Measurement of intracellular ribavirin mono-, di- and triphosphate using solid phase extraction and LC-MS/MS quantification

A novel LC-MS/MS method for the determination of favipiravir ribofuranosyl-5'-triphosphate (T-705-RTP) in human peripheral mononuclear cells

Favipiravir is a broad-spectrum antiviral that is metabolised intracellularly into the active form, favipiravir ribofuranosyl-5'-triphosphate (F-RTP). Measurement of the intracellular concentration of F-RTP in mononuclear cells is a crucial step to characterising the pharmacokinetics of F-RTP and to enable more appropriate dose selection for the treatment of COVID-19 and emerging infectious diseases. The described method was validated over the range 24 - 2280 pmol/sample. Peripheral blood mononuclear cells (PBMCs) were isolated from whole blood and lysed using methanol-water (70:30, v/v) before cellular components were precipitated with acetonitrile and the supernatant further cleaned by weak anion exchange solid phase extraction. The method was found to be both precise and accurate and was successfully utilised to analyse F-RTP concentrations in patient samples collected as part of the AGILE CST-6 clinical trial.

LC-MS/MS separation and quantitation of ribavirin in chicken and comparison of different mass spectrometric platforms

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the analysis of ribavirin in chicken. Samples was extracted with 0.1% formic acid and purified by Hypercarb cartridge prior to LC-MS/MS analysis. The eluates were evaporated to dryness, reconstituted in 1 mL 5mM ammonium acetate containing 5% acetonitrile (v/v) and 0.1% (v/v) formic acid. Chromatographic separation was performed on a Hypercarb analytical column under a gradient elution program with acetonitrile and 0.1% (v/v) formic acid in 5 mM ammonium acetate at a flow rate of 0.6 ml/min. The intraday and interday accuracy ranged from - 7.83 - 1.39%, and - 6.38 - 2.25%, with precisions between 1.34 - 3.88%% and 1.10 - 4.67%. The limits of detection (LODs) and limits of quantitation (LOQs) of ribavirin was 0.1 ng/mL and 0.5 ng/mL, respectively. The method was validated for linearity, accuracy, precision, matrix effect and stability. Application of the method confirmed 3 ribavirin positive samples out of 50 commercial chicken samples, with concentrations of ribavirin ranging from 0.9 μg/kg to 5.8 μg/kg a, respectively. Additionally, both AB Sciex 5500 and Agilent 6945B were proven to be suitable in ribavirin separation and quantification. The described method is suitable for the determination of ribavirin in chicken in analytical practice to monitor illegal addition of this kind of anti-viral drug.

Development and validation of an LC-MS/MS method to quantify the alcohol biomarker phosphatidylethanol 16:0/18:1 in dried blood spots for clinical research purposes

Phosphatidylethanol (PEth) is a group of phospholipids detectable in red blood cells exclusively following ethanol consumption. The primary PEth analog, PEth 16:0/18:1, has an extended half-life in red cells, providing a long window of detection and tremendous potential for the quantification of cumulative alcohol consumption. We developed and validated an LC/MS-MS method to quantify PEth 16:0/18:1 in dried blood spots (DBS) for clinical research purposes. Method development and validation followed FDA guidance but expanded on prior published methods through the evaluation of additional DBS-specific factors such as sample hematocrit, punch location, and spot volume. This method was applied to the quantification of PEth in participant samples.

Analytical Methods for the Determination of Major Drugs Used for the Treatment of COVID-19. A Review

At the beginning of the COVID-19 outbreak (end 2019 - 2020), therapeutic treatments based on approved drugs have been the fastest approaches to combat the new coronavirus pandemic. Nowadays several vaccines are available. However, the worldwide vaccination program is going to take a long time and its success will depend on the vaccine public's acceptance. Therefore, outside of vaccination, the repurposing of existing antiviral, anti-inflammatory and other types of drugs, have been considered an alternative medical strategy for the COVI-19 infection. Due to the broad clinical potential of the drugs, but also to their possible side effects, analytical methods are needed to monitor the drug concentrations in biological fluids and pharmaceutical products. This review deals with analytical methods developed in the period 2015 - July 2021 to detect potential drugs that, according to a literature survey, have been taken into consideration for the treatment of COVID-19. The drugs considered here have been selected on the basis of the number of articles published in the period January 2020-July 2021, using the combination of the keywords: COVID-19 and drugs or SARS-CoV-2 and drugs. A section is also devoted to monoclonal antibodies. Over the period considered, the analytical methods have been employed in a variety of real samples, such as body fluids (plasma, blood and urine), pharmaceutical products, environmental matrices and food.

