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.

Abstract P6-09-11: Genetic variation in CYP3A affects steady-state exemestane concentrations but does not explain inter-race difference

Background: Exemestane is a third generation steroidal aromatase inhibitor (AI) used for the treatment of estrogen receptor (ER) positive breast cancer in postmenopausal women. Differences in AI treatment efficacy and side effects may be due, in part, to variability in drug exposure. We previously reported that patients who self-report as white and those who carry the low-activity CYP3A4*22 single nucleotide polymorphism (SNP) have increased exemestane steady-state concentrations. Additional SNPs in CYP3A may contribute to pharmacokinetic variability and explain this inter-race difference. CYP3A5*3 (rs776746) is a non-expresser genotype that is far more common in European (minor allele frequency (MAF)∼0.94) than African (MAF∼0.18) individuals. CYP3A7*1C (rs45446698) is believed to tag adult expression of the fetal CYP3A7 enzyme and is relatively uncommon in tested cohorts (European MAF=0.04, African MAF<0.01). The objective of this secondary analysis was to determine whether these additional CYP3A SNPs contribute to variability in steady state exemestane concentrations and explain the inter-race difference.

Methods: 500 patients were randomly assigned to either drug on the Exemestane and Letrozole Pharmacogenetics (ELPh) Study. Clinical data and DNA were collected at baseline and blood samples were collected after 1 or 3 months of treatment to measure steady-state exemestane concentration via HPLC/MS. Genotyping for CYP3A5*3 and CYP3A7*1C was performed via Taqman Allelic Discrimination. Pharmacogenetic association with log-transformed concentrations were tested for each variant by inclusion in a multivariable model with CYP3A4*22 and self-reported race, assuming additive genetic effect, using Tobit regression to censor concentrations below the lower limit of quantification. SNPs with suggestive p-values <0.10 were included in a multivariable model with relevant covariates (AST or ALT>40, body mass index (BMI), and prior chemotherapy) to assess their independent contribution.

Results: In 231 evaluable patients there was a suggestive trend toward lower steady-state exemestane concentrations for CYP3A7*1C carriers (6.3 vs. 8.0 ng/mL) in the model including CYP3A4*22 and race (p=0.083). In the final multivariable model each CYP3A7*1C allele decreased exemestane concentration 31.5% (p=0.035, Table 1). CYP3A5*3 was not associated with exemestane concentration (p>0.2).

Multivariable Model of Exemestane Concentration % change in concentration (95% CI)p-valueCYP3A4*22 (rs35599367)64.5% (23%, 120%)0.0008CYP3A7*1C (rs45446698)-31.5% (-52%, -2.6%)0.035Self-Reported White47.2% (9.0%, 99%)0.012AST or ALT>4041.3% (1.0%, 98%)0.044BMI-0.9% (-2.4%, 0.55%)0.22Prior Chemotherapy-23.5% (-37%, -7.6%)0.006CI: Confidence Interval

Conclusions: Patients with breast cancer who carry CYP3A7*1C have lower steady-state exemestane concentrations but this association does not explain the greater concentrations in self-reported white patients. Ongoing analyses will determine whether exemestane concentration predicts treatment efficacy or toxicity, and if so, whether genetic and clinical factors can be useful for individualizing dosing to optimize outcomes. CYP3A7*1C should be prioritized for analyses of pharmacokinetic variability of other CYP3A substrates.

Citation Format: Hertz DL, Kidwell KM, Gersch CL, Desta Z, Storniolo AM, Stearns V, Skaar TC, Hayes DF, Henry NL, Rae JM. Genetic variation in CYP3A affects steady-state exemestane concentrations but does not explain inter-race difference [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-09-11.

Implementation of a pharmacogenomics consult service to support the INGENIOUS trial

Hospital systems increasingly utilize pharmacogenomic testing to inform clinical prescribing. Successful implementation efforts have been modeled at many academic centers. In contrast, this report provides insights into the formation of a pharmacogenomics consultation service at a safety-net hospital, which predominantly serves low-income, uninsured, and vulnerable populations. The report describes the INdiana GENomics Implementation: an Opportunity for the UnderServed (INGENIOUS) trial and addresses concerns of adjudication, credentialing, and funding.

Abstract P5-12-05: CYP3A4*22 polymorphism is associated with increased exemestane concentrations in postmenopausal breast cancer patients

Background: Exemestane is a second generation steroidal aromatase inhibitor (AI) used for the treatment of estrogen receptor (ER) positive breast cancer in postmenopausal women. Variability in AI treatment efficacy and side effects seen across patients may be due, in part, to inter-patient differences in drug exposure. This exposure variability is likely caused by patient genetics factors, such as single nucleotide polymorphisms (SNPs) in drug metabolizing enzymes, or clinical factors such as patient body size, organ function, and comorbidities. The objective of this secondary correlative analysis was to identify genetic and clinical characteristics that affect steady state exemestane concentration, with a specific focus on the influence of inherited genetic variants and baseline hepatic function.

