Discrepancies between Dihydropyrimidine dehydrogenase phenotyping and genotyping: what are the explanatory factors?

AIM

Dihydropyrimidine dehydrogenase (DPD) deficiency can be detected by phenotyping (measurement of plasma uracil (U), with U≥16μg/L defining a partial deficiency) and/or by genotyping (screening for the four most frequent DPYD variants). We aimed to determine the proportion of discrepancies between phenotypic and genotypic approaches and to identify possible explanatory factors.

METHODS

Data from patients who underwent both phenotyping and genotyping were retrospectively collected. Complementary genetic analyses (genotyping of the variant c.557A>G and DPYD sequencing) were performed for patients with U≥16μg/L without any common variants. The characteristics of patients classified according to the congruence of the phenotyping and genotyping approaches were compared (Kruskal-Wallis test) and determinants of U levels were studied in the whole cohort (linear model).

RESULTS

Among the 712 included patients, phenotyping and genotyping were discordant for 12.5%, with 63 (8.8%) having U≥16μg/L in the absence of a common variant. Complementary genetic investigations marginally reduced the percentage of discrepancies to 12.1%: among the nine additional identified variants, only the c.557A>G variant, carried by three patients, had been previously reported to be associated with DPD deficiency. Liver dysfunction could explain certain discordances, as ASAT, ALP, GGT, and bilirubin levels were significantly elevated, with more frequent liver metastases in patients with U≥16μg/L and the absence of a DPYD variant. The impact of cytolysis was confirmed, as ASAT levels were independently associated with increased U (p<0.001).

CONCLUSION

The frequent discordances between DPD phenotyping and genotyping approaches highlight the need to perform these two approaches to screen for all DPD deficiencies.

Variability of Tacrolimus Trough Concentration in Liver Transplant Patients: Which Role of Inflammation?

Tacrolimus presents high intra and inter-individual variability in its blood trough concentration (Cmin). Knowledge of the factors that are involved in tacrolimus Cmin variability is thus clinically important to prevent or limit it. Inflammation can affect the pharmacokinetic properties of drugs. We evaluated the contribution of acute inflammation in the pharmacokinetic variability of tacrolimus blood Cmin in a large cohort of liver transplant patients. Demographic, biological, and clinical data from 248 liver transplant patients treated with tacrolimus from January 2010 to December 2016 were retrospectively collected from medical records. In total, 1573 Cmin/dose and concomitant C-reactive protein (CRP) measurements were analysed. In multivariate analysis, the log Cmin/dose of tacrolimus was significantly and positively associated with the hematocrit, ALAT, and CRP concentrations. CRP concentrations were higher (p = 0.003) for patients with tacrolimus overexposure (i.e., tacrolimus Cmin > 15 µg/L) (median CRP (10th–90th percentiles): 27 mg/L (3–149 mg/L), n = 91) than they were for patients with a tacrolimus Cmin ≤ 15 µg/L (13 mg/mL (3–95 mg/L), n = 1482)). CRP in the fourth quartile (49 to 334 mg/L) was associated with a 2.6-fold increased risk of tacrolimus Cmin overexposure. Our study provides evidence that inflammation contributes to tacrolimus Cmin variability and suggests that inflammation should be considered for the correct interpretation of tacrolimus blood concentration.

A simple and easy-to-perform liquid chromatography-mass spectrometry method for the quantification of tacrolimus and its metabolites in human whole blood. Application to the determination of metabolic ratios in kidney transplant patients