A selectivity-enhanced ratiometric fluorescence imprinted sensor based on synergistic effect of covalent and non-covalent recognition units for ultrasensitive detection of ribavirin

Development of methods with high selectivity and sensitivity for detection of trace ribavirin (RBV) is of great importance for environmental protection and food safety. Herein, we proposed a simple yet valid strategy to construct the highly selective ratiometric fluorescence sensing platform (BA-LMOFs@MIP) for analysis of RBV based on boric acid-functionalized lanthanide metal-organic framework (BA-LMOFs) coupled with molecularly imprinted polymer (MIP). In this strategy, BA-LMOFs featured with dual-emission and pH-responsive behavior were first synthesized as supporter. Benefiting from boric acid group of BA-LMOFs, RBV was easily immobilized onto its surface, taking advantage of template immobilization-based surface imprinting means to fabricate BA-LMOFs@MIP with dual recognition sites for the first time. The synergistic effect of covalent boronate affinity-based recognition unit and non-covalent imprinting sites enabled BA-LMOFs@MIP to exhibit superior selectivity and binding efficiency to RBV. BA-LMOFs as signal tag endowed BA-LMOFs@MIP with desirable sensitivity, photostability and hydrophilicity. More importantly, BA-LMOFs@MIP-based sensor displayed a wide linear range for RBV from 25 to 1200 ng mL^-1 with a detection limit down to 7.62 ng mL^-1. The sensor was finally applied to RBV determination in real samples, and the obtained results revealed that BA-LMOFs@MIP would be a promising candidate for monitoring of RBV in complex systems.

Challenges and stepwise fit-for-purpose optimization for bioanalyses of remdesivir metabolites nucleotide monophosphate and triphosphate in mouse tissues using LC-MS/MS

•

A robust and reliable LC–MS/MS method for the quantification of RMP and RTP was optimized and validated.

•

The novel method solved the major challenges of direct determination of RMP and RTP in biological matrix through improvement of LC retention, stability and recovery.

•

The method was validated and successfully applied to mouse tissue distribution study.

•

This method provides useful information for further study of remdesivir as well as extends the approach for phosphate determination.

•

The method solved the major challenges for determining RMP and RTP in biological matrix such as LC retention, stability and recovery.

Remdesivir is a prodrug of the nucleotide analogue and used for COVID-19 treatment. However, the bioanalysis of the active metabolites remdesivir nucleotide triphosphate (RTP) and its precursor remdesivir nucleotide monophosphate (RMP) is very challenging. Herein, we established a novel method to separate RTP and RMP on a BioBasic AX column and quantified them by high-performance liquid chromatography-tandem mass spectrometry in positive electrospray ionization mode. Stepwise, we optimized chromatographic retention on an anion exchange column, improved stability in matrix through the addition of 5,5′-dithiobis-(2nitrobenzoic acid) and PhosSTOP EASYpack, and increased recovery by dissociation of tight protein binding with 2 % formic acid aqueous solution. The method allowed lower limit of quantification of 20 nM for RMP and 10 nM for RTP. Method validation demonstrated acceptable accuracy (93.6%–103% for RMP, 94.5%–107% for RTP) and precision (RSD < 11.9 % for RMP, RSD < 11.4 % for RTP), suggesting that it was sensitive and robust for simultaneous quantification of RMP and RTP. The method was successfully applied to analyze RMP and RTP in mouse tissues. In general, the developed method is suitable to monitor RMP and RTP, and provides a useful approach for exploring more detailed effects of remdesivir in treating diseases.