Methods: 500 patients were enrolled on the Exemestane and Letrozole Pharmacogenetics (ELPh) Study and randomized to either drug. Clinical data and DNA were collected at baseline and blood samples were collected after 1 or 3 months of treatment to measure steady-state exemestane concentration via HPLC/MS. Genotyping was performed on a custom Sequenom MassARRAY iPLEX that included the recently discovered low activity CYP3A4*22 (rs35599367) SNP and several other SNPs with putative functional consequence in enzymes thought to be involved in exemestane metabolism (CYP1A1/2, CYP1B1, CYP3A4, CYP4A11, AKR1C3/4, AKR7A2). Our primary hypothesis was that patients carrying CYP3A4*22 variants would have higher serum exemestane concentrations. Other SNPs and clinical characteristics (hepatic and renal function, age, body mass index (BMI), time of sample collection, prior chemotherapy) were assessed for independent association, and then adjusted for in a multivariable tobit regression model for CYP3A4*22 on log-transformed censored exemestane concentration.

Results: 246 (225 randomized to exemestane arm, 21 crossed-over from letrozole arm) patients had exemestane steady state levels and were evaluable in this analysis. As hypothesized, the CYP3A4*22 polymorphism (minor allele frequency=0.06) was associated with a 54% increase in exemestane concentration (95% CI: 14% - 109%, p<0.01). Exemestane concentration was 44% greater in patients who had evidence of hepatic impairment (AST or ALT>40) at baseline (95% CI: 2% - 104%, p=0.02), 1% lower per unit increase in BMI (95% CI: 0% - 3%, p=0.05), and 20% lower in patients who received prior chemotherapy (95% CI: 4% - 34%, p=0.03). Age, renal impairment, and other SNPs were not associated with exemestane concentration. After adjustment for significant clinical covariates the CYP3A4*22 SNP remained significant (p<0.01).

Conclusions: Genetic and clinical predictors of exemestane concentration were discovered in a large cohort of prospectively enrolled estrogen responsive breast cancer patients. Ongoing analyses will determine whether the variability in exemestane concentration was associated with downstream effects on estrogen depletion or treatment-related toxicity. If so, these genetic and clinical characteristics could be useful for individualizing dosing of exemestane to ensure that all patients are receiving maximal benefit with minimal toxicity.

Citation Format: Hertz DL, Kidwell KM, Seewald NJ, Gersch CL, Desta Z, Flockhart DA, Storniolo AM, Stearns V, Skaar TC, Hayes DF, Henry NL, Rae JM. CYP3A4*22 polymorphism is associated with increased exemestane concentrations in postmenopausal breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-12-05.

Age-Related Changes in MicroRNA Expression and Pharmacogenes in Human Liver

Developmental changes in the liver can significantly impact drug disposition. Due to the emergence of microRNAs (miRNAs) as important regulators of drug disposition gene expression, we studied age-dependent changes in miRNA expression. Expression of 533 miRNAs was measured in 90 human liver tissues (fetal, pediatric [1-17 years], and adult [28-80 years]; n = 30 each). In all, 114 miRNAs were upregulated and 72 were downregulated from fetal to pediatric, and 2 and 3, respectively, from pediatric to adult. Among the developmentally changing miRNAs, 99 miRNA-mRNA interactions were predicted or experimentally validated (e.g., hsa-miR-125b-5p-CYP1A1; hsa-miR-34a-5p-HNF4A). In human liver samples (n = 10 each), analyzed by RNA-sequencing, significant negative correlations were observed between the expression of >1,000 miRNAs and mRNAs of drug disposition and regulatory genes. Our data suggest a mechanism for the marked changes in hepatic gene expression between the fetal and pediatric developmental periods, and support a role for these age-dependent miRNAs in regulating drug disposition.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Selective Serotonin Reuptake Inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are primary treatment options for major depressive and anxiety disorders. CYP2D6 and CYP2C19 polymorphisms can influence the metabolism of SSRIs, thereby affecting drug efficacy and safety. We summarize evidence from the published literature supporting these associations and provide dosing recommendations for fluvoxamine, paroxetine, citalopram, escitalopram, and sertraline based on CYP2D6 and/or CYP2C19 genotype (updates at www.pharmgkb.org).

Prerequisites to implementing a pharmacogenomics program in a large health-care system

Pharmacogenomics (PGx) technology is advancing rapidly; however, clinical adoption is lagging. The Indiana Institute of Personalized Medicine (IIPM) places a strong focus on translating PGx research into clinical practice. We describe what have been found to be the key requirements that must be delivered in order to ensure a successful and enduring PGx implementation within a large health-care system.