Tacrolimus is the cornerstone of immunosuppressive therapy in solid organ transplantation and its blood concentrations are routinely monitored. Tacrolimus is extensively metabolized into metabolites that are supposed to be nephrotoxic. Yet, few analytical methods have been described to simultaneously quantify tacrolimus and its main metabolites. We developed and validated a simple liquid chromatography-mass spectrometry method for the quantification of tacrolimus and its three desmethylated metabolites, 13-O, 15-O, and 31-O-desmethylated tacrolimus (M-I, M-III, and M-II respectively) in human whole blood. Protein precipitation of 50 µL of whole blood with 100 µL methanol and zinc sulfate was used as a single-extraction procedure. Tacrolimus and its metabolites were quantified using electrospray ionization-triple quadrupole mass spectrometry in combination with selected reaction monitoring detection in the positive ionization mode. The method was validated following FDA recommendations. This method was precise (intra- and inter-assay coefficients of variation: 2.88-7.81% and 3.96-12.10% for low and high levels of internal quality controls, respectively) and accurate (intra- and inter-assay biases: -1.67-10.30%, and -0.77--9.36%, respectively). In adult kidney transplant patients who were treated with tacrolimus prolonged release formulation, the median (10th-90th percentiles) trough concentrations (n = 16) of tacrolimus, M-I, and M-III were 5.85 (3.37-7.09), 0.100 (0.037-0.168), 0.051 (0.03-0.104), respectively. M-II was measured in only 2 trough samples. The metabolic ratios M-I/tacrolimus and M-III/tacrolimus were 0.017 (0.009-0.027) and 0.009 (0.006-0.015) when measured on trough concentration and 0.022 (0.011-0.037) and 0.008 (0.006-0.015) when measured on area under the curves 0-24 h. This method is a suitable and easy-to-perform tool for future pharmacokinetic-pharmacodynamics studies investigating the importance of tacrolimus and its metabolites blood exposure for solid organ graft survival.

Preservation of epoxyeicosatrienoic acid bioavailability prevents renal allograft dysfunction and cardiovascular alterations in kidney transplant recipients

This study addressed the hypothesis that epoxyeicosatrienoic acids (EETs) synthesized by CYP450 and catabolized by soluble epoxide hydrolase (sEH) are involved in the maintenance of renal allograft function, either directly or through modulation of cardiovascular function. The impact of single nucleotide polymorphisms (SNPs) in the sEH gene EPHX2 and CYP450 on renal and vascular function, plasma levels of EETs and peripheral blood monuclear cell sEH activity was assessed in 79 kidney transplant recipients explored at least one year after transplantation. Additional experiments in a mouse model mimicking the ischemia–reperfusion (I/R) injury suffered by the transplanted kidney evaluated the cardiovascular and renal effects of the sEH inhibitor t-AUCB administered in drinking water (10 mg/l) during 28 days after surgery. There was a long-term protective effect of the sEH SNP rs6558004, which increased EET plasma levels, on renal allograft function and a deleterious effect of K55R, which increased sEH activity. Surprisingly, the loss-of-function CYP2C9*3 was associated with a better renal function without affecting EET levels. R287Q SNP, which decreased sEH activity, was protective against vascular dysfunction while CYP2C8*3 and 2C9*2 loss-of-function SNP, altered endothelial function by reducing flow-induced EET release. In I/R mice, sEH inhibition reduced kidney lesions, prevented cardiac fibrosis and dysfunction as well as preserved endothelial function. The preservation of EET bioavailability may prevent allograft dysfunction and improve cardiovascular disease in kidney transplant recipients. Inhibition of sEH appears thus as a novel therapeutic option but its impact on other epoxyfatty acids should be carefully evaluated.

Optimization of voriconazole therapy for treatment of invasive aspergillosis: Pharmacogenomics and inflammatory status need to be evaluated

AIMS

Cytochrome 2C19 genotype-directed dosing of voriconazole (VRC) reduces the incidence of insufficient VRC trough concentrations (C_min ) but does not account for CYP3A polymorphisms, also involved in VRC metabolism. This prospective observational study aimed to evaluate the utility of a genetic score combining CYP2C19 and CYP3A genotypes to predict insufficient initial VRC C_min (<1 mg/L).

METHODS

The genetic score was determined in hematological patients treated with VRC. The higher the genetic score, the faster the metabolism of the patient. The impact of the genetic score was evaluated considering initial VRC C_min and all VRC C_min (n = 159) determined during longitudinal therapeutic drug monitoring.

RESULTS

Forty-three patients were included, of whom 41 received VRC for curative indication. Thirty-six patients had a genetic score ≥2, of whom 11 had an initial insufficient VRC C_min . A genetic score ≥2 had a positive predictive value of 0.31 for having an initial insufficient VRC C_min and initial VRC C_min was not associated with the genetic score. The lack of association between the genetic score and VRC C_min may be related to the inflammatory status of the patients (C-reactive protein [CRP] levels: median [Q1-Q3]: 43.0 [11.0-110.0] mg/L), as multivariate analysis performed on all VRC C_min identified CRP as an independent determinant of the VRC C_min adjusted for dose (P < .0001).

