MPL- and SI/DES-ratio's.

Methods

Definition of the SI/MPL-ratio: relation between significant inhibitory effects in vitro/ex vivo and the maximal plasma level after systemic administration in vivo (6.4 ng/ml for SRL). Definition of the SI/DES-ratio: relation between significant inhibitory effects in vitro/ex vivo and the drug concentration in DES (7.5 mg/ml in the ISAR drug-eluting stent platform). Part I of the study investigated in cytoflow studies the effect of SRL (0.01–1000 ng/ml) on TNF-α induced expression of intercellular adhesion molecule 1 (ICAM-1) in human coronary endothelial cells (HCAEC) and human coronary smooth muscle cells (HCMSMC). Part II of the study analysed the effect of SRL (0.01–1000 ng/ml) on cell migration of HCMSMC. In part III, IV, and V of the study ex vivo angioplasty (9 bar) was carried out in a human organ culture model (HOC-model). SRL (50 ng/ml) was added for a period of 21 days, after 21 and 56 days cell proliferation, apoptosis, and neointimal hyperplasia was studied.

Results

Expression of ICAM-1 was significantly inhibited both in HCAEC (SRL ≥ 0.01 ng/ml) and HCMSMC (SRL ≥ 10 ng/ml). SRL in concentrations ≥ 0.1 ng/ml significantly inhibited migration of HCMSMC. Cell proliferation and neointimal hyperplasia was inhibited at day 21 and day 56, significance (p < 0.01) was achieved for the inhibitory effect on cell proliferation in the media at day 21. The number of apoptotic cells was always below 1%.

Conclusion

SI/MPL-ratio's ≤ 1 (ICAM-1 expression, cell migration) characterize inhibitory effects of SRL that can be theoretically expected both after systemic and local high dose administration, a SI/MPL-ratio of 7.81 (cell proliferation) represents an effect that was achieved with drug concentrations 7.81-times the MPL. SI/DES-ratio's between 10^-6 and 10^-8 indicate that the described inhibitory effects of SRL have been detected with micro to nano parts of the SRL concentration in the ISAR drug-eluting stent platform. Drug concentrations in DES will be a central issue in the future.

Systemic immunosuppressive therapy inhibits in-stent restenosis in patients with renal allograft

BACKGROUND

Cyclosporine is used routinely for prophylaxis for renal allograft rejection. In experimental animal studies, cyclosporine had been shown to inhibit smooth muscle cell proliferation during the arterial response to injury. We investigated whether systemic immunosuppression may inhibit in-stent restenosis in renal transplant patients undergoing coronary stenting.

METHODS

From 1993 to 2003, 33 renal transplant patients with 45 coronary lesions and 37 dialysis patients with 52 lesions underwent coronary stenting using bare metal stents at our center. We followed all patients clinically for a mean period of 37 +/- 31 months and 40 patients angiographically at 14 +/- 15 months after coronary intervention. Cyclosporine was combined with corticosteroids in 32 patients and one patient received tacrolimus instead of cyclosporine.

RESULTS

The baseline clinical and angiographical characteristics were similar and the success rate of the procedure was 100% in both groups. In renal transplant group, the mean dose of cyclosporine was 192.5 +/- 68 mg/day and the blood cyclosporine level at the time of procedure was 152.9 +/- 51.5 ng/mL. The rate of in-stent restenosis was 7.1% in renal transplant group and 57.1% in dialysis group (P < 0.0001). The mean late loss was 0.47 +/- 0.57 mm in renal transplant group when compared with 1.51 +/- 1.09 mm in dialysis group (P = 0.004). The overall rate of major adverse cardiac events (MACEs) was 6.1% in renal transplant group and 35.1% in dialysis group (P < 0.0001).

CONCLUSIONS

Renal transplant patients receiving combined immunosuppressive agents showed markedly low rates of in-stent restenosis and MACE after coronary revascularization with stent. We consider that this result may be related to the ability of combined immunosuppressive therapy to inhibit inflammatory reaction and vascular smooth muscle cell proliferation induced by coronary stenting.

Triple-coated stents (Hirudin/Iloprost/Paclitaxel): an in vitro approach for characterizing the antiproliferative potential of each individual compound

BACKGROUND

Hirudin (H)/iloprost (I)/paclitaxel (P)-coated stents represent a multifactorial approach to reducing the proliferative response caused by ballooning and stenting. The study presented compares the net effect of each individual compound of HIP-coated stents with the summed effect of the compounds in the stent coating.

METHODS AND RESULTS

For proliferation prescreening studies, human coronary smooth muscle cells were incubated with H (0.005-500 microg/ml), I (0.00001-1 microg/ml), and P (0.0001-10 microg/ml). After 5 days, cell number was studied in a cell analyzer system. Secondly, 8-mm stents were coated with (1) HI, (2) HIP-10 microg/20 microg/40 microg (HIP5%/10%/20%), (3) P-40 microg (P), (4) IP-40 microg (IP), and (5) HP-40 microg (HP). After 5 days, the effect on cell proliferation and cytoskeletal structures was studied. No antiproliferative effect was found after incubation with H; significant inhibition was seen after incubation with I (p<0.05) or lipophilically dissolved P (p<0.001). After 5 days incubation with HIP5%-, HIP10%-, HIP20%-, P20%-, IP20%-, and HP20%-coated stents, cell proliferation was inhibited by 55.5% (p<0.05), 61% (p<0.05), 57.9% (p<0.05), 59.5% (p<0.001), 59.8% (p<0.001), and 63.3% (p<0.001), respectively. HI- and HIP-coated stents caused a severe destruction of the cytoskeletal structures smooth muscle alpha-actin and alpha-tubulin; despite the destruction, vital cells could be identified with positive FDA staining.