Impact of CYP2D6 polymorphisms on clinical efficacy and tolerability of metoprolol tartrate

Metoprolol is a selective β-1 adrenergic receptor blocker that undergoes extensive metabolism by the polymorphic enzyme, CYP2D6. Our objective was to investigate the influence of CYP2D6 polymorphisms on efficacy and tolerability of metoprolol tartrate. 281 study participants with uncomplicated hypertension received 50 mg of metoprolol twice daily followed by response guided titration to 100 mg twice daily. Phenotypes were assigned based on results of CYP2D6 genotyping and copy number variation assays. Clinical response to metoprolol and adverse effect rates were analyzed in relation to CYP2D6 phenotypes by using appropriate statistical tests. Heart rate response differed significantly by CYP2D6 phenotype (p-value <0.0001) with poor metabolizers & intermediate metabolizers showing greater HR reduction. However, blood pressure response and adverse effect rates were not significantly different by CYP2D6 phenotype. Other than a significant difference in heart rate response, CYP2D6 polymorphisms were not a determinant of the variability in response or tolerability to metoprolol.

Clinical Pharmacogenetics Implementation Consortium guidelines for cytochrome P450 2D6 genotype and codeine therapy: 2014 update

Codeine is bioactivated to morphine, a strong opioid agonist, by the hepatic cytochrome P450 2D6 (CYP2D6); hence, the efficacy and safety of codeine are governed by CYP2D6 activity. Polymorphisms are a major cause of CYP2D6 variability. We summarize evidence from the literature supporting this association and provide therapeutic recommendations for codeine based on CYP2D6 genotype. This document is an update to the 2012 Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for CYP2D6 genotype and codeine therapy.

Genome-wide discovery of genetic variants affecting tamoxifen sensitivity and their clinical and functional validation

BACKGROUND

Beyond estrogen receptor (ER), there are no validated predictors for tamoxifen (TAM) efficacy and toxicity. We utilized a genome-wide cell-based model to comprehensively evaluate genetic variants for their contribution to cellular sensitivity to TAM.

DESIGN

Our discovery model incorporates multidimensional datasets, including genome-wide genotype, gene expression, and endoxifen-induced cellular growth inhibition in the International HapMap lymphoblastoid cell lines (LCLs). Genome-wide findings were further evaluated in NCI60 cancer cell lines. Gene knock-down experiments were performed in four breast cancer cell lines. Genetic variants identified in the cell-based model were examined in 245 Caucasian breast cancer patients who underwent TAM treatment.

RESULTS

We identified seven novel single-nucleotide polymorphisms (SNPs) associated with endoxifen sensitivity through the expression of 10 genes using the genome-wide integrative analysis. All 10 genes identified in LCLs were associated with TAM sensitivity in NCI60 cancer cell lines, including USP7. USP7 knock-down resulted in increasing resistance to TAM in four breast cancer cell lines tested, which is consistent with the finding in LCLs and in the NCI60 cells. Furthermore, we identified SNPs that were associated with TAM-induced toxicities in breast cancer patients, after adjusting for other clinical factors.

CONCLUSION

Our work demonstrates the utility of a cell-based model in genome-wide identification of pharmacogenomic markers.

Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for codeine therapy in the context of cytochrome P450 2D6 (CYP2D6) genotype

Codeine is bioactivated to morphine, a strong opioid agonist, by the hepatic cytochrome P450 2D6 (CYP2D6); hence, the efficacy and safety of codeine as an analgesic are governed by CYP2D6 polymorphisms. Codeine has little therapeutic effect in patients who are CYP2D6 poor metabolizers, whereas the risk of morphine toxicity is higher in ultrarapid metabolizers. The purpose of this guideline (periodically updated at http://www.pharmgkb.org) is to provide information relating to the interpretation of CYP2D6 genotype test results to guide the dosing of codeine.

A SNP in steroid receptor coactivator-1 disrupts a GSK3β 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)β phosphorylation site that was confirmed by in vitro kinase assays. Finally, knockdown of GSK3β increased SRC-1 protein levels, mimicking the loss of phosphorylation at P1272S. These findings are similar to the GSK3β-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 GSK3β phosphorylation site, which was also associated with decreased bone mineral density in tamoxifen-treated women.

Use of germ-line single nucleotide polymorphisms (SNPs) in drug transporters (ABCG2/ABCB1) and tubulin (TUBB4) to predict survival in patients with metastatic castrate-resistant prostate cancer (CRPC) receiving docetaxel

58

Background: Multiple treatment options now exist for metastatic CRPC patients (pts). Germ-line SNPs in docetaxel (D) transport, metabolism, binding site, and degradation genes may contribute to variability in outcomes observed in D treated CRPC pts.

Methods: Between 1/07 and 10/08, all PCa pts seen in the Indiana University Simon Cancer Center oncology clinics were approached for recruitment to the Prostate Cancer Genetic Risk Evaluation of SNPs Study (PROGRESS). Participants completed a demographic and clinical questionnaire and provided a blood sample. Only CRPC pts treated with D were included in this analysis. Germ-line DNA was analyzed for SNP genotyping on a 128-SNP chip using a TaqMan OpenArray GT Kit (Applied Biosystems). The chip included genes critical to D signaling, transport, and elimination with minor allele frequencies > 5%. Pts were followed for progression-free (PFS) and overall survival (OS). Univariable analyses were performed to identify significant associations between SNP genotype, clinical parameters, and PFS and OS outcomes.

