Effect of sirolimus on the metabolism of apoB100- containing lipoproteins in renal transplant patients

Cardiometabolic Consequences of Targeted Anticancer Therapies

ABSTRACT

Cardiometabolic disease (CMD) is the most common preventable cause of death in the world. A number of components are included in the spectrum of CMD, such as metabolic syndrome/obesity, hyperglycemia/diabetes, dyslipidemia, and hypertension, which are independently associated with cardiovascular disease risk. These conditions often occur together, and patients with cancer frequently undergo treatments that can generate or worsen CMD. This review highlights and presents mechanistic and epidemiological evidence regarding CMD in 4 categories of anticancer medications, namely, mTOR/PI3K-Akt inhibitors, multitargeted tyrosine kinase inhibitor, immune checkpoint inhibitor therapy, and endocrine therapy. Patients taking these medications need careful monitoring during therapy. There is a role for cardio-oncology and onco-primary care specialists in optimally managing patients at risk to mitigate CMD during treatment with these and other investigational anticancer medications.

Haematological Drugs Affecting Lipid Metabolism and Vascular Health

Many drugs affect lipid metabolism and have side effects which promote atherosclerosis. The prevalence of cancer-therapy-related cardiovascular (CV) disease is increasing due to development of new drugs and improved survival of patients: cardio-oncology is a new field of interest and research. Moreover, drugs used in transplanted patients frequently have metabolic implications. Increasingly, internists, lipidologists, and angiologists are being consulted by haematologists for side effects on metabolism (especially lipid metabolism) and arterial circulation caused by drugs used in haematology. The purpose of this article is to review the main drugs used in haematology with side effects on lipid metabolism and atherosclerosis, detailing their mechanisms of action and suggesting the most effective therapies.

Dyslipidemia in Renal Transplant Recipients

Dyslipidemia is a frequent complication after kidney transplantation (KT) and is an important risk factor for cardiovascular disease (CVD). Renal transplant recipients (RTRs) are considered at high, or very high, risk of CVD, which is a leading cause of death in this patient group. Despite many factors of post-transplant dyslipidemia, the immunosuppressive treatment has the biggest influence on a lipid profile. There are no strict dyslipidemia treatment guidelines for RTRs, but the ones proposing an individual approach regarding CVD risk seem most suitable. Proper diet and physical activity are the main general measures to manage dyslipidemia and should be introduced initially in every patient after KT. In the case of an insufficient correction of lipemia, statins are the basis for hypolipidemic treatment. Statins should be introduced with caution to avoid serious side-effects (e.g., myopathy) or drug-drug interactions, especially with immunosuppressants. To lower the incidence of adverse effects, and improve medication adherence, ezetimibe in combination with statins is recommended. Fibrates and bile sequestrants are not recommended due to their side-effects and variable efficacy. However, several new lipid-lowering drugs like Proprotein convertase subtilisin/Kexin type9 (PCSK9) inhibitors may have promising effects in RTRs, but further research assessing efficacy and safety is yet to be carried out.

The Induction of Endothelial Autophagy and Its Role in the Development of Atherosclerosis

Increasing attention is now being paid to the important role played by autophagic flux in maintaining normal blood vessel walls. Endothelial cell dysfunction initiates the development of atherosclerosis. In the endothelium, a variety of critical triggers ranging from shear stress to circulating blood lipids promote autophagy. Furthermore, emerging evidence links autophagy to a range of important physiological functions such as redox homeostasis, lipid metabolism, and the secretion of vasomodulatory substances that determine the life and death of endothelial cells. Thus, the promotion of autophagy in endothelial cells may have the potential for treating atherosclerosis. This paper reviews the role of endothelial cells in the pathogenesis of atherosclerosis and explores the molecular mechanisms involved in atherosclerosis development.

Treatment optimization of maintenance immunosuppressive agents in pediatric renal transplant recipients

Introduction: Graft survival in pediatric kidney transplant patients has increased significantly within the last three decades, correlating with the discovery and utilization of new immunosuppressants as well as improvements in patient care. Despite these developments in graft survival for patients, there is still improvement needed, particularly in long-term care in pediatric patients receiving grafts from deceased donor patients. Maintenance immunosuppressive therapies have narrow therapeutic indices and are associated with high inter-individual and intra-individual variability.Areas covered: In this review, we examine the impact of pharmacokinetic variability on renal transplantation and its association with age, genetic polymorphisms, drug-drug interactions, drug-disease interactions, renal insufficiency, route of administration, and branded versus generic drug formulation. Pharmacodynamics are outlined in terms of the mechanism of action for each immunosuppressant, potential adverse effects, and the utility of pharmacodynamic biomarkers.Expert opinion: Acquiring abetter quantitative understanding of immunosuppressant pharmacokinetics and pharmacodynamic components should help clinicians implement treatment regimens to maintain the balance between therapeutic efficacy and drug-related toxicity.