CONCLUSIONS

Although both lipophilically dissolved P and hydrophilically dissolved I contributed to the antiproliferative effect, no additive effect of the two compounds was detected. In vivo P can be released more easily from the coating material due to the permanent lipophilic contact of the stent struts with the vessel wall. The current study is the first report on a clear and uncomplicated technique to obtain information on the antiproliferative potential of coated stents before large experimental studies are initiated.

Antiproliferative profile of sirolimus and mycophenolate mofetil: impact of the SI/MPL ratio

BACKGROUND

Recently, preliminary data of the ORBIT study have been presented; coronary restenosis after oral treatment with sirolimus (SRL) was merely 7.7%. The present study thought to investigate the antiproliferative profile of SRL and mycophenolate mofetil (MMF), both as individual compounds and as a combined therapy.

METHODS AND RESULTS

Proliferation studies were carried out with smooth muscle cells of human coronary arteries (human coronary smooth muscle cells, HCMSMC). SRL (0.01-1000 ng/ml) and MMF (0.005-500 microg/ml) were added in six descending concentrations, cell proliferation was studied at day 5. To characterize the clinical relevance of the data, the authors calculated a SI/MPL ratio between a significant antiproliferative effect (SI) in vitro and the maximal systemic plasma level (MPL) in vivo. The SI/MPL ratios of SRL and MMF were 0.16 and 0.014, respectively. Second, SRL (1 and 0.1 ng/ml) was combined with four concentrations of MMF (0.5 and 0.05 microg/ml) and MMF was combined with four concentrations of SRL. Additive and overadditive antiproliferative effects were found, no destruction of alpha-tubulin was detected.

CONCLUSIONS

Thus, SRL and MMF exhibit dose-dependent direct antiproliferative effects with SI/MPL ratios smaller than one. Both agents, as individual compounds or as combined therapy, are candidates for an oral therapy of human coronary restenosis.

Simultaneous intra/extravascular administration of antiproliferative agents as a new strategy to inhibit restenosis: the peak of reactive cell proliferation as a hallmark for the duration of the treatment

BACKGROUND

Strictly intravascular approaches for the treatment of postangioplasty restenosis are effective in the intima and the inner parts of the media but may be insufficient to control redundant pathways in the more outer parts of the media and the adventitia. An inverse situation may occur subsequently to a strictly extravascular approach, like the recently suggested pericardial approach in pigs. We hypothesized that simultaneous intra/extravascular administration of anti-restenotic agents inhibits restenosis by blocking all stimulatory pathways in the entire arterial wall.

METHODS

Fresh hearts of 25 domestic pigs were obtained from a local slaughterhouse. Left anterior descending coronary arteries (LAD) were harvested, cut into cylindric 5 mm segments, and cultured as ex vivo porcine organ cultures (POCs). After 9 bar ballooning simultaneous intra/extravascular administration of high dose diltiazem (50 microg/mL) was carried out for a period of 1, 2, 3, 4, 5, 6, and 7 days. At day 7 and 28 proliferative activity (BrdU), neointimal thickening, and staining against smooth muscle alpha-actin and vWF was analysed.

RESULTS

7 days after ballooning administration of diltiazem for 4, 5, 6, and 7 days inhibited reactive cell proliferation by more than 50% (n.s.) as compared to control, 28 days after ballooning administration for 6 and 7 days inhibited neointimal thickening by more than 75% (p < 0.05). Simultaneous intra/extravascular administration of high dose diltiazem did not affect the expression of vWF in endothelial cells or smooth muscle alpha-actin in smooth muscle cells.

CONCLUSIONS

Simultaneous intra/extravascular administration of high dose diltiazem (50 microg/mL) has to be maintained for at least 6 days to achieve a significant inhibition of neointimal thickening. The data demonstrate the importance of the maximal reactive cell proliferation (= day 7 in the POC-model) for the calculation of the duration of the treatment period.

Different radiosensitivity of smooth muscle cells and endothelial cells in vitro as demonstrated by irradiation from a Re-188 filled balloon catheter

There is an increasing interest in irradiation to control restenosis after balloon angioplasty by an internal radioactive source. Differences in radiosensitivity of the predominant cells of the human coronary artery (i.e. endothelial cells (HCAEC), smooth muscle cells from the media (HCMSMC) and from plaque material (HCPSMC), are issues of controversal discussion. Therefore, we investigated the graded inhibition of cells by irradiation from a balloon catheter filled with a high-energy beta-emitter (Rhenium-188) in vitro. HCPSMC, HCMSMC and HCAEC were cultured and irradiated with increasing dose from 7.5 to 37.5 Gy at a dose rate of 1.5+/-0.3 Gy/min. After irradiation, bromodeoxyuridine (BrdU) was added and cells were fixed 18 h later. In a limited field opposite to the balloon, the number of BrdU-positive cells were analysed in comparison to non-irradiated controls. Significant inhibition was demonstrated in HCPSMC and HCMSMC at 7.5 Gy while HCAEC needed 22.5 Gy for similar effects. The antiproliferative effect was dose dependent in all cell strains. The effect of irradiation with 22.5 Gy on smooth muscle alpha-actin, vimentin, and alpha-tubulin of HCPSMC and HCMSMC and on von Willebrand factor (vWF), vimentin, and alpha-tubulin of HCAEC was investigated by means of indirect immunofluorescence. Within 18 h after irradiation no effect on cytoskeletal components and vWF was documented. This in vitro study demonstrates that irradiation inhibits HCMSMC and HCPSMC at lower dose rates compared to HCAEC.