Ribavirin and cellular ribavirin-triphosphate concentrations in blood and bronchoalveolar lavage fluid in two lung transplant patients with respiratory syncytial virus

Respiratory syncytial virus (RSV) is responsible for significant morbidity and mortality in the lung transplant population. Oral and aerosolized ribavirin may improve outcomes in lung transplant patients with RSV; however, data relating ribavirin concentrations in plasma and intracellular ribavirin triphosphate (iRTP) concentrations in blood and bronchoalveolar lavage (BAL) fluid cells with efficacy and safety are lacking. We describe ribavirin and iRTP concentrations within various compartments in two adult lung transplant recipients with RSV who were sampled throughout successful treatment courses with oral and inhaled ribavirin. In patient 1, iRTP BAL concentrations decreased by 45% over 3 days after changing inhaled ribavirin to oral (6.32 to 3.43 pmol/10⁶ cells). In patient 2, iRTP BAL concentrations were 103 pmol/10⁶ cells after 5 days of oral followed by 5 days of inhaled ribavirin. Further study is needed to describe ribavirin pharmacokinetics in the respiratory compartment to inform clinical use of ribavirin for respiratory viruses.

Direct and indirect quantification of phosphate metabolites of nucleoside analogs in biological samples

Nucleoside reverse transcriptase inhibitors (NRTIs) are prodrugs that require intracellular phosphorylation to active triphosphate nucleotide metabolites (NMs) for their pharmacological activity. However, monitoring these pharmacologically active NMs is challenging due to their instability, high hydrophilicity, and their low concentrations in blood and tissues. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard technique for the quantification of NRTIs and their phosphorylated NMs. In this review, an overview of the publications describing the quantitative analysis of intracellular and total tissue concentration of NMs is presented. The focus of this review is the comparison of the different approaches and challenges associated with sample collection, tissue homogenization, cell lysis, cell counting, analyte extraction, sample storage conditions, and LC-MS analysis. Quantification methods of NMs via LC-MS can be categorized into direct and indirect methods. In the direct LC-MS methods, chromatographic retention of the NMs is accomplished by ion-exchange (IEX), ion-pairing (IP), hydrophilic interaction (HILIC), porous graphitic carbon (PGC) chromatography, or capillary electrophoresis (CE). In indirect methods, parent nucleosides are 1st generated from the dephosphorylation of NMs during sample preparation and are then quantified by reverse phase LC-MS as surrogates for their corresponding NMs. Both approaches have advantages and disadvantages associated with them, which are discussed in this review.

Current antiviral drugs and their analysis in biological materials-Part I: Antivirals against respiratory and herpes viruses

This review article is the first in the series providing an overview of currently used antiviral drugs and presenting contemporary approaches to their analysis. Large number of available antivirals and their structural variability makes this task very challenging. Trying to cover this topic comprehensively while maintaining reasonable size of the article, the review is presented in two parts. For the purpose of the overall review, antivirals were divided into four groups: (i) antivirals against herpes viruses, (ii) antivirals against respiratory viruses, (iii) antivirals against hepatitis viruses, and (iv) antivirals against HIV. Part one is devoted to the groups (i) and (ii) and also concerns the key features of the bioanalytical method. The mechanisms of action of antivirals against respiratory and herpes viruses and their use in clinical practice are briefly outlined, and the analytical methods for selected representatives of each class are described in more detail. The methods developed for the determination of drugs from these classes mostly include conventional procedures. In contrast, current trends such as UHPLC are used rarely and proper method validation based on requirements of bioanalytical guidelines can be often considered insufficient.