Combined application of rapamycin and atorvastatin improves lipid metabolism in apolipoprotein E-deficient mice with chronic kidney disease

Atherosclerosis arising from the pro-inflammatory conditions associated with chronic kidney disease (CKD) increases major cardiovascular morbidity and mortality. Rapamycin (RAPA) is known to inhibit atherosclerosis under CKD and non-CKD conditions, but it can cause dyslipidemia; thus, the co-application of lipid-lowering agents is recommended. Atorvastatin (ATV) has been widely used to reduce serum lipids levels, but its synergistic effect with RAPA in CKD remains unclear. Here, we analyzed the effect of their combined treatment on atherosclerosis stimulated by CKD in apolipoprotein E-deficient (ApoE^−/−) mice. Oil Red O staining revealed that treatment with RAPA and RAPA＋ ATV, but not ATV alone, significantly decreased the atherosclerotic lesions in the aorta and aortic sinus, compared to those seen in the control (CKD) group. The co-administration of RAPA and ATV improved the serum lipid profile and raised the expression levels of proteins involved in reverse cholesterol transport (LXRα, CYP7A1, ABCG1, PPARγ, ApoA1) in the liver. The CKD group showed increased levels of various genes encoding atherosclerosis-promoting cytokines in the spleen (Tnf-α, Il-6 and Il-1β) and aorta (Tnf-α and Il-4), and these increases were attenuated by RAPA treatment. ATV and RAPA＋ATV decreased the levels of Tnf-α and Il-1β in the spleen, but not in the aorta. Together, these results indicate that, in CKD-induced ApoE^−/− mice, RAPA significantly reduces the development of atherosclerosis by regulating the expression of inflammatory cytokines and the co-application of ATV improves lipid metabolism.

Sirolimus and mTOR Inhibitors: A Review of Side Effects and Specific Management in Solid Organ Transplantation

Inhibitors of mechanistic target of rapamycin (mTOR inhibitors) are used as antiproliferative immunosuppressive drugs and have many clinical applications in various drug combinations. Experience in transplantation studies has been gained regarding the side effect profile of these drugs and the potential benefits and limitations compared with other immunosuppressive agents. This article reviews the adverse effects of mTOR inhibitors in solid organ transplantation, with special attention given to mechanisms hypothesized to cause adverse events and their management strategies.

Expert opinion on the metabolic complications of mTOR inhibitors

Using mTOR inhibitors (mTORi) as anticancer drugs led to hyperglycemia (12-50%) and hyperlipidemia (7-73%) in phase-III trials. These high rates require adapted treatment in cancer patients. Before initiating mTORi treatment, lipid profile screening should be systematic, with fasting glucose assay in non-diabetic patients and HbA_1C in diabetic patients. After initiation, lipid profile monitoring should be systematic, with fasting glucose assay in non-diabetic patients, every 2 weeks for the first month and then monthly. The HbA_1C target is≤8%, before and after treatment initiation in known diabetic patients and in case of onset of diabetes under mTORi. LDL-cholesterol targets should be adapted to general health status and cardiovascular and oncologic prognosis. If treatment is indicated, pravastatin should be prescribed in first line; atorvastatin and simvastatin are contraindicated. Fenofibrate should be prescribed for hypertriglyceridemia>5g/l resisting dietary measures adapted to oncologic status. In non-controllable hypertriglyceridemia exceeding 10g/l, mTORi treatment should be interrupted and specialist opinion should be sought.

The immune system as a chronotoxicity target of the anticancer mTOR inhibitor everolimus

The circadian timing system controls many biological functions in mammals including xenobiotic metabolism, detoxification, cell proliferation, apoptosis and immune functions. Everolimus is a mammalian target of rapamycin inhibitor, whose immunosuppressant properties are both desired in transplant patients and unwanted in cancer patients, where it is indicated for its antiproliferative efficacy. Here we sought whether everolimus circadian timing would predictably modify its immunosuppressive effects so as to optimize this drug through timing. C57BL/6J mice were synchronized with light-dark 12h:12h, with L onset at Zeitgeber Time (ZT) 0. Everolimus was administered orally to male (5 mg/kg/day) and female mice (15 mg/kg/day) at ZT1, during early rest span or at ZT13, during early activity span for 4 weeks. Body weight loss, as well as hematological, immunological and biochemical toxicities, were determined. Spleen and thymus were examined histologically. Everolimus toxicity was less severe following dosing at ZT13, as compared to ZT1, as shown with least body weight inhibition in both genders; least reductions in thymus weight both in males (p < 0.01) and females (p < 0.001), least reduction in female spleen weight (p < 0.05), and less severe thymic medullar atrophy both in males (p < 0.001) and females (p < 0.001). The mean circulating counts in total leukocytes, total lymphocytes, T-helper and B lymphocytes displayed minor and non-significant changes following dosing at ZT13, while they were decreased by 56.9% (p < 0.01), 45.5% (p < 0.01), 43.1% (p < 0.05) and 48.7% (p < 0.01) after everolimus at ZT1, respectively, in only male mice. Chronotherapy of everolimus is an effective way to increase the general tolerability and decrease toxicity on the immune system.