Results: 60 pts with metastatic CRPC initiated on D enrolled. Demographics included: age (median) – 69 yrs, ECOG PS 0– 40%, prostate specific antigen (PSA) (median) – 129.9 ng/ml, PSA doubling time (median) – 1.8 months, visceral mets –25%. No clinical parameters were associated with PFS and OS. Significant SNP associations are summarized below.

Conclusions: Differences in germ-line ABCG2, ABCB1, and TUBB4 SNPs may contribute to variation in clinical outcomes in CRPC pts treated with D.

[Table: see text]

[Table: see text]

Germ-line single nucleotide polymorphism (SNP) predictors of progression-free survival and overall survival in patients with advanced prostate cancer treated with androgen-deprivation therapy (ADT)

51

Background: Significant variation in response duration and overall survival exists among prostate cancer (PCa) patients treated with ADT. Germ-line SNPs affecting function of genes critical to hormone synthesis, transport, metabolism, binding sites, and degradation may contribute to variability in clinical outcomes observed in PCa patients treated with ADT.

Methods: Between 1/07 and 10/08, all PCa patients seen in the Indiana University Simon Cancer Center oncology clinics were approached for recruitment to the Prostate Cancer Genetic Risk Evaluation of SNPs Study (PROGRESS). Participants completed a demographic and clinical questionnaire and provided a peripheral blood sample. Only patients with confirmed ADT initiation dates were included in this analysis. Germ-line DNA was analyzed for SNP genotyping on a 128-SNP chip using a TaqMan OpenArray GT Kit (Applied Biosystems). The chip included genes critical to hormone signaling, transport, and elimination pathways with minor allele frequencies > 5%. Patients were followed for progression-free survival (PFS) and overall survival (OS) endpoints. Univariable analyses were performed to identify significant associations between SNP genotype, clinical parameters, and PFS and OS outcomes.

Results: 107 patients with PCa initiated on ADT enrolled. Demographics included: age (median)–69 yrs, prostate specific antigen (PSA) (median)–28.0 ng/ml, PSA doubling time (median)–4.9 months, biochemical/metastatic–25%/75%, concurrent anti-androgen therapy–44%. No clinical parameters were associated with PFS and OS. Significant SNP associations with PFS and OS are summarized in the Table.

Conclusions: Interpatient differences in hormone pathway germ-line SNPs may contribute to variability in clinical outcomes in patients treated with ADT.

[Table: see text]

[Table: see text]

Androgen pathway constitutional polymorphism predictors of progression-free and overall survivals in advanced castrate-resistant prostate cancer (CRPC) patients treated with ketoconazole (KC)

54

Background: Recent trials have highlighted the clinical utility of second-line hormonal therapies for CRPC. KC, an oral inhibitor of CYP3A4 and CYP17, is commonly used in this setting. Germline SNPs in genes critical to hormone synthesis, transport, metabolism, binding sites, and degradation may contribute to variability in outcomes observed in KC treated CRPC pts.

Methods: Between 1/07 and 10/08, all PCa pts seen in the Indiana University Simon Cancer Center oncology clinics were approached for recruitment to the Prostate Cancer Genetic Risk Evaluation of SNPs Study (PROGRESS). Participants completed a demographic and clinical questionnaire and provided a peripheral blood sample. Only pts with initiated on KC were included in this analysis. Germline DNA was analyzed for SNP genotyping on a 128-SNP chip using a TaqMan OpenArray GT Kit. The chip included genes critical to hormone signaling, transport, and elimination pathways with minor allele frequencies > 5%. Pts were followed for progression-free survival (PFS) and overall survival (OS) endpoints. Univariable analyses were performed to identify significant associations between SNP genotype, clinical parameters, and PFS and OS outcomes.

Results: Between January 2007 and October 2008, 39 pts with CRPC initiated on KC therapy enrolled. Demographics included: age (median) – 70 yrs, prostate specific antigen (PSA) (median) – 13.0 ng/ml, PSA doubling time (median) – 2.9 months, metastatic –85%, ECOG PS 0– 74%. Age < 70 was associated with shorter PFS (p=0.010) and age > 70 was associated with shorter OS (p=0.030). SNPs significantly associated with PFS and OS are summarized in the table.

Conclusions: Interpatient differences in hormonal pathway germline SNPs may contribute to variability in clinical outcomes in pts treated with KC.

[Table: see text]

No significant financial relationships to disclose.

