Determination of octreotide and assessment of matrix effects in human plasma using ultra high performance liquid chromatography-tandem mass spectrometry

Quantitative spectrofluorimetric method for determination of octreotide acetate synthetic peptide derivative in pure and its Sandostatin ampules forms

A unique spectrofluorimetric protocol has been conceived for octreotide (a synthetic peptide drug) quantitation in both its authentic form and its application to dosage form. The protocol has been established simply upon condensation of octreotide by ninhydrin / phenyl acetaldehyde reagent in buffered media (pH 6.2). An intense fluorescence product has been formed and quantified at 463 nm (390 nm for excitation). After optimization for various experimental conditions, a wide linear interval (0.2-4.0 µg/ml) has been used to construct the calibration curve with a determination coefficient (r2) of 0.9994, a slope ± SD of 81.147 ± 0.7985, and a highly sensitive detection and quantitation limits nearly equal to 0.066 and 0.2 µg/ml, respectively. A proposed protocol has been checked in accordance with ICH validation guidelines, which indicate good accuracy and high precision of the proposed method. Furthermore, this protocol could be perfectly applied for the quantitative estimation of octreotide in its ampoules with a high degree of accuracy and precision. As a result, a developed protocol is ideally appropriate for fast and simple octreotide quantitative estimation in quality control laboratories.

Molecularly imprinted electrochemical sensor for the selective and sensitive determination of octreotide in cancer patient plasma sample

In this study, a molecularly imprinted polymer film (P (ANI)@MIP) on the electrode surface was fabricated using aniline as a functional monomer and octreotide (OC) as a template molecule. The developed P (ANI)@MIP was electrochemically electropolymerized on a glassy carbon electrode (GCE) surface. Each step of MIP production was evaluated by viewing the [Fe (CN)₆]^3-/4- signal obtained using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The P (ANI)@MIP film layer was studied with a scanning electron microscope (SEM), Raman, and contact angle measurements. The parameters consisting of monomer, template ratio, cycle number, removal solution, removal time, and rebinding time were optimized to obtain the best electrochemical sensor. The developed method was validated in line with ICH guidelines. The linear range, LOD, and LOQ were found as 10-80 fM, 0.801 fM, and 2.670 fM, respectively. The selectivity of the method was tested with the response of somatostatin and lanreotide from the same growth hormone family by comparing the OC response. The developed P (ANI)@MIP/GCE sensor is the first reported method for electrochemical analysis of OC. The P (ANI)@MIP/GCE sensor exhibited high sensitivity and selectivity for OC. The novel MIP sensor was used to determine OC in cancer patient plasma samples. The concentration of OC in cancer patients varied between 8.98 ng/mL and 10.10 ng/mL.

Optimization and validation of the liquid chromatography coupled to tandem mass spectrometry method for assessing octreotide release from microspheres during inflammation in rabbit models

To study the effect of acute-phase reaction (APR) of inflammation on the release of octreotide acetate microsphere (Sandostatin®, SLAR) at a clinical dose, a more sensitive liquid chromatography coupled to tandem mass spectrometry analysis method needs to be developed because of the low plasma concentrations of octreotide. Solid-phase microextraction with an Oasis® HLB μElution plate was adopted for sample preparation. Extraction recovery ranged from 65.7 % to 73.2 %, and the matrix effect was negligible. High sensitivity and an intense chromatographic peak were acquired by optimizing the chromatography and mass spectrometry conditions. The lower limit of quantitation (LLOQ) was 0.01 ng/mL based on 100 μL of plasma, and linearity ranged from 0.01 to 5.0 ng/mL. The coefficients of variations for intraday and interday precision were less than 4.4 %, and the relative error of accuracy was within 5.7 %. The validated method was successfully applied to pharmacokinetics studies of SLAR in a seven-day inflammation model of rabbits, indicating that the APR did not affected the release and pharmacokinetics of the octreotide microspheres.