Sirolimus and Everolimus Pathway: Reviewing Candidate Genes Influencing Their Intracellular Effects

Sirolimus (SRL) and everolimus (EVR) are mammalian targets of rapamycin inhibitors (mTOR-I) largely employed in renal transplantation and oncology as immunosuppressive/antiproliferative agents. SRL was the first mTOR-I produced by the bacterium Streptomyces hygroscopicus and approved for several medical purposes. EVR, derived from SRL, contains a 2-hydroxy-ethyl chain in the 40th position that makes the drug more hydrophilic than SRL and increases oral bioavailability. Their main mechanism of action is the inhibition of the mTOR complex 1 and the regulation of factors involved in a several crucial cellular functions including: protein synthesis, regulation of angiogenesis, lipid biosynthesis, mitochondrial biogenesis and function, cell cycle, and autophagy. Most of the proteins/enzymes belonging to the aforementioned biological processes are encoded by numerous and tightly regulated genes. However, at the moment, the polygenic influence on SRL/EVR cellular effects is still not completely defined, and its comprehension represents a key challenge for researchers. Therefore, to obtain a complete picture of the cellular network connected to SRL/EVR, we decided to review major evidences available in the literature regarding the genetic influence on mTOR-I biology/pharmacology and to build, for the first time, a useful and specific “SRL/EVR genes-focused pathway”, possibly employable as a starting point for future in-depth research projects.

Low-Density Lipoprotein Receptor-Dependent and Low-Density Lipoprotein Receptor-Independent Mechanisms of Cyclosporin A-Induced Dyslipidemia

OBJECTIVE

Cyclosporin A (CsA) is an immunosuppressant commonly used to prevent organ rejection but is associated with hyperlipidemia and an increased risk of cardiovascular disease. Although studies suggest that CsA-induced hyperlipidemia is mediated by inhibition of low-density lipoprotein receptor (LDLr)-mediated lipoprotein clearance, the data supporting this are inconclusive. We therefore sought to investigate the role of the LDLr in CsA-induced hyperlipidemia by using Ldlr-knockout mice (Ldlr(-/-)).

APPROACH AND RESULTS

Ldlr(-/-) and wild-type (wt) C57Bl/6 mice were treated with 20 mg/kg per d CsA for 4 weeks. On a chow diet, CsA caused marked dyslipidemia in Ldlr(-/-) but not in wt mice. Hyperlipidemia was characterized by a prominent increase in plasma very low-density lipoprotein and intermediate-density lipoprotein/LDL with unchanged plasma high-density lipoprotein levels, thus mimicking the dyslipidemic profile observed in humans. Analysis of specific lipid species by liquid chromatography-tandem mass spectrometry suggested a predominant effect of CsA on increased very low-density lipoprotein-IDL/LDL lipoprotein number rather than composition. Mechanistic studies indicated that CsA did not alter hepatic lipoprotein production but did inhibit plasma clearance and hepatic uptake of [(14)C]cholesteryl oleate and glycerol tri[(3)H]oleate-double-labeled very low-density lipoprotein-like particles. Further studies showed that CsA inhibited plasma lipoprotein lipase activity and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9.

CONCLUSIONS

We demonstrate that CsA does not cause hyperlipidemia via direct effects on the LDLr. Rather, LDLr deficiency plays an important permissive role for CsA-induced hyperlipidemia, which is associated with abnormal lipoprotein clearance, decreased lipoprotein lipase activity, and increased levels of apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9. Enhancing LDLr and lipoprotein lipase activity and decreasing apolipoprotein C-III and proprotein convertase subtilisin/kexin type 9 levels may therefore provide attractive treatment targets for patients with hyperlipidemia receiving CsA.

