Women Administered Standard Dose Imatinib for Chronic Myeloid Leukemia Have Higher Dose-Adjusted Plasma Imatinib and Norimatinib Concentrations Than Men.

BACKGROUND: The standard dose of imatinib for the treatment of chronic-phase chronic myeloid leukemia (CML) is 400 mg·d. A predose plasma imatinib concentration of >1 mg·L is associated with improved clinical response. This study aimed to assess the plasma imatinib and norimatinib concentrations attained in patients with chronic myeloid leukemia administered standard doses of imatinib adjusted for dose, age, sex, body weight, and response. METHODS: We evaluated data from a cohort of patients treated between 2008 and 2014 with respect to dose, age, sex, body weight, and response. RESULTS: The study comprised 438 samples from 93 patients (54 male, 39 female). The median imatinib dose was 400 mg·d in men and in women. The plasma imatinib concentration ranged 0.1-5.0 mg·L and was below 1 mg·L in 20% and 16% of samples from men and women, respectively. The mean dose normalized plasma imatinib and norimatinib concentrations were significantly higher in women in comparison with men. This was partially related to body weight. Mixed effects ordinal logistic regression showed no evidence of an association between sex and plasma imatinib (P = 0.13). However, there was evidence of an association between sex and plasma norimatinib, with higher norimatinib concentrations more likely in women than in men (P = 0.02). CONCLUSIONS: Imatinib therapeutic drug monitoring only provides information on dosage adequacy and on short-term adherence; longer-term adherence cannot be assessed. However, this analysis revealed that approximately 1 in 5 samples had a plasma imatinib concentration <1 mg·L, which was suggestive of inadequate dosage and/or poor adherence and posed a risk of treatment failure. Higher imatinib exposure in women may be a factor in the increased rate of long-term, stable, deep molecular response (undetectable breakpoint cluster-Abelson (BCR-ABL) transcript levels with a PCR sensitivity of 4.5 log, MR4.5) reported in women.

Automated Analysis of Clozapine and Norclozapine in Human Plasma Using Novel Extraction Plate Technology and Flow-Injection Tandem Mass Spectrometry.

BACKGROUND: Analysis of plasma clozapine and N-desmethylclozapine (norclozapine) for therapeutic drug monitoring purposes is well established. To minimize analysis times and facilitate rapid reporting of results, we have fully automated sample preparation using novel AC Extraction Plates and a Tecan Freedom EVO 100 liquid handling platform, and minimized extract analysis times using flow-injection tandem mass spectrometry (FIA-MS/MS). METHODS: Analytes and deuterium-labeled internal standards were extracted from plasma (100 µL) at pH 10.6 and extracts analyzed directly using tandem mass spectrometry [20 µL injection, 0.7 mL/min methanol carrier flow, analysis time (injection-to-injection) approximately 60 seconds]. RESULTS: Validation data showed excellent intraplate and interplate accuracy (95%-104% nominal concentrations). Interbatch precision (% RSD) at the limit of quantitation (0.01 mg/L) was 3.5% and 5.5% for clozapine and norclozapine, respectively. Matrix effects were observed for both clozapine and norclozapine, but were compensated for by the internal standards. Overall process efficiency was 56%-70% and 66%-77% for clozapine and norclozapine, respectively. Mean relative process efficiency was 98% and 99% for clozapine and norclozapine, respectively. Comparison of results from patient samples (n = 81) analyzed using (1) manual liquid-liquid extraction with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and (2) automated extraction with FIA-MS/MS gave y = 1.01x - 0.002, R(2) = 0.9943 and y = 1.01x + 0.009, R(2) = 0.9957 for clozapine and norclozapine, respectively. Bland-Altman plots revealed a [mean (95% limits of agreement) bias of 0.0074 (-0.04 to 0.06) mg/L and of 0.015 (-0.02 to 0.05) mg/L for clozapine and norclozapine, respectively]. CONCLUSIONS: FIA-MS/MS used with automated extraction offers a rapid, simple, cost-effective alternative to manual liquid-liquid extraction and conventional LC analysis for clozapine therapeutic drug monitoring.