Genetic variation in radiation and platinum pathways predicts severe acute radiation toxicity in patients with esophageal adenocarcinoma treated with cisplatin-based preoperative radiochemotherapy: results from the Eastern Cooperative Oncology Group

PURPOSE

Germline genetic variations may partly explain the clinical observation that normal tissue tolerance to radiochemotherapy varies by individual. Our objective was to evaluate the association between single-nucleotide polymorphisms (SNPs) in radiation/platinum pathways and serious treatment-related toxicity in subjects with esophageal adenocarcinoma who received cisplatin-based preoperative radiochemotherapy.

METHODS

In a multicenter clinical trial (E1201), 81 eligible treatment-naïve subjects with resectable esophageal adenocarcinoma received cisplatin-based chemotherapy concurrent with radiotherapy, with planned subsequent surgical resection. Toxicity endpoints were defined as grade ≥3 radiation-related or myelosuppressive events probably or definitely related to therapy, occurring during or up to 6 weeks following the completion of radiochemotherapy. SNPs were analyzed in 60 subjects in pathways related to nucleotide/base excision- or double stranded break repair, or platinum influx, efflux, or detoxification.

RESULTS

Grade ≥3 radiation-related toxicity (mostly dysphagia) and myelosuppression occurred in 18 and 33% of subjects, respectively. The variant alleles of the XRCC2 5' flanking SNP (detected in 28% of subjects) and of GST-Pi Ile-105-Val (detected in 65% of subjects) were each associated with higher odds of serious radiation-related toxicity compared to the major allele homozygote (47% vs. 9%, and 31% vs. 0%, respectively; P = 0.005). No SNP was associated with myelosuppression.

CONCLUSIONS

This novel finding in a well-characterized cohort with robust endpoint data supports further investigation of XRCC2 and GST-Pi as potential predictors of radiation toxicity.

Risk of breast cancer recurrence in women initiating tamoxifen with CYP2D6 inhibitors

CRA508

Background: Tamoxifen (TAM) is metabolized to its active form, endoxifen, by hepatic cytochrome P450 (CYP) 2D6. Diminished CYP2D6 function, both by genetic variation or concurrent use of pharmacologic inhibitors, can significantly reduce endoxifen plasma concentrations and may lead to reduced TAM effectiveness. Methods: We interrogated an integrated research database comprised of de-identified medical and pharmacy claims (Rx) data for 10.7 million U.S. health plan members to identify women with breast cancer (BrCa) new to TAM therapy in a 30-month period from 2003 to 2005, and investigated the risk of recurrent BrCa as a function of concurrent use of potent and moderate inhibitors of CYP2D6. Inclusion criteria were: greater than or equal to 24 months of follow-up data and adherence to TAM (medication possession ratio > 70%) over 2 years (N = 1,298). Disease recurrence was defined by BrCa ICD-9 codes or CPT codes for mastectomy, lumpectomy, lymph node dissection, or radiation therapy occurring at least 6 months after the index TAM Rx. Two study groups were identified: TAM alone (N = 945) or TAM + a CYP2D6 inhibitor concomitantly (N = 353). BrCa recurrence rates were compared using Kaplan-Meier analysis with log-rank test, and univariate hazard ratios (HR) with 95% confidence intervals (CI) were estimated by Cox proportional hazards model. Results: The study groups were similar at baseline. Median age was 52 years (TAM) and 53 years (TAM + CYP2D6 inhibitor). Interventions performed in the TAM alone group included mastectomy in 54%, lumpectomy in 36%, and radiation therapy in 47%, and were 52%, 38%, 46%, respectively, in the TAM + CYP2D6 inhibitor group. Among women on a CYP2D6 inhibitor, the median duration of overlap with TAM was 255 days. Patients receiving TAM + a CYP2D6 inhibitor had a 2-year BrCa recurrence rate of 13.9% versus 7.5% in patients receiving TAM alone (HR 1.92, 95% CI 1.33–2.76, p < 0.001). Conclusions: Our findings support the presence of a clinically significant drug interaction between TAM and known CYP2D6 inhibitors. This resulted in a significant 1.9 fold higher BrCa recurrence within 2 years of initiating TAM therapy.

[Table: see text]

Risk of breast cancer recurrence in women initiating tamoxifen with CYP2D6 inhibitors

CRA508

The full, final text of this abstract will be available in Part II of the 2009 ASCO Annual Meeting Proceedings, distributed onsite at the Meeting on May 30, 2009, and as a supplement to the June 20, 2009, issue of the Journal of Clinical Oncology.

[Table: see text]

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.

