Functional characterization of the G162R and D216H genetic variants of human CYP17A1.

Cytochrome P450 17A1 (CYP17A1) is a dual-function enzyme catalyzing reactions necessary for cortisol and androgen biosynthesis. CYP17A1 is a validated drug target for prostate cancer as CYP17A1 inhibition significantly reduces circulating androgens and improves survival in castration-resistant prostate cancer. Germline CYP17A1 genetic variants with altered CYP17A1 activity manifesting as various endocrinopathies are extremely rare; however, characterizing these variants provides critical insights into CYP17A1 protein structure and function. By querying the dbSNP online database and publically available data from the 1000 genomes project (http://browser.1000genomes.org), we identified two CYP17A1 nonsynonymous genetic variants with unknown consequences for enzymatic activity and stability. We hypothesized that the resultant amino acid changes would alter CYP17A1 stability or activity. To test this hypothesis, we utilized a HEK-293T cell-based expression system to characterize the functional consequences of two CYP17A1 variants, D216H (rs200063521) and G162R (rs141821705). Cells transiently expressing the D216H variant demonstrate a selective impairment of 16α-hydroxyprogesterone synthesis by 2.1-fold compared to wild-type (WT) CYP17A1, while no effect on 17α-hydroxyprogesterone synthesis was observed. These data suggest that substrate orientations in the active site might be altered with this amino acid substitution. In contrast, the G162R substitution exhibits decreased CYP17A1 protein stability compared to WT with a near 70% reduction in protein levels as determined by immunoblot analysis. This variant is preferentially ubiquitinated and degraded prematurely, with an enzyme half-life calculated to be ∼2.5 h, and proteasome inhibitor treatment recovers G162R protein expression to WT levels. Together, these data provide new insights into CYP17A1 structure-function and stability mechanisms.

Elevated S100A8 protein expression in breast cancer cells and breast tumor stroma is prognostic of poor disease outcome.

PURPOSE: Elevated S100A8 expression has been observed in cancers of the bladder, esophagus, colon, ovary, and breast. S100A8 is expressed by breast cancer cells as well as by infiltrating immune and myeloid cells. Here we investigate the association of elevated S100A8 protein expression in breast cancer cells and in breast tumor stroma with survival outcomes in a cohort of breast cancer patients. PATIENTS AND METHODS: Tissue microarrays (TMA) were constructed from breast cancer specimens from 417 patients with stage I-III breast cancer treated at the University of Michigan Comprehensive Cancer Center between 2004 and 2006. Representative regions of non-necrotic tumor and distant normal tissue from each patient were used to construct the TMA. Automated quantitative immunofluorescence (AQUA) was used to measure S100A8 protein expression, and samples were scored for breast cancer cell and stromal S100A8 expression. S100A8 staining intensity was assessed as a continuous value and by exploratory dichotomous cutoffs. Associations between breast cancer cell and stromal S100A8 expression with disease-free survival and overall survival were determined using the Kaplan-Meier method and Cox proportional hazard models. RESULTS: High breast cancer cell S100A8 protein expression (as indicated by AQUA scores), as a continuous measure, was a significant prognostic factor for OS [univariable hazard ratio (HR) 1.24, 95% confidence interval (CI) 1.00-1.55, p = 0.05] in this patient cohort. Exploratory analyses identified optimal S100A8 AQUA score cutoffs within the breast cancer cell and stromal compartments that significantly separated survival curves for the complete cohort. Elevated breast cancer cell and stromal S100A8 expression, indicated by higher S100A8 AQUA scores, significantly associates with poorer breast cancer outcomes, regardless of estrogen receptor status. CONCLUSIONS: Elevated breast cancer cell and stromal S1008 protein expression are significant indicators of poorer outcomes in early stage breast cancer patients. Evaluation of S100A8 protein expression may provide additional prognostic information beyond traditional breast cancer prognostic biomarkers.

CYP2D6 genotype is not associated with survival in breast cancer patients treated with tamoxifen: results from a population-based study.