Development and Validation of an LC-MS/MS Method for Simultaneous Determination of Short Peptide-Based Drugs in Human Blood Plasma

A novel HPLC-ESI-MS/MS method for simultaneous gonadotropin-releasing hormone (GnRH) analogs and somatostatin analog quantitation was developed and validated. The developed method was successfully applied to pharmacokinetic studies. The sample preparation process included solid-phase extraction (SPE). Effective chromatographic separation of the analytes and internal standard (dalargin) was achieved with a C18 column, using a gradient elution with two mobile phases: 0.1% v/v formic acid (aqueous solution) and 0.1% v/v formic acid (acetonitrile solution). The linearity of the method was demonstrated within a concentration range of 0.5-20 ng/mL, with correlation coefficients between 0.998-0.999 for goserelin, buserelin, triptorelin, and octreotide, respectively. The relative standard deviation (RSD, %) values for method accuracy and precision did not exceed 20% at the lower level of quantitation (LLOQ) or 15% at other concentration levels.

IVIVC of Octreotide in PLGA-Glucose Microsphere Formulation, Sandostatin® LAR

In vitro-in vivo correlation (IVIVC) analysis reveals a relationship between in vitro release and in vivo pharmacokinetic response of the drug of interest. Sandostatin LAR Depot (SLD) for endocrine tumors and acromegaly is a sustained-release formulation of octreotide, a cyclic oligomer of 8 amino acids, which prolongs therapeutic efficacy and enhances medication compliance of octreotide. Since the efficacy of SLD is dependent on the pharmacokinetic characteristics of octreotide released from a biodegradable matrix polymer, poly(lactide-co-glycolide)-glucose, of SLD, the IVIVC of SLD is critical for predicting an in vivo behavior of the octreotide. In this study, in vitro release of octreotide from SLD was investigated using the release test media each containing 0.02% or 0.5% surfactant and having different pH values of 7.4 and 5.5. In vivo pharmacokinetic profiles of SLD were determined by LC-MS/MS analysis of the systemic blood concentration of octreotide after the SLD injection to rodents. In IVIVC analysis, the Weibull model was adopted as a drug release model for biodegradable microsphere formulation. The IVIVC analyses revealed the in vitro release test condition of SLD with the highest IVIV correlation coefficient. By applying the in vitro release data to the model derived from the IVIVC analysis, pharmacokinetic parameters of SLD could be predicted with the prediction error of ± 10 ~ 15%. IVIVC analysis and pharmacokinetic prediction model of SLD in our study can be an efficient tool for the development of long-acting pharmaceutical dosage forms.

Facile spectrofluorimetric quantitation of octreotide, a synthetic peptide, in its pure form and pharmaceutical formulation; Evaluation of the method greenness

A new, rapid, highly sensitive, and affordable spectrofluorimetric approach has been constructed and validated for the determination of octreotide in its authentic form and pharmaceutical dosage form. Octreotide is an important synthetic analog of the naturally occurring somatostatin hormone. The developed spectrofluorimetric approach is actually dependent on the measurement of octreotide native fluorescence at emission wavelength of 342 nm after excitation at 218 nm. At optimal reaction circumstances, the calibration curve has been constructed over the concentration range of 200- 2000 ng ml^-1 , with excellent linearity. The limits of detection and quantitation values were found to be 55 and 169 ng ml^-1 , respectively. The developed approach has been effectively used to determine octreotide in its pharmaceutical ampoules, without interference from the excipients in the dosage form. The developed approach is simple, time-saving, and does not require multiple pretreatment steps for samples, costly apparatus, or dangerous materials. As a result, it can be actually used to detect and quantify octreotide acetate in quality control laboratories.

Magnetic solid-phase extraction of high molecular weight peptides using stearic acid-functionalized magnetic hydroxyapatite nanocomposite: determination of some hypothalamic agents in biological samples