Effects of ribavirin/sofosbuvir treatment and ITPA phenotype on endogenous purines

Ribavirin (RBV), a purine analog, causes hemolytic anemia in some patients. In vitro, anemia appears to result from depletion of endogenous purines, but there are limited data in vivo. Single nucleotide polymorphisms in the gene encoding the inosine triphosphatase (ITPA) enzyme have been associated with protection against RBV-induced anemia and may mediate the effect of RBV treatment on endogenous purines. The purpose of this work was to determine the effect of RBV treatment on endogenous purine concentrations in individuals being treated for chronic hepatitis C virus (HCV) infection. Adenosine triphosphate (ATP), guanosine triphosphate (GTP), inosine triphosphate (ITP) and ribavirin triphosphate (RTP) were measured in whole blood obtained from 47 HCV-infected individuals at day zero (baseline), day three, day 28 and day 84 of RBV/sofosbuvir (SOF) treatment. ATP decreased -35.1% and -38.6% (p < 0.0001) at day 28 and day 84 of treatment, respectively compared to baseline. The decrease in ATP was greater in patients with ≤60% ITPA activity compared to those with 100% ITPA activity (-29.4% vs. -9.6%). GTP did not change during treatment but was 16.5% (p = 0.01) higher per 100 pmol/106 cells RTP in those with 100% ITPA activity. No significant change or effect of RTP or ITPA phenotype was noted for ITP. In summary, only ATP was reduced by RBV/SOF treatment and ITPA variants had larger reductions in ATP suggesting RBV-induced anemia is due to a different mechanism than predicted from in-vitro studies. These data emphasize the importance of characterizing the effect of nucleos(t)ide analog treatment on endogenous purines in-vivo.

Variant Inosine Triphosphatase Phenotypes Are Associated With Increased Ribavirin Triphosphate Levels

Individuals with lower inosine triphosphatase (ITPA) enzyme activity have a reduced likelihood of experiencing hemolytic anemia during hepatitis C virus (HCV) treatment containing ribavirin (RBV). Because ITPA degrades purines and RBV is a purine analogue, it is conceivable that ITPA activity may affect intracellular RBV concentrations. Here we assessed the association between ITPA activity phenotype and concentrations of RBV triphosphate (RBV-TP) in red blood cells (RBCs) during HCV treatment. RBV-TP was quantified in the RBCs of 177 HCV-infected individuals at a median (range) of 84 (19 to 336) days into HCV treatment that included RBV. Mean (SD) RBV-TP concentrations were 92.8 (51.6), 101.3 (53.5), 184.8 (84.5), and 197.7 (64.6) pmol/106 cells for 100%, 60%, 30%, and ≤10% ITPA activity groups, respectively. Overall, RBV-TP was approximately 2-fold higher in patients with ≤30% ITPA activity compared to 100% activity (P < .0001). Despite higher RBV-TP levels, individuals with variant ITPA phenotypes had less anemia. The 100% activity group had, on average, a -2.20 g/dL drop in hemoglobin vs -1.43 g/dL (P = .04) for 60% activity, -1.14 g/dL (P = .008) for 30% activity, and -0.70 g/dL (P = .06) for ≤10% activity. This finding of higher RBV-TP concentrations in RBCs in ITPA variants was unexpected given that ITPA activity-deficient individuals have a reduced likelihood of RBV-induced anemia. It also refutes the hypothesis that the mechanism by which ITPA variants are protected against anemia is due to lower RBV-TP levels in RBCs.

A LC-MS/MS Method for Quantifying Adenosine, Guanosine and Inosine Nucleotides in Human Cells

PURPOSE

To develop and validate a method for the simultaneous measurement of adenosine, guanosine, and inosine derived from mono (MP) and triphosphate (TP) forms in peripheral blood mononuclear cells (PBMCs), red blood cells (RBCs) and dried blood spots (DBS).

METHODS

Solid phase extraction of cell lysates followed by dephosphorylation to molar equivalent nucleoside and LC-MS/MS quantification.

RESULTS

The assay was linear for each of the three quantification ranges: 10-2000, 1.0-200 and 0.25-50 pmol/sample for adenosine, guanosine, and inosine, respectively. Intraassay (n = 6) and interassay (n = 18) precision (%CV) were within 1.7 to 16% while accuracy (%deviation) was within -11.5 to 14.7% for all three analytes. Nucleotide monophosphates were less concentrated than triphosphates (except for inosine) and levels in PBMCs were higher than RBCs for all three nucleotides (10, 55, and 5.6 fold for ATP, GTP and ITP, respectively). DBS samples had an average (SD) of -26% (22.6%) lower TP and 184% (173%) higher MP levels compared to paired RBC lysates, suggesting hydrolysis of the TP in DBS.