PURPOSE: A number of studies have tested the hypothesis that breast cancer patients with low-activity CYP2D6 genotypes achieve inferior benefit from tamoxifen treatment, putatively due to lack of metabolic activation to endoxifen. Studies have provided conflicting data, and meta-analyses suggest a small but significant increase in cancer recurrence, necessitating additional studies to allow for accurate effect assessment. We conducted a retrospective pharmacogenomic analysis of a prospectively collected community-based cohort of patients with estrogen receptor-positive breast cancer to test for associations between low-activity CYP2D6 genotype and disease outcome in 500 patients treated with adjuvant tamoxifen monotherapy and 500 who did not receive any systemic adjuvant therapy. METHODS: Tumor-derived DNA was genotyped for common, functionally consequential CYP2D6 polymorphisms (*2, *3, *4, *6, *10, *41, and copy number variants) and assigned a CYP2D6 activity score (AS) ranging from none (0) to full (2). Patients with poor metabolizer (AS = 0) phenotype were compared to patients with AS > 0 and in secondary analyses AS was analyzed quantitatively. Clinical outcome of interest was recurrence free survival (RFS) and analyses using long-rank test were adjusted for relevant clinical covariates (nodal status, tumor size, etc.). RESULTS: CYP2D6 AS was not associated with RFS in tamoxifen treated patients in univariate analyses (p > 0.2). In adjusted analyses, increasing AS was associated with inferior RFS (Hazard ratio 1.43, 95% confidence interval 1.00-2.04, p = 0.05). In patients that did not receive tamoxifen treatment, increasing CYP2D6 AS, and AS > 0, were associated with superior RFS (each p = 0.0015). CONCLUSIONS: This population-based study does not support the hypothesis that patients with diminished CYP2D6 activity achieve inferior tamoxifen benefit. These contradictory findings suggest that the association between CYP2D6 genotype and tamoxifen treatment efficacy is null or near null, and unlikely to be useful in clinical practice.

Steroid receptor coactivator-1 can regulate osteoblastogenesis independently of estrogen.

Steroid receptor coactivator-1 (SRC-1), a well-studied coactivator of estrogen receptor (ER), is known to play an important and functional role in the development and maintenance of bone tissue. Previous reports suggest SRC-1 maintains bone mineral density primarily through its interaction with ER. Here we demonstrate that SRC-1 can also affect bone development independent of estrogen signaling as ovariectomized SRC-1 knockout (SRC-1 KO) mouse had decreased bone mineral density. To identify estrogen-independent SRC-1 target genes in osteoblastogenesis, we undertook an integrated analysis utilizing ChIP-Seq and mRNA microarray in transformed osteoblast-like U2OS-ERα cells. We identified critical osteoblast differentiation genes regulated by SRC-1, but not by estrogen including alkaline phosphatase and osteocalcin. Ex vivo primary culture of osteoblasts from SRC-1 wild-type and KO mice confirmed the role of SRC-1 in osteoblastogenesis, associated with altered ALPL levels. Together, these data indicate that SRC-1 can impact osteoblast function in an ER-independent manner.

Polymorphisms in drug-metabolizing enzymes and steady-state exemestane concentration in postmenopausal patients with breast cancer.

Discovery of clinical and genetic predictors of exemestane pharmacokinetics was attempted in 246 postmenopausal patients with breast cancer enrolled on a prospective clinical study. A sample was collected 2 h after exemestane dosing at a 1- or 3-month study visit to measure drug concentration. The primary hypothesis was that patients carrying the low-activity CYP3A4*22 (rs35599367) single-nucleotide polymorphism (SNP) would have greater exemestane concentration. Additional SNPs in genes relevant to exemestane metabolism (CYP1A1/2, CYP1B1, CYP3A4, CYP4A11, AKR1C3/4, AKR7A2) were screened in secondary analyses and adjusted for clinical covariates. CYP3A4*22 was associated with a 54% greater exemestane concentration (P<0.01). Concentration was greater in patients who reported White race, had elevated aminotransferases, renal insufficiency, lower body mass index and had not received chemotherapy (all P<0.05), and CYP3A4*22 maintained significance after adjustment for covariates (P<0.01). These genetic and clinical predictors of exemestane concentration may be useful for treatment individualization in patients with breast cancer.

Evaluation of chronic toxicity and carcinogenicity of ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate in Sprague-Dawley rats.

Ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate, developed for use as a polymerization processing aid in the manufacture of fluoropolymers, was tested for its potential chronic toxicity and carcinogenicity in a 2-year oral dosing study in Sprague-Dawley rats. Male rats were given daily doses of either 0, 0.1, 1 or 50 mg/kg; females were given either 0, 1, 50 or 500 mg/kg. Body weights, food consumption and clinical signs were monitored daily; clinical pathology was conducted at designated intervals and animals were given a complete pathological evaluation after 12 months and 24 months of dosing. Normal survival was seen in all groups, no abnormal clinical signs were seen, and body weight gain was reduced only in female rats at 500 mg/kg. Both sexes at the high dose had mild decreases in red cell mass which were somewhat more pronounced in females. Clinical pathology indicative of liver injury was present in males that received 50 mg/kg and correlated with histomorphological liver changes that included both hypertrophic and degenerative/necrotic lesions. Similar histomorphological lesions were seen in the livers of females at 500 mg/kg. Previous shorter term toxicity studies have identified this chemical as a PPARα agonist and the finding of benign tumors of the liver, pancreas and/or testes in males at 50 mg/kg and females at 500 mg/kg is consistent with the rat response to peroxisome proliferators and is of questionable human relevance. Changes in the kidney, tongue, and stomach were observed only at the highest dose of 500 mg/kg in females. The no-observed-adverse-effect-level in this study lies between 1 and 50 mg/kg for males and between 50 and 500 mg/kg for females.

Aromatase inhibitor-induced modulation of breast density: clinical and genetic effects.

BACKGROUND: Change in breast density may predict outcome of women receiving adjuvant hormone therapy for breast cancer. We performed a prospective clinical trial to evaluate the impact of inherited variants in genes involved in oestrogen metabolism and signalling on change in mammographic percent density (MPD) with aromatase inhibitor (AI) therapy. METHODS: Postmenopausal women with breast cancer who were initiating adjuvant AI therapy were enrolled onto a multicentre, randomised clinical trial of exemestane vs letrozole, designed to identify associations between AI-induced change in MPD and single-nucleotide polymorphisms in candidate genes. Subjects underwent unilateral craniocaudal mammography before and following 24 months of treatment. RESULTS: Of the 503 enrolled subjects, 259 had both paired mammograms at baseline and following 24 months of treatment and evaluable DNA. We observed a statistically significant decrease in mean MPD from 17.1 to 15.1% (P<0.001), more pronounced in women with baseline MPD ≥20%. No AI-specific difference in change in MPD was identified. No significant associations between change in MPD and inherited genetic variants were observed. CONCLUSION: Subjects with higher baseline MPD had a greater average decrease in MPD with AI therapy. There does not appear to be a substantial effect of inherited variants in biologically selected candidate genes.

A SNP in steroid receptor coactivator-1 disrupts a GSK3ß phosphorylation site and is associated with altered tamoxifen response in bone.

The coregulator steroid receptor coactivator (SRC)-1 increases transcriptional activity of the estrogen receptor (ER) in a number of tissues including bone. Mice deficient in SRC-1 are osteopenic and display skeletal resistance to estrogen treatment. SRC-1 is also known to modulate effects of selective ER modulators like tamoxifen. We hypothesized that single nucleotide polymorphisms (SNP) in SRC-1 may impact estrogen and/or tamoxifen action. Because the only nonsynonymous SNP in SRC-1 (rs1804645; P1272S) is located in an activation domain, it was examined for effects on estrogen and tamoxifen action. SRC-1 P1272S showed a decreased ability to coactivate ER compared with wild-type SRC-1 in multiple cell lines. Paradoxically, SRC-1 P1272S had an increased protein half-life. The Pro to Ser change disrupts a putative glycogen synthase 3 (GSK3)ß phosphorylation site that was confirmed by in vitro kinase assays. Finally, knockdown of GSK3ß increased SRC-1 protein levels, mimicking the loss of phosphorylation at P1272S. These findings are similar to the GSK3ß-mediated phospho-ubiquitin clock previously described for the related coregulator SRC-3. To assess the potential clinical significance of this SNP, we examined whether there was an association between SRC-1 P1272S and selective ER modulators response in bone. SRC-1 P1272S was associated with a decrease in hip and lumbar bone mineral density in women receiving tamoxifen treatment, supporting our in vitro findings for decreased ER coactivation. In summary, we have identified a functional genetic variant of SRC-1 with decreased activity, resulting, at least in part, from the loss of a GSK3ß phosphorylation site, which was also associated with decreased bone mineral density in tamoxifen-treated women.

High-efficiency genotype analysis from formalin-fixed, paraffin-embedded tumor tissues.

