Genetics of drug response to immunosuppressive treatment and prospects for personalized therapy

A retrospective analysis of tacrolimus pharmacokinetic in Saudi paediatric patients in early post-liver transplantation period

BACKGROUND

Tacrolimus is an essential immunosuppressive medication in paediatric patients' post-liver transplantation. Achieving tacrolimus target concentration in early post-transplantation is crucial to minimise the risk of acute rejection; however, this is challenging due to inter- and intra-patient variability in tacrolimus metabolism and clearance. Therefore, our study aims to describe tacrolimus trough concentration variability and pharmacokinetics in paediatric post-liver transplantation during the first two weeks post-transplantation.

METHOD

This retrospective multicentre observational study included paediatric patients post-liver transplantation. Post-operative data was collected within the initial 14 days using electronic health records, including daily tacrolimus doses, measured trough concentrations, graft data, surgical data, and documented acute rejection. Pharmacokinetic analysis was completed using the Monolix software. We used the empirical Bayesian estimates of clearance and volume of distribution for covariate testing to assess possible correlations. We performed a stepwise regression analysis (alpha = 0.05).

RESULTS

Ninety-one paediatric patients were included in the study, with a mean age of 4.1 years (SD = 4.6). The mean graft-to-recipient weight ratio (GRWR) was 3% (SD = 6). The vast majority of the patients received the liver from living donors (n = 84, 92.3%). The average time needed to reach therapeutic concentration was 4.6 (SD = 2.8) days. The initial clearance (Clini) was very low at baseline (0.012 L/h), then increased dramatically to 9.84 L/h at 14 days post-transplantation. The clearance appeared to be time-dependent, and the time needed to reach 50% of maximum clearance was five days post-transplantation. The covariates that significantly affected clearance included bodyweight and aspartate transaminase, while the only significant covariate for volume of distribution was bodyweight.

CONCLUSION

Tacrolimus is a drug with high intra- and interindividual variability, making dosing challenging in the paediatric liver transplantation population. Prospective studies with more intensive sampling are needed to address the time-dependent changes in clearance, which will aid in establishing the optimal dosing regimens in this population.

Personalized nanomedicine advancements for stem cell tracking

Recent technological developments in biomedicine have facilitated the generation of data on the anatomical, physiological and molecular level for individual patients and thus introduces opportunity for therapy to be personalized in an unprecedented fashion. Generation of patient-specific stem cells exemplifies the efforts toward this new approach. Cell-based therapy is a highly promising treatment paradigm; however, due to the lack of consistent and unbiased data about the fate of stem cells in vivo, interpretation of therapeutic effects remains challenging hampering the progress in this field. The advent of nanotechnology with a wide palette of inorganic and organic nanostructures has expanded the arsenal of methods for tracking transplanted stem cells. The diversity of nanomaterials has revolutionized personalized nanomedicine and enables individualized tailoring of stem cell labeling materials for the specific needs of each patient. The successful implementation of stem cell tracking will likely be a significant driving force that will contribute to the further development of nanotheranostics. The purpose of this review is to emphasize the role of cell tracking using currently available nanoparticles.

Hematologic abnormalities following renal transplantation

Recipients of renal allografts are surviving longer and, consequently, may experience a variety of complications related not only to the transplanted kidney, but also to the hematopoietic system. Common hematologic complications in the renal transplant patient include abnormalities of one cell line, such as post-transplantation erythrocytosis or anemia, that are often treatable with simple measures. Conversely, pathologies involving the leukocyte and platelet population often exist in the context of pancytopenia, which may be a manifestation of systemic infection (e.g., cytomegalovirus, human herpesvirus 8) or malignancy (post-transplantation lymphoproliferative disorders). Uncommon, but life-threatening, processes complicating renal transplantation include hepatosplenic gammadelta T-cell lymphoma and viral-induced hemophagocytic syndrome, both of which are associated with severe pancytopenia and, often, death. Since this patient population is often managed in a multidisciplinary fashion by nephrologists, infection specialists, transplant surgeons, hematologists, and internal medicine physicians, a succinct review of this topic is warranted.

Efficacy and safety of basiliximab in kidney transplantation

The efficacy and safety of basiliximab, in combination with different maintenance regimens, are extensively addressed in the available literature. Basiliximab reduces the incidence of acute rejection, allows a safe reduction of steroid dosage, and is associated with economic savings, although there is substantially no proof that basiliximab prolongs either patient or graft survival. Initial basiliximab administration entails a low-risk and is associated with fewer adverse events than T cell depleting agents. However, life-threatening reactions were reported following re-exposure to basiliximab in recipients who lost graft function early after transplantation and, therefore, discontinued all immunosuppressive agents.