Tyrosine kinase inhibitors impair B-cell immune responses in CML through off-target inhibition of kinases important for cell signaling.

Tyrosine kinase inhibitors (TKIs) have significant off-target multikinase inhibitory effects. We aimed to study the impact of TKIs on the in vivo B-cell response to vaccination. Cellular and humoral responses to influenza and pneumococcal vaccines were evaluated in 51 chronic phase chronic myeloid leukemia (CML) patients on imatinib, or second-line dasatinib and nilotinib, and 24 controls. Following vaccination, CML patients on TKI had significant impairment of IgM humoral response to pneumococcus compared with controls (IgM titer 79.0 vs 200 U/mL, P = .0006), associated with significantly lower frequencies of peripheral blood IgM memory B cells. To elucidate whether CML itself or treatment with TKI was responsible for the impaired humoral response, we assessed memory B-cell subsets in paired samples collected before and after imatinib therapy. Treatment with imatinib was associated with significant reductions in IgM memory B cells. In vitro coincubation of B cells with plasma from CML patients on TKI or with imatinib, dasatinib, or nilotinib induced significant and dose-dependent inhibition of Bruton's tyrosine kinase and indirectly its downstream substrate, phospholipase-C-γ2, both important in B-cell signaling and survival. These data indicate that TKIs, through off-target inhibition of kinases important in B-cell signaling, reduce memory B-cell frequencies and induce significant impairment of B-cell responses in CML.

A novel approach to quantitative LC-MS/MS: therapeutic drug monitoring of clozapine and norclozapine using isotopic internal calibration.

Therapeutic drug monitoring (TDM) requires timely results in order to be clinically helpful. Such assays, when carried out using mass spectrometry-based methods, typically involve a batched sample approach with multipoint calibration. Isotopic internal calibration offers the possibility of open-access mass spectrometric analysis with consequent shortening of turnaround times. We measured plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in (1) external quality assessment (EQA) samples (N = 22) and (2) patient samples (N = 100) using liquid chromatography-tandem mass spectrometry with isotopic internal calibration (ICAL-LC-MS/MS). Analyte concentrations were calculated from graphs of the response of three internal calibrators (clozapine-D4, norclozapine-D8, and clozapine-D8) against concentration. Precision (% RSD) and accuracy (% nominal concentrations) for the ICAL-LC-MS/MS method were <5 % and 104-112 %, respectively for both analytes. There was excellent agreement with consensus mean and with 'spiked' values on analysis of the EQA samples (R (2) = 0.98 and 0.97, respectively, inclusive of clozapine and norclozapine results). In the patient samples, comparison against traditionally calibrated HPLC-UV and LC-MS/MS methods showed excellent agreement (R (2) = 0.97 or better) with small albeit significant mean differences (<0.041 and <0.042 mg/L for clozapine and norclozapine, respectively). These differences probably reflect discrepancies in the in-house preparation of calibrators and/or interference in the UV method. Internal calibration offers a novel and attractive alternative to traditionally calibrated batch analysis in analytical toxicology. The method described has been validated for use in the high-throughput TDM of clozapine and norclozapine, and allows for (1) same-day reporting of results and (2) significant cost savings.

Analytical Detection of Novel Stimulants by Immunoassay and Liquid Chromatography-High Resolution Mass Spectrometry: Case Studies on Ethylphenidate and Mephedrone.