Single-nucleotide polymorphisms (SNPs) can be assayed using DNA isolated from archival formalin-fixed, paraffin-embedded (FFPE) samples, making retrospective pharmacogenetic studies possible. In this study, we describe methods that significantly increase the number of SNP determinations possible using FFPE samples. Quantifying the amount of DNA amenable to PCR (amplification-quality DNA, AQ-DNA) allows a significant reduction in the amount of sample required for Taqman-based SNP assays. Optimizing AQ-DNA input increases PCR amplification efficiency and SNP determination accuracy. DNA was extracted from 39 FFPE tumor sections and matched tumor and stromal cores, which were of the type used to generate tissue microarrays. Sections and tumor cores yielded sufficient AQ-DNA for more than 1000 SNP determinations. Seven SNPs were assessed following individual assay optimization for minimal AQ-DNA. Genotypes from tumor cores for single SNPs were 92.3-100% concordant with those obtained from sections. Using these methods, the number of SNP genotypes that can be determined from single FFPE samples is greatly increased expanding the genetic association studies possible from limited archival specimens. The use of tumor cores is of particular importance as the harvesting of tumor cores has minimal impact on the utility of the donor blocks for other purposes.

Estrogen receptor genotypes, menopausal status, and the effects of tamoxifen on lipid levels: revised and updated results.

We previously reported that the ESR1 XbaI genotypes were associated with baseline and tamoxifen-induced serum lipid profiles. The analysis in that study was carried out by PCR followed by restriction-enzyme digestion. After reanalysis using more robust TaqMan assays, the findings related to ~10% of the genotypes for the ESR1 XbaI single-nucleotide polymorphism (SNP) were revised. For the other genotypes (i.e., ESR1 PvuII, ESR2, and CYP2D6), the results were nearly identical to those in the previous study. Upon reanalysis, previously reported associations between the ESR1 Xba1 genotypes and baseline triglyceride and low-density lipoprotein (LDL) cholesterol levels were no longer observed. Previously reported associations between the ESR1 XbaI genotypes and tamoxifen-induced changes in levels of total cholesterol, triglycerides, and high-density lipoprotein (HDL) cholesterol were also no longer observed. However, the following observations from the original report did not change: (i) the levels of circulating lipids are lower in women taking tamoxifen; (ii) there is an association between the ESR2-02 genotypes and changes in triglyceride levels; and (iii) neither ESR1 PvuII nor CYP2D6 is associated with any changes in serum lipid concentrations in patients receiving treatment with tamoxifen.

Efavirenz directly modulates the oestrogen receptor and induces breast cancer cell growth.

OBJECTIVES: Efavirenz-based HIV therapy is associated with breast hypertrophy and gynaecomastia. Here, we tested the hypothesis that efavirenz induces gynaecomastia through direct binding and modulation of the oestrogen receptor (ER). METHODS: To determine the effect of efavirenz on growth, the oestrogen-dependent, ER-positive breast cancer cell lines MCF-7, T47D and ZR-75-1 were treated with efavirenz under oestrogen-free conditions in the presence or absence of the anti-oestrogen ICI 182,780. Cells treated with 17ß-oestradiol in the absence or presence of ICI 182,780 served as positive and negative controls, respectively. Cellular growth was assayed using the crystal violet staining method and an in vitro receptor binding assay was used to measure the ER binding affinity of efavirenz. RESULTS: Efavirenz induced growth in MCF-7 cells with an estimated effective concentration for half-maximal growth (EC(50)) of 15.7 µM. This growth was reversed by ICI 182,780. Further, efavirenz binds directly to the ER [inhibitory concentration for half maximal binding (IC(50)) of ∼52 µM] at a roughly 1000-fold higher concentration than observed with 17ß-oestradiol. CONCLUSIONS: Our data suggest that efavirenz-induced gynaecomastia may be caused, at least in part, by drug-induced ER activation in breast tissues.

Lack of association between oestrogen receptor polymorphisms and change in bone mineral density with tamoxifen therapy.

BACKGROUND: Tamoxifen, a selective oestrogen receptor (ER) modulator, increases bone mineral density (BMD) in postmenopausal women and decreases BMD in premenopausal women. We hypothesised that inherited variants in candidate genes involved in oestrogen signalling and tamoxifen metabolism might be associated with tamoxifen effects in bone. METHODS: A total of 297 women who were initiating tamoxifen therapy were enrolled in a prospective multicentre clinical trial. Lumbar spine and total hip BMD values were measured using dual-energy X-ray absorptiometry (DXA) at baseline and after 12 months of tamoxifen therapy. Single-nucleotide polymorphisms (SNPs) in ESR1, ESR2, and CYP2D6 were tested for associations in the context of menopausal status and previous chemotherapy, with a mean percentage change in BMD over 12 months. RESULTS: The percentage increase in BMD was greater in postmenopausal women and in those patients who had been treated with chemotherapy. No significant associations between tested SNPs and either baseline BMD or change in BMD with 1 year of tamoxifen therapy were detected. CONCLUSION: The evaluated SNPs in ESR and CYP2D6 do not seem to influence BMD in tamoxifen-treated subjects.