Cellular and molecular effects of the mTOR inhibitor everolimus

mTOR (mechanistic target of rapamycin) functions as the central regulator for cell proliferation, growth and survival. Up-regulation of proteins regulating mTOR, as well as its downstream targets, has been reported in various cancers. This has promoted the development of anti-cancer therapies targeting mTOR, namely fungal macrolide rapamycin, a naturally occurring mTOR inhibitor, and its analogues (rapalogues). One such rapalogue, everolimus, has been approved in the clinical treatment of renal and breast cancers. Although results have demonstrated that these mTOR inhibitors are effective in attenuating cell growth of cancer cells under in vitro and in vivo conditions, subsequent sporadic response to rapalogues therapy in clinical trials has promoted researchers to look further into the complex understanding of the dynamics of mTOR regulation in the tumour environment. Limitations of these rapalogues include the sensitivity of tumour subsets to mTOR inhibition. Additionally, it is well known that rapamycin and its rapalogues mediate their effects by inhibiting mTORC (mTOR complex) 1, with limited or no effect on mTORC2 activity. The present review summarizes the pre-clinical, clinical and recent discoveries, with emphasis on the cellular and molecular effects of everolimus in cancer therapy.

Medical management of the kidney transplant recipient: a practical approach for the primary care provider

Kidney transplant recipients (KTRs) commonly present with complex medical issues that are best managed jointly by both their primary care physician and the kidney transplant center. Hypertension, diabetes, dyslipidemias, and obesity are frequently present in the KTR population and the successful management of these comorbidities is essential in achieving excellent posttransplant outcomes. Cardiovascular disease is the leading cause of mortality in KTRs, and interventions that mitigate the risk factors that contribute to these adverse outcomes are an important part of the long-term management of a KTR.

Treatment of dyslipidemia in allogeneic hematopoietic stem cell transplant patients

As survival rates in allogeneic hematopoietic stem cell transplantation (HSCT) continue to improve, attention to long-term complications, including cardiovascular disease, becomes a major concern. Cardiovascular disease and dyslipidemia are a common, yet often overlooked occurrence post-HSCT that results in significant morbidity and mortality. Also, increasing evidence shows that several anti-hyperlipidemia medications, the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors in particular, may have a role in modulating graft-versus-host disease (GVHD). However, factors such as drug-drug interactions, adverse effect profiles, and the relative efficacy in lowering cholesterol and triglyceride levels must be taken into account when choosing safe and effective lipid-lowering therapy in this setting. This review seeks to provide guidance to the clinician in the management of dyslipidemia in the allogeneic HSCT population, taking into account the recently published American College of Cardiology/American Heart Association guidelines on hyperlipidemia management, special considerations in this challenging population, and the evidence for each agent's potential role in modulating GVHD.

Toxicity of targeted therapy: Implications for response and impact of genetic polymorphisms

Targeted therapies have unique toxicity profiles. Common adverse events include rash, diarrhea, hypertension, hypothyroidism, proteinuria, depigmentation, and hepatotoxicity. Some of these toxicities are caused by on-target, mechanism-associated effects, which can be stratified as to whether or not the targets are relevant to response. Other toxicities are off-target and may be caused by the class of agent, e.g. antibody vs small molecule tyrosine kinase inhibitor, or by immune reactions or toxic metabolites. Both on- and off-target toxicities may be due to higher drug concentrations or altered end-organ sensitivity, which in turn can be a consequence of genetic polymorphisms controlling metabolism or tissue responsiveness. On-target toxicities are important to identify as some correlate with response and, hence, amelioration of these side effects is preferable to dose reduction or stopping drug. Toxicities secondary to relevant target impact may be recognized when distinct types of agents, such as antibodies and small molecule kinase inhibitors, with the same target have a similar side effect. For example, both bevacizumab and vascular endothelial growth factor receptor (VEGFR) kinase inhibitors cause hypertension; both epidermal growth factor receptor (EGFR) antibodies and kinase inhibitors cause rash; and these toxicities correlate with response. Herein we review common targeted agent-related toxicities, relevant genetic polymorphisms, and implications for response and patient management.

Targeting the PI3K-AKT-mTOR signaling network in cancer

The phosphoinositide 3-kinase-AKT-mammalian target of rapamycin (PI3K-AKT-mTOR) pathway is a frequently hyperactivated pathway in cancer and is important for tumor cell growth and survival. The development of targeted therapies against mTOR, a vital substrate along this pathway, led to the approval of allosteric inhibitors, including everolimus and temsirolimus, for the treatment of breast, renal, and pancreatic cancers. However, the suboptimal duration of response in unselected patients remains an unresolved issue. Numerous novel therapies against critical nodes of this pathway are therefore being actively investigated in the clinic in multiple tumour types. In this review, we focus on the progress of these agents in clinical development along with their biological rationale, the need of predictive biomarkers and various combination strategies, which will be useful in counteracting the mechanisms of resistance to this class of drugs.

Effects of atorvastatin on the pharmacokinetics of everolimus among kidney transplant recipients

BACKGROUND

Hyperlipidemia occurs in up to 50% of kidney transplant (KT) recipients who take everolimus (EVL). As a result of this, statins are the most commonly prescribed lipid-lowering drugs among these patients. However, we are concerned whether there are any drug interactions between EVL and statins, because both of these drugs use the same pharmacokinetics pathway. Therefore, we assessed the effects of concomitant use of EVL and atorvastatin.