CONCLUSION

The combined genetic score did not predict low VRC exposure in patients with inflammation, which is frequent in patients with invasive fungal infections. Strategies for the individualization of VRC dose should integrate the inflammatory status of patients in addition to pharmacogenetic variants.

Unexpected overdose blood concentration of tacrolimus: Keep in mind the role of inflammation

Tacrolimus is the cornerstone of the therapeutic immunosuppressive strategy in liver transplantation. The inter-individual and intra-individual variability of its trough blood concentrations is a surrogated biomarker of allograft rejection. Here we described two cases of patients with liver transplant who exhibited increases of tacrolimus blood trough concentration adjusted on the dose while experiencing acute inflammatory episodes. These case reports highlight the inhibitory effect of acute inflammation on tacrolimus metabolism and show that it accounts for the longitudinal intra-individual variability of tacrolimus blood concentrations, beyond drug-drug interaction and observance.

Tablets or oral suspension for posaconazole in lung transplant recipients? Consequences for trough concentrations of tacrolimus and everolimus

AIMS

A new formulation of posaconazole (PCZ), delayed-release tablets (PCZ-tab), increases PCZ bioavailability and plasma trough concentrations (C_min ) over those achieved with an oral suspension (PCZ-susp). PCZ is an inhibitor of cytochrome P450 3A4 and P-glycoprotein. We therefore investigated the impact of PCZ-tab treatment on blood C_min and doses of tacrolimus (TAC) and everolimus (EVR).

METHODS

Eighteen lung transplant patients receiving TAC (n = 13) or TAC + EVR (n = 5) between June 2015 and March 2016 were retrospectively included. Ten of these patients received both PCZ-tab and PCZ-susp (i.e. switched patients); the other 8 received only PCZ-tab. Plasma C_min of PCZ (n = 64), blood C_min of TAC (n = 299) and EVR (n = 80) were determined during routine therapeutic drug monitoring by liquid chromatography-tandem mass spectrometry.

RESULTS

PCZ C_min on PCZ-tab treatment (n = 48) was 2.5 times higher than that on PCZ-susp therapy (n = 16), for both PCZ patients (P < .0001) and for switched patients (P = .003). PCZ initiation, regardless of galenic form, increased TAC and EVR C_min adjusted for dose (D), 3-fold and 3.5-fold, respectively (P < .0001 for both). PCZ-tab treatment was associated with a higher TAC C_min /D (PCZ-tab vs PCZ-susp: 0.004 ± 0.004 L^-1 vs 0.009 ± 0.006 L^-1 , P < .0001) and lower TAC daily dose than PCZ-susp (PCZ-tab vs PCZ-susp: 1.08 ± 0.92 vs 2.32 ± 1.62 mg d^-1 , P < .0001). EVR C_min /D was higher and EVR dose tended to be lower on PCZ-tab than on PCZ-susp.

CONCLUSION

The greater PCZ exposure achieved during PCZ-tab treatment increased drug-drug interactions with TAC and EVR, resulting in greater exposure, potentially exposing patients to higher risks of adverse effects.

Inflammation is a potential risk factor of voriconazole overdose in hematological patients

Voriconazole (VRC) overdoses are frequent and expose patients at high risk of adverse effects. This case-control study performed in hematological patients who benefited from VRC therapeutic drug monitoring from January 2012 to December 2015 aimed to identify risk factors of VRC overdose. Pharmacogenetic, biological, and demographic parameters at the time of VRC trough concentration (C_min ) were retrospectively collected from medical records. Cases (VRC overdose: defined by a VRC C_min ≥ 4 mg/L; n = 31) were compared to controls (no VRC overdose: defined by VRC C_min < 4 mg/L; n = 31) using nonparametric or chi-square tests followed by multivariable analysis. VRC overdoses were significantly associated with high CRP and bilirubin levels, intravenous administration, and age in univariable analysis. In contrast, the proportion of CYP genotypes (CYP2C19, CYP3A4, or CYP3A5, considered alone or combined in a combined genetic score) were not significantly different between patients who experienced a VRC overdose and those who did not. In multivariable analysis, the class of CRP level (defined by median CRP levels of 96 mg/L) was the sole independent risk factor of VRC overdose (P < 0.01). Patients with CRP levels > 96 mg/L) had a 27-fold (IC 95%: [6-106]) higher risk of VRC overdose than patients with CRP levels ≤ 96 mg/L. This study demonstrates that inflammatory status, assessed by CRP levels, is the main risk factor of VRC overdose in French hematological patients, whereas pharmacogenetic determinants do not appear to be involved.

Integrating anatomo-physiological changes and pharmacogenomics in anti-infective therapy management: is it a major concern?

Success of anti-infective therapy is a major challenge in some patients given anatomo-physiological changes and genetic variations. In this case anecdote, we report the management strategy of a patient suffering from chronic pulmonary aspergillosis in a context of anorexia nervosa and genetic polymorphism.

Symptomatic Hypoglycemia Associated with Trimethoprim/Sulfamethoxazole and Repaglinide in a Diabetic Patient

Objective

To report a case of clinically significant hypoglycemia attributed to the concomitant use of trimethoprim/sulfamethoxazole (TMP/SMX) and repaglinide by a diabetic patient.

Case summary

A 76-year-old diabetic patient with impaired renal function and no history of hypoglycemia was receiving treatment with repaglinide 1 mg 3 times daily. Five days after TMP/SMX therapy was started for a urinary tract infection, the man developed symptomatic hypoglycemia. Repaglinide and TMP/SMX were stopped and intravenous d-glucose was administered to normalize glucose levels. Repaglinide, but not TMP/SMX, was reintroduced 5 days later and no other hypoglycemic episode occurred. Objective causality assessments revealed that the interaction was probable (World Health Organization-Uppsala Monitoring Centre) or possible (Horn Drug Interaction Probability Scale).

Discussion

This interaction between TMP/SMX and repaglinide was predictable according to available pharmacokinetic data in healthy subjects. Trimethoprim induced CYP2C8 inhibition, thus increasing the plasma concentration of repaglinide. This interaction is mentioned in the repaglinide product information. To our knowledge, however, no case of symptomatic hypoglycemia associated with a combination of repaglinide and trimethoprim has been described before. This discrepancy may be explained by the subtherapeutic dosage used in the pharmacokinetic study. Moreover, our patient had impaired renal function, which may have led to trimethoprim accumulation and potentiated its interaction with repaglinide. A direct lowering of blood glucose levels due to sulfamethoxazole, also potentiated by renal failure, could also be involved in triggering hypoglycemia.

Conclusions

This interaction between TMP/SMX and repaglinide may have involved inhibition of CYP2C8 by trimethoprim. Clinicians should be aware that this association may lead to symptomatic hypoglycemia, particularly in patients with renal dysfunction.

Pharmacogenetics may influence the impact of inflammation on voriconazole trough concentrations

How pharmacogenetics modulates the inhibitory effects of inflammation on voriconazole trough concentration (Cmin) remains unknown. In 29 recipients of allogeneic hematopoietic stem cell transplantation retrospectively studied, both a genetic score (which aggregated CYP2C19 and CYP3A genotypes) and inflammation significantly influenced voriconazole Cmin (n = 260). A trend toward (p = 0.03) a greater impact of inflammation in patients with the highest genetic score (corresponding to ultra-rapid metabolizers) was observed. Further researches are needed to confirm these data.

[Pharmacokinetic drug interaction between miconazole mucoadhesive tablet and tacrolimus: About 3 case-reports in transplant patients]

Loramyc^® is a mucoadhesive tablet of miconazole, indicated for the treatment of oropharyngeal candidiasis in immunocompromised patients. Miconazole, as others azole antifungals, is known for its potent inhibitory properties of cytochromes P450 enzymes and P-glycoprotein (P-gp). Inhibition of cytochromes P450 enzymes and P-gp can produce pharmacokinetic drug interaction. Immunosuppressive agents, such as calcineurin inhibitors (tacrolimus, cyclosporine) are substrates of cytochromes P450 3A4 and P-gp. Nevertheless, the impact of systemic absorption of miconazole mucoadhesive tablet has not been investigated by the laboratory before regulatory approval. No recommendation currently exists in case of co-prescription of Loramyc^® and immunosuppressive agents which are counter-indicated as a matter of principle. Herein, we present 3 cases of transplanted patients, requiring miconazole mucoadhesive tablet, who presented a tacrolimus overdose. These cases illustrate that of therapeutic drug monitoring is feasible in order to prevent the occurrence of overdoses and adverse reactions related.

