Evaluation of an immunoassay (Abbott-IMX Analyzer) allowing routine determination of sirolimus: comparison with LC-MS method

The effects of lyophilization on the physico-chemical stability of sirolimus liposomes

PURPOSE

The major limitation in the widespread use of liposome drug delivery system is its instability. Lyophilization is a promising approach to ensure the long-term stability of liposomes. The aim of this study was to prepare sirolimus-loaded liposomes, study their stability and investigate the effect of lyophilization either in the presence or in the absence of lyoprotectant on liposome properties.

METHODS

Two types of multi-lamellar liposomes, conventional and fusogenic, containing sirolimus were prepared by modified thin film hydration method with different ratio of dipalmitoylphosphatidylcholine (DPPC), cholesterol and dioleoylphosphoethanolamine (DOPE), and were lyophilized with or without dextrose as lyoprotectant. Chemical stability investigation was performed at 4°C and 25°C until 6 months using a validated HPLC method. Physical stability was studied with determination of particle size (PS) and encapsulation efficiency (EE %) of formulations through 6 months.

RESULTS

Chemical stability test at 4°C and 25°C until 6 months showed that drug content of liposomes decreased 8.4% and 20.2% respectively. Initial mean EE % and PS were 72.8 % and 582 nm respectively. After 6 months mean EE % for suspended form, lyophilized without lyoprotectant and lyophilized with lyoprotectant were 54.8 %, 62.3% and 67.1 % at 4°C and 48.2%, 60.4 % and 66.8 % at 25°C respectively. Corresponding data for mean PS were 8229 nm, 2397 nm and 688nm at 4°C and 9362 nm, 1944 nm and 737 nm at 25°C respectively.

CONCLUSION

It is concluded that lyophilization with and without dextrose could increase shelf life of liposome and dextrose has lyoprotectant effect that stabilized liposomes in the lyophilization process.

Protein biochip array technology to monitor rituximab in rheumatoid arthritis

In rheumatoid arthritis (RA) there are currently no good indicators to predict a clinical response to rituximab. The purpose of this study was to monitor and determine the role of peripheral blood cytokine profiling in differentiating between a good versus poor response to rituximab in RA. Blood samples were collected at baseline and at 3 months from 46 RA patients who were treated with rituximab. Responders are defined by the presence of three of four American College of Rheumatology criteria: >or=20% decrease in C-reactive protein, visual analogical score of disease activity, erythrocyte sedimentation rate and improvement of the disease activity score (28) (four values) by >or=1.2 obtained at 3 months. Twelve cytokines were measured from serum collected on days 0 and 90 by proteomic array, including interleukin-6 (IL-6), tumour necrosis factor-alpha, IL-1a, IL-1b, IL-2, IL-8, interferon-gamma, IL-4, IL-10, monocyte chemoattractant protein-1, epidermal growth factor and vascular growth factor. We showed that C-reactive protein and IL-6 levels decrease significantly at 3 months in the responder group compared with baseline. At day 90 we identified a cytokine profile which differentiates responders and non-responders. High serum levels of two proinflammatory cytokines, monocyte chemoattractant protein-1 and epidermal growth factor, were significantly higher in the responder group at day 90 compared with non-responders. However, we were not able to identify a baseline cytokine profile predictive of a good response at 3 months. These findings suggest that cytokine profiling by proteomic analysis may be a promising tool for monitoring rituximab and may help in the future to identify responder RA patients.

Determination of blood sirolimus concentrations in liver and kidney transplant recipients using the Innofluor fluorescence polarization immunoassay: comparison with the microparticle enzyme immunoassay and high-performance liquid chromatography-ultraviolet method

BACKGROUND

Although high-performance liquid chromatography (HPLC) is the method of choice for blood sirolimus determination, the microparticle enzyme immunoassay (MEIA) run on the IMx analyser is widely used in therapeutic monitoring of this immunosuppressant agent. The aim of our study was to evaluate the possible determination of sirolimus using the fluorescence polarization immunoassay (FPIA) commercialized for everolimus quantification.

METHODS

Sirolimus concentrations were determined in whole-blood samples from liver and kidney transplant recipients using the Innofluor Certican FPIA (Seradyn Inc.) run on a TDx analyser (Abbott Laboratories), Sirolimus MEIA run on an IMx analyser (Abbott Laboratories), and HPLC (UV detection) methods.

RESULTS

The Innofluor FPIA has a similar cross-reactivity with everolimus and sirolimus, and the within- and between-run coefficients of variation obtained for sirolimus determination were 2.7%-13.3%. In analysing different blood samples from liver and kidney transplant patients the linear regressions obtained were: FPIA = 1.12 HPLC + 0.43 (n=104, r=0.874), MEIA = 1.14 HPLC (n=146, r=0.892), and FPIA = 1.00 MEIA + 0.29 (n=106, r=0.941). Better correlation coefficients were obtained between the methods in the liver transplant samples (r>or=0.900) than in the kidney transplant samples (r>or=0.849). No significant effect was found for sirolimus clearance or the blood hematocrit on the relationship between the results produced by both immunoassays and HPLC.

CONCLUSION

The Innofluor FPIA is a valid alternative with an analogous performance to the MEIA for the therapeutic monitoring of sirolimus.

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.

Protein biochip array technology for cytokine profiling predicts etanercept responsiveness in rheumatoid arthritis

In rheumatoid arthritis (RA) there are currently no useful indicators to predict a clinical response to tumour necrosis factor-alpha (TNF-alpha) blockade. The purpose of this study was to determine the role of peripheral blood cytokine profiling in differentiating between a good versus poor response to etanercept in RA. Peripheral blood samples were collected at baseline and at 3 months from 33 patients with active disease who were treated twice weekly by etanercept therapy. Responders are defined by the presence of three of four American College of Rheumatology criteria: > or =20% decrease in C-reactive protein (CRP), visual analogue score of disease activity, erythrocyte sedimentation rate and improvement of the disease activity score (28; four values) by > or =1.2 obtained at 3 months. Twelve cytokines were measured from serum collected on days 0 and 90 by proteomic array (protein biochip array, Investigator Evidence, Randox France), including interleukin (IL)-6, TNF-alpha, IL-1a, IL-1b, IL-2, IL-8, interferon-gamma, IL-4, IL-10, monocyte chemoattractant protein (MCP)-1, epidermal growth factor (EGF) and vascular endothelium growth factor. Our results showed that high serum levels of MCP-1 and EGF were associated with a response to etanercept. In addition, the increase of two combined parameters CRP and EGF was predictive of a response to etanercept treatment at 3 months (sensitivity: 87.5% and specificity: 75%, accuracy: 84.4%). These findings suggest that cytokine profiling by proteomic analysis before treatment initiation may help to identify a responder patient to TNF-alpha blocking agents in RA.

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.