Use of rapamycin-impregnated stents in coronary arteries

Acute Thrombus Burden on Coated Flow Diverters Assessed by High Frequency Optical Coherence Tomography

PURPOSE

The implantation of flow diverters requires administration of dual anti-platelet therapy, posing the potential for complications. The p48MW HPC (phenox, Bochüm, Germany) hydrophilic-coated flow diverting stent is designed to be anti-thrombotic, thus opening the potential for single anti-platelet therapy. We deploy a novel intravascular high-resolution imaging technique, high-frequency optical coherence tomography (HF-OCT), to study in an animal model the acute thrombus formation on coated p48MW devices versus uncoated control devices.

METHODS

Three pigs were implanted with 4 flow diverters each, two test hydrophilic-coated devices, and two control uncoated devices (p48MW). Each pig was treated with a different anti-platelet regime: no anti-platelet therapy, aspirin only, aspirin and clopidogrel. Twenty minutes after the flow diverter was implanted, an HF-OCT data set was acquired. Acute clot formed on the flow diverter at each covered side branch was measured from the HF-OCT slices. Factors considered to be important were the device type (pHPC versus bare metal), aspirin, clopidogrel, and vessel location. A linear model was constructed from the significant factors.

RESULTS

Both coating (p < 0.001) and aspirin (p = 0.003) were significantly related to reduction in clot burden, leading to an approximate 100-fold and 50-fold reduction in clot, respectively.

CONCLUSIONS

This study shows the power of HF-OCT not only in the detection of clot but also the quantification of clot burden. In an animal model, the pHPC-coated p48MW significantly reduced acute thrombus formation over jailed side branches as compared to the bare metal p48MW that was nearly eliminated when combined with aspirin administration.

Drug-eluting coronary stents - focus on improved patient outcomes

The development of stent has been a major advance in the treatment of obstructive coronary artery disease since the introduction of balloon angioplasty. Subsequently, neointimal hyperplasia within the stent leading to in-stent restenosis emerged as a major obstacle in long-term success of percutaneous coronary intervention. Recent introduction of drug-eluting stents is a major breakthrough to tackle this problem. This review article summarizes stent technology, reviews progress of drug-eluting stents and discusses quality of life, patient satisfaction, and acceptability of percutaneous coronary intervention.

mTOR in renal cell cancer: modulator of tumor biology and therapeutic target

Elucidation of the crucial role of the PI3K/Akt/mTOR pathway in the pathogenesis of cancer has led to the development of various drugs targeting this signaling cascade at distinct levels. mTOR, a serine/threonine kinase plays a pivotal role in coupling growth stimuli to cell cycle progression. There are two distinct macromolecular complexes of mTOR: mTORC1, which is rapamycin-sensitive and contains raptor; and mTORC2, which is rapamycin-insensitive and contains rictor. However, in recent preclinical studies a sustained exposure of cancer cells to rapamycin has been shown to inhibit the function of both mTORC1 and mTORC2 complexes. Downstream targets of these complexes, which involve HIF-1alpha and HIF-2alpha, cyclin D1 and PKC-alpha, are responsible for the activation of various intracellular processes leading to the activation of cell proliferation, and induction of angiogenesis, metastasis or chemoresistance. Since the biology of renal cell cancer (RCC) is tightly controlled by mTOR, targeted inhibition of mTOR function appeared to be a promising therapeutic approach for RCC patients. To date, results of two, large, Phase III clinical trials evaluating the efficacy of rapamycin derivatives (i.e., temsirolimus and everolimus) in the treatment of RCC have been published. First-line temsirolimus (CCI-779) administered to metastatic, poor-prognosis RCC patients significantly prolonged overall and progression-free survival when compared with IFN-alpha. Treatment of metastatic RCC patients refractory to tyrosine kinase inhibitors with everolimus (RAD-001) significantly prolonged progression-free survival when compared with placebo. Therapeutic strategies based on mTOR inhibition in RCC demonstrated a significant clinical activity. However, there are still patients refractory to mTOR inhibitors. Various molecular mechanisms of resistance to rapalogues have been identified and will have to be targeted simultaneously with mTOR in order to achieve a complete inhibition of signaling pathways crucial for the pathogenesis of RCC. Such clinical trials evaluating a combination of mTOR inhibitors with other targeted therapies are ongoing.

The potential role of mTOR inhibitors in non-small cell lung cancer

The mammalian target of rapamycin (mTOR), a serine/threonine kinase, is a downstream mediator in the phosphatidylinositol 3-kinase/Akt signaling pathway, which plays a critical role in regulating basic cellular functions including cellular growth and proliferation. Currently, the mTOR inhibitor rapamycin and its analogues (CCI-779, RAD001, AP23573), which induce cell-cycle arrest in the G(1) phase, are being evaluated in cancer clinical trials. The mTOR inhibitors appear to be well tolerated, with skin reactions, stomatitis, myelosuppression, and metabolic abnormalities the most common toxicities seen. These adverse events are transient and reversible with interruption of dosing. Several pieces of evidence suggest a certain antitumor activity, including tumor regressions and prolonged stable disease, which has been reported among patients with a variety of malignancies, including non-small cell lung cancer (NSCLC). These promising preliminary clinical data have stimulated further research in this setting. Here, we review the basic structure of the pathway together with current results and future developments of mTOR inhibitors in the treatment of NSCLC patients.