Prospects for personalized immunosuppression: pharmacologic tools--a review

In the last few years, novel immunosuppressive agents and new formulations, including sirolimus, mycophenolic acid (the active metabolite of mycophenolate mofetil), tacrolimus, and microemulsion cyclosporine, have significantly improved the clinical outcome of transplant recipients. However, the majority of immunosuppressive agents need a constant monitoring of drug levels to reduce the risk of graft rejection as well as drug-induced toxicities. Many factors may affect the pharmacokinetic characteristics of immunosuppressive agents, potentially reducing treatment effectiveness. Absorption and metabolism of immunosuppressive drugs are influenced by patient genotype and comedications, while comorbidities (ie, diabetes and cystic fibrosis) are responsible for altered pharmacokinetics. Dose individualization in transplant recipients is performed according to their health status, graft function, and drug therapeutic range. With respect to the last issue, therapeutic drug monitoring (TDM) plays a crucial role in achieving optimal immunosuppression, improving the efficacy of drugs, and lowering toxic effects. Pharmacokinetic analysis allowed the identification of specific parameters, such as plasma or blood levels, immediately before dosing (C(min) or trough levels) or 2 hours after administration (C(2)), which are significantly related to tissue exposure to the drug. More recently, studies have investigated treatment individualization by evaluating drug pharmacogenetics based on the expression level or mutations of their molecular targets, including calcineurin for cyclosporine and tacrolimus, and inosine monophosphate dehydrogenase for mycophenolic acid. Although no conclusive data may be drawn from these preliminary trials, further studies are underway to address the role of pharmacogenetics in clinical decision making.

Hematologic toxicity of immunosuppressive treatment

The administration of immunosuppressive agents may be associated with the occurrence of hematologic toxicity, such as anemia, due to bone marrow suppression or hemolysis, leukopenia, and thrombocytopenia. The administration of azathioprine and mycophenolate mofetil is more frequently associated with bone marrow suppression, while hemolytic-uremic syndrome may occur after administration of cyclosporine, tacrolimus, or muromonab (OKT3) and may be associated with the loss of the allograft. Moreover, microangiopathic hemolytic anemia and thrombocytopenia are rare, but potentially severe, complications of immunosuppressive treatment with tacrolimus and cyclosporine; they are characterized by intravascular hemolysis due to mechanical destruction of red cells as a result of pathological changes in small blood vessels. Viral infections (cytomegalovirus), administration of antiviral agents (gancyclovir), inhibitors of angiotensin-converting enzyme and angiotensin II receptor antagonists, antibacterial agents (sulfamethoxazole and trimethoprim), and allopurinol may aggravate bone marrow suppression, particularly when administered with agents that interfere with purine biosynthesis, including azathioprine and mycophenolate mofetil.

Pharmacogenetics in cancer chemotherapy: balancing toxicity and response

The goal of chemotherapy is the elimination of tumor cells from the host. This is achieved by the use of therapeutic agents that are often more harmful to normal tissues than to the targeted tumor. Many chemotherapeutic agents are designed to damage cell replication machinery either directly at the level of DNA or indirectly, by inhibiting enzymes involved with DNA repair and synthesis. Novel therapeutic agents that exert their effects at signal transduction pathways have advanced chemotherapy; however, a role for the classic chemotherapeutic agents remains. These classic agents are associated with tumor cell resistance, toxicity, and occasionally secondary neoplasia. Current practices for the dosing of therapeutic agents rely on height and body surface measurements or drug monitoring and Bayesian adaptive control. Pharmacogenetics is emerging as an alternate approach to managing chemotherapy that may prevent undertreatment while avoiding overtreatment and associated toxicities. By determining the polymorphic genetic makeup of the host and, in some instances, the altered genetic expression of the tumor, chemotherapy can be tailored for interindividual response and toxicity avoidance. Chemotherapy is particularly applicable to the pharmacogenetic approach to tailored therapy for a number of reasons. The margin of safety is low with chemotherapeutic agents. Some drugs require biotransformation for activation. Drug activation correlates with toxicity. The pathways of drug clearance or inactivation exhibit polymorphic differences. Interindividual, race-specific, and age-related responses to chemotherapeutic agents are common. Last, drug resistance can be inherent to the tumor as a result of the suppression of apoptosis. Variations in response and toxicity to a specific drug can be caused by alterations in drug-metabolizing enzymes or receptor expression. These effects can be classed as pharmacokinetic and pharmacogenetic differences. Some of the genes known to display polymorphic differences include FLT3 receptor tyrosine kinase, FCG3RA IgG FC receptor, thymidylate synthase, methylenetetrahydrofolate reductase, thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, aldehyde dehydrogenase, glutathione S-transferase, uridine diphosphate glyuronosyl transferases, N-acetyl transferases, cytochrome P450, and the DNA repair enzymes XPD and XRCC1. To be successful a pharmacogenetic approach to individualized chemotherapy must selectively take advantage of a determination of direct enzyme activity, gene expression, and genotype.

From pharmacokinetics to pharmacogenomics: a new approach to tailor immunosuppressive therapy

One of the main tasks in the management of organ transplantation is the optimization of immunosuppressive therapy, in order to provide therapeutic efficacy limiting drug-related toxicity. In the past years major efforts have been carried out to define therapeutic windows based on blood/plasma levels of each immunosuppressant relating those concentrations to drug dosing and clinical events. Although this traditional approach is able to identify environmental and nongenetic factors that can influence drug exposure during the course of treatment, it presents limitations. Therefore, complementary strategies are advocated. The advent of the genomic era gives birth to pharmacogenomics, a science that studies how the genome as a whole, including single genes as well as gene-to-gene interactions, may affect the action of a drug. This science is of particular importance for drugs characterized by a narrow therapeutic index, such as the immunosuppressants. Preliminary studies focused on polymorphisms of genes encoding for enzymes actively involved in drug metabolism, drug transport and pharmacological target. Pharmacogenomics holds promise for improvement in the ability to individualize immunosuppressive therapy based on the patient's genetic profile, and can be viewed as a support to traditional therapeutic drug monitoring. However, the clinical applicability of this approach is still to be proven.

Pharmacogenomic considerations for immunosuppressive therapy

Immunosuppression, the art of suppressing the endogenous immune system to allow organ transplantation or treatment of autoimmune disease, is a clinico-pharmacological field that has markedly developed over the past three decades with the advent of highly potent and rationally targeted immunosuppressive agents. Pharmacogenomics, the art of providing tailored pharmacological therapy with the highest therapeutic index based on the genomic composition of the individual, is a science that has rapidly developed over the past decade, along with the advances in the human genome project and in biotechnology. Pharmacogenomics of immunosuppression is the combined art of tailoring specific immunosuppressive drug therapy to specific immune-mediated clinical entities which require immunosuppression, with optimum matching of the drug to the individual's genomic makeup. Timely and judicious application of pharmacogenomics to clinical immunosuppression should direct the clinician to the best immunosuppressive drug for any given clinical condition, and markedly increase its efficacy as well as decreasing the incidence of side effects and toxicity, thereby decreasing morbidity and prolonging survival. Is this a description of an ongoing clinical evolution in immunosuppression or a prediction of future events? The promises of pharmacogenomics of immunosuppression are high, yet the availability and/or application and/or realization of the promises of this highly specialized clinical science are very slow to come.

Insights into pharmacogenomics and its impact upon immunosuppressive therapy

The advent of the genomic era has brought about several new fields of study, one of them being pharmacogenomics, which seeks to link drug treatment (pharmaco-) with the individual's genetic make-up (genomics). Pharmacogenomics holds many promises for improved treatment of a large variety of medical conditions, including immunosuppression for organ transplantation and autoimmune disease. Many of these promises have, however, not yet been fulfilled. In this brief overview of the subject, we attempt to provide insights into the evolving field of pharmacogenomics and discuss some of its potential benefits and promises, technological tools used by pharmacogenomics, the reasons for delays in breakthroughs in the field, and the relevance of pharmacogenornics to immunosuppression.

Successful treatment of myasthenia gravis with tacrolimus

Tacrolimus (FK-506) is a calcium-calcineurin inhibitor, successfully used in transplant recipients. We report the successful use of tacrolimus as a single immunosuppressant in a patient who had developed myasthenia gravis (MG) during interferon alpha treatment. In this case, the coexistence of hepatitis C and type 2 diabetes mellitus contraindicated the use of both steroids and azathioprine, and cyclosporine A, although effective, had induced renal failure. Tacrolimus proved to be effective in the treatment of MG, was not significantly hepatotoxic, and was less nephrotoxic than cyclosporine.