METHODS

In this randomized, open-label, crossover study, 20 KT patients were assigned (1:1) to receive EVL with or without 20 mg atorvastatin for 1 month. One-month washout period was used before crossover. Plasma EVL concentrations were measured by homogeneous particle-enhanced turbidimetric immunoassay. Twelve-hour area under the time-concentration curve (AUC0-12) of EVL was calculated with the use of whole-blood EVL concentrations from 10 different time points (0, 0.5, 1, 1.5, 2, 2.5, 4, 6, 8, and 12 hours).

RESULTS

The mean (SD) AUC0-12 for EVL and EVL plus atorvastatin was 155.9 (41.6) ng·h/mL and 151.3 (51.4) ng·h/mL, respectively (P > .05; paired t test). No difference of EVL Cmax or Tmax was found after atorvastatin coadministration. Even though the EVL AUC0-12 levels were not affected by atorvastatin coadministration in one-half of the subjects, for the rest of the patients, there were unpredictable changes in the EVL AUC0-12 levels. This may be due to the high intrapatient variability of EVL drug concentration (coefficient of variation ranges from 9.8% to 34.1%).

CONCLUSIONS

Coadministration of atorvastatin with EVL in KT recipients did not affect the pharmacokinetics of EVL.

Endocrine side effects of anti-cancer drugs: effects of anti-cancer targeted therapies on lipid and glucose metabolism

During the past years, targeted therapies for cancer have been developed using drugs that have significant metabolic consequences. Among them, the mammalian target of rapamycin (mTOR) inhibitors and, to a much lesser extent, the tyrosine kinase inhibitors (TKIs) are involved. mTOR plays a key role in the regulation of cell growth as well as lipid and glucose metabolism. Treatment with mTOR inhibitors is associated with a significant increase in plasma triglycerides and LDL cholesterol. mTOR inhibitors seem to increase plasma triglycerides by reducing the activity of the lipoprotein lipase which is in charge of the catabolism of triglyceride-rich lipoproteins. The increase in LDL cholesterol observed with mTOR inhibitors seems to be due to a decrease in LDL catabolism secondary to a reduction of LDL receptor expression. In addition, treatment with mTOR inhibitors is associated with a high incidence of hyperglycemia, ranging from 13 to 50% in the clinical trials. The mechanisms responsible for hyperglycemia with new onset diabetes are not clear, but are likely due to the combination of impaired insulin secretion and insulin resistance. TKIs do not induce hyperlipidemia but alter glucose homeostasis. Treatment with TKIs may be associated either with hyperglycemia or hypoglycemia. The molecular mechanism by which TKIs control glucose homeostasis remains unknown. Owing to the metabolic consequences of these agents used as targeted anti-cancer therapies, a specific and personalized follow-up of blood glucose and lipids is recommended when using mTOR inhibitors and of blood glucose when using TKIs.

mTOR inhibition: a promising strategy for stabilization of atherosclerotic plaques

Statins are currently able to stabilize atherosclerotic plaques by lowering plasma cholesterol and pleiotropic effects, but a residual risk for atherosclerotic disease remains. Therefore, effective prevention of atherosclerosis and treatment of its complications is still a major clinical challenge. A large body of evidence indicates that mammalian target of rapamycin (mTOR) inhibitors such as rapamycin or everolimus have pleiotropic anti-atherosclerotic effects so that these drugs can be used as add-on therapy to prevent or delay the pathogenesis of atherosclerosis. Moreover, bioresorbable scaffolds eluting everolimus trigger a healing process in the vessel wall, both in pigs and humans, that results in late lumen enlargement and plaque regression. At present, this phenomenon of atheroregression is poorly understood. However, given that mTOR inhibitors suppress cell proliferation and trigger autophagy, a cellular survival pathway and a process linked to cholesterol efflux, we hypothesize that these compounds can inhibit (or reverse) the basic mechanisms that control plaque growth and destabilization. Unfortunately, adverse effects associated with mTOR inhibitors such as dyslipidemia and hyperglycemia have recently been identified. Dyslipidemia is manageable via statin treatment, while the anti-diabetic drug metformin would prevent hyperglycemia. Because metformin has beneficial macrovascular effects, this drug in combination with an mTOR inhibitor might have significant promise to treat patients with unstable plaques. Moreover, both statins and metformin are known to inhibit mTOR via AMPK activation so that they would fully exploit the beneficial effects of mTOR inhibition in atherosclerosis.