Impact of SNPs in ERα corepressor SMRT on breast cancer risk and response to endocrine therapy

Abstract #1043

Approximately 1/3 of hormone dependent breast cancers do not respond to tamoxifen treatment. The fact that these tumors are intrinsically resistant suggests that underlying genetic factors are responsible for this phenotype. The two major types of genetic variation are single nucleotide polymorphisms (SNPs) and copy number variations (CNVs). SNPs are the most common form of genetic alteration with an estimated 10 million SNPs across the genome and likely influence both disease susceptibility and response to therapy.&#x2028; Traditionally, researchers have attempted to identify SNPs associated with a clinical outcome in a “top-down” approach by conducting linkage and SNP association studies. However, here we report on a “bottom-up” approach whereby SNPs are first tested in vitro for a functional effect. This awards two benefits over a “top-down” approach: 1) identification of functional SNPs and 2) detailed characterization of the SNP so that the clinical association studies can be designed accordingly.&#x2028; Tamoxifen acts by blocking estradiol (E2) from binding to the estrogen receptor (ERα) and by recruiting corepressors, which then actively repress gene transcription. The critical role of corepressors, especially SMRT, in the proper action of tamoxifen makes them likely to be involved in tamoxifen resistance. Thus, we used a “bottom-up” approach to identify SNPs in ERα corepressors which affect the ability of tamoxifen to suppress ERα function.&#x2028; Here we report the detailed in vitro characterization of a number of SNPs in SMRT (NCoR2) with respect to altered ERα function in the presence of tamoxifen. Further, these SNPs are currently being genotyped so that associations can be made in a population of women receiving tamoxifen as either preventative or adjuvant therapy in which extensive surrogate markers for ERα function were collected during the 1-year follow (hot flash rate, hot flash intensity, lipid profiles, and bone mineral density).&#x2028; Through the discovery of common polymorphisms affecting Tamoxifen response, we hope to identify new diagnostic criteria to predict which patients will respond to anti-estrogen therapy and which will be better candidates for another line of therapy, such as aromatase inhibitors.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1043.

Constitutive expression of the steroid sulfatase gene supports the growth of MCF-7 human breast cancer cells in vitro and in vivo

Many human breast tumors are driven by high intratumor concentrations of 17beta-estradiol that appear to be locally synthesized. The role of aromatase is well established, but the possible contribution of the steroid sulfatase (STS), which liberates estrogens from their biologically inactive sulfates, has been inadequately assessed and remains unclear. To evaluate the role of STS further, we transduced estrogen-dependent MCF-7 human breast cancer cells with a retroviral vector directing the constitutive expression of the human STS gene. Gene integration was confirmed by Southern hybridization, production of the appropriately sized messenger RNA by Northern hybridization, and expression of functional protein by metabolism of [(3)H]estrone sulfate to [(3)H]estrone. Maximum velocity estimates of estrone formation are 64.2 pmol estrone/mg protein.h in STS-transduced cells (STS Clone 20), levels comparable to those seen in some human breast tumors. Lower levels of endogenous activity are seen in MCF-7 cells (13.0 pmol estrone/mg protein.h) and in cells transduced with vector lacking the STS gene (Vector 3 cells; 12.0 pmol estrone/mg protein.h). 17beta-Estradiol sulfate induces expression of the progesterone receptor messenger RNA only in STS Clone 20 cells, whereas estrone sulfate produces the greatest stimulation of anchorage-independent growth in these cells. STS Clone 20 cells retain responsiveness to antiestrogens, which block the ability of estrogen sulfate to increase the proportion of cells in both the S and G(2)/M phases of the cell cycle. Consistent with these in vitro observations, only STS Clone 20 cells exhibit a significant increase in the proportion of proliferating tumors in nude ovariectomized mice supplemented with 17beta-estradiol sulfate. The primary activity in vivo appears to be from intratumor STS, rather than hepatic STS. Surprisingly, 17beta-estradiol sulfate appears more effective than 17beta-estradiol when both are administered at comparable concentrations. This effect, which is seen only in STS Clone 20 cells, may reflect differences in the cellular pharmacology of exogenous estrogens compared with those released by the activity of intracellular STS. These studies directly demonstrate that intratumor STS activity can support estrogen-dependent tumorigenicity in an experimental model and may contribute to the promotion of human breast tumors.

Cellular and molecular pharmacology of antiestrogen action and resistance

Antiestrogen therapy remains one of the most widely used and effective treatments for the management of endocrine responsive breast cancers. This reflects the ability of antiestrogens to compete with estrogens for binding to estrogen receptors. Whereas response rates of up to 70% are reported in patients with tumors expressing estrogen and progesterone receptors, most responsive tumors will eventually acquire resistance. The most important factor in de novo resistance is lack of expression of these receptors. However, the mechanisms driving resistance in tumors that express estrogen and/or progesterone receptors are unclear. A tamoxifen-stimulated phenotype has been described, but seems to occur only in a minority of patients. Most tumors (>80%) may become resistant through other, less well defined, resistance mechanisms. These may be multifactorial, including changes in immunity, host endocrinology, and drug pharmacokinetics. Significant changes within the tumor cells may also occur, including alterations in the ratio of the estrogen receptor alpha:beta forms and/or other changes in estrogen receptor-driven transcription complex function. These may lead to perturbations in the gene network signaling downstream of estrogen receptors. Cells may also alter paracrine and autocrine growth factor interactions, potentially producing a ligand-independent activation of estrogen receptors by mitogen-activated protein kinases. Antiestrogens can affect the function of intracellular proteins and signaling that may, or may not, involve estrogen receptor-mediated events. These include changes in oxidative stress responses, specific protein kinase C isoform activation, calmodulin function, and cell membrane structure/function.

