The relative proportions of sirolimus metabolites in blood using HPLC with mass-spectrometric detection

Comparison of whole-blood sirolimus concentrations measured by EMIT-based Siemens Viva-ProE® System and LC-MS/MS in Chinese transplant patients

Sirolimus (SRL) is commonly used in transplant patients to prevent organ transplant rejection. The current guidelines recommend to perform SRL therapeutic drug monitoring regularly to improve treatment outcomes and avoid adverse effects. Consequently, a precise and accurate method for determining SRL is crucial in clinical practice. Currently, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunoassays have been widely adopted for determining SRL concentrations. However, previous studies have shown that immunoassays exhibit a positive bias compared to LC-MS/MS. As the new updated version of the EMIT-based Viva-E® System (SVPS), this study aims to compare SRL blood concentrations measured by the SVPS and LC-MS/MS. The residual whole-blood samples obtained from transplant patients were simultaneously analyzed using the SVPS and LC-MS/MS, respectively. The correlation between the two assays was analyzed using the linear regression analysis and Deming linear regression. The Pearson correlation coefficient and Intraclass correlation coefficient (ICC) analysis were executed. The Paired Wilcoxon test and Bland-Altman analysis were performed to assess the concordance between the two methods. The SVPS considerably increased SRL concentration value by 46.62 % as compared to the LC-MS/MS method. When SRL concentrations measured by the SVPS were above 4.0 ng/mL, there was no significant difference between the corrected SVPS concentrations after using the Deming linear regression equation, indicating their interchangeability. Given the significant disparities observed between EMIT and LC-MS/MS, it is crucial to indicate the methodology and instruments in both TDM reports and future clinical guidelines. Our study also provides the conversion formulas between the SVPS and LC-MS/MS, which can be applied as a reference for different clinical centers.

Vascular surgery in liver resection

Vascular surgery in liver resection is a standard part of liver transplantation, but is also used in oncological liver surgery. Malignant liver tumors with vascular involvement have a poor prognosis without resection. Surgery is currently the only treatment to provide long-term survival in advanced hepatic malignancy. Even though extended liver resections are increasingly performed, vascular involvement with need of vascular reconstruction is still considered a contraindication for surgery in many institutions. However, vascular resection and reconstruction in liver surgery-despite being complex procedures-are safely performed in specialized centers. The improvements of the postoperative results with reduced postoperative morbidity and mortality are a result of rising surgical and anesthesiological experience and advancements in multimodal treatment concepts with preconditioning measures regarding liver function and systemic treatment options. This review focuses on vascular surgery in oncological liver resections. Even though many surgical techniques were developed and are also used during liver transplantation, this special procedure is not particularly covered within this review article. We provide a summary of vascular reconstruction techniques in oncological liver surgery according to the literature and present also our own experience. We aim to outline the current advances and standards in extended surgical procedures for liver tumors with vascular involvement established in specialized centers, since curative resection improves long-term survival and shifts palliative concepts to curative therapy.

Successful management of sirolimus toxicity in a hematopoietic stem cell transplant patient using automated red blood cell exchange

BACKGROUND

Sirolimus is an immunosuppressive agent used in organ rejection prophylaxis in solid-organ transplantation, graft-vs-host disease prophylaxis in hematopoietic stem cell transplantation, and as an immune modulator for patients with lymphangioleiomyomatosis and vascular malformations. Sirolimus has a narrow therapeutic index with potential severe side effects, including hypertension, hepatotoxicity, nephrotoxicity, and neurotoxicity.

CASE REPORT

We report a case of a 19-year-old woman with severe sickle cell disease who underwent a matched unrelated hematopoietic stem cell transplantation, whose course was complicated by sirolimus toxicity. This case was challenging because sirolimus has no specific antidote, is largely bound to red blood cells (RBCs), has a high distribution volume, and cannot be removed by dialysis or plasmapheresis.

RESULT

Due to the concern for toxicity, we looked into possibilities for rapid sirolimus clearance using automated RBC exchange. The treatment was effective in decreasing blood sirolimus levels within the therapeutic ranges.

CONCLUSION

The use of RBC exchange is potentially safe and effective in the management of a case of sirolimus toxicity.

Antineoplastic drugs and their analysis: a state of the art review

We provide an overview of the analytical methods available for the quantification of antineoplastic drugs in pharmaceutical formulations, biological and environmental samples.

