Elevated fatty acid amide hydrolase in the prefrontal cortex of borderline personality disorder: a [11C]CURB positron emission tomography study

Amygdala-prefrontal cortex (PFC) functional impairments have been linked to emotion dysregulation and aggression in borderline personality disorder (BPD). Fatty acid amide hydrolase (FAAH), the major catabolic enzyme for the endocannabinoid anandamide, has been proposed as a key regulator of the amygdala-PFC circuit that subserves emotion regulation. We tested the hypothesis that FAAH levels measured with [¹¹C]CURB positron emission tomography in amygdala and PFC would be elevated in BPD and would relate to hostility and aggression. Twenty BPD patients and 20 healthy controls underwent FAAH genotyping (rs324420) and scanning with [¹¹C]CURB. BPD patients were medication-free and were not experiencing a current major depressive episode. Regional differences in [¹¹C]CURB binding were assessed using multivariate analysis of covariance with PFC and amygdala [¹¹C]CURB binding as dependent variables, diagnosis as a fixed factor, and sex and genotype as covariates. [¹¹C]CURB binding was marginally elevated across the PFC and amygdala in BPD (p = 0.08). In a priori selected PFC, but not amygdala, [¹¹C]CURB binding was significantly higher in BPD (11.0%, p = 0.035 versus 10.6%, p = 0.29). PFC and amygdala [¹¹C]CURB binding was positively correlated with measures of hostility in BPD (r > 0.4; p < 0.04). This study is the first to provide preliminary evidence of elevated PFC FAAH binding in any psychiatric condition. Findings are consistent with the model that lower endocannabinoid tone could perturb PFC circuitry that regulates emotion and aggression. Replication of these findings could encourage testing of FAAH inhibitors as innovative treatments for BPD.

Progress in pharmacogenomics: bridging the gap from research to practice

Genetic information is increasingly used to optimize clinical treatment of patients, but obstacles remain to practical implementation as well as challenges to our understanding of genetic variation in drug response. These areas that particularly require research attention include gene-environment interactions, the consequences of genetic variation, and the impact of epigenetics on gene expression and function. In this issue of Clinical Pharmacology & Therapeutics focused on pharmacogenetics, we discuss some of the recent advances in understanding from a variety of viewpoints.

Cytochrome P450 (CYP) 2A6 Genetic Variation Predicts Letrozole Plasma Concentrations in Postmenopausal Women with Breast Cancer

Background: The potent aromatase inhibitor (AI) letrozole is effective in the treatment of postmenopausal women with steroid-hormone-receptor–positive breast cancer (metastatic, neoadjuvant and adjuvant). The beneficial and adverse effects of letrozole vary widely among patients, and differences in pharmacokinetics may contribute to this variability. Letrozole is primarily cleared by hepatic metabolism. Since CYP2A6 has been implicated in letrozole metabolism in vitro, we tested the influence CYP2A6 genetic variants on plasma concentrations of letrozole in breast cancer patients. Methods: Postmenopausal women with early stage hormone receptor-positive breast cancer were recruited into an ongoing multicenter randomized clinical trial to study the pharmacogenomics of two AIs, exemestane (25 mg/day) and letrozole (2.5 mg/day) given orally. Total accrual to the trial is anticipated to be 250 in each arm. Three months plasma letrozole concentrations were measured by HPLC from 146 patients who were randomized to the letrozole arm and multiple CYP2A6 variants were genotyped from genomic DNA. Results: Plasma concentrations of letrozole showed wide variability among patients (16.6 ng/ml to 141.2 ng/ml; 8.5-fold difference). Genotypes were grouped based in to normal (*1/*1), intermediate (*1/*9 and *1/*12, n=23) and slow (*9/*12, *1/*2, *2/*9, *1/*35, *1/*4E; n=12) metabolizers based on genotyped predicted phenotype. A statistically significant difference in letrozole concentrations was observed among the patients with the different genotype groups (p&lt;0.0001; one-way ANOVA), with strong gene-dose effect relationship (r2=0.28; p&lt;0.0001). Letrozole plasma concentrations were significantly higher in patients with the slow or intermediate genotypes than those with normal genotype (p &lt; 0.0001; Dunn's post-test for multiple comparison correction).Conclusions: Polymorphisms in the CYP2A6 gene account for ∼28% of variability in letrozole concentrations in breast cancer patients. Prior genotyping for CYP2A6 variants may help to identify patients who benefit from letrozole and who experience adverse effects from the drug.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5160.