Molecular and pharmacological aspects of antiestrogen resistance

Endocrine therapy is effective in approximately one-third of all breast cancers and up to 80% of tumors that express both estrogen and progesterone receptors. Despite the low toxicity, good overall response rates, and additional benefits associated with its partial agonist activity, most Tamoxifen-responsive breast cancers acquire resistance. The development of new antiestrogens, both steroidal and non-steroidal, provides the opportunity for the development of non-cross-resistant therapies and the identification of additional mechanisms of action and resistance. Drug-specific pharmacologic mechanisms may confer a resistance phenotype, reflecting the complexities of both tumor biology/pharmacology and the molecular endocrinology of steroid hormone action. However, since all antiestrogens will be effective only in cells that express estrogen receptors (ER), many mechanisms will likely be directly related to ER expression and signaling. For example, loss of ER expression/function is likely to confer a cross-resistance phenotype across all structural classes of antiestrogens. Altered expression of ERalpha and ERbeta, and/or signaling from transcription complexes driven by these receptors, may produce drug-specific resistance phenotypes. We have begun to study the possible changes in gene expression that may occur as cells acquire resistance to steroidal and non-steroidal antiestrogens. Our preliminary studies implicate the altered expression of several estrogen-regulated genes. However, resistance to antiestrogens is likely to be a multigene phenomenon, involving a network of interrelated signaling pathways. The way in which this network is adapted by cells may vary among tumors, consistent with the existence of a highly plastic and adaptable genotype within breast cancer cells.

Autoantibodies to the nuclear phosphoprotein nucleophosmin in breast cancer patients

Nucleophosmin (NPM) is an estrogen-regulated nucleolar phosphoprotein; a substrate for phosphorylation by p34cdc2 kinase, protein kinase C, and casein kinase II; and a repressor of the transcriptional regulating activities of the YY1 and IFN regulatory factor-1 transcription factors. We have completed a pilot study to determine whether autoantibodies to NPM are present in breast cancer patients and explored the ability of these autoantibodies to predict recurrence in breast cancer patients. One hundred breast cancer patients were studied: 50 who recurred, and 50 matched for age and length of follow-up but who did not recur. Patients' sera were collected at the times of diagnosis (T1), six months before recurrence (T2), and at recurrence (T3). Recurrent and nonrecurrent patients did not differ in autoantibody levels at the times of diagnosis or recurrence. However, antiNPM autoantibody levels increase significantly between diagnosis and six months before recurrence in recurrent patients, whereas no change occurs over the comparable time period in nonrecurrent patients (repeated measures ANOVA; P = 0.041). At recurrence, the levels return to those seen at diagnosis. The greater the change in levels between T1 and T2, the greater the risk of recurrence within the next 6 months (conditional logistic regression: increase in risk for highest versus lowest tertile of change from T1 to T2; odds ratio, 3.25; 95% confidence interval, 1.04-10.18; P = 0.043). Consistent with the estrogenic/antiestrogenic regulation of the antigen in breast cancer cells, the levels of antiNPM autoantibodies are decreased 6 months before recurrence in patients treated with the antiestrogen tamoxifen (P = 0.012). The association between antiNPM levels and recurrence remained after adjustment for confounding factors. Further study of antiNPM autoantibody levels as a new and simple, intermediate serum biomarker for predicting both the timing of recurrence and monitoring response to endocrine manipulations in breast cancer patients is warranted.

Two-dimensional gel electrophoresis analyses identify nucleophosmin as an estrogen regulated protein associated with acquired estrogen-independence in human breast cancer cells

We have used two-dimensional gel electrophoresis to identify proteins associated with estrogen-induced proliferation in MCF-7 breast cancer cells and their progression to estrogen-independent proliferation. We compared the total cellular proteins from MCF-7 cells and an estrogen independent derivative of the MCF-7 cells MCF-7/LCC1 (Brünner et al. Cancer Research 1993, 53, 283-290), each grown with and without estradiol. These comparisons reveal seven estrogen-regulated proteins. Three of these proteins (HI-1: 36 kDa/pI 4.5, HI-10: 40 kDa/pI 5.5 and HI-19: 62 kDa/pI 5.0) exhibit a 'progression-like' pattern, being induced by estradiol in MCF-7 cells and constitutively present/upregulated in the MCF-7/LCC1 growing without estradiol. HI-11 (65 kDa/pI 5.5) is strongly induced by estradiol in MCF-7 cells but constitutively downregulated and unresponsive to estradiol in the MCF-7/LCC1 cells. Two proteins exhibit a suppressor pattern and are downregulated by estradiol in the estrogen-dependent MCF-7 cells (HI-3: 44 kDa/pI 4.4 and HI-4: 56 kDa/ pI 5.2) and present in MCF-7/LCC1 cells growing without estradiol at levels comparable to that seen in estrogen-treated MCF-7 cells. One protein (HI-9: 68 kDa/pI 5.5) exhibits a marked estrogen regulated pI shift, rather than changes in abundance. We purified and sequenced the HI-10 protein, which we identified as the nucleolar protein, nucleophosmin (NPM). One- and two-dimensional Western blot analyses of MCF-7/LCC1 cell lysates confirmed that HI-10 is immunoreactive with an antinucleophosmin antibody. Western blotting also confirmed the estrogenic regulation of NPM seen in the initial two-dimensional gel electrophoresis studies. Thus, NPM is induced by estradiol in the MCF-7 cells and upregulated in the MCF-7/LCC1 cells growing without estrogen, clearly associating its expression with an acquired estrogen-independent phenotype. NPM has several potentially important roles in regulating cell function and signaling. It is a substrate for phosphorylation by p34cdc2 kinase, protein kinase C and nuclear kinase II, and a repressor of the transcriptional regulating activities of both the IRF-1 tumor suppressor protein and the YY1 transcription factor. Studies are currently underway to determine which of these NPM functions may be involved in the hormonal progression of breast cancer.

