Fast quantification method for sirolimus and its major metabolites

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.

FDG uptake is a surrogate marker for defining the optimal biological dose of the mTOR inhibitor everolimus in vivo

This study aimed to test whether [¹⁸F]fluoro-D-glucose (FDG) uptake of tumours measured by positron emission tomography (PET) can be used as surrogate marker to define the optimal biological dose (OBD) of mTOR inhibitors in vivo. Everolimus at 0.05, 0.5, 5 and 15 mg kg⁻¹ per day was administered to gastric cancer xenograft-bearing mice for 23 days and FDG uptake of tumours was measured using PET from day 1 to day 8. To provide standard comparators for FDG uptake, tumour volume, S6 protein phosphorylation, Ki-67 staining and everolimus blood levels were evaluated. Everolimus blood levels increased in a dose-dependent manner but antitumour activity of everolimus reached a plateau at doses ⩾5 mg kg⁻¹ per day (tumour volume treated vs control (T/C): 51% for 5 mg kg⁻¹ per day and 57% for 15 mg kg⁻¹ per day). Correspondingly, doses ⩾5 mg kg⁻¹ per day led to a significant reduction in FDG uptake of tumours. Dose escalation above 5 mg kg⁻¹ per day did not reduce FDG uptake any further (FDG uptake T/C: 49% for 5 mg kg⁻¹ per day and 52% for 15 mg kg⁻¹ per day). Differences in S6 protein phosphorylation and Ki-67 index reflected tumour volume and changes in FDG uptake but did not reach statistical significance. In conclusion, FDG uptake might serve as a surrogate marker for dose finding studies for mTOR inhibitors in (pre)clinical trials.

Sirolimus: the evidence for clinical pharmacokinetic monitoring

This review seeks to apply a decision-making algorithm to establish whether clinical pharmacokinetic monitoring (CPM) of sirolimus (rapamycin) in solid organ transplantation is indicated in specific patient populations. The need for CPM of sirolimus, although a regulatory requirement in Europe, has not yet been firmly established in North America and other parts of the world. Sirolimus has demonstrated immunosuppressive efficacy in renal, pancreatic islet cell, liver and heart transplant recipients. The pharmacological response of immunosuppressive therapy with sirolimus cannot be readily evaluated; however, a relationship between trough blood sirolimus concentrations, area under the plasma concentration-time curve (AUC) and the incidence of rejection has been proposed. Furthermore, sirolimus can be measured in whole blood by several assays--high-performance liquid chromatography with detection by tandem mass spectrometry, or with ultraviolet detection, radioreceptor assay or microparticle enzyme immunoassay. Both experimental animal and clinical data suggest that adverse events and their associated severity are correlated with blood concentrations. To prevent rejection and minimise toxicity, a therapeutic range of 4-12 microg/L (measured via chromatographic assays) is recommended when sirolimus is used in conjunction with ciclosporin. If ciclosporin therapy is discontinued, a target trough range of 12-20 microg/L is recommended. Sirolimus pharmacokinetics display large inter- and intrapatient variability, which may change in specific patient populations due to disease states or concurrent immunosuppressants or other interacting drugs. Due to the long half-life of sirolimus, dosage adjustments would ideally be based on trough levels obtained more than 5-7 days after initiation of therapy or dosage change. Once the initial dose titration is complete, monitoring sirolimus trough concentrations weekly for the first month and every 2 weeks for the second month appears to be appropriate. After the first 2 months of dose titration, routine CPM of sirolimus is not necessary in all patients, but may be warranted to achieve target concentrations in certain populations of patients, but the frequency of further monitoring remains to be determined and should be individualised.

A novel technique for on-capillary preconcentration of anionic compounds applied to the trace analysis of rapamycin in human blood by capillary electrophoresis

A capillary electrophoretic (CE) method with UV detection at 278 nm has been developed for analysis of the immunosuppressant rapamycin (sirolimus) in human blood at low microg.L(-1) levels. Separation has been achieved in an acidic carrier electrolyte containing sodium dodecyl sulfate and 20% v/v methanol. For sample cleanup and preconcentration, both an off-line solid-phase extraction step using a silica-based reversed-phase material and a newly developed on-capillary focusing technique have been employed. The subsequent treatment of rapamycin under alkaline conditions leads to a cleavage of the lacton bond of the molecule, generating a negatively charged carboxylic group which allows electrokinetic injection into the CE instrument. During the injection process, the negatively charged analyte migrates into an acidic carrier electrolyte, so that it becomes neutral due to protonation and is focused at the capillary inlet. Injection times of 300 s at -7.5 kV could be applied without band-broadening. Results for real samples indicated that the method is fully suited for routine applications and may be an attractive alternative to established liquid chromatographic techniques.

Determination of rapamycin: quantification of the sodiated species by an ion trap mass spectrometer as an alternative to the ammoniated complex analysis by triple quadrupole

Rapamycin is a potent immunosuppressive drug capable of significantly reducing acute graft rejection in kidney, liver and heart transplant patients. Its immunosuppressive activity and adverse effects have been related to rapamycin concentration, and therapeutic drug monitoring of the drug is deemed appropriate. This work was aimed at developing a new quantification method based on the isolation of the [M+Na]+ ion as precursor and its further fragmentation through an ion trap mass spectrometer equipped with an electrospray ionization source. A limit of detection (LOD) of 0.7 ng/mL was obtained, while the lower limit of quantification (LLOQ) was 2.4 ng/mL. The accuracy and reproducibility of the responses were evaluated and compared with results obtained when the [M+NH4]+ ion was chosen as the precursor in a triple quadrupole mass spectrometer. In this case the LOD was 0.5 ng/mL and the LLOQ 1.7 ng/mL. Data showed that it would be possible to use the quantification of the sodiated species for the routine determination of rapamycin, as an alternative to the commonly adopted method based on the ammoniated complex.