Consensus statements from the Second International Lung Cancer Molecular Biomarkers Workshop: a European strategy for developing lung cancer molecular diagnostics in high risk populations

The Second Molecular Biomarkers Workshop was held at the Roy Castle International Centre for Lung Cancer Research in Liverpool, in June 2001 and it brought together experts in the clinical, epidemiological and molecular-pathology of lung cancer from Europe and the USA, to address issues surrounding the development of a European strategy for early lung cancer detection. The 2001 Workshop Breakout Groups concentrated on the current challenges in the early detection of lung cancer which need to be addressed in the light of the recent surge in interest in many countries for mounting new clinical trials to evaluate the utility of Spiral CT in early lung cancer detection. If population-based trials of CT screening are mounted it will also be a favorable clinical environment in which to evaluate efficiently recent advances in molecular screening and genotyping. The Workshop focused specifically on: a) clinical and molecular biomarkers, b) sputum as an early detection and diagnostic tool, c) validation of molecular markers prior to their use in early detection trials and d) ethical issues that have to be considered in early lung cancer detection trials. A distillation of the Workshop discussions is given in this article.

Identification of a new variant CYP2D6 allele lacking the codon encoding Lys-281: possible association with the poor metabolizer phenotype

A variant CYP2D6(C) P450 protein was found in a liver characterized by deficient microsomal metabolism of bufuralol and sparteine, prototypical substrates for the debrisoquine-sparteine drug oxidation polymorphism. This protein was present at decreased levels in liver and had a slightly different relative mobility on SDS-polyacrylamide gels. The cDNA cloning and sequencing of the variant, designated CYP2D6(C), revealed that its mRNA lacked a single codon resulting in deletion of Lys281. This was the result of a three base pair deletion at the 3' end of CYP2D6 exon 5. The CYP2D6(C) P450, produced in HepG2 cells using vaccinia virus mediated cDNA expression displayed Km values toward bufuralol, debrisoquine and sparteine that were not significantly different from wild type CYP2D6. These data suggest that the poor metabolizer phenotype in livers expressing CYP2D6(C) is not due to a catalytically defective enzyme but perhaps due to decreased levels of the P450 protein in microsomal membranes. Low microsomal CYP2D6(C) contents could result from deficient membrane insertion or decreased stability of the P450 protein. A polymerase chain reaction-based procedure, developed to detect CYP2D6(C) alleles, indicates that this variant probably represents less than 1.5% of all CYP2D6 alleles.

Cytochrome P-450 hPCN3, a novel cytochrome P-450 IIIA gene product that is differentially expressed in adult human liver. cDNA and deduced amino acid sequence and distinct specificities of cDNA-expressed hPCN1 and hPCN3 for the metabolism of steroid hormones and cyclosporine

Immunoblotting analysis of human liver microsome preparations revealed that human cytochrome P-450 PCN1 (hPCN1, Mr approximately 52,000) was expressed in each of 40 individual specimens examined. In about 10-20% of the livers, an immunologically related protein having a lower electrophoretic mobility (Mr approximately 52,500) was also detected. A single liver was found that expressed only the lower mobility protein, designated hPCN3, and RNA isolated from this liver was used to construct a lambda gt11 library. The library was screened with an hPCN1 cDNA probe resulting in the isolation of a unique full-length cDNA that was sequenced and shown to encode hPCN3. The deduced amino acid sequence of this cDNA contained 502 residues, a calculated molecular mass of 57,115 daltons, and displayed 84% similarity with hPCN1. The deduced amino-terminal sequence of hPCN3 was identical to that of HFLa, a major cytochrome P-450 expressed in human fetal liver that is immunologically cross-reactive with several family III cytochrome P-450s. hPCN1 and hPCN3 cDNAs were expressed in Hep G2 cells using a vaccinia virus expression system and shown to encode active enzymes, both characterized by reduced CO-binding spectra with lambda max at 450 nm. Enzymatic analysis revealed that both cytochrome P-450s were similarly active in catalyzing oxidation of the calcium channel blocking drug nifedipine. Both enzymes also catalyzed 6 beta-hydroxylation of the steroid hormones testosterone, progesterone, and androstenedione, although hPCN1 exhibited several-fold higher expressed activity than hPCN3. Several minor oxidation products of these steroids (e.g. 15 beta-hydroxytestosterone), comprising up to approximately 20% of the total metabolites, were formed by hPCN1 but not hPCN3, indicating that hPCN3 is a more highly regiospecific monooxygenase catalyst with steroid substrates. Clear differences were also detected in their catalytic activities toward the immunosuppressive drug cyclosporine, with two hydroxylated metabolites (M1 and M17) and one demethylated metabolite (M21) formed by hPCN1 but only one metabolite (M1) formed by hPCN3. These studies establish that hPCN3 is a newly described cytochrome P-450 that is differentially expressed in the adult human population and that has overlapping substrate specificity compared to hPCN1 for metabolism of steroid and drug substrates.