[Not Available]

Azathioprine, 6-mercaptopurine, and 6-thioguanine are immunosuppressive drugs indicated in the prevention of graft rejection, and treatment of auto-immune disease or inflammatory bowel disease. Their anti-nucleotidic properties are also used for the treatment of acute leukaemia. Their metabolism involves thiopurine methyl transferase, which activity varies according to genetic polymorphisms. In inflammatory bowel disease patients, there is no recommended therapeutic range of intra-erythrocyte 6-thioguanine nucleotide concentration, the active metabolite. Therapeutic drug monitoring of 6-thioguanine nucleotide concentrations is however proposed in the following clinical situations: to check the observance, to try to explain therapeutic failure, to manage patients with limited thiopurine methyl transferase activity or patients treated with associated drugs that can modify thiopurine methyl transferase activity. The literature review shows that high concentrations of 6-thioguanine nucleotides and methylated metabolites are associated with an increased risk of bone marrow toxicity. In addition, high concentrations of methylated metabolite might increase the risk of hepatic toxicity. These major side-effects can be prevented by the use of pre-treatment screening for thiopurine methyl transferase activity or genotype in inflammatory bowel disease patients in order to propose an adapted dosing.

Should busulfan therapeutic range be narrowed in pediatrics? Experience from a large cohort of hematopoietic stem cell transplant children

Busulfan, the corner stone of hematopoietic stem cell transplantation regimens, has a narrow therapeutic window. Therapeutic drug monitoring (TDM)-guided dosing to reach the conventional area under the concentration-time curve (AUC) target range of 900-1500 μmol min/L is associated with better outcomes. We report our experience with busulfan TDM in a large cohort of children. The aims were to investigate the relevance of using a more restricted therapeutic range and investigate the association between busulfan therapeutic range and clinical outcome. This study includes 138 children receiving 16 doses of intravenous busulfan, with the first dose assigned based on weight and doses adjusted to a local AUC target range of 980-1250 μmol min/L. Busulfan TDM combined with model-based dose adjustment was associated with an increased probability of AUC target attainment, for both target range: 90.8% versus 74.8% for the conventional target range and 66.2% versus 43.9% for the local target range (P<0.001). The median follow-up was 56.2 months. Event-free survival was 88.5%, overall survival was 91.5% and veno-occlusive disease occurred in 18.3% of patients. No difference was observed for clinical outcomes depending on the selected target range. Pharmacokinetic monitoring and individualization of busulfan dosage regimen are useful in improving target attainment, but using a restricted target range has no impact on clinical outcomes.

[Drug-drug interaction with telaprevir or boceprevir in liver transplant patients: about four cases]

Boceprevir and telaprevir are both direct-acting antivirals indicated, as part of combination therapy for the management of chronic hepatitis C virus (HCV) genotype 1 infection. Transplanted patients treated with anticalcineurines (tacrolimus and cyclosporine) are confronted with major risks of interactions. Indeed, these antiviral are strong inhibitors of the enzyme cytochrome 3A4/A5, responsible for the metabolisme of ciclosprine and tacrolimus. The literature gives evidence of the dangerousness of this drug-drug interaction. We report four clinical cases illustrating the dosage adaptations at liver transplant patients and treated by telaprevir or boceprevir. To protect the immunosuppressive efficiency, a multidisciplinary care and narrow monitoring of the interaction between immunosuppressing agents and protease inhibitors were necessary.

Parthenolide inhibits tubulin carboxypeptidase activity

Microtubules are centrally involved in cell division, being the principal components of mitotic spindle. Tubulin, the constituent of microtubules, can be cyclically modified on its alpha-subunit by enzymatic removal of the COOH-terminal tyrosine residue by an ill-defined tubulin carboxypeptidase (TCP) and its readdition by tubulin tyrosine ligase (TTL). We and others have previously shown that suppression of TTL and resulting accumulation of detyrosinated tubulin are frequent in human cancers of poor prognosis. Explanations for the involvement of TTL and detyrosinated tubulin in tumor progression arise from the recent discovery that tubulin detyrosination leads to CAP-Gly protein mislocalization, which correlates with defects in spindle positioning during mitosis. Impaired control of spindle positioning is one factor favoring tumor invasiveness. Thus, TCP could be a target for developing novel therapeutic strategies against advanced stages of cancers. Inhibitors of TCP, by reversing abnormal detyrosinated tubulin accumulation in tumor cells, could impair tumor progression. TCP has never been isolated and this has hampered search of specific inhibitors. In this article, we describe a cell-based assay of TCP activity and its use to screen a library of natural extracts for their inhibitory potency. This led to the isolation of two sesquiterpene lactones. We subsequently found that parthenolide, a structurally related compound, can efficiently inhibit TCP. This inhibitory activity is a new specific property of parthenolide independent of its action on the nuclear factor-kappaB pathway. Parthenolide is also known for its anticancer properties. Thus, TCP inhibition could be one of the underlying mechanisms of these anticancer properties.

Miniaturization and validation of a sensitive multiparametric cell-based assay for the concomitant detection of microtubule-destabilizing and microtubule-stabilizing agents

The authors describe a cell-based assay for anti-microtubule compounds suitable for automation. This assay allows the identification, in a single screening campaign, of both microtubule-destabilizing and microtubule-stabilizing agents. Its rationale is based on the substrate properties of the tubulin-modifying enzymes involved in the tubulin tyrosination cycle. This cycle involves the removal of the C-terminal tyrosine of the tubulin alpha-subunit by an ill-defined tubulin carboxypeptidase and its readdition by tubulin tyrosine ligase. Because of the substrate properties of these enzymes, dynamic microtubules, sensitive to depolymerizing drugs, are composed of tyrosinated tubulin, whereas non-dynamic, stabilized microtubules are composed of detyrosinated tubulin. Thus depolymerization or stabilization of the microtubule network can easily be detected with double-immunofluorescence staining using antibodies specific to tyrosinated and detyrosinated tubulin. The authors have scaled this assay to the 96-well plate format and adapted its process for an automated handling, including a readout using a microplate reader. They describe the different steps of this adaptation. This assay was validated using known compounds. This new cell-based assay represents an alternative to both global cytotoxicity assays and in vitro tubulin assembly assays commonly used for the detection of microtubule poisons.

In vitro hypoxia-conditioned colon cancer cell lines derived from HCT116 and HT29 exhibit altered apoptosis susceptibility and a more angiogenic profile in vivo

Hypoxia is an important selective force in the clonal evolution of tumours. Through HIF-1 and other transcription factors combined with tumour-specific genetic alterations, hypoxia is a dominant factor in the angiogenic phenotype. Cellular adaptation to hypoxia is an important requirement of tumour progression independent of angiogenesis. The adaptive changes, insofar as they alter hypoxia-induced apoptosis, are likely to determine responsiveness to antiangiogenic strategies. To investigate this adaptation of tumour cells to hypoxia, we recreated in vitro the in vivo situation of chronic intermittent exposure to low-oxygen levels. The colon carcinoma cell lines HT29 and HCT116 were subjected to 40 episodes of sublethal hypoxia (4 h) three times a week. The resulting two hypoxia-conditioned cell lines have been maintained in culture for more than 2 years. In both cell lines changes in doubling times occurred: in HT29 an increase, and in HCT116 a decrease. Cell survival in response to hypoxia and to DNA damage differed strikingly in the two cell lines. The HT29 hypoxia-conditioned cells were more resistant than the parental line to a 24 h hypoxic challenge, while those from HCT116 surprisingly were more sensitive. Sensitivity to cisplatin in vitro was also significantly different for the hypoxia-conditioned compared with the parental lines, suggesting a change in pathways leading to apoptosis following DNA damage signaling. The growth of both conditioned cell lines in vivo as xenografts in immunodeficient (SCID) mice was more rapid than their parental lines, and was accompanied in each by evidence of enhanced vascular proliferation as a consequence of the hypoxia-conditioning. Thus the changes in apoptotic susceptibility were independent of altered angiogenesis. The derivation of these lines provides a model for events within hypoxic regions of colon cancers, and for the acquisition of resistance and sensitivity characteristics that may have therapeutic implications for the use of antiangiogenesis drugs.