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

Rapid genotyping of single nucleotide polymorphisms influencing warfarin drug response by surface-enhanced laser desorption and ionization time-of-flight (SELDI-TOF) mass spectrometry

Warfarin exhibits significant interindividual variability in dosing requirements. Different drug responses are partly attributed to the single nucleotide polymorphisms (SNPs) that influence either drug action or drug metabolism. Rapid genotyping of these SNPs helps clinicians to choose appropriate initial doses to quickly achieve anticoagulation effects and to prevent complications. We report a novel application of surface-enhanced laser desorption and ionization time-of-flight mass spectrometry (SELDI-TOF MS) in the rapid genotyping of SNPs that impact warfarin efficacy. The SNPs were first amplified by PCR and then underwent single base extension to generate the specific SNP product. Next, genetic variants displaying different masses were bound to Q10 anionic proteinChips and then genotyped by using SELDI-TOF MS in a multiplex fashion. SELDI-TOF MS offered unique properties of on-chip sample enrichment and clean-ups, which streamlined the testing procedures and eliminated many tedious experimental steps required by the conventional MS-based method. The turn-around time for genotyping three known warfarin-related SNPs, CYP2C9*2, CYP2C9*3, and VKORC1 3673G>A by SELDI-TOF MS was less than 5 hours. The analytical accuracy of this method was confirmed both by bidirectional DNA sequencing and by comparing the genotype results (n = 189) obtained by SELDI-TOF MS to reports from a clinical reference laboratory. This new multiplex genotyping method provides an excellent clinical laboratory platform to promote personalized medicine in warfarin therapy.

Quantification of sirolimus and everolimus by immunoassay techniques: test specificity and cross-reactivity evaluation

The possible cross-reactivity of immunoassays with structurally-related drugs was investigated. Innofluor Certican (FPIA) calibrators were measured by using IMx Sirolimus assay (MEIA) and MEIA Sirolimus calibrators were analysed by using FPIA Certican assay. Drug concentrations were measured in 95 and 100 samples from renal transplanted patients (RTP) on sirolimus or everolimus treatment by using immunoassays and LC/ESI-MSMS. A high cross-reactivity was found both for MEIA and FPIA. High correlation degrees, confirmed by the Bland-Altman and the Eksborg tests, were found between drug concentrations measured in real samples by both immunoassays (r = 0.909 and r = 0.970, respectively). LC/ESI-MSMS analysis of samples containing sirolimus showed no positivity for everolimus. Similarly, samples from patients on treatment with everolimus resulted negative as far as regards sirolimus. MEIA and FPIA could be considered mutually reliable and accurate alternatives for the specific-drug immunoassay. It should be noticed that in patients switching from one drug to the other unreal overestimation of the blood levels of the current administered immunosuppressant can occur.

Stability of sirolimus and everolimus measured by immunoassay techniques in whole blood samples from kidney transplant patients

The measurement of blood concentration of immunosuppressive drugs is strongly recommended because of the narrow therapeutic range. An important aspect in the therapeutic monitoring of a drug is its possible degradation. This paper is aimed at investigating the stability of two widely-used immunosuppressants, sirolimus and everolimus. Short (storage at 30 degrees C for 3 or 7 days) and long term (storage at -20 degrees C for 0-90 days with a single freeze-thaw cycle) stability of sirolimus and everolimus in whole blood samples from kidney transplant patients were examined by using MEIA and FPIA. Sirolimus and everolimus samples stored at 30 degrees C in light for up to a week showed a decrement in concentration of 5.2 percent and 6.1 percent, respectively. Our findings on long term stability for both sirolimus and everolimus highlight the possibility of storing samples at -20 degrees C for up to 90 days, without the need to use lower storage temperatures. The results have important implications for patients living far from laboratories where drug concentration is measured or when the storing of blood samples is needed for pharmacokinetic studies.

Immunoassay determination of rapamycin: reliability of the method with respect to liquid chromatography mass spectrometric quantification

Immunochemical assays represent a promising tool for quantification of immunosuppressants in organ transplanted patients, because they require small sample volumes and minimum sample pre-treatment; nevertheless considerations about method specificity, sensitivity and reproducibility cannot be overlooked. The present paper investigates the reliability of using the immunoparticle enzyme immunoassay (MEIA) for the quantification of blood rapamycin (RAPA) levels in therapeutic drug monitoring of renal transplanted patients with respect to a validated liquid chromatography tandem mass spectrometric (LC/ESI-MSMS) method, used as reference. Linearity of MEIA was tested over the range 0.0-30.0 ng/mL, with accuracy and precision within acceptable limits. Fifty-two blood samples were collected from 42 renal transplanted patients and analyzed simultaneously by both methods. The Pearson's regression analysis gave the following parameters: correlation equation [RAPA](MEIA) = 1.330 + 0.776 [RAPA](LC/ESI-MSMS), r = 0.8526, SD = 1.778, p < 0.0001. The obtained average rapamycin concentration was 8.8 +/- 3.4 ng/mL using MEIA and 9.6 +/- 3.7 ng/mL for LC/ESI-MSMS, with an overall underestimation of about 6% of the immunoenzymatic test. Accuracy of MEIA ranged from -33% to 36% with respect to the reference mass spectrometric method. Although immunoenzymatic test represents a fast and sufficiently accurate method for its use in clinical practice, specificity of the assay is still not sufficiently investigated and reference methods and/or Proficiency Testing Scheme should be used as external control.

Identification of a highly effective rapamycin schedule that markedly reduces the size, multiplicity, and phenotypic progression of tobacco carcinogen-induced murine lung tumors

PURPOSE

Human and murine preneoplastic lung lesions induced by tobacco exposure are characterized by increased activation of the Akt/mammalian target of rapamycin (mTOR) pathway, suggesting a role for this pathway in lung cancer development. To test this, we did studies with rapamycin, an inhibitor of mTOR, in A/J mice that had been exposed to the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

EXPERIMENTAL DESIGN

Tumorigenesis was induced by i.p. injection of NNK, and rapamycin was administered 1 or 26 weeks after NNK administration. Biomarkers associated with mTOR inhibition were assessed in lung and/or surrogate tissues using immunohistochemistry and immunoblotting. Rapamycin levels were measured using mass spectroscopy.

RESULTS

Rapamycin was administered on a daily (5 of 7 days) regimen beginning 26 weeks after NNK decreased tumor size, proliferative rate, and mTOR activity. Multiplicity was not affected. Comparing this regimen with an every-other-day (qod) regimen revealed that rapamycin levels were better maintained with qod administration, reaching a nadir of 16.4 ng/mL, a level relevant in humans. When begun 1 week after NNK, this regimen was well tolerated and decreased tumor multiplicity by 90%. Tumors that did develop showed decreased phenotypic progression and a 74% decrease in size that correlated with decreased proliferation and inhibition of mTOR.

CONCLUSIONS

Tobacco carcinogen-induced lung tumors in A/J mice are dependent upon mTOR activity because rapamycin markedly reduced the development and growth of tumors. Combined with the Food and Drug Administration approval of rapamycin and broad clinical experience, these studies provide a rationale to assess rapamycin in trials with smokers at high risk to develop lung cancer.

Accurate determination of an immunosuppressant in stented swine tissues with LC–MS/MS

During stent development, accurate monitoring of the drug concentration in animal tissues can provide critical information on how the drug is released into the circulation and the surrounding tissues. To establish the relationship between the drug concentration and the distance from the stent to the target tissue, a comprehensive strategy was developed for sample collection, sample homogenization and sample storage as well as sample analysis. This strategy was developed with the analytical chemists and animal surgical specialists working together as a team. The optimized sampling process was designed to yield a representative sample, appropriately located and of an appropriate size. The sampling process was also designed to eliminate the potential for carryover and cross-contamination. During sample processing, the analyte solution was spiked into blank tissues using a sharp needle and a gas-tight syringe to prepare tissue quality control samples. These tissue quality controls were then used to evaluate the stability of the drug in solid tissue and homogenate, the homogenization carryover, the cross-contamination and the recovery of the drug during method validation and to monitor the overall process of drug analysis of the swine tissues. This thorough strategy has been applied to the accurate determination of zotarolimus in swine tissues for regulated toxicology studies. The entire process was controlled, including precise tissue sampling, compound-based tissue homogenization, method validation, and the application of the method to regulated toxicokinetics studies. The results demonstrate that analytical chemistry concepts can be successfully integrated into toxicokinetics studies in order to collect precise samples and obtain meaningful results. The strategy can be applied to similar toxicokinetics studies of locally administrated drugs in tissues.

Determination of sirolimus in rabbit arteries using liquid chromatography separation and tandem mass spectrometric detection

Sirolimus, an effective immunosuppressive agent, is used for drug eluting stents. During stent development, an analytical method for the determination of sirolimus in tissue needs to be established. Normally, tissue samples are homogenized and then analyzed against the calibration standards prepared in a tissue homogenate. This approach provides insufficient control of the homogenization process. In this paper, tissue quality control samples were introduced for the optimization of the homogenization process during method development, but also allowance for the performance evaluation of the entire analytical process. In addition, a new approach using rabbit blood as a homogenization medium was developed to stabilize sirolimus in rabbit tissue homogenates. Calibration standards and quality controls were prepared by spiking different sirolimus working solutions into rabbit blood. Homogenization quality control samples were prepared by injecting other sirolimus working solutions into empty test tubes and pre-cut arteries within pre-defined masses. A high-throughput homogenization procedure was optimized based on the specific chemical properties of sirolimus. The linear dynamic range was between 49.9 pg/mL and 31.9 ng/mL to accommodate the expected artery homogenate concentrations. Additionally, quality controls in rabbit blood were also used in the extraction to support the calibration standards. The accuracy and precision of the quality controls in rabbit blood reflect the extraction performance and the accuracy and precision of the homogenization tissue quality controls reflect the overall performance of the method. The mean bias was between -4.5 and 0.2% for all levels of quality controls in the blood and between 4.8 and 14.9% for all levels of the homogenization tissue quality controls. The CVs of all concentration levels were < or =5.3% for the quality controls in blood and < or =9.2% for the homogenization tissue quality controls. The method was successfully applied to determine the concentration of sirolimus in the rabbit arteries.