MCF7/LCC9: an antiestrogen-resistant MCF-7 variant in which acquired resistance to the steroidal antiestrogen ICI 182,780 confers an early cross-resistance to the nonsteroidal antiestrogen tamoxifen

Acquired resistance to antiestrogens is a major problem in the clinical management of initially endocrine responsive metastatic breast cancer. We have shown previously that estrogen-independent and -responsive MCF7/LCC1 human breast cancer cells selected for resistance to the triphenylethylene tamoxifen produce a variant (MCF7/LCC2) that retains sensitivity to the steroidal antiestrogen ICI 182,780 (N. Brunner et al., Cancer Res., 53: 3229-3232, 1993). We have now applied stepwise selections in vitro from 10 pM to 1 microM ICI 182,780 against MCF7/LCC1 and obtained a stable ICI 182,780-resistant variant designated MCF7/LCC9. In contrast to 4-hydroxytamoxifen-selected MCF7/LCC2 cells, MCF7/LCC9 cells exhibit full cross-resistance to tamoxifen, despite never having been exposed to this drug. Significantly, tamoxifen cross-resistance arose early in the selection, appearing following selection against only 0.1 nM ICI 182,780. Although limited resistance to ICI 182,780 also was observed, full ICI 182,780 resistance was not detected until the selective pressure increased to 100 nM ICI 182,780. Cross-resistance to tamoxifen persisted throughout these additional selections. Despite their antiestrogen cross-resistance, MCF7/LCC9 cells retain a level of estrogen receptor expression comparable to that of their parental MCF7/LCC1 cells. Whereas MCF7/LCC1 cells retain an estrogen-inducible expression of progesterone receptors, MCF7/LCC9 cells exhibit an up-regulated expression of both progesterone receptor mRNA and protein that is no longer estrogen responsive. Estrogen-independent and -responsive components of the MCF7/LCC9 phenotype are apparent in vivo. These cells form slowly growing tumors in ovariectomized athymic nude mice but respond mitogenically upon estrogenic supplementation. The in vivo growth of MCF7/LCC9 tumors is not affected by treatment with ICI 182,780. Although there is some evidence of tamoxifen stimulation of tumor growth, this did not reach statistical significance. If this pattern of cross-resistance occurs in some breast cancer patients, administering triphenylethylene antiestrogens as a first-line therapy with a cross-over to steroidal compounds upon recurrence may be advantageous.

Diet effects and ontogeny of alterations of circulating insulin-like growth factor binding proteins in newborn dairy calves

Insulin-like growth factors (IGF) are important growth regulators in many species, and their effects are influenced by their association with IGF-binding proteins (IGFBP). The objectives of this study were to characterize the ontogeny of the blood plasma IGFBP in calves and to determine the effect of dietary IGF-I neonatal plasma IGFBP. Plasma from newborn and 7-d-old male calves fed milk replacer, milk replacer + recombinant human IGF-I (rhIGF-I), or colostrum for 2 d followed by milk replacer was analyzed for IGFBP by ligand blot analysis. In addition, plasma samples from 1-, 12-, 24-, and 45-wk-old male calves were analyzed for IGFBP and IGF-I. Newborn and 7-d-old calf plasma contained IGFBP with M(r) of 26, 34, and 42 to 48 kDa. These profiles were not affected by the dietary treatments; however, a slight increase in the 34-kDa IGFBP and a slight decrease in the 26- and 42- to 48-kDa IGFBP were detected from birth to 7 d of age. The 34-kDa was confirmed to be bovine IGFBP-2 by immunoblot and the 42- to 48-kDa is likely IGFBP-3. The 29-, 31-, and 42- to 48-kDa IGFBP increased between 1 and 45 wk of age. Similarly, plasma IGF-I concentrations were increased from 49.7 to 449.7 ng/mