An isotope dilution LC-MS/MS based candidate reference method for the quantification of cyclosporine A, tacrolimus, sirolimus and everolimus in human whole blood

A Narrative Review of Chromatographic Bioanalytical Methods for Quantifying Everolimus in Therapeutic Drug Monitoring Applications

BACKGROUND

Methods for measuring drug levels in the body are crucial for improving therapeutic drug monitoring (TDM) and personalized medicine. In solid-organ transplants, TDM is essential for the management of immunosuppressive drugs to avoid toxicity and organ rejection. Everolimus is a commonly used immunosuppressant with a small range of safe doses; therefore, it is important to adjust the dose according to each patient's needs. Therefore, reliable methods are required to accurately measure everolimus levels. This study aims to conduct a comprehensive and updated narrative review of chromatographic bioanalytical methods for everolimus quantification.

METHODS

The authors searched for original research articles published between 2013 and 2023 in Scopus and PubMed and found 295 articles after removing duplicates. Based on their titles and summaries, 30 articles were selected for a detailed review and 25 articles were included in the final analysis.

RESULTS

Among the 25 studies, 16 used protein precipitation, mainly with methanol, to prepare the samples, 12 used high-performance liquid chromatography, 11 used ultra-performance liquid chromatography, and 2 used both. Almost all the studies (24 of 25) used tandem mass spectrometry for detection, whereas only 1 used ultraviolet.

CONCLUSIONS

This comprehensive review of bioanalytical methods for measuring everolimus using chromatography is a useful resource for researchers developing bioanalytical methods for TDM applications. Future trends in everolimus measurement include achieving lower detection limits, owing to the trend of reducing drug doses in therapy by improving sample extraction techniques and using more sensitive methods.

Toward Analytical Performance Specifications for Immunosuppressive Drug Quantification in Transplantation: An Opinion Article

BACKGROUND

Analytical methods require performance that meets the clinical needs. Different approaches for setting up permissible analytical imprecision goals (pCVA%) for drug analyses have been reported. The aim of this study was to calculate the pCVA% for cyclosporine, tacrolimus, everolimus, sirolimus, and mycophenolic acid using 4 alternative approaches, to compare the results and to critically discuss advantages and disadvantages of each model.

METHODS

The approaches to evaluate pCVA% were (A) based on biological variation observed in routine measurement results between 2022 and 2023 in the authors' laboratory, (B) derived from the terminal elimination half-life and dosing interval of the drugs, and (C and D) explored from the width of the therapeutic ranges (TR) by the 2 methods. For approach A, routine measurement data for cyclosporine and tacrolimus, obtained through liquid chromatography-tandem mass spectrometry and electrochemiluminescence immunoassays, were evaluated separately.

RESULTS

The 4 alternative approaches for deriving pCVA% yielded similar results, for cyclosporine and tacrolimus in an analytical method dependent manner. The average pCVA% was 5.2%, 5.6%, 5.1%, 4.8%, and 7.7% for cyclosporine, tacrolimus, everolimus, sirolimus, and mycophenolic acid, respectively. The most challenging goals were those using TR-related approaches, while those using the biological variation approach were most easily achievable. Approach B resulted in more stringent goals for drugs with longer elimination half-lives (eg, everolimus and sirolimus).

CONCLUSIONS

There is no single ideal approach for setting goals of drug analysis. However, the pCVA% values derived from the various approaches are similar and confirm that a <6% target proposed by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology is adequate and realistic in combination with state-of-the-art measurement technologies. In the authors' opinion, approaches based on the width of the TR are preferable, as they represent a common basis for clinical decisions and reflect elements of biological variation and analytics used to establish the TR.

Everolimus Personalized Therapy: Second Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

The Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology established the second consensus report to guide Therapeutic Drug Monitoring (TDM) of everolimus (EVR) and its optimal use in clinical practice 7 years after the first version was published in 2016. This version provides information focused on new developments that have arisen in the last 7 years. For the general aspects of the pharmacology and TDM of EVR that have retained their relevance, readers can refer to the 2016 document. This edition includes new evidence from the literature, focusing on the topics updated during the last 7 years, including indirect pharmacological effects of EVR on the mammalian target of rapamycin complex 2 with the major mechanism of direct inhibition of the mammalian target of rapamycin complex 1. In addition, various concepts and technical options to monitor EVR concentrations, improve analytical performance, and increase the number of options available for immunochemical analytical methods have been included. Only limited new pharmacogenetic information regarding EVR has emerged; however, pharmacometrics and model-informed precision dosing have been constructed using physiological parameters as covariates, including pharmacogenetic information. In clinical settings, EVR is combined with a decreased dose of calcineurin inhibitors, such as tacrolimus and cyclosporine, instead of mycophenolic acid. The literature and recommendations for specific organ transplantations, such as that of the kidneys, liver, heart, and lungs, as well as for oncology and pediatrics have been updated. EVR TDM for pancreatic and islet transplantation has been added to this edition. The pharmacodynamic monitoring of EVR in organ transplantation has also been updated. These updates and additions, along with the previous version of this consensus document, will be helpful to clinicians and researchers treating patients receiving EVR.

Metabolic network and proteomic expression perturbed by cyclosporine A to model microbe Escherichia coli

Cyclosporine A (CsA) is a model drug that has caused great concern due to its widespread use and abuse in the environment. However, the potential harm of CsA to organisms also remains largely unknown, and this issue is exceptionally important for the health risk assessment of antibiotics. To address this concern, the crosstalk between CsA stress and cellular metabolism at the proteomic level in Escherichia coli was investigated and dissected in this study. The results showed that CsA inhibited E. coli growth in a time-dependent manner. CsA induced reactive oxygen species (ROS) overproduction in a dose- and time-dependent manner, leading to membrane depolarization followed by cell apoptosis. In addition, translation, the citric acid cycle, amino acid biosynthesis, glycolysis and responses to oxidative stress and heat were the central metabolic pathways induced by CsA stress. The upregulated proteins, including PotD, PotF and PotG, controlled cell growth. The downregulated proteins, including SspA, SspB, CstA and DpS, were regulators of self-feedback during the starvation process. And the up- and downregulated proteins, including AtpD, Adk, GroS, GroL and DnaK, controlled energy production. These results provide an important reference for the environmental health risk assessment of CsA.

Bioproperties, Nanostructured System and Analytical and Bioanalytical Methods for Determination of Rapamycin: A Review

The drug rapamycin is a potent inhibitor of the mTOR complex, acting directly in the signaling cascade of this protein complex; interrupting cell proliferation, in addition to being an extremely efficient immunosuppressant. Currently this drug is being used in several types of cancer. Rapamycin has been a target of great interest within nanomedicine involving nanostructured systems for drug delivery aiming to increase the bioactivity and bioavailability of this drug. In addition, there is a constant search for analytical methods to identify and quantify this drug. Numerous high-performance liquid chromatography analytical techniques, mass spectrometry and immunoassay techniques have been employed efficiently in an attempt to develop increasingly sensitive analytical methods. Thus, this review sought to bring together current and relevant scientific works involving rapamycin and; besides analytical methods more used for quantification of this molecule.

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of levetiracetam in human serum and plasma

OBJECTIVES

To develop an isotope dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based candidate reference measurement procedure (RMP) for levetiracetam quantification in human serum and plasma.

METHODS

Quantitative nuclear magnetic resonance spectroscopy (qNMR) was used to characterize the RMP material to ensure traceability to SI units. To quantify levetiracetam, an LC-MS/MS method was optimized using a C8 column for chromatographic separation following protein-precipitation-based sample preparation. Spiked matrix samples of serum and plasma were used to test selectivity and specificity. Matrix effects were determined by performing a post-column infusion experiment and comparing standard line slopes. Precision and accuracy were evaluated over 5 days. Measurement uncertainty was evaluated according to the Guide to the Expression of Uncertainty in Measurement (GUM).

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of levetiracetam within the range of 1.53-90.0 μg/mL. Intermediate precision was <2.2% and repeatability was 1.1-1.7% across all concentrations. The relative mean bias ranged from -2.5% to -0.3% across all levels and matrices within the measuring range. Diluted samples were found with a mean bias ranging from -0.1 to 2.9%. The predefined acceptance criterion for measurement uncertainty was met and determined for individual measurements independently of the concentration level and sample type to be ≤4.0% (k=2).

CONCLUSIONS

We present a novel LC-MS/MS)-based candidate RMP for levetiracetam in human serum and plasma. Its expanded measurement uncertainty of ≤4.0% meets the clinical needs in levetiracetam monitoring. Utilizing qNMR to characterize levetiracetam reference materials allowed metrological traceability to SI units.

Determination of five mTOR inhibitors in human plasma for hepatocellular carcinoma treatment using QuEChERS-UHPLC-MS/MS

A fast and reliable QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method for pre-processing combined with Ultra - high performance liquid chromatography - tandem mass spectrometry (UHPLC-MS/MS) was established for the analysis of five mammalian rapamycin target protein (mTOR) inhibitors (vistusertib, AZD8055, pictilisib, everolimus, temsirolimus)in human plasma. Extraction was achieved by addition of acetonitrile to the sample followed by anhydrous magnesium sulfate and 30 mg C18 for salting out and purification, respectively. MTOR inhibitors were detected using selective response monitoring (SRM) under positive ion electrospray mode. Vistusertib, AZD8055 and pictilisib showed good linearity with a range of 1-80 ng/ml, Additionally, the concentration of everolimus and temsirolimus was 2.5-200 ng/ml and10-800 ng/ml, respectively. The linear correlation coefficient (R2) of each analysis was ≥ 0.9950. The limit of detection (LOD) and Limit of Quantitation (LOQ) were 0.015-0.75 ng/ml and 1-10 ng/ml, respectively. This method showed a high accuracy with high recovery rate and excellent stability. This method is fast, accurate and reliable, suitable for quantitative detection of mTOR inhibitors in human plasma.

Dynamic Monitoring of Intracellular Tacrolimus and Mycophenolic Acid Therapy in Renal Transplant Recipients Using Magnetic Bead Extraction Combined with LC-MS/MS

BACKGROUND

Tacrolimus (TAC) and mycophenolic acid (MPA) are commonly used immunosuppressive therapies after renal transplant. Our objective was to quantify TAC and MPA concentrations in peripheral blood mononuclear cells (PBMCs) using liquid chromatography tandem mass spectrometry (LC-MS/MS) and to evaluate and validate the performance of the methodology. A prospective follow-up cohort study was conducted to determine whether intracellular concentrations were associated with adverse outcomes in renal transplants.

METHODS

PBMCs were prepared using the Ficoll separation technique and purified with erythrocyte lysis. The cells were counted using Sysmex XN-3100 and then packaged and frozen according to a 50 µL volume containing 1.0 × 106 cells. TAC and MPA were extracted using MagnaBeads and quantified using an LC-MS/MS platform. The chromatography was run on a reversed-phase Waters Acquity UPLC BEH C18 column (1.7 µm, 50 mm × 2.1 mm) for gradient elution separation with a total run time of 4.5 min and a flow rate of 0.3 mL/min. Mobile phases A and B were water and methanol, respectively, each containing 2 mM ammonium acetate and 0.1% formic acid. Renal transplant recipients receiving TAC and MPA in combination were selected for clinical validation and divided into two groups: a stable group and an adverse outcome group. The concentrations were dynamically monitored at 5, 7, 14, and 21 days (D5, D7, D14, and D21) and 1, 2, 3, and 6 months (M1, M2, M3, and M6) after operation.

RESULTS

Method performance validation was performed according to Food and Drug Administration guidelines, showing high specificity and sensitivity. The TAC and MPA calibration curves were linear (r2 = 0.9988 and r2 = 0.9990, respectively). Both intra-day and inter-day imprecision and inaccuracy were less than 15%. Matrix effects and recoveries were satisfactory. The TAC and MPA concentrations in 304 "real" PBMC samples from 47 renal transplant recipients were within the calibration curve range (0.12 to 16.40 ng/mL and 0.20 to 4.72 ng/mL, respectively). There was a weak correlation between PBMC-C0TAC and WB-C0TAC (p < 0.05), but no correlation was found for MPA. The level of immunosuppressive intra-patient variation (IPV) was higher in PBMC at 77.47% (55.06, 97.76%) than in WB at 34.61% (21.90, 49.85%). During the dynamic change in C0TAC, PBMC-C0TAC was in a fluctuating state, and no stable period was found. PBMC-C0TAC did not show a significant difference between the stable and adverse outcome group, but the level of the adverse outcome group was generally higher than that of the stable group.

CONCLUSIONS

Compared with conventional therapeutic drug monitoring, the proposed rapid and sensitive method can provide more clinically reliable information on drug concentration at an active site, which has the potential to be applied to the clinical monitoring of intracellular immunosuppressive concentration in organ transplantation. However, the application of PBMC-C0TAC in adverse outcomes of renal transplant should be studied further.

Liquid chromatography-tandem mass spectrometry for therapeutic drug monitoring of immunosuppressants and creatinine from a single dried blood spot using the Capitainer® qDBS device

In recent years, a lot of attention has been given to a more patient-centric therapeutic drug monitoring (TDM) of immunosuppressant drugs (tacrolimus, sirolimus, everolimus and cyclosporin A) by the use of microsampling techniques. By adopting Dried Blood Spots (DBS) after a finger prick, instead of conventional venous blood draws, follow-up can (partially) be established from patients' homes. Despite the many advantages of DBS, one of the major disadvantages associated with this technique is the well described hematocrit (hct) effect. In order to overcome the hct area bias, different strategies have been proposed, amongst which the use of dried blood sampling techniques based on the volumetric collection of blood. The aim of this study was to evaluate the use of the Capitainer® qDBS (quantitative Dried Blood Spot) device for the combined TDM of four immunosuppressants and creatinine from a single qDBS. The set-up of an adequate sample preparation allowing both immunosuppressants and creatinine quantification was one of the key challenges in the method development due to device-specific interferences. Liquid chromatography tandem-mass spectrometry methods for the quantification of tacrolimus, sirolimus, everolimus, cyclosporin A and creatinine from qDBS (10 μL) were developed and validated based on international guidelines, also taking into account DBS-specific parameters. The methods proved to be accurate and reproducible, with absolute biases below 10% and within-run CVs (%) below 8% over a calibration range from 1 to 50 ng/mL for tacrolimus, sirolimus and everolimus, 20-1500 ng/mL for cyclosporin A, and 15-700 μmol/L for creatinine. Reproducible (CV < 15%) IS-compensated relative recovery values were obtained, showing no hematocrit-dependence (compared to a hct of 0.37), except for cyclosporin A at higher hct values. Application on venous blood left-over patient samples showed good agreement between the results of Capitainer® qDBS and whole blood with 98% (47/48), 93% (41/44), 89% (41/46), 88% (38/43) and 89% (116/131) of the samples lying within 20% of the whole blood result for tacrolimus, sirolimus, everolimus, cyclosporin A and plasma/serum for creatinine, respectively. For creatinine a blood/plasma ratio of 0.85 was found and used to convert qDBS results to plasma/serum results. As a next step, capillary finger prick samples will need to demonstrate the clinical applicability of the method in a real life setting.

Immunosuppressant Monitoring-Performance of the First Mass Spectrometry-Based Automated Clinical Analyzer Cascadion

BACKGROUND

Automatic analyzers simplify processes and may help improve standardization. The first automated analyzer based on mass spectrometry is available and offers a panel for monitoring cyclosporin A, tacrolimus, sirolimus, and everolimus. Method comparisons and evaluation tests are presented to verify the capability of the Cascadion system for use in a clinical laboratory.

METHODS

Sample preparation and measurements were performed using the Cascadion clinical analyzer. More than 1000 measurement values of patient samples were compared with an in vitro diagnostic-certified assay run on a liquid chromatography tandem mass spectrometry instrument. Precision and accuracy were determined using commercial quality control and external quality assessment (EQA) samples.

RESULTS

A good correlation between the 2 instruments was observed (Pearson correlation r = 0.956-0.996). Deming regression revealed 95% confidence intervals of slopes and intercepts covering the values 1 and 0, for sirolimus and everolimus, respectively, indicating equivalence of both measuring systems. However, for cyclosporin A, a bias was observed and confirmed using a Bland-Altman plot (-9.1%). Measurement repeatability and intermediate measurement precision were appropriate showing coefficients of variation of 0.9%-6.1% and 2.0%-5.3%, respectively. Accuracy according to internal quality controls was 85%-111% and 81%-100% in the EQA samples of Reference Institute of Bioanalytics and Laboratory of the Government Chemist, respectively. High robustness was found with regard to the linearity of the calibration lines (linear regression coefficient r2 > 0.99). Carryover was negligible (0.1%).

CONCLUSIONS

The Cascadion automatic analyzer produced convincing results in the measurement of patient, control, and EQA samples. The throughput was sufficient for routine use. Overall, it can be used as an alternative to open liquid chromatography tandem mass spectrometry instruments for immunosuppressant monitoring, simplifying processes without the need for specially trained personnel.

Dried blood microsampling-assisted therapeutic drug monitoring of immunosuppressants: An overview

In the field of solid organ transplantation, chemotherapy and autoimmune disorders, treatment with immunosuppressant drugs requires intensive follow-up of the blood concentrations via therapeutic drug monitoring (TDM) because of their narrow therapeutic window and high intra- and inter-subject variability. This requires frequent hospital visits and venepunctures to allow the determination of these analytes, putting a high burden on the patients. In the context of patient-centric thinking, it is becoming increasingly established that at least part of these conventional blood draws could be replaced by microsampling, allowing home-sampling and increasing the quality of life for these patients. In this review we discuss the published methods - mostly using liquid chromatography coupled to tandem mass spectrometry - that have utilized (volumetric) dried blood samples as an alternative for conventional liquid whole blood for the TDM of immunosuppressant drugs. Furthermore, some pre-analytical considerations using DBS or volumetric alternatives are considered, as well as the applicability on clinical samples. The implementation status in clinical practice is also discussed, including (1) the cost-effectiveness of this approach compared to venepuncture, (2) the availability of multiplexed methods, (3) the status of harmonization and (4) patient perception. A brief perspective on potential future developments for the dried blood-based TDM of immunosuppressant drugs is provided, by considering how obstacles for the implementation of these strategies into clinical practice might be overcome.

High-Sensitivity and High-Throughput Quantification of Everolimus in Human Whole Blood Using Ultrahigh-Performance Liquid Chromatography Coupled With Tandem Mass Spectrometry

BACKGROUND

Rigorous dose adjustment by therapeutic drug monitoring (TDM) is recommended when everolimus (EVR) is administered for immunosuppression. In this study, the authors developed a highly sensitive ultrahigh-performance liquid chromatography coupled with the tandem mass spectrometry (UHPLC-MS/MS) method for measuring EVR concentrations in whole blood using a high-throughput solid-phase extraction method for sample pretreatment. Furthermore, the blood EVR concentrations in routine TDM samples from patients who underwent renal transplantation measured using the established UHPLC-MS/MS method were compared with those measured using the latex agglutination turbidimetric immunoassay (LTIA).

METHODS

Blood samples were pretreated by solid-phase extraction using a 96-well HLB µElution plate. The clinical application of the newly developed method was evaluated using 87 blood samples from 19 patients who underwent kidney transplant.

RESULTS

The calibration curve showed good linearity over a wide range of 0.1-50 ng/mL, with relative error ≤15% obtained from the back calculation of calibrators, and ≤20% for the lower limit of quantification. Within-batch and batch-to-batch accuracies and precisions fulfilled the acceptance criteria of the US Food and Drug Administration guidelines for bioanalytical method validation. The extraction recovery rates were good (≥65.2%), and almost no matrix effects were found in any of the quality control samples. Blood EVR concentrations measured by UHPLC-MS/MS were positively correlated with those measured by LTIA. A Bland-Altman plot indicated that the UHPLC-MS/MS method yielded better measurements than the LTIA method, regardless of the concentration.

CONCLUSIONS

Therefore, the authors succeeded in developing a novel high-sensitivity and high-throughput method for measuring blood EVR concentration by UHPLC-MS/MS using a µElution plate for sample pretreatment.

Interlaboratory comparison study of immunosuppressant analysis using a fully automated LC-MS/MS system

OBJECTIVES

All guidelines recommend LC-MS/MS as the analytical method of choice for the quantification of immunosuppressants in whole blood. Until now, the lack of harmonization of methods and the complexity of the analytical technique have prevented its widespread use in clinical laboratories. This can be seen in international proficiency schemes, where more than half of the participants used immunoassays. With the Cascadion SM Clinical analyzer (Thermo Fisher Scientific, Oy, Vantaa, FI) a fully automated LC-MS/MS system has been introduced, which enables the use of LC-MS/MS without being an expert in mass spectrometry.

METHODS

To verify the interlaboratory comparison of the immunosuppressant assay on this type of instrument, three centers across Europe compared 1097 routine whole blood samples, each site sharing its own samples with the other two. In other experiments, the effects of freezing and thawing of whole blood samples was studied, and the use of secondary cups instead of primary tubes was assessed.

RESULTS

In the Bland-Altman plot, the comparison of the results of tacrolimus in fresh and frozen samples had an average bias of only 0.36%. The respective data for the comparison between the primary and secondary tubes had an average bias of 1.14%. The correlation coefficients for patient samples with cyclosporine A (n=411), everolimus (n=139), sirolimus (n=114) and tacrolimus (n=433) were 0.993, 0.993, 0.993 and 0.990, respectively.

CONCLUSIONS

The outcome of this study demonstrates a new level of result harmonization for LC-MS/MS based immunosuppressant analysis with a commercially available fully automated platform for routine clinical application.

Effect of gravimetric correction and type of pipettes used in sample preparation on the precision of LC-MS/MS-based analyses

BACKGROUND

Currently, manual pipetting of human sample material is still a key process in sample preparation for chromatographic and mass spectrometric analyses in the clinical laboratory. In most cases, however, pipettes used in clinical laboratories are only specified for handling water-like liquids. Actual pipetted liquid volumes can be verified by weighing within the sample preparation process, and the results can be corrected accordingly (gravimetric correction). The aim of our study was to evaluate and compare the effects of gravimetric correction in terms of accuracy and precision for an air cushion and direct replacement pipette.

METHODS

Forty-fold serial determination of linezolid in a spiked serum sample by ID-LC-MS/MS was applied as an exemplary measurement procedure. Polypropylene tubes were weighed before the addition of 50 µL serum, after the addition, and after the addition of the internal standard solution. Coefficients of variation (CV) were calculated as an indicator of measurement precision.

RESULTS

The use of a direct replacement pipette was associated with improved measurement imprecision than an air cushion pipette (CV 1.70% vs 2.49% for serum, uncorrected results). The results obtained after gravimetric correction showed improved precision with the use of an air cushion pipette compared to the conventional approach (CV 1.51% vs 1.61%). Using a direct replacement pipette, the impact of gravimetric correction on imprecision was negligible.

CONCLUSION

Using direct replacement pipettes in sample preparation enables more precise ID-LC-MS/MS analyses than using air cushion pipettes. Gravimetric correction can be a useful tool to improve the precision of LC-MS/MS measurement procedures when complex matrices such as human serum are handled with commonly used air cushion pipettes.

Quantitative NMR-Based Biomedical Metabolomics: Current Status and Applications

Nuclear Magnetic Resonance (NMR) spectroscopy is a quantitative analytical tool commonly utilized for metabolomics analysis. Quantitative NMR (qNMR) is a field of NMR spectroscopy dedicated to the measurement of analytes through signal intensity and its linear relationship with analyte concentration. Metabolomics-based NMR exploits this quantitative relationship to identify and measure biomarkers within complex biological samples such as serum, plasma, and urine. In this review of quantitative NMR-based metabolomics, the advancements and limitations of current techniques for metabolite quantification will be evaluated as well as the applications of qNMR in biomedical metabolomics. While qNMR is limited by sensitivity and dynamic range, the simple method development, minimal sample derivatization, and the simultaneous qualitative and quantitative information provide a unique landscape for biomedical metabolomics, which is not available to other techniques. Furthermore, the non-destructive nature of NMR-based metabolomics allows for multidimensional analysis of biomarkers that facilitates unambiguous assignment and quantification of metabolites in complex biofluids.

Bioproperties, Nanostructured System and Analytical and Bioanalytical Methods for Determination of Rapamycin: A Review

The drug rapamycin is a potent inhibitor of the mTOR complex, acting directly in the signaling cascade of this protein complex; interrupting cell proliferation, in addition to being an extremely efficient immunosuppressant. Currently this drug is being used in several types of cancer. Rapamycin has been a target of great interest within nanomedicine involving nanostructured systems for drug delivery aiming to increase the bioactivity and bioavailability of this drug. In addition, there is a constant search for analytical methods to identify and quantify this drug. Numerous high-performance liquid chromatography analytical techniques, mass spectrometry and immunoassay techniques have been employed efficiently in an attempt to develop increasingly sensitive analytical methods. Thus, this review sought to bring together current and relevant scientific works involving rapamycin and; besides analytical methods more used for quantification of this molecule.