Clinical laboratory diagnostics of immunosuppressants: One laboratory’s journey

Laboratory support for the organ transplant patient is the provision of the best testing technology for a specific and accurate determination of immunosuppressive drug level. This translates to better management with the therapeutic cocktail of immunosuppressive drugs used with a lesser incidence of organ rejection and side effects. Over the years, development of automated immunoassay/chemistry test platforms with standardization of test protocols has demonstrated great improvements. The present clinical laboratory services with tandem mass spectrometry in our hospital present more precise and specific therapeutic drug monitoring so necessary still for the patient. This article follows the evolving testing technologies over the years for immunosuppressive drug monitoring following the organ transplants programme (renal in general) in Singapore General Hospital.

Long-term evaluation of analytical methods used in sirolimus therapeutic drug monitoring

Results of therapeutic monitoring of sirolimus blood concentrations are assay and laboratory dependent. This study compared performance over time of the IMx microparticle enzyme immunoassay (MEIA), Architect chemiluminescent microparticle immunoassay (CMIA), and liquid chromatography with mass spectrometric detection (LC/MS/MS) as part of a proficiency testing scheme. Pooled samples from sirolimus-treated patients and whole-blood samples spiked with known quantities of sirolimus were assayed monthly between 2004 and 2012. When results of pooled patient samples were compared with LC/MS/MS, the MEIA assay showed an overall mean percent bias of -2.3% ± 11.2% that, although initially positive, became increasingly negative from 2007 through 2009. The CMIA, which replaced the MEIA assay, had a mean percent bias of 21.9% ± 12.3%, remaining stable from 2007 through 2012. Similarly, for spiked samples, the MEIA showed an increasingly negative bias over time vs. LC/MS/MS, whereas CMIA maintained a stable positive bias. Based on comparison of immunoassay measurements on individual patient samples, CMIA values were more than 25% higher than MEIA values. These results highlight the importance of continued proficiency testing and regular monitoring of sirolimus assay performance. Clinicians must be aware of the methodology used and adjust target levels accordingly to avoid potential effects on efficacy and toxicity.

An accurate quantitative LC/ESI-MS/MS method for sirolimus in human whole blood

Sirolimus is a widely used immunosuppressant that requires therapeutic drug monitoring (TDM). We optimized a preanalytical procedure that allows for the accurate quantiation of sirolimus in whole blood by LC/ESI-MS/MS with minimal matrix effects. Sirolimus is highly lipophilic, and solvents containing greater than 50% methanol were required to maintain sirolimus recovery. The final pretreatment procedure developed consists of a zinc sulfate protein precipitation, an extraction using octadecyl silyl-silica gel for eliminating water-soluble and hydrophilic compounds, and HybridSPE cartridge treatment to eliminate phospholipids. Using this procedure prior to LC/ESI-MS/MS led to the accurate and reproducible quantitation of sirolimus in human whole blood. The linear range of detection was 0.5-50 ng/mL, a range appropriate for TDM, and the method demonstrated good repeatability and intermediate precision within this quantitative range. In order to investigate the quantitative performance of this method, we compared it to two commercially available sirolimus immunoassays and our previously reported LC/ESI-MS/MS method. The immunoassays gave consistently greater values for the sirolimus concentration, and this may be related to antibody cross-reactivity with sirolimus metabolites and/or other matrix effects. Although our procedure is too long to support real-time TDM for outpatients, it can serve as reference method to assess the performance of other analytical methods that are currently available or may be developed in the future.

Characterization of sirolimus metabolites in pediatric solid organ transplant recipients

Potential age-dependent changes of sirolimus metabolite patterns in pediatric renal transplant recipients remain elusive. Thirteen pediatric solid organ transplant recipients (10 kidney, one combined liver-kidney, two liver, mean age 8.0 +/- 5.0 yr) underwent a sirolimus pharmacokinetic profile in steady-state with 10 samples drawn over 12 h post-intake to calculate the AUC(0-12 h). Concentrations of sirolimus and metabolite were quantified using a validated LC-MS/MS assay and metabolite structures were identified directly in blood extracts using LC-MS/iontrap. Average sirolimus AUC(0-12 h) was 64.9 +/- 29.7 ng h/mL. Median (range) AUC(0-12 h) for each metabolite (ng h/mL) was: 12-hydroxy-sirolimus 7.6 (0.2-18.8), 46-hydroxy sirolimus 3.1 (0.0-12.4), 24-hydroxy sirolimus 4.3 (0.0-12.6), piperidine-hydroxy sirolimus 3.5 (0.0-8.3), 39-O-desmethyl sirolimus 3.6 (0.0-11.3), 16-O-desmethyl sirolimus 5.0 (0.1-9.9), and di-hydroxy sirolimus 4.3 (0.0-32.5). The metabolites reached a median total AUC(0-12 h) of 60% of that of sirolimus. The range was 2.6-136%, indicating significant variability. In all, 77.5% of the metabolites were hydroxylated, while 39-O-desmethyl sirolimus accounted for only 8.4% of the AUC(0-12 h). This is clinically relevant as 39-O-desmethyl sirolimus shows 86-127% cross-reactivity with the antibody of the widely used Abbott sirolimus immunoassay. The metabolism of sirolimus in the children included in our study differed from that reported in adults, which should be considered when monitoring sirolimus exposure immunologically.