Determination of Sirolimus Blood Concentration Using High-Performance Liquid Chromatography with Ultraviolet Detection

BACKGROUND

Different HPLC methods have been developed and used to determined sirolimus blood concentrations. These methods show different performance characteristics, mostly related to peak interference, recovery, assay sensitivity, and turnaround times.

OBJECTIVE

We adapted, improved, and validated an HPLC method with UV detection for measurement of sirolimus in whole blood clinical samples.

METHODS

The standards, quality controls, or patient samples (0.25 or 0.5 mL) and internal standard (desmethoxysirolimus) were extracted with 1-chlorobutane. After evaporation, the extract was reconstituted in a 70% acetonitrile/water mixture and analyzed onto a reverse-phase C18 column at 50 degrees C under a flow rate of 1.0 mL/min in the HPLC system. Ultraviolet detection was performed at 278 nm, with sensitivity setting of 0.010 AUFS. Identification of peaks of interest was by retention time; quantification of sirolimus was based on a peak area ratio.

RESULTS

Analytic recovery ranging from 96 to 120% (CV = 3.7 to 16.8%; bias = -4.2 to 16.7%) was observed throughout the assay's linear range (2.5-150.0 ng/mL). The lower limit of quantification for both sample volumes (0.25 or 0.5 mL) was 2.5 ng/mL (CV = 12 and 15%, bias = -1.2 and 4%, respectively). The intra- and interassay imprecision ranged from 6.2 to 14.4% and from 9.1 to 18.6%, with bias ranging from 1.3 to 12.9% and -1.8% to 7.1, for quality control levels of 3, 10, and 20 ng/mL. Whole blood and extracted samples are stable at room temperature and at 4 and -20 degrees C for 1 week and 3 days, respectively. Chromatograms showed good separation free of interfering peaks. A set of 45 samples can be extracted in 2 h, allowing results within 24 h.

CONCLUSION

This HPLC-UV method shows good and reproducible performance, satisfying all requirements of an assay designated to be applied in therapeutic drug monitoring strategies after organ transplantation.

Sirolimus/cyclosporine/tacrolimus interactions on bile flow and biliary excretion of immunosuppressants in a subchronic bile fistula rat model

The new immunosuppressive agent sirolimus generally is combined in transplant patients with cyclosporine and tacrolimus which both exhibit cholestatic effects. Nothing is known about possible cholestatic effects of these combinations which might be important for biliary excretion of endogenous compounds as well as of immunosuppressants. Rats were daily treated with sirolimus (1 mg kg(-1) p.o.), cyclosporine (10 mg kg(-1) i.p.), tacrolimus (1 mg kg(-1) i.p.), or a combination of sirolimus with cyclosporine or tacrolimus. After 14 days a bile fistula was installed to investigate the effects of the immunosuppressants and their combinations on bile flow and on biliary excretion of bile salts, cholesterol, and immunosuppressants. Cyclosporine as well as tacrolimus reduced bile flow (-22%; -18%), biliary excretion of bile salts (-15%;-36%) and cholesterol (-15%; -47%). Sirolimus decreased bile flow by 10%, but had no effect on cholesterol or bile salt excretion. Combination of sirolimus/cyclosporine decreased bile flow and biliary bile salt excretion to the same extent as cyclosporine alone, but led to a 2 fold increase of biliary cholesterol excretion. Combination of sirolimus/tacrolimus reduced bile flow only by 7.5% and did not change biliary bile salt and cholesterol excretion. Sirolimus enhanced blood concentrations of cyclosporine (+40%) and tacrolimus (+57%). Sirolimus blood concentration was increased by cyclosporine (+400%), but was not affected by tacrolimus. We conclude that a combination of sirolimus/tacrolimus could be the better alternative to the cotreatment of sirolimus/cyclosporine in cholestatic patients and in those facing difficulties in reaching therapeutic ranges of sirolimus blood concentration.

Quantification of sirolimus by liquid chromatography-tandem mass spectrometry using on-line solid-phase extraction

Quantification of the new immunosuppressant sirolimus (syn. rapamycin; Rapamune) in whole blood by chromatography is essential for its clinical use since no immunoassay is available although monitoring is mandatory. Here we report on a rapid and convenient liquid chromatography (LC-tandem mass spectrometry method and describe our practical experience with its routine use. Whole blood samples were hemolyzed and deproteinized using an equal volume (150 microl) of a mixture of methanol/zinc sulfate solution containing the internal standard desmethoxy-rapamycin. After centrifugation, the clear supernatants were submitted to an on-line solid-phase extraction procedure using the polymeric Waters Oasis HLB material, with elution of the extracts onto the analytical column in the back-flush mode by column switching. For analytical chromatography a RP-C18 column was used with 90/10 methanol/2 mM ammonium acetate as the mobile phase. A 1:10 split was used for the transfer to the mass spectrometer, a Micromass Quattro LC-tandem mass spectrometry system equipped with a Z-spray source and used in the positive electrospray ionization mode. The following transitions were recorded: sirolimus, 931>864 m/z, and desmethoxy-rapamycin (I.S.), 901>834 m/z. The analytical running time was 5 min, including on-line extraction. The method has a linear calibration curve (r>0.99; range 1.6-50 microg/l) and is rugged and precise with monthly CVs <7% at a sirolimus concentration of 13.1 microg/l in routine use; the instrumentation proved to be reliable and required minimal maintenance. Clin Chem