Correlation of GREB1 mRNA with protein expression in breast cancer: validation of a novel GREB1 monoclonal antibody.

Studies of gene regulated by estrogen in breast cancer 1 (GREB1) have focused on mRNA levels with limited evidence about GREB1 protein expression in normal and breast cancer cells. A monoclonal antibody that recognizes GREB1 protein in breast tissues could be applied to correlate protein expression with established mRNA expression data. A hybridoma expressing a murine monoclonal antibody targeting a 119 amino acid peptide specific to human GREB1 was generated. The novel monoclonal GREB1 antibody (GREB1ab) was validated for use in Western blotting as well as immunohistochemical (IHC) applications. GREB1ab detects a 216 kDa protein corresponding to GREB1 in estrogen receptor alpha (ERalpha+) breast cancer cells as well as ERalpha- breast cancer cells transduced with a GREB1 expression vector. GREB1ab specificity was verified using an ERalpha antagonist to prevent GREB1 induction as well as a silencing siRNA targeting GREB1 mRNA. GREB1ab was further validated for detection of GREB1 by IHC in breast cancer cell lines and breast tissue microarrays (TMA). ERalpha+ cell lines were observed to express GREB1 while ERalpha- cell lines did not express detectable levels of the protein. Using breast cancer tissue whole sections, IHC with the GREB1ab identified protein expression in ERalpha+ breast cancer tissue as well as normal breast tissue, with little GREB1 expression in ERalpha- breast cancer tissue. Furthermore, these data indicate that GREB1 mRNA expression correlates well with protein expression. The novel monoclonal GREB1ab is specific for GREB1 protein. This antibody will serve as a tool for investigations focused on the expression, distribution, and function of GREB1 in normal breast and breast cancer tissues.

Cytochrome P450 2D6 activity predicts discontinuation of tamoxifen therapy in breast cancer patients.

The selective estrogen receptor modulator tamoxifen is routinely used for treatment and prevention of estrogen-receptor-positive breast cancer. Studies of tamoxifen adherence suggest that over half of patients discontinue treatment before the recommended 5 years. We hypothesized that polymorphisms in CYP2D6, the enzyme responsible for tamoxifen activation, predict for tamoxifen discontinuation. Tamoxifen-treated women (n=297) were genotyped for CYP2D6 variants and assigned a 'score' based on predicted allele activities from 0 (no activity) to 2 (high activity). Correlation between CYP2D6 score and discontinuation rates at 4 months was tested. We observed a strong nonlinear correlation between higher CYP2D6 score and increased rates of discontinuation (r(2)=0.935, P=0.018). These data suggest that presence of active CYP2D6 alleles may predict for higher likelihood of tamoxifen discontinuation. Therefore, patients who may be most likely to benefit from tamoxifen may paradoxically be most likely to discontinue treatment prematurely.

Rifampin is a selective, pleiotropic inducer of drug metabolism genes in human hepatocytes: studies with cDNA and oligonucleotide expression arrays.

We used expression microarrays to test the effects of rifampin on the overall pattern of mRNA expression of multiple metabolic enzymes in primary human hepatocytes. Two microarrays were utilized, a cDNA-based array and one that is oligonucleotide-based. The cDNA-based expression arrays showed that rifampin caused a 7.7 +/- 6.6-fold induction in CYP2A6 and a 4.0 +/- 2.0-fold increase in the CYP2C family of enzymes while having little effect on CYP2E1 or CYP2D6. Many non-P450 enzymes were also induced including FMO-4 and -5, UGT-1A, MAO-B, and GST-P1. The oligonucleotide-based array made it possible to detect different levels of induction within the CYP2C family, with rifampin causing a 6.5-fold increase in expression of CYP2C8 and a 3.7-fold increase in CYP2C9 while having no effect on the level of CYP2C18 mRNA. Rifampin also induced other CYP enzymes including CYP2B6 and all three members of the CYP3A family, with CYP3A4 showing the highest level of induction at 55.1-fold. RNase protection assays were used to validate results from the arrays and a comparison of all three methods of mRNA detection showed qualitatively similar results. These data make it clear that rifampin treatment brings about broad changes in the pattern of gene expression, rather than increased expression of a small number of metabolic enzymes. Clinicians and researchers who use and study rifampin and other drugs that induce drug metabolism should be alert to the possibility of multiple effects.