CONCLUSION

This method was accurate and precise for physiologically relevant concentrations of adenosine, guanosine and inosine nucleotides in mono- and triphosphate forms, providing a bioanalytical tool for quantitation of nucleotides for clinical studies.

Plasma and intracellular ribavirin concentrations are not significantly altered by abacavir in hepatitis C virus-infected patients

OBJECTIVES

The objective of this study was to evaluate the effects of abacavir on intracellular ribavirin triphosphate and plasma ribavirin trough concentrations.

METHODS

Hepatitis C virus-infected subjects who had been cured or failed prior treatment were randomized to 8 weeks of ribavirin alone (N = 14; weight-based dosing) or weight-based ribavirin + abacavir (N = 14; 300 mg orally every 12 h). Ribavirin trough concentrations were measured on days 14, 28, 42 and 56; PBMCs for ribavirin triphosphate determination were sampled on days 28 and 56, pre-dose and at 6 and 12 h post-dose. ClinicalTrials.gov: NCT01052701.

RESULTS

Twenty-six subjects completed the study (24 males, 17 Caucasians, median age 52 years); 2 were excluded for missed pharmacokinetic visits. Fourteen subjects received ribavirin + abacavir and 12 received ribavirin alone. Mean ± SD plasma ribavirin trough concentrations (μg/mL) on days 14, 28, 42 and 56, respectively, were not significantly different with coadministration of abacavir (1.54 ± 0.60, 1.93 ± 0.54, 2.14 ± 0.73 and 2.54 ± 1.05) compared with ribavirin alone (1.48 ± 0.32, 2.08 ± 0.41, 2.32 ± 0.47 and 2.60 ± 0.62) (P > 0.40). Mean ribavirin triphosphate intracellular concentrations (pmol/10(6) cells) on days 28 and 56, respectively, did not differ statistically between abacavir users (11.98 ± 9.86 and 15.87 ± 12.52) and non-users (15.91 ± 15.58 and 15.93 ± 12.69) (P > 0.4). Adverse events were mild or moderate, except for three grade 3 occurrences of transaminitis, cholecystitis and low absolute neutrophil count that resolved and were judged not attributable to study medications.

CONCLUSIONS

Abacavir did not significantly alter ribavirin or ribavirin triphosphate concentrations.

Validation and Application of a Liquid Chromatography-Tandem Mass Spectrometry Method To Determine the Concentrations of Sofosbuvir Anabolites in Cells

Sofosbuvir (SOF) is a highly efficacious and well-tolerated uridine nucleotide analog that inhibits the hepatitis C virus (HCV) NS5B polymerase enzyme. SOF is administered as a prodrug, which undergoes intracellular phosphorylation by host enzymes to a monophosphate, diphosphate, and finally a pharmacologically active triphosphate. In order to fully understand the clinical pharmacology of SOF, there is a great need to determine the intracellular phosphate concentrations of the drug. We describe the validation and utilization of a method to characterize SOF's disposition into various in vivo cell types, including hepatocytes, peripheral blood mononuclear cells (PBMC), and red blood cells (RBC). Standard bioanalytical validation criteria were applied to lysed cellular matrices, with a validated linear range of 50 to 50,000 fmol/sample for each phosphate moiety. The assay was utilized to collect the first data demonstrating concentrations of phosphorylated anabolites formed in PBMC, hepatocytes, and RBC in vivo during SOF therapy. Median concentrations in PBMC were 220 (range, 51.5 to 846), 70.2 (range, 25.8 to 275), and 859 (range, 54.5 to 6,756) fmol/10(6) cells in the monophosphate, diphosphate, and triphosphate fractions, respectively. In contrast, RBC triphosphate concentrations were much lower than those of PBMC, as the median concentration was 2.91 (range, 1.14 to 10.4) fmol/10(6) cells. The PBMC triphosphate half-life was estimated at 26 h using noncompartmental approaches, while nonlinear mixed-effect modeling was used to estimate a 69 h half-life for this moiety in RBC. The validated method and the data it generates provide novel insight into the cellular disposition of SOF and its phosphorylated anabolites in vivo.

Serum and cellular ribavirin pharmacokinetic and concentration-effect analysis in HCV patients receiving sofosbuvir plus ribavirin

OBJECTIVES

Ribavirin concentrations may impact hepatitis C virus (HCV) treatment outcome. We modelled ribavirin serum and intracellular ribavirin monophosphate (RBV-MP) and ribavirin triphosphate (RBV-TP) pharmacokinetics in red blood cells (RBC) using samples collected during the NIAID SPARE trial to explore associations with treatment outcome and the development of anaemia.

PATIENTS AND METHODS

Individuals infected with HCV genotype 1 (GT1) received 400 mg of sofosbuvir and either low-dose or weight-based ribavirin as part of the NIAID SPARE trial. Concentrations were modelled using NONMEM and associated with treatment outcomes using unpaired t-tests or Pearson's rho correlations.

RESULTS

Average day 14 RBV-MP concentrations were higher in subjects with haemoglobin nadir <10 g/dL relative to patients with haemoglobin nadir ≥10 g/dL (6.54 versus 4.48 pmol/10(6) cells; P = 0.02). Additionally, day 14 RBV-MP average concentrations trended towards being higher in subjects that achieved sustained virological response (SVR) as compared with patients who relapsed (4.97 versus 4.09 pmol/10(6) cells; P = 0.07). Receiver operating characteristic curves suggested day 14 RBV-MP concentration thresholds of 4.4 pmol/10(6) cells for SVR (P = 0.06) and 6.1 pmol/10(6) cells for haemoglobin nadir <10 versus ≥10 g/dL (P = 0.02), with sensitivity and specificity ≥60%. Dosing simulations showed that 800 mg of ribavirin once daily produced day 14 RBV-MP concentrations within the 4.4-6.1 pmol/10(6) cells range.

CONCLUSIONS

RBV-MP concentrations in RBC at day 14 were related to anaemia and SVR. A therapeutic range was identified for RBV-MP in persons with HCV GT1 disease receiving 24 weeks of sofosbuvir plus ribavirin, suggesting a potential pharmacological basis for individualized ribavirin dosing in IFN-free regimens.

Population pharmacokinetic modeling of plasma and intracellular ribavirin concentrations in patients with chronic hepatitis C virus infection

Ribavirin, a guanosine analog, is a broad-spectrum antiviral agent. Ribavirin has been a fundamental component of the treatment of hepatitis C virus (HCV) infection for decades, but there is a very limited understanding of the clinical pharmacology of this drug. Furthermore, it is associated with a major dose-limiting toxicity, hemolytic anemia. Ribavirin undergoes intracellular phosphorylation by host enzymes to ribavirin monophosphate (RMP), ribavirin diphosphate (RDP), and ribavirin triphosphate (RTP). The intracellular forms have been associated with antiviral and toxic effects in vitro, but the kinetics of these phosphorylated moieties have not been fully elucidated in vivo. We developed a model to characterize the plasma pharmacokinetics of ribavirin and the difference between intracellular phosphorylation kinetics in red cells (nonnucleated) and in peripheral blood mononuclear cells (nucleated). A time-independent two-compartment model with first-order absorption described the plasma data well. The cellular phosphorylation kinetics was described by a one-compartment model for RMP, with the formation rate driven by plasma concentrations and the first-order degradation rate. RDP and RTP rapidly reached equilibrium with RMP. Concomitant telaprevir use, inosine triphosphatase genetics, creatinine clearance, weight, and sex were significant covariates. The terminal ribavirin half-life in plasma and phosphorylated anabolites in cells was approximately 224 h. We found no evidence of time-dependent kinetics. These data provide a foundation for uncovering concentration-effect associations for ribavirin and determining the optimal dose and duration of this drug for use in combination with newer direct-acting HCV agents. (This study has been registered at ClinicalTrials.gov under registration no. NCT01097395.).