Obesity, metabolic syndrome and diabetes mellitus after renal transplantation: prevention and treatment

The prevalence of the metabolic syndrome in dialysis patients is high and further increases after transplantation due to weight gain and the detrimental metabolic effects of immunosuppressive drugs. Corticosteroids cause insulin resistance, hyperlipidemia, abnormal glucose metabolism and arterial hypertension. The calcineurin inhibitor tacrolimus is diabetogenic by inhibiting insulin secretion, whereas cyclosporine causes hypertension and increases cholesterol levels. Mtor antagonists are responsible for hyperlipidemia and abnormal glucose metabolism by mechanisms that also implicate insulin resistance. The metabolic syndrome in transplant recipients has numerous detrimental effects such as increasing the risk of new onset diabetes, cardiovascular disease events and patient death. In addition, it has also been linked with accelerated loss of graft function, proteinuria and ultimately graft loss. Prevention and management of the metabolic syndrome are based on increasing physical activity, promotion of weight loss and control of cardiovascular risk factors. Bariatric surgery before or after renal transplantation in patients with body mass index >35 kg/m(2) is an option but its long term effects on graft and patient survival have not been investigated. Steroid withdrawal and replacement of tacrolimus with cyclosporine facilitate control of diabetes, whereas replacement of cyclosporine and mtor antagonists can improve hyperlipidemia. The new costimulation inhibitor belatacept has potent immunosuppressive properties without metabolic adverse effects and will be an important component of immunosuppressive regimens with better metabolic risk profile. Medical treatment of cardiovascular risk factors has to take potential drug interactions with immunosuppressive medication and drug accumulation due to renal insufficiency into account.

Attenuation of cardiac allograft vasculopathy by sirolimus: Relationship to time interval after heart transplantation

BACKGROUND

The aim of the study was to assess temporal changes in plaque size and components after heart transplantation (HTx), and to evaluate the differences in treatment effects on plaque progression between sirolimus and calcineurin inhibitors (CNIs).

METHODS

The study comprised 146 HTx recipients who were converted from CNIs to sirolimus as primary immunosuppressant (sirolimus group, n = 61) and those who were maintained on CNIs (CNI group, n = 85). A retrospective compositional analysis of serial virtual histology-intravascular ultrasound was performed.

RESULTS

During a median follow-up of 2.8 years, there was a significant difference in plaque volume in favor of sirolimus between groups (p = 0.004). When subjects were sub-classified according to the time interval between HTx and study inclusion, those in the early group (≤2 years after HTx) had a greater increase in plaque volume (p = 0.006), characterized by a higher progression rate of fibrous plaque volume (p = 0.01). The treatment difference between groups in plaque volume was identified in the early group in favor of sirolimus with attenuating effects on the progression of fibrous plaque component (both p = 0.03 for interaction). By contrast, there were significant differences in necrotic core and dense calcium volume (both p < 0.05 for interaction) in favor of CNIs in the late group (≥6 years after HTx).

CONCLUSIONS

Compared with continued CNI therapy, sirolimus attenuated plaque progression in recipients with early conversion, but contributed to increases in necrotic core and dense calcium volume in those with late conversion. Our study supports the hypothesis that early initiation of sirolimus offers greater benefits in the treatment of CAV.

The role of mechanistic target of rapamycin (mTOR) complexes signaling in the immune responses

The mechanistic Target of Rapamycin (mTOR) is an evolutionarily conserved serine/threonine kinase which is a member of the PI3K related kinase (PIKK) family. mTOR emerged as a central node in cellular metabolism, cell growth, and differentiation, as well as cancer metabolism. mTOR senses the nutrients, energy, insulin, growth factors, and environmental cues and transmits signals to downstream targets to effectuate the cellular and metabolic response. Recently, mTOR was also implicated in the regulation of both the innate and adaptive immune responses. This paper will summarize the current knowledge of mTOR, as related to the immune microenvironment and immune responses.

Associations of ABCB1 and IL-10 genetic polymorphisms with sirolimus-induced dyslipidemia in renal transplant recipients

BACKGROUND

Hyperlipidemia is a common adverse effect of sirolimus (SRL). We previously showed significant associations of ABCB1 3435C>T and IL-10 -1082G>A with log-transformed SRL dose-adjusted weighted-normalized trough. We further examined to see whether these polymorphisms were also associated with SRL-induced dyslipidemia.

METHODS

Genotyping was performed for ABCB1 1236C>T, 2677 G>T/A, and 3435C>T; CYP3A4 -392A>G; CYP3A5 6986A>G and 14690G>A; IL-10 -1082G>A; TNF -308G>A; and ApoE ε2, ε3, and ε4 alleles. The longitudinal changes of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) levels after SRL treatment before statin therapy were analyzed by a linear mixed-effects model, with adjustments for selected covariates for each lipid.

