Rebecca Blanchard

A proposed nomenclature system for the cytosolic sulfotransferase (SULT) superfamily.

A nomenclature system for the cytosolic sulfotransferase (SULT) superfamily has been developed. The nomenclature guidelines were applied to 65 SULT cDNAs and 18 SULT genes that were characterized from eukaryotic organisms. SULT cDNA and gene sequences were identified by querying the GenBank databases and from published reports of their identification and characterization. These sequences were evaluated and named on the basis of encoded amino acid sequence identity and, in a few cases, a necessity to maintain historical naming convention. Family members share at least 45% amino acid sequence identity whereas subfamily members are at least 60% identical. cDNAs which encode amino acid sequences of at least 97% identity to each other were assigned identical isoform names. We also attempted to categorize orthologous enzymes between various species, where these have been identified, and the nomenclature includes a species descriptor. We present recommendations for the naming of allelic variants of SULT genes and their derived allozymes arising from single nucleotide polymorphisms and other genetic variation. The superfamily currently comprises 47 mammalian SULT isoforms, one insect isoform and eight plant enzymes, and collectively these sequences represent nine separate SULT families and 14 subfamilies. It is hoped that this nomenclature system will be widely adopted and that, as novel SULTs are identified and characterized, investigators will name their discoveries according to these guidelines.

Sulfotransferase (SULT) 1A1 polymorphic variants *1, *2, and *3 are associated with altered enzymatic activity, cellular phenotype, and protein degradation

The superfamily of sulfotransferase (SULT) enzymes catalyzes the sulfate conjugation of several pharmacologically important endo- and xenobiotics. SULT1A1 catalyzes the sulfation of small planar phenols such as neurotransmitters, steroid hormones, acetaminophen, and p-nitrophenol (PNP). Genetic polymorphisms in the human SULT1A1 gene define three alleles, SULT1A1*1, *2, and *3. The enzyme activities of the SULT1A1 allozymes were studied with a variety of substrates, including PNP, 17β-estradiol, 2-methoxyestradiol, catecholestrogens, the antiestrogen 4-hydroxytamoxifen (OHT), and dietary flavonoids. Using purified recombinant SULT1A1 protein, marked differences in *1, *2, and *3 activity toward every substrate studied were noted. Substrate inhibition was observed for most substrates. In general, the trend in Vmax estimates was *1 > *3 > *2; however, Vmax/Km estimate trends varied with substrate. In MCF-7 cells stably expressing either SULT1A1*1 or *2, the antiestrogenic response to OHT was found to be allele-specific: the cells expressing *2 exhibited a better antiproliferative response. The intracellular stability of the *1 and *2 allozymes was examined in insect as well as mammalian cells. The SULT1A1*2 protein had a shorter half-life than the *1 protein. In addition, the *2 protein was ubiquitinated to a greater extent than *1, suggesting increased degradation via a proteasome pathway. The results of this study suggest marked differences in activity of polymorphic SULT1A1 variants, including SULT1A1*3, toward a variety of substrates. These differences are potentially critical for understanding interindividual variability in drug response and toxicity, as well as cancer risk and incidence.

Pharmacogenetics of uridine diphosphoglucuronosyltransferase (UGT) 1A family members and its role in patient response to irinotecan

Glucuronidation, catalyzed by the glucuronosyltransferase (UGT) superfamily, is a major biotransformation pathway for several drugs, including irinotecan. Irinotecan is commonly used in colorectal cancer chemotherapy. Irinotecan undergoes metabolism in humans and is converted to its active metabolite SN-38, a topoisomerase I inhibitor. SN-38 is inactivated via glucuronidation catalyzed by various hepatic and extrahepatic UGT1A isozymes. Although the role of the UGT1A1 *28 genetic variant has received much attention in altered toxicity upon irinotecan treatment, other UGT1A enzymes also play an important role. This review summarizes pharmacokinetic, toxicologic, and pharmacogenetic studies carried out to date in irinotecan and SN-38 disposition.