Analysis of Clinical Factors that Influence Re-stenosis after Percutaneous Coronary Stenting

Evidence has recently been accumulating that a sirolimus-eluting stent (DES) is superior to a bare-metal stent (BMS) in preventing restenosis after percutaneous coronary intervention (PCI), and an increasing number of Japanese hospitals have been adopting DES. We conducted a retrospective study to identify clinical factors that influence the risk of restenosis after PCI, including stent types, by analyzing the data of 49 continuous patients who received PCI and follow-up coronary angiography in Hiratsuka City Hospital between March, 2004 and March, 2005. Age, sex, body mass index, smoking, complications, clinical diagnosis before PCI, the site and number of stenoses, implanted stent type (BMS or DES), the number of stents used, maximum inflating pressure and withdrawal of ticlopidine due to its adverse drug reactions were chosen as potential factors that may influence the risk of restenosis, and the correlation between these factors and restenosis was tested by Student's t-test or chi-square test. Coronary restenosis developed in 10 out of 49 patients, and factors having significant correlation with restenosis were age (73+/-7 in the restenosis group (R) and 64+/-12 in the non-restenosis group (N) (p<0.05)) and the type of stent (DES used in only one of 10 cases in R whereas in 24 of 39 in N (p<0.001)). Multivariate analysis showed older age (odds ratio (OR): 1.200 (95% CI: 1.038-2.823)) and the use of DES are independent predictors for restenosis (OR: 0.015 (95%CI: 0.001-0.249)). Our study further supports the efficacy of DES in PCI, but its long-term outcome is yet to be confirmed.

Drug-eluting stent: a review and update

The development of stent has been a major advance in the treatment of obstructive coronary artery disease since the introduction of balloon angioplasty. However, neointimal hyperplasia occurring within the stent leading to in-stent restenosis is a main obstacle in the long-term success of percutaneous coronary intervention (PCI). The recent introduction of drug-eluting stents (DES) contributes a major breakthrough to interventional cardiology. Many large randomized clinical trials using DES have shown a remarkable reduction in angiographic restenosis and target vessel revascularization when compared with bare metal stents. The results of these trials also appear to be supported by evidence from everyday practice and noncontrolled clinical trials. However, the expanded applications of DES, especially in treating complex lesions such as left main trunk, bifurcation, saphenous vein graft lesions, or in-stent restenosis, are still under evaluation with ongoing studies. With the availability of different types of DES in the market, the issue of cost should not be a deterrent and DES will eventually be an economically viable option for all patients. The adoption of DES in all percutaneous coronary intervention may become a reality in the near future. In this review article, we summarize the recent development and progress of DES as well as compare and update the results of clinical trials.

Rapamycin is a neuroprotective treatment for traumatic brain injury

The mammalian target of rapamycin, commonly known as mTOR, is a serine/threonine kinase that regulates translation and cell division. mTOR integrates input from multiple upstream signals, including growth factors and nutrients to regulate protein synthesis. Inhibition of mTOR leads to cell cycle arrest, inhibition of cell proliferation, immunosuppression and induction of autophagy. Autophagy, a bulk degradation of sub-cellular constituents, is a process that keeps the balance between protein synthesis and protein degradation and is induced upon amino acids deprivation. Rapamycin, mTOR signaling inhibitor, mimics amino acid and, to some extent, growth factor deprivation. In the present study we examined the effect of rapamycin, on the outcome of mice after brain injury. Our results demonstrate that rapamycin injection 4 h following closed head injury significantly improved functional recovery as manifested by changes in the Neurological Severity Score, a neurobehavioral testing. To verify the activity of the injected rapamycin, we demonstrated that it inhibits p70S6K phosphorylation, reduces microglia/macrophages activation and increases the number of surviving neurons at the site of injury. We therefore suggest that rapamycin is neuroprotective following traumatic brain injury and as a drug used in the clinic for other indications, we propose that further studies on rapamycin should be conducted in order to consider it as a novel therapy for traumatic brain injury.

Current development of mTOR inhibitors as anticancer agents

Mammalian target of rapamycin (mTOR) is a kinase that functions as a master switch between catabolic and anabolic metabolism and as such is a target for the design of anticancer agents. The most established mTOR inhibitors--rapamycin and its derivatives--showed long-lasting objective tumour responses in clinical trials, with CCI-779 being a first-in-class mTOR inhibitor that improved the survival of patients with advanced renal cell carcinoma. This heralded the beginning of extensive clinical programmes to further evaluate mTOR inhibitors in several tumour types. Here we review the clinical development of this drug class and look at future prospects for incorporating these agents into multitarget or multimodality strategies against cancer.

