Influence of the CYP2B6 polymorphism on the pharmacokinetics of mitotane.

OBJECTIVE: The aim of this study was to assess the potential impact of the pharmacogenetic variability of CYP2B6 and ABCB1 genes on the pharmacokinetics of mitotane. METHODS: A retrospective analysis was carried out on 27 patients with adrenocortical carcinoma on postoperative adjunctive mitotane. CYP2B6 and ABCB1 polymorphisms were genotyped and tested for an association with plasma trough concentration after 3, 6, 9, and 12 months of therapy. RESULTS: Patients with the GT/TT genotype had higher mitotane plasma concentrations compared with patients with GG at 3 months (14.80 vs. 8.01 µg/ml; P=0.008) and 6 months (17.70 vs. 9.75 µg/ml; P=0.015). Multivariate logistic regression analysis showed that only the CYP2B6 rs3745274GT/TT genotype (odds ratio=10.7; P=0.017) was a predictor of mitotane plasma concentrations of at least 14 µg/ml after 3 months of treatment. Mitotane concentrations were not influenced by the polymorphisms of the ABCB1 gene. CONCLUSION: Evaluation of the CYP2B6 polymorphism enabled prediction of the individual response to adjuvant mitotane treatment.

Circannual variation of mitotane and its metabolites plasma levels in patients with adrenocortical carcinoma.

OBJECTIVES: Mitotane is the reference drug for the adrenocortical carcinoma treatment; its pharmacological activity seems to depend on drug transformation in two active metabolites: o,p'-DDE (dichlorodiphenylethene) and o,p'-DDA (dichlorodiphenylacetate). Mitotane and metabolites are lipophilic agents; thus, they tend to accumulate into adipose tissues (white and brown), which change their prevalence seasonally. Aim of the work was to evaluate mitotane and metabolites plasma levels variation over the year, in adrenocortical cancer patients treated with Lysodren® for at least 6 months. METHODS: We enrolled a group of 86 adrenocortical carcinoma diagnosed patients, who underwent radical surgery and started mitotane as adjuvant treatment. For drug and metabolites plasma level (from samples collected ~12 h after the dose administration of mitotane, just before the subsequent administration) determination, a validated chromatographic method was used. KEY FINDINGS: Results showed an evidence of a seasonal trend for the three substance (o,p'-DDD, o,p'-DDE and o,p'-DDA) plasma levels, in terms of acrophases and lower values. Furthermore, it came out that male patients need a higher significant mitotane drug dose than female patients to reach mitotane therapeutic window. CONCLUSIONS: In conclusion, this is the first study assessing a mitotane plasma level variation over the year, but further studies in larger cohorts are required.

A new simple HPLC method for measuring mitotane and its two principal metabolites Tests in animals and mitotane-treated patients.

A new C18 reversed-phase column and UV HPLC method for the detection of mitotane, its principal metabolites, dichlorodiphenylacetate and dichlrodiphenylethene, and its precursor DDT is described. In this article mitotane, dichlorodiphenylacetate, and dichlrodiphenylethene concentrations in organs of rats fed on a mitotane diet, and the effects of erythromycin and grapefruit juice as cytochrome P450 common inhibitors are presented. Tissue accumulation of mitotane and dichlrodiphenylethene, the acquired ability to eliminate dichlorodiphenylacetate, and inhibition of beta-hydroxylation by both inhibitors are illustrated here. Blood samples from mitotane-treated patients revealed two correlations: plasma mitotane/dichlrodiphenylethene and plasma mitotane/red cell mitotane.

A new HPLC-UV validated method for therapeutic drug monitoring of tyrosine kinase inhibitors in leukemic patients.

Development and validation of simple, rapid, and reliable high-performance liquid chromatography (HPLC)-UV method for quantification of major tyrosine kinase inhibitors, imatinib, dasatinib, and nilotinib, in human plasma is presented. Chromatographic separation of the drugs is achieved on an RP-C(18) column at flow rate of 0.9 mL/min at 35°C; eluate is monitored at 267 nm. Mean intra-day and inter-day precision for all compounds are 2.5 and 13.3%; mean accuracy is 13.9%; extraction recovery ranges within 40.24 and 81.81%. Calibration curves range from 10 to 0.005 µg/mL. Limits of detection are 10 ng/mL for imatinib and nilotinib, 50 ng/mL for dasatinib; limits of quantitation are 50 ng/mL for imatinib and nilotinib, 100 ng/mL for dasatinib. Although this method allows the detection of dasatinib, levels found in patients plasma are close to the limit of detection, then below the limit of quantitation. Quantification with HPLC-mass spectrometry, then, is required for dasatinib to give a correct evaluation. In conclusion, the sensitivity of this new method is sufficient to perform therapeutic monitoring and pharmacokinetic studies of imatinib and nilotinib but not dasatinib in CML patients.

New HPLC-MS method for the simultaneous quantification of the antileukemia drugs imatinib, dasatinib, and nilotinib in human plasma.

A new method using high performance liquid chromatography coupled with electrospray mass spectrometry is described for the quantification of plasma concentration of tyrosine kinase inhibitors imatinib, dasatinib and nilotinib. A simple protein precipitation extraction procedure was applied on 250 microl of plasma aliquots. Chromatographic separation of drugs and Internal Standard (quinoxaline) was achieved with a gradient (acetonitrile and water + formic acid 0.05%) on a C18 reverse phase analytical column with 20min of analytical run, at flow rate of 1 ml/min. Mean intra-day and inter-day precision for all compounds were 4.3 and 11.4%; mean accuracy was 1.5%; extraction recovery ranged within 95 and 114%. Calibration curves ranged from 10,000 to 62.5 ng/ml. The limit of quantification was set at 78.1 ng/ml for imatinib and at 62.5 ng/ml for dasatinib and nilotinib. This novel developed methodology allows a specific, sensitive and reliable simultaneous determination of the three tyrosine kinase inhibitors imatinib, dasatinib and nilotinib in a single chromatographic run, useful for drugs estimation in plasma of patients affected by chronic myeloid leukemia.

The combined low-dose dexamethasone suppression corticotropin-releasing hormone test as a tool to rule out Cushing's syndrome.

OBJECTIVE: It remains to be evaluated whether the combined low-dose dexamethasone suppression corticotropin-releasing hormone test (LDDST-CRH test) may add to the diagnostic approach of patients suspected to have Cushing's syndrome (CS). The aim of the present study was to evaluate whether the LDDST-CRH test may have a place in the diagnostic strategy of CS. DESIGN: Prospective evaluation of a consecutive series of patients with suspected CS from 2004 to 2006. METHODS: All the subjects underwent the same screening protocol including 1 mg dexamethasone suppression test, 24-h urinary free cortisol (UFC), and midnight serum cortisol, followed by the LDDST-CRH test whose results were not used to establish a definitive diagnosis. Plasma dexamethasone concentration was measured 2 h after the last dose of dexamethasone. Patients qualified for CS when at least two screening tests were positive. RESULTS: Sixteen patients had CS while in the remaining 15 subjects CS was excluded. Even if not statistically significant, the sensitivity and the negative predictive value of the cortisol 15 min after CRH were better than the other tests; on the other hand, the test specificity was lower. All of the patients classified as indeterminate were correctly diagnosed by the LDDST-CRH test. Nevertheless, the repeated assessment of the screening tests and the active follow-up gave the same correct results. In all of the patients misclassified by the LDDST-CRH test, the plasma dexamethasone concentrations were in the normal range. CONCLUSIONS: Based on our findings, we suggest that the LDDST-CRH test may still find a place as a rule-out procedure in patients who present with indeterminate results after screening and may be unavailable to repeat testing during follow-up.