In Vivo Quantification of Calcitonin Gene-Related Peptide Receptor Occupancy by Telcagepant in Rhesus Monkey and Human Brain Using the Positron Emission Tomography Tracer [11C]MK-4232

Calcitonin gene-related peptide (CGRP) is a potent neuropeptide whose agonist interaction with the CGRP receptor (CGRP-R) in the periphery promotes vasodilation, neurogenic inflammation and trigeminovascular sensory activation. This process is implicated in the cause of migraine headaches, and CGRP-R antagonists in clinical development have proven effective in treating migraine-related pain in humans. CGRP-R is expressed on blood vessel smooth muscle and sensory trigeminal neurons and fibers in the periphery as well as in the central nervous system. However, it is not clear what role the inhibition of central CGRP-R plays in migraine pain relief. To this end, the CGRP-R positron emission tomography (PET) tracer [11C]MK-4232 (2-[(8R)-8-(3,5-difluorophenyl)-6,8-[6-11C]dimethyl-10-oxo-6,9-diazaspiro[4.5]decan-9-yl]-N-[(2R)-2′-oxospiro[1,3-dihydroindene-2,3′-1H-pyrrolo[2,3-b]pyridine]-5-yl]acetamide) was discovered and developed for use in clinical PET studies. In rhesus monkeys and humans, [11C]MK-4232 displayed rapid brain uptake and a regional brain distribution consistent with the known distribution of CGRP-R. Monkey PET studies with [11C]MK-4232 after intravenous dosing with CGRP-R antagonists validated the ability of [11C]MK-4232 to detect changes in CGRP-R occupancy in proportion to drug plasma concentration. Application of [11C]MK-4232 in human PET studies revealed that telcagepant achieved only low receptor occupancy at an efficacious dose (140 mg PO). Therefore, it is unlikely that antagonism of central CGRP-R is required for migraine efficacy. However, it is not known whether high central CGRP-R antagonism may provide additional therapeutic benefit.

PhRMA White Paper on ADME Pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross‐industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003–2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug‐metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

Genetic polymorphisms in human SULT1A1 and UGT1A1 genes associate with breast tumor characteristics: a case-series study

IntroductionEstrogens are important in breast cancer development. SULT1A1 and UGT1A1 catalyze estrogen metabolism and are polymorphic. The SULT1A1*2 protein exhibits low activity, and a TA repeat within the UGT1A1 promoter alters the level of expression of the protein. We hypothesized that the SULT1A1*2 allozyme has decreased capacity to sulfate estrogens, that the SULT1A1*2 allele conferred increased capacity of cells to proliferate in response to estrogens, and that individuals with the variant SULT1A1 and UGT1A1 genotypes exhibited different breast tumor characteristics.MethodsThe capacity for SULT1A1*2 to sulfate 17β-estradiol and the capacity for cells expressing SULT1A1*1 or SULT1A1*2 to proliferate in response to 17β-estradiol was evaluated. A case-series study was performed in a total of 210 women with incident breast cancer, including 177 Caucasians, 25 African-Americans and eight women of other ethnic background. The SULT1A1 and UGT1A1 genotypes were determined and a logistic regression model was used to analyze genotype–phenotype associations.ResultsWe determined that the SULT1A1*1/*1 high-activity genotype was associated with tumor size ≤2 cm (odds ratio = 2.63, 95% confidence interval = 1.25–5.56, P = 0.02). Individuals with low-activity UGT1A1 genotypes (UGT1A1*28/*28 or UGT1A1*28/*34) were more likely to have an age at diagnosis ≥60 years (odds ratio = 3.70, 95% confidence interval = 1.33–10.00, P = 0.01). Individuals with both SULT1A1 and UGT1A1 high-activity genotypes had low tumor grade (odds ratio = 2.56, 95% confidence interval = 1.04–6.25, P = 0.05). Upon stratification by estrogen receptor status, significant associations were observed predominantly in estrogen receptor-negative tumors.ConclusionThe data suggest that genetic variation in SULT1A1 and UGT1A1 may influence breast cancer characteristics and might be important for breast cancer prognosis.

Single- and Multiple-Dose Pharmacokinetics and Tolerability of Telcagepant, an Oral Calcitonin Gene-Related Peptide Receptor Antagonist, in Adults

Telcagepant is a novel, orally active, and selective calcitonin gene‐related peptide receptor antagonist being developed for acute treatment of migraine with and without aura. Three separate clinical studies were conducted to evaluate the pharmacokinetics and tolerability of telcagepant following single oral doses in healthy young and elderly men and women and multiple oral doses in men. Telcagepant was rapidly absorbed with a time to maximum concentration of approximately 1.5 hours. The terminal half‐life was approximately 6 hours. A greater than dose‐proportional increase was observed in the area under the plasma concentration versus time curve from zero to infinity. Following twice‐daily dosing, with each dose separated by 2 hours, steady state was achieved in approximately 3 to 4 days with an accumulation ratio of approximately 2. There were no clinically meaningful pharmacokinetic differences when compared across age and gender. Telcagepant was generally well tolerated up to single doses of 1200 mg and multiple doses of 400 mg twice daily.