RESULTS

Under the dominant genetic model, ABCB1 3435C>T was associated with TC (P=0.0001) and LDL-C (P<0.0001) values after SRL administration. Mean TC and LDL-C levels were 26.9 and 24.9 mg/dL higher, respectively, in ABCB1 3435T carriers than 3435CC homozygotes at an average SRL trough concentration of 4 ng/mL without concomitant medication. ABCB1 1236C>T under the recessive model and IL-10 -1082G>A under the dominant model were associated with log-transformed TG values (P=0.0051 and 0.0436, respectively). Mean TG value was 25.1% higher in ABCB1 1236TT homozygotes compared with ABCB1 1236C carriers and was 12.4% higher in IL-10 -1082AA homozygotes than -1082G carriers.

CONCLUSIONS

ABCB1 polymorphisms were found to be associated with lipid responses to SRL treatment, confirming the role of ABCB1 gene in SRL pharmacokinetics and pharmacodynamics. Further studies are necessary to define the role of ABCB1 and IL-10 polymorphisms on SRL-induced dyslipidemia in renal transplantation.

Management of metabolic effects associated with anticancer agents targeting the PI3K-Akt-mTOR pathway

Agents inhibiting the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin (PAM) pathway are currently in various stages of clinical development in oncology, ranging from some in early-phase evaluations to others that have already received regulatory approval for treatment in advanced cancers. The administration of PAM pathway inhibitors has been associated with metabolic toxicities of hyperlipidemia and hyperglycemia. The PAM Task Force of the National Cancer Institute Investigational Drug Steering Committee convened an interdisciplinary expert panel to review the pathophysiology of hyperlipidemia and hyperglycemia induced by PAM pathway inhibitors, summarize the incidence of these metabolic toxicities induced by such agents in the current literature, advise on clinical trial screening and monitoring criteria, and provide management guidance and therapeutic goals on occurrence of these toxicities. The overarching aim of this consensus report is to raise awareness of these metabolic adverse events to enable their early recognition, regular monitoring, and timely intervention in clinical trials. Hyperglycemia and hyperlipidemia are generally not acutely toxic and most often reversible with therapeutic intervention. Dose modifications or discontinuation of PAM pathway inhibitors should only be considered in situations of severe events or if progressive metabolic derangement persists after therapeutic interventions have been attempted for a sufficient duration. Specialty consultation should be sought to aid clinical trial planning and the management of these metabolic adverse events.

Sirolimus in pediatric renal transplantation

SRL, an mTOR inhibitor that inhibits cell cycle progression, represents an important alternative to CNIs, which are still the cornerstones of pediatric solid organ tx. Because there are still limited data on SRL use among pediatric solid organ recipients, further studies are needed to verify the efficacy and safety of SRL. It has unique pharmacokinetic characteristics concerning dosing intervals and reduction of the dose in combination with other immunosuppressants. SRL also has antineoplastic, antiviral, and antiatherogenic advantages over other immunosuppressive agents. The adverse effects of SRL including thrombocytopenia, hyperlipidemia, proteinuria, impaired wound healing, mouth ulcers, edema, male hypogonadism, TMA, and interstitial pneumonitis must be considered carefully in pediatric population. This article reviews the most recent data on SRL application in the field of pediatric renal tx.

Prospects for mTOR inhibitor use in patients with polycystic kidney disease and hamartomatous diseases

Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.

Population pharmacokinetics of sirolimus in de novo Chinese adult renal transplant patients

AIMS

This study was aimed at determining the population pharmacokinetics of sirolimus and identifying factors that explain pharmacokinetic variability in de novo Chinese adult renal transplant patients.

METHODS

Data were retrospectively extracted from a formal multicentre clinical trial, which was originally designed to evaluate the safety and efficacy of cyclosporin dose reduction and cyclosporin elimination in patients receiving sirolimus. All patients received 12-month treatment, i.e. induction therapy with cyclosporin, sirolimus and corticosteroids during the first 3 months followed by either cyclosporin dose reduction or cyclosporin discontinuation thereafter. Eight-hundred and four sirolimus trough blood concentrations (C(0)) from 112 patients were used to develop a population pharmacokinetic model using the NONMEM program. A one-compartment model with first-order absorption and elimination was selected as the base model. The influence of demographic characteristics, biochemical and haematological indices, cyclosporin daily dose, cyclosporin C(0) as well as other commonly used co-medications were explored.

RESULTS

The typical values with interindividual variability for apparent clearance (CL/F) and apparent volume of distribution (V/F) were 10.1 l h(-1) (23.8%) and 3670 l (56.7%), respectively. The residual variability was 29.9%. CL/F decreased significantly with silymarin or glycyrrhizin co-therapy in hepatically impaired patients, and with increasing total cholesterol levels or cyclosporin C(0). Moreover, CL/F increased nonlinearly with increasing sirolimus daily dose. The median parameter estimates from a nonparametric bootstrap procedure were comparable and within 5% of the estimates from NONMEM.

CONCLUSIONS

These results provide important information for clinicians to optimize sirolimus regimens in Chinese renal transplant patients.

Mammalian target of rapamycin: discovery of rapamycin reveals a signaling pathway important for normal and cancer cell growth

Since the discovery of rapamycin, considerable progress has been made in unraveling the details of the mammalian target of rapamycin (mTOR) signaling network, including the upstream mechanisms that modulate mTOR signaling functions, and the roles of mTOR in the regulation of mRNA translation and other cell growth-related responses. mTOR is found in two different complexes within the cell, mTORC1 and mTORC2, but only mTORC1 is sensitive to inhibition by rapamycin. mTORC1 is a master controller of protein synthesis, integrating signals from growth factors within the context of the energy and nutritional conditions of the cell. Activated mTORC1 regulates protein synthesis by directly phosphorylating 4E-binding protein 1 (4E-BP1) and p70S6K (S6K), translation initiation factors that are important to cap-dependent mRNA translation, which increases the level of many proteins that are needed for cell cycle progression, proliferation, angiogenesis, and survival pathways. In normal physiology, the roles of mTOR in both glucose and lipid catabolism underscore the importance of the mTOR pathway in the production of metabolic energy in quantities sufficient to fuel cell growth and mitotic cell division. Several oncogenes and tumor-suppressor genes that activate mTORC1, often through the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, are frequently dysregulated in cancer. Novel analogs of rapamycin (temsirolimus, everolimus, and deforolimus), which have improved pharmaceutical properties, were designed for oncology indications. Clinical trials of these analogs have already validated the importance of mTOR inhibition as a novel treatment strategy for several malignancies. Inhibition of mTOR now represents an attractive anti-tumor target, either alone or in combination with strategies to target other pathways that may overcome resistance. The far-reaching downstream consequences of mTOR inhibition make defining the critical molecular effector mechanisms that mediate the anti-tumor response and associated biomarkers that predict responsiveness to mTOR inhibitors a challenge and priority for the field.

Fifteen years of clinical studies and clinical practice in renal transplantation: reviewing outcomes with de novo use of sirolimus in combination with cyclosporine

Over the course of 15 years the use of sirolimus, a macrocyclic lactone, has evolved from an adjunct to calcineurin inhibitors (CNI) to the foundation of therapy due to the drug's unique properties: First, it displays synergistic pharmacodynamic interactions with CNI. Even among high immunologic risk patients, this regimen attenuates the risk of acute allograft rejection episodes when used in combination with cyclosporine or tacrolimus. Indeed >80% reduction in CNI exposure de novo yields better long-term renal function than full cyclosporine (CsA) doses, a useful tradeoff, despite the augmented occurrence of lymphoceles and impaired wound healing. Second, by inhibiting mammalian target of rapamycin (mTOR), it exerts profound anti-neoplastic effects reducing the incidence and mediating the regression of tumors displaying PTEN-deletions and/or Akt-activations in transplant and non-transplant patients. Third, it is relatively non-nephrotoxic although it may exacerbate that property of CNI agents. Fourth, it allows prompt withdrawal of steroid therapy. Fifth, it displays reduced rates of cytomegalovirus, and BK virus infections. The major adverse reactions can generally be controlled with countermeasure therapy. Myelosuppressive effects, which tend to be transient (unless sirolimus is combined with mycophenolic acid), are readily amenable to treatment with granulocyte colony stimulating factor for leukopenia, interleukin 11 for thrombocytopenia and erythropoietin for anemia. Combinations of statins and fibrates represent effective countermeasure therapy for hypercholesterolemia and hypertriglyceridemia, respectively. Idiosyncratic reactions include hypoxemic pulmonary toxicity, refractory edema and diarrhea. Thus, sirolimus represents the vanguard of a new class of maintenance agents for immunosuppression.

The emerging safety profile of mTOR inhibitors, a novel class of anticancer agents

Mammalian target of rapamycin (mTOR) has emerged as an important target for cancer therapy. Rapamycin has a distinct, well-documented toxicity profile and most of the toxicity data has been reported in patients with organ transplantation. Newer mTOR inhibitors have slightly different pharmacokinetic properties, yet they present toxicity profiles similar to rapamycin. Most of these toxicities are mild to moderate in severity and can be managed clinically by dose modification and supportive measures. Mucositis and pneumonitis are the most commonly reported toxicities, but they rarely lead to treatment discontinuation. Pathogenesis of pneumonitis is uncertain, but various hypotheses have been suggested, including cell-mediated immune response to the drug.