Evaluation of rapamycin chemical stability in volatile-organic solvents by HPLC

Rapamycin or sirolimus is a carboxylic lactone-lactam macrolide with a potent immunosuppressive activity. It can be successfully used to impregnate stents inserted in coronary arteries during surgical applications, preventing fatal infection and rejection adverse effect. The chemical stability of rapamycin in several organic-volatile solvents (acetone, chloroform, dichloromethane, hexane, ethyl alcohol, ethyl acetate, methyl alcohol, pentane and tetrahydrofurane) was established by HPLC-DAD-MS in reverse phase analysis. Results permitted to exclude rapamycin chemical degradation and to reveal a typical chemical isomerization, favoured in accordance to the solvent used. Two typical peaks appear, denominated beta and gamma, the time retention of which are, respectively, 11.3 and 15.0 min. Thanks to data recovered by NMR, spectrophotometric UV and mass analyses, it was possible to establish that both peaks correspond to two different isomeric forms of rapamycin. In addition, it was possible to establish that the relative percentage peak area varies according to the solvent and to the experimental time. The two isomeric forms are in equilibrium and each solvent concurs to differently displace this equilibrium versus one form rather than another, according to their both polarity index and aproticity.

mTOR-targeted therapy of cancer with rapamycin derivatives

Rapamycin and its derivatives (CCI-779, RAD001 and AP23576) are immunosuppressor macrolides that block mTOR (mammalian target of rapamycin) functions and yield antiproliferative activity in a variety of malignancies. Molecular characterization of upstream and downstream mTOR signaling pathways is thought to allow a better selection of rapamycin-sensitive tumours. For instance, a loss of PTEN functions results in Akt phosphorylation, cell growth and proliferation; circumstances that can be blocked using rapamycin derivatives. From recent studies, rapamycin derivatives appear to display a safe toxicity profile with skin rashes and mucositis being prominent and dose-limiting. Sporadic activity with no evidence of dose-effect relationship has been reported. Evidence suggests that rapamycin derivatives could induce G1-S cell cycle delay and eventually apoptosis depending on inner cellular characteristics of tumour cells. Surrogate molecular markers that could be used to monitor biological effects of rapamycin derivatives and narrow down biologically active doses in patients, such as the phosphorylation of P70S6K or expression of cyclin D1 and caspase 3, are currently evaluated. Since apoptosis induced by rapamycin is blocked by BCL-2, strategies aimed at detecting human tumours that express BCL-2 and other anti-apoptotic proteins might allow identification of rapamycin-resistant tumours. Finally, we discuss current and future placements of rapamycin derivatives and related translational research into novel therapeutic strategies against cancer.

Advances in the medical and surgical treatment of Takayasu arteritis

PURPOSE OF REVIEW

Takayasu arteritis remains a therapeutic challenge. In spite of current treatments, progression of vascular lesions is observed frequently. The purpose of this article is to describe advances in therapeutic strategies for Takayasu arteritis.

RECENT FINDINGS

Immunosuppressive agents including methotrexate, mycophenolate mofetil, and azathioprine added to corticosteroids can bring Takayasu arteritis into remission in many patients. Unfortunately, relapse is common when prednisone is tapered to dosages of 15 mg/day or less. A better understanding of pathogenesis has lead to trials with anti-tumor necrosis factor-alpha agents in patients with refractory disease. Preliminary results are encouraging. For patients who require revascularization intervention, both surgical and endovascular procedures can be performed that are safe, with low morbidity and mortality. The best long-term outcomes are achieved with conventional bypass grafts. Percutaneous transluminal angioplasty provides good results for short lesions. In contrast to the results in treating atherosclerosis, the use of conventional stents may not yield long-term vessel patency in Takayasu arteritis. Persistent inflammation and endothelial dysfunction may put patients with Takayasu arteritis at risk for premature atherosclerosis.

SUMMARY

In the future, greater therapeutic success may be achieved by addressing both the inflammatory and the myointimal proliferative components of Takayasu arteritis. New drugs that target intimal hyperplasia, as well as drug-eluting stents, deserve to be studied for possible utility as adjuncts to present treatments.

Drug-coated Stents

Since its introduction in 1977, the success of percutaneous interventional cardiology has been limited by the occurrence of restenosis. Drug-eluting stents, particularly sirolimus- and paclitaxel-coated stents, have been shown in randomized controlled trials to dramatically reduce restenosis in single, de novo, native coronary arteries. Over the last 2 years, investigators have reported that these stents can also reduce restenosis in more complex patient situations such as in diabetics, during acute coronary syndromes, in long atherosclerotic lesions and small arteries, and even after in-stent restenosis. These outcomes increase the clinical value of this technology to "real world" practice. This article reviews the current state of our knowledge regarding drug-eluting stents and identifies areas for further research.