Therapeutic peptides have an important effect on physiological function and human health, so it is momentous to quantify and detect low levels of these biomolecules in biological samples for treatment and diagnostic purposes. In the present study, an efficient magnetic solid-phase extraction (MSPE) method was developed based on stearic acid-functionalized magnetic hydroxyapatite nanocomposite (MHAP/SA) as a novel and cost-effective adsorbent for extraction of five hypothalamic-related peptides (goserelin, octreotide, triptorelin, somatostatin, and cetrorelix) from biological samples. To characterize the morphology and physicochemical properties of MHAP/SA, Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning microscopy (FE-SEM), CHNS elemental analysis, Brunauer-Emmett-Teller (BET), and vibrating sample magnetometry (VSM) were applied. Under optimum conditions, the proposed method (MSPE-HPLC-UV) represented favorable linearity with R² ≥ 0.9987, suitable intra- and inter-day precisions (RSD ≤ 6.9% and RSD ≤ 8.1%, respectively, n = 3), and limits of detection and quantification in the range of 0.75-1.12 ng mL^-1 and 2.50-3.75 ng mL^-1, respectively. Eventually, the proposed method was used for the extraction and quantification of target therapeutic peptides in plasma and urine samples, and satisfactory relative recoveries were achieved in the range of 90.6-110.3%.

Hydrophilic Interaction Liquid Chromatography Coupled with Fluorescence Detection (HILIC-FL) for the Quantitation of Octreotide in Injection Forms

Octreotide is a synthetic cyclic octapeptide analogue of somatostatin-14. It is mainly administered for the treatment of acromegaly, severe diarrhea, and neuroendocrine neoplasias. In this work, a hydrophilic interaction liquid chromatography (HILIC) method with fluorescence (FL) detection was developed and validated for the quantitation of octreotide in solutions for injection. Chromatographic separation was performed on an XBridge®-HILIC analytical column under isocratic elution with a short chromatographic run time of less than 10 min. The mobile phase consisted of ammonium bicarbonate 8.6 mM (pH 8.1)/acetonitrile 35/65 (v/v). The high sensitivity and selectivity of the fluorescence detection, with the excitation wavelength (λexcitation) set at 280 nm and the emission wavelength set at (λemission) 330 nm, enabled a simple sample preparation procedure that included only dilution steps. The calibration curve showed good linearity with a correlation coefficient greater than 0.998. The method was successfully applied to the analysis of commercially available octreotide injection forms.

Salcaprozate sodium (SNAC) enhances permeability of octreotide across isolated rat and human intestinal epithelial mucosae in Ussing chambers

Octreotide is approved as a one-month injectable for treatment of acromegaly and neuroendocrine tumours. Oral delivery of the octapeptide is a challenge due mainly to low intestinal epithelial permeability. The intestinal permeation enhancer (PE) salcaprozate sodium (SNAC) has Generally Regarded As Safe (GRAS) status and is a component of an approved oral peptide formulation. The purpose of the study was to examine the capacity of salcaprozate sodium (SNAC), to increase its permeability across isolated rat intestinal mucosae from five regions and across human colonic mucosae mounted in Ussing chambers. Apical-side buffers were Kreb's-Henseleit (KH), fasted simulated intestinal fluid (FaSSIF-V2), rat simulated intestinal fluid (rSIF), and colonic simulated intestinal fluid (FaSSCoF). The basal apparent permeability coefficient (P_app) of [³H]-octreotide was equally low across rat intestinal regional mucosae in KH, rSIF, and FaSSIF-V2. Apical addition of 20 mM SNAC increased the P_app across rat tissue in KH: colon (by 3.2-fold) > ileum (3.4-fold) > upper jejunum (2.3-fold) > duodenum (1.4-fold) > stomach (1.4-fold). 20 mM and 40 mM SNAC also increased the P_app by 1.5-fold and 2.1-fold respectively across human colonic mucosae in KH. Transepithelial electrical resistance (TEER) values were reduced in the presence in SNAC especially in colonic regions. LC-MS/MS analysis of permeated unlabelled octreotide across human colonic mucosae in the presence of SNAC indicated that [³H]-octreotide remained intact. No gross damage was caused to rat or human mucosae by SNAC. Attenuation of the effects of SNAC was seen in rat jejunal mucosae incubated with FaSSIF-V2 and rSIF, and also to some extent in human colonic mucosae using FaSSCoF, suggesting interaction between SNAC with buffer components. In conclusion, SNAC showed potential as an intestinal permeation enhancer for octreotide, but in vivo efficacy may be attenuated by interactions with GI luminal fluid contents.