Pairwise Combinations of Estrogen Metabolism Genotypes in Postmenopausal Breast Cancer Etiology

Estrogen exposures have been associated with breast cancer risk, and genes involved in estrogen metabolism have been reported to mediate that risk. Our goal was to better understand whether combinations of candidate estrogen metabolism genotypes are associated with breast cancer etiology. A population-based case-control study in three counties of the Philadelphia Metropolitan area was undertaken. We evaluated seven main effects and 21 first-order interactions in African Americans and European Americans for genotypes at COMT, CYP1A1, CYP1A2, CYP1B1, CYP3A4, SULT1A1, and SULT1E1 in 878 breast cancer cases and 1,409 matched random digit–dialed controls. In European Americans, we observed main effect associations of genotypes containing any CYP1A1*2C (odds ratio, 1.71; 95% confidence interval, 1.09-2.67) and breast cancer. No significant main effects were observed in African Americans. Three significant first-order interactions were observed. In European Americans, interactions between SULT1A1*2 and CYP1A1*2C genotypes (Pinteraction < 0.001) and between SULT1E1 and CYP1A2*1F genotypes were observed (Pinteraction = 0.006). In African Americans, an interaction between SULT1A1*2 and CYP1B1*4 was observed (Pinteraction = 0.041). We applied the false-positive report probability approach, which suggested that these associations were noteworthy; however, we cannot rule out the possibility that chance led to these associations. Pending future confirmation of these results, our data suggest that breast cancer etiology in both European American and African American postmenopausal women may involve the interaction of a gene responsible for the generation of catecholestrogens with a gene involved in estrogen and catecholestrogen sulfation. (Cancer Epidemiol Biomarkers Prev 2007;16(3):444–50)

A randomized, placebo-controlled study of the effects of telcagepant on exercise time in patients with stable angina

Telcagepant is a calcitonin gene‐related peptide (CGRP) receptor antagonist being evaluated for acute migraine treatment. CGRP is a potent vasodilator that is elevated after myocardial infarction, and it delays ischemia during treadmill exercise. We tested the hypothesis that CGRP receptor antagonism does not reduce treadmill exercise time (TET). The effects of supratherapeutic doses of telcagepant on TET were assessed in a double‐blind, randomized, placebo‐controlled, two‐period, crossover study in patients with stable angina and reproducible exercise‐induced angina. Patients received telcagepant (600 mg, n = 46; and 900 mg, n = 14) or placebo and performed treadmill exercise at Tmax (2.5 h after the dose). The hypothesis that telcagepant does not reduce TET was supported if the lower bound of the two‐sided 90% confidence interval (CI) for the mean treatment difference (telcagepant–placebo) in TET was more than −60 s. There were no significant between‐treatment differences in TET (mean treatment difference: −6.90 (90% CI: −17.66, 3.86) seconds), maximum exercise heart rate, or time to 1‐mm ST‐segment depression using pooled data or with stratification for dose.

The potent calcitonin gene-related peptide receptor antagonist, telcagepant, does not affect nitroglycerin-induced vasodilation in healthy men

AIMS To assess the effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, telcagepant, on the haemodynamic response to sublingual nitroglycerin (NTG). METHODS Twenty-two healthy male volunteers participated in a randomized, placebo-controlled, double-blind, two-period, crossover study. Subjects received 500 mg telcagepant or placebo followed, 1.5 h later, by 0.4 mg NTG. To assess the haemodynamic response the following vascular parameters were measured: blood pressure, aortic augmentation index (AIx) and brachial artery diameter (BAD). Data are presented as mean (95% confidence interval, CI). RESULTS The aortic AIx following NTG decreased by -18.50 (-21.02, -15.98) % after telcagepant vs. -17.28 (-19.80, -14.76) % after placebo. The BAD fold increase following NTG was 1.14 (1.12, 1.17) after telcagepant vs. 1.13 (1.10, 1.15) after placebo. For both AIx and BAD, the hypothesis that telcagepant does not significantly affect the changes induced by NTG is supported (P < 0.0001). In addition, no vasoconstrictor effect of telcagepant could be demonstrated. CONCLUSIONS Telcagepant did not affect NTG-induced haemodynamic changes. These data suggest that NTG-induced vasodilation is not CGRP dependent.