Identification of Everolimus Metabolite Patterns in Trough Blood Samples of Kidney Transplant Patients

Everolimus is used as an immunosuppressant after organ transplantation. It is extensively metabolized, mainly by cytochrome P4503A enzymes, resulting in several hydroxylated and demethylated metabolites. The structures of these metabolites after in vitro metabolism of everolimus by human liver microsomes have recently been identified. It was the goal to elucidate the everolimus metabolite patterns in 128 trough blood samples from kidney graft patients using high-performance liquid chromatography (LC)-ion trap mass spectrometry (MS) in combination with analysis of the fragmentation patterns of the metabolites isolated from patient blood and comparison with the metabolites generated in vitro. After identification, concentrations of the metabolites were estimated using LC-MS. Relative to the everolimus concentrations in trough blood samples, metabolite concentrations were [median (range), n = 128] 46-hydroxy 44.1% (0-784%), 24-hydroxy 7.7% (0-85.6%), and 25-hydroxy 14.4% (0-155.4%); 11-Hydroxy, 12-hydroxy, 14-hydroxy, 49-hydroxy, two hydroxy-piperidine everolimus metabolites, 16-O-desmethyl, 16,39-O-didesmethyl, 16,27-O-didesmethyl, and 27,39-O-didesmethyl everolimus were also detected. However, when detectable, concentrations were consistently between the lower limit of detection (0.1 microg/L) and the lower limit of quantification (0.25 microg/L) of our LC-MS assay. In most trough blood samples, the total metabolite concentrations were between 50% and 100% of the everolimus concentrations. The clinical importance of everolimus metabolites in blood of patients including pharmacodynamics, toxicodynamics, and cross-reactivity with the antibodies of immunoassays used for therapeutic drug monitoring remains to be evaluated.

Comparison of the CEDIA® and MEIA® assays for the measurement of sirolimus in organ transplant recipients

OBJECTIVES

This study evaluated two immunoassays, the CEDIA assay and the MEIA assay, used for the measurement of whole blood levels of sirolimus in organ transplant recipients.

DESIGN AND METHODS

We report on the performance characteristics (total precision, limit of quantitation (functional sensitivity), limit of detection (analytical sensitivity), linearity, accuracy) for each assay. Patient correlation studies were performed, and the results were analyzed using Bland-Altman plots and Passing-Bablok analysis.

RESULTS

Total precision for the MEIA assay, corresponding to three mean concentrations of 5.0, 10.6 and 20.2 ng/mL, was 10.5, 8.5, and 6.7%, respectively. The limit of detection was determined to be 1.1 ng/mL and the limit of quantitation was 1.5 ng/mL. The mean recovery for CEDIA was 105.4%, and analysis of proficiency material demonstrated a large negative bias with respect to the mass spectrometry peer mean-later determined to be due to matrix interference. Results for the CEDIA assay showed a total precision, corresponding to a mean concentration of 5.4, 10.5 and 20.7 ng/mL, of 13.5, 5.6, and 4.1%, respectively. The limit of detection was found to be 4.8 ng/mL, with a limit of quantitation of 5.2 ng/mL. The mean recovery for MEIA was 110.1%, and analysis of proficiency material demonstrated good agreement with the mass spectrometry peer mean with a slight positive bias. Both assays were acceptably linear over the reportable range of the assay. Patient correlation studies demonstrated a positive average bias for both assays versus results from LC-MS measurement (0.9 ng/mL for MEIA, 2.1 ng/mL for CEDIA).

CONCLUSION

Based on this evaluation, the MEIA demonstrated acceptable performance for use in clinical monitoring of sirolimus. However, based on a higher limit of quantitation that falls within the therapeutic interval, the CEDIA is not recommended for clinical monitoring of sirolimus.