Sensitive quantification of the somatostatin analog AP102 in plasma by ultra-high pressure liquid chromatography-tandem mass spectrometry and application to a pharmacokinetic study in rats

AP102 is a di-iodinated octapeptide somatostatin agonist (SSA) designed to treat acromegaly and neuroendocrine tumors. A sensitive and selective method was validated for the quantification of AP102 in plasma following the European Medicines Agency (EMA) and Food and Drug Administration (FDA) guidelines. Sample preparation was performed using solid-phase extraction microplates. Chromatographic separation was achieved on an ultra-high pressure liquid chromatography (UHPLC) C18 column in 6.0 minutes. The compounds were quantified using multiple reaction monitoring on a tandem quadrupole mass spectrometer with ¹³ C,¹⁵ N-labeled AP102 as internal standard. Calibration ranged from 50 to 10000 pg/mL. The lower limit of quantification (LLOQ) was measured at 20 pg/mL, and robust analytical performances were obtained with trueness at 99.2%-100.0%, intra-assay imprecision at 2.5%-4.4%, and inter-assay imprecision at 8.9%-9.7%. The accuracy profiles (total error) built on the 3 concentrations levels showed accuracy within the 70%-130% range. AP102 is remarkably stable since no proteolytic fragments were detected on plasma samples analyzed by Orbitrap-MS. Pharmacokinetic studies were conducted in rats, after single dose (1, 3, and 10 μg/kg, sc) and continuous subcutaneous administration (osmotic minipumps for 28 days, 3.0 or 10.0 μg/kg/h). AP102 showed a rapid absorption by the subcutaneous route (T_max : 15-30 minutes) and a fast elimination (t_1/2 : 33-86 minutes). The PK profile of AP102 exhibited a mean clearance of 1.67 L/h and a mean distribution volume at steady state of 7.16 L/kg, about 10-fold higher than those observed with other SSA or non- and mono-iodinated AP102. LogD_7.4 determination confirmed the lipophilic properties of AP102 that might influence its distribution in tissues.

Development of a high-throughput UHPLC-MS/MS (SRM) method for the quantitation of endogenous glucagon from human plasma

BACKGROUND

Published LC-MS/MS methods are not sensitive enough to quantify endogenous levels of glucagon.

RESULTS

An ultra high performance liquid chromatography-MS/MS (SRM) method for the quantitation of endogenous levels glucagon was successfully developed and qualified. A novel 2D extraction procedure was used to reduce matrix suppression, background noise and interferences. Glucagon levels in samples from healthy volunteers were found to agree with radioimmunoassay (RIA) derived literature values. Bland-Altman analysis showed a concentration-dependent positive bias of the LC/MS-MS assay versus an RIA. Both assays produced similar pharmacokinetic profiles, both of which were feasible considering the nature of the study.

CONCLUSION

Our method is the first peer reviewed LC-MS/MS method for the quantitation of endogenous levels of glucagon, and offers a viable alternative to RIA-based approaches.

PK study of octreotide based on LC–MS/MS combining protein precipitation and impurity extraction technique

Aim: To establish a robust methodology for quantitative analysis of therapeutic peptide in biological samples. Materials & Methods: Octreotide was chosen as a model therapeutic peptide, and oxidized-octreotide was synthesized as internal standard. Protein precipitation combining liquid-liquid extraction technique was adopted to enhance the recovery and reduce the endogenous interferences effectively. A LC–MS/MS method for the quantification of octreotide in plasma has been optimized and validated according to FDA guidelines. Results: Linearity, selectivity, accuracy, precision, stability, matrix effect and recovery were within bioanalytical method validation acceptance criteria as FDA guidelines. The methodology was then successfully applied into the studies for octreotide. Conclusion: This robust methodology would be useful for the PK studies for octreotide and other therapeutic peptides.

Reverse-polynomial dilution calibration methodology extends lower limit of quantification and reduces relative residual error in targeted peptide measurements in blood plasma

Matrix effect is the alteration of an analyte's concentration-signal response caused by co-existing ion components. With electrospray ionization (ESI), matrix effects are believed to be a function of the relative concentrations, ionization efficiency, and solvation energies of the analytes within the electrospray ionization droplet. For biological matrices such as plasma, the interactions between droplet components is immensely complex and the effect on analyte signal response not well elucidated. This study comprised of three sequential quantitative analyses: we investigated whether there is a generalizable correlation between the range of unique ions in a sample matrix (complexity); the amount of matrix components (concentration); and matrix effect, by comparing an E. coli digest matrix (∼2600 protein proteome) with phospholipid depleted human blood plasma, and unfractionated, nondepleted human plasma matrices (∼10(7) proteome) for six human plasma peptide multiple reaction monitoring assays. Our data set demonstrated analyte-specific interactions with matrix complexity and concentration properties resulting in significant ion suppression for all peptides (p < 0.01), with nonuniform effects on the ion signals of the analytes and their stable-isotope analogs. These matrix effects were then assessed for translation into relative residual error and precision effects in a low concentration (∼0-250 ng/ml) range across no-matrix, complex matrix, and highly complex matrix, when a standard addition stable isotope dilution calibration method was used. Relative residual error (%) and precision (CV%) by stable isotope dilution were within <20%; however, error in phospholipid-depleted and nondepleted plasma matrices were significantly higher compared with no-matrix (p = 0.006). Finally a novel reverse-polynomial dilution calibration method with and without phospholipid-depletion was compared with stable isotope dilution for relative residual error and precision. Reverse-polynomial dilution techniques extend the Lower Limit of Quantification and reduce error (p = 0.005) in low-concentration plasma peptide assays and is broadly applicable for verification phase Tier 2 multiplexed multiple reaction monitoring assay development within the FDA-National Cancer Institute (NCI) biomarker development pipeline.

A liquid chromatography-mass spectrometry assay for quantification of Exendin[9-39] in human plasma

Exendin[9-39] is a glucagon-like peptide-1 receptor (GLP-R) antagonist and a potential therapeutic drug for treatment of congenital hyperinsulism by lowering insulin concentration in plasma. A specific and sensitive LC-MS/MS method was validated for quantification of Exendin[9-39] in human plasma. Exendin[9-39] and the stable isopically labeled internal standard eluted at 9.2 min and were analyzed by single reaction monitoring (SRM) of the transitions m/z 842.9→991.8 and 848.2→998.8, respectively. The calibration curve was linear in the range 15-1260 ng/mL with a limit of detection of 1.3 ng/mL. The CVs of the standards were 2.7-13.1% within-run and 3.1-13.2% between-run. The matrix effect was >100% and the SPE recovery was 98.4±12.9%. In absence of protease inhibitors, short-term stability at room temperature was only one hour. Accordingly, samples were kept on ice and sample processing was kept below 1h. Human plasma samples from a clinical pilot study in which Exendin[9-39] was administered intravenously were analyzed and concentrations up to 600 ng/mL were reported Plasma samples from the study were stored at -80 °C with internal standard and successfully reanalyzed after 12 months.

UHPLC for the separation of proteins and peptides

There is increasing interest within the pharmaceutical industry in the development of proteins and peptides as drugs in addition to their use as biomarkers. Immunochemistry-based techniques have been traditionally used for the quantitation of proteins and peptides; however, LC-MS-based methodologies are being increasingly adopted as they offer several advantages. UHPLC is well established within the small-molecule community as a means to increase resolution and/or the speed of separations prior to MS detection; however, it is rarely applied to proteins or peptides separations. In this paper, current applications of UHPLC to such separations are reviewed, as well as considerations with regard to the effect of altering various chromatographic parameters.

Quantitative imaging of a therapeutic peptide in biological tissue sections by MALDI MS

BACKGROUND

Therapeutic peptides and proteins are being increasingly explored as potential therapeutic agents for molecular-targeted therapy, and the requirement for quantitative bioanalytical tools for such molecules has been discussed.

RESULTS

The distribution of octreotide, a synthetic octapeptide analog of somatostatin, in the liver and kidney of mice administered with the analog was clearly visualized by MALDI-Imaging MS (IMS). The developed MALDI-IMS analytical method successfully quantified the amount of octreotide on tissue sections (accuracy was 76-127%) and the 2,5-dihydroxybenzoic acid-based normalization method was effective.

CONCLUSION

The results of this study suggest that MALDI-IMS enables the quantification of an administered therapeutic peptide on biological tissue sections, as well as visualization of the in vivo distribution of the peptide.

Challenges in the development of bioanalytical liquid chromatography-mass spectrometry method with emphasis on fast analysis

The development of bioanalytical methods has become more and more challenging over the past years due to very demanding requirements in terms of method reliability, sensitivity, speed of analysis and sample throughput. LC-MS/MS has established itself as a method of choice for routine analysis of biological materials. A development of such method consists of several steps including sample preparation and clean-up step, efficient chromatographic separation, sensitive and selective detection of analytes in complex matrices, a choice of convenient data processing and calibration approach and finally method validation. Each of these steps has its own constraints and challenges, which are discussed in detail in this review. Novel and modern approaches in sample preparation, chromatography and detection are especially emphasized. Attention is paid to proper calibration approach and matrix effects that can seriously affect method accuracy and precision.

Determination of oxyntomodulin, an anorectic polypeptide, in rat plasma using 2D-LC-MS/MS coupled with ion pair chromatography

Polypeptide therapeutics present a challenge for quantitative analysis when using immunoassays or recently, liquid chromatography-tandem mass spectrometry because of their structural similarities to endogenous proteins and peptides in plasma. In this assay, a Waters Oasis® mixed-mode anion exchange (MAX) microelution modified solid phase extraction (SPE) method coupled with two-dimensional reversed phase ion pair chromatography-tandem mass spectrometry was used for the validation and analysis of oxyntomodulin in rat plasma. Oxyntomodulin (OXM) and its isotope labeled internal standard were extracted from rat plasma and analyzed with a chromatographic run time of 8 min. Modified SPE, two-dimensional liquid chromatography coupled with 3-nitrobenzyl alcohol as a mobile phase additive, and monitoring of multiply charged SRM transitions (+7 charge state) of OXM were necessary to achieve a lower limit of quantification of 1 ng/mL. The method was validated with a linear range of 1-1000 ng/mL, with average R² of 0.992, and reversed calculated residuals between -8.6% and 6.0%. Precision and accuracy for inter- and intra-day were determined to be ±17%. Following a complete validation, the method was applied to show utility using rat plasma samples that were intravenously dosed with oxyntomodulin.

Recent advances in column switching sample preparation in bioanalysis

Column switching techniques, using two or more stationary phase columns, are useful for trace enrichment and online automated sample preparation. Target fractions from the first column are transferred online to a second column with different properties for further separation. Column switching techniques can be used to determine the analytes in a complex matrix by direct sample injection or by simple sample treatment. Online column switching sample preparation is usually performed in combination with HPLC or capillary electrophoresis. SPE or turbulent flow chromatography using a cartridge column and in-tube solid-phase microextraction using a capillary column have been developed for convenient column switching sample preparation. Furthermore, various micro-/nano-sample preparation devices using new polymer-coating materials have been developed to improve extraction efficiency. This review describes current developments and future trends in novel column switching sample preparation in bioanalysis, focusing on innovative column switching techniques using new extraction devices and materials.

On-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection for the determination of benzotriazole UV stabilizers in coastal marine and wastewater samples

Benzotriazoles are a group of UV absorbing compounds considered emerging contaminants that are used in different personal care products, and therefore, it is of high interest to develop sensitive and fast methods for investigating their presence in the environment. In this work, we present the development and application of a novel method based on on-line solid-phase extraction coupled to ultra-performance liquid chromatography with tandem mass spectrometry detection (SPE-UPLC-MS/MS) for the determination of seven benzotriazole UV stabilizers (BUVSs) in coastal marine and wastewater samples. This process is compared with a conventional off-line SPE procedure followed by UPLC-MS/MS. The parameters affecting the performance of the sample preparation and determination processes were evaluated. The results indicate that the on-line procedure provides for better sensitivity and reproducibility and is faster and easier than the off-line procedure. The detection limits and quantification limits achieved were in the range of 0.6-4.1 ng∙L(-1) and 2.1-14 ng∙L(-1) and relative standard deviation between 6.2 and 10%. The developed method was applied to coastal marine and wastewater samples from Gran Canaria Island (Spain). All of the BUVSs studied were detected in the samples from wastewater treatment plants and two were found in the seawater samples (UV P in the range of 2.8-4.4 ng∙L(-1) and UV 360 between 3.6 and 5.2 ng∙L(-1)).