The advent of hundreds of new compounds aimed at the substance misuse market has posed new analytical challenges. A semi-quantitative liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method has been developed to detect exposure to two novel stimulants, mephedrone and ethylphenidate, and selected metabolites. Centrifuged urine (50 µL) was diluted with LC eluent containing internal standards (mephedrone-d3, methylphenidate-d9 and ritalinic acid-d10; all 0.02 mg/L) (450 µL). Intra- and inter-assay accuracy and precision were within ±15% and <6%, respectively, for all analytes. The limit of detection was 0.01 mg/L for all analytes. Urine samples from mephedrone and ethylphenidate users were analyzed using immunoassay (amphetamine-group cloned enzyme donor immunoassay [CEDIA]) and LC-HRMS. Ethylphenidate, mephedrone and selected metabolites all had low cross-reactivity (<1%) with the immunoassay. The median (range) amphetamine-group CEDIA concentration in urine samples from mephedrone users (n = 11) was 0.30 (<0.041-3.04) mg/L, with only 1 sample giving a positive CEDIA result. The amphetamine-group CEDIA concentration in the urine sample from an ethylphenidate user was <0.041 mg/L. Improving the detection of novel compounds is of increasing importance to enable accurate diagnosis and treatment. Immunoassay methods used for drug screening may be inappropriate and lead to false-negative results. Conversely, detection of these compounds is possible through use of LC-HRMS and can provide information on the metabolites present after exposure to these drugs.

Buprenorphine detection in urine using liquid chromatography-high-resolution mass spectrometry: comparison with cloned enzyme donor immunoassay (ThermoFisher) and homogeneous enzyme immunoassay (immunalysis).

A sensitive liquid chromatographic-high-resolution mass spectrometric (LC-HR-MS) assay for buprenorphine and its urinary metabolites has been developed that requires minimal sample preparation. The results obtained have been compared with those given by (i) cloned enzyme donor immunoassay (CEDIA) and (ii) homogeneous enzyme immunoassay (HEIA) in the analysis of patient urines submitted for buprenorphine analysis. Centrifuged urine (100 µL) was diluted with internal standard solution (25 µL) + LC eluent (875 µL), and 50 µL of the prepared sample were analyzed (Accucore Phenyl-Hexyl column). MS detection was in alternating positive and negative mode using heated electrospray ionization (ThermoFisher Q Exactive). Intra- and inter-assay accuracy and precision were 104-128 and <11%, respectively, at 5 µg/L. Limits of detection were 1.3 µg/L (buprenorphine, norbuprenorphine and buprenorphine glucuronide) and 2.5 µg/L (norbuprenorphine glucuronide). Immunoassay sensitivity and selectivity were 97 and 100% (HEIA) and 99 and 84% (CEDIA), respectively, compared with LC-HR-MS. In 120 patient urines, norbuprenorphine glucuronide was easily the most abundant analyte except when adulteration with buprenorphine had occurred. The median immunoreactive buprenorphine species present (unhydrolysed urine) were 7.5 and 13% for HEIA and CEDIA, respectively. However, codeine, dihydrocodeine, morphine and morphine-3-glucuronide did not interfere in the HEIA assay.

Genetic differences in cytochrome P450 enzymes and antidepressant treatment response.

AIMS: Antidepressant response varies between patients, possibly due to differences in the rate cytochrome P450 enzymes metabolise antidepressants into inactive compounds. Drug metabolism rates are influenced by common variants in the genes encoding these enzymes. However, it remains unclear whether treatment outcomes can be predicted by either CYP450 genotype or antidepressant serum concentration. METHODS: In GENDEP (a pharmacogenetic study of depressed individuals treated with either escitalopram or nortriptyline), serum concentrations of antidepressants and their primary metabolite were measured after eight weeks treatment and variants in CYP2D6 and CYP2C19 were genotyped. RESULTS: Amongst patients taking escitalopram (n=223), the genotype CYP2C19 was significantly associated with escitalopram serum concentrations and desmethylescitalopram:escitalopram ratio. For those taking nortriptyline (n=161), the CYP2D6 genotype was significantly associated with nortriptyline and 10-hydroxynortriptyline serum concentrations and 10-hydroxynortriptyline:nortrip-tyline ratio. CYP450 genotypes conferring greater enzyme activity were linked to lower drug serum concentrations and higher metabolite:drug ratios. Nonetheless, no significant association was found between either CYP450 genotype or antidepressant serum concentration and treatment response. CONCLUSIONS: While there is a significant relationship between the CYP450 genotype and serum concentrations of escitalopram and nortriptyline, the genotypes are not predictive of differences in treatment response for either drug. Furthermore, differences in antidepressant serum concentrations are not associated with variability in treatment response.