[Comparison of high-resolution liquid chromatography versus microparticle enzyme immunoassay for the measurement of sirolimus levels in renal transplantation]

OBJECTIVE

To compare sirolimus levels measured in whole blood using two analytical techniques: high-resolution liquid chromatography and microparticle enzyme immunoassay, and to evaluate whether hemoglobin, hematocrit, and time from kidney transplantation influence results obtained using the immune-enzymatic technique.

METHOD

A retrospective, observational study in which all transplanted patients with at least one measurement of sirolimus levels using high-resolution liquid chromatography or microparticle enzyme immunoassay from October 2004 to May 2005 were consecutively included. For statistical comparisons simple linear regression, ANCOVA, intra-class correlation coefficient, and the method of agreement limits were all used.

RESULTS

Ninety-one patients were assessed for a total of 307 measurements (median: 2, inter-quartile range: 1-4, range: 1-15) of sirolimus levels. The straight-line equation using the linear regression analysis was as follows: MEIA = 0.70 (95% CI: 0.39-1.01) + 1.14 (95% CI: 1.10-1.17) x HPLC/UV. The intra-class correlation coefficient between both measurements was 0.955 (95% CI 0.944-0.964). Mean overestimation using enzyme immunoassay was 24.8% +/- 19.4%. Difference in means between both measurements was 1.9 +/- 1.3 ng/mL. Agreement limits were established between -0.8 ng/mL (95% CI: -1.05; -0.55) and +4.6 ng/mL (95% CI: 4.35; 4.85). Factors such as post-transplant time, hemoglobin, and hematocrit did not influence overestimates obtained using enzyme immunoassays. These results were not influenced by non-independence in measurements.

CONCLUSIONS

Despite enzyme immunoassay overestimates in establishing sirolimus levels in whole blood, its correlation with chromatography is acceptable. Added to its benefits versus chromatographic techniques, this renders enzyme immunoassay a good alternative for the measurement of sirolimus levels in whole blood.

Multi-center evaluation of analytical performance of the microparticle enzyme immunoassay for sirolimus

OBJECTIVES

This study evaluated the analytical characteristics of the new Abbott microparticle enzyme immunoassay (MEIA) for sirolimus.

DESIGN AND METHODS

The protocol consisted of nine sections: evaluation of antibody specificity, linearity, detection limit, quantification limit, endogenous interferents, exogenous interferents, precision, proficiency testing panel, and method comparison.

RESULTS

The mean analytical detection limit was 0.68 microg/L. The sirolimus concentration corresponding to a total CV of 20% was 1.5 microg/L. Linearity of response was demonstrated across the dynamic range of the assay. Total precision (CVs) at QC control levels from 5 to 22 microg/L ranged from 5.7 to 12.6%. Assay standardization was found to be in good agreement with LC/MS/MS as compared with target values for spiked sirolimus proficiency samples from an international sirolimus proficiency testing program. Good correlations (R values) of the immunoassay were observed in comparisons to LC/MS/MS. R values tended to be lower in comparisons with LC/UV methods. Across both LC-based methods and all study sites, there was approximately 25% overall positive slope bias due to cross reactivity of the MEIA antibody to metabolites of sirolimus. The assay cross-reactivity to metabolites of sirolimus parent drug ranged from 6 to 63%. Assay interferences were minimal with the exception of hematocrit, which presented a negative relationship to measured sirolimus concentration.

CONCLUSIONS

The MEIA demonstrated acceptable analytical characteristics for use for routine monitoring of sirolimus immunosuppressive therapy, and is a viable alternative to HPLC-based methods for sirolimus monitoring.

A microparticle enzyme immunoassay to measure sirolimus

Measurement of sirolimus as a guide to therapy is widely accepted. Since the commercial introduction of the drug, the only method available to measure blood concentrations has been high-performance liquid chromatography (HPLC). Only a limited number of centers have the facilities to perform this technique and, as a result, the measurement of the drug has been performed in central laboratories, often some distance from the clinical centers. This article describes a single-center assessment of a new immunoassay to measure sirolimus, including a comparison between immunoassay results and a chromatographic technique. Calibration accuracy was good, reproducibility at 11 ng/mL was better than 6%, and sensitivity was better than 2 ng/mL; all these parameters are appropriate for routine clinical use. There was a mean positive bias of almost 20% for the measurement of sirolimus in clinical samples from kidney transplant patients receiving the drug, compared with HPLC. This bias was most likely due to cross-reactivity with metabolites of the drug and was of the order noted when an earlier configuration of this immunoassay was used in clinical practice. We conclude that, despite the analytical bias, this immunoassay offers a viable alternative to the use of HPLC and would be an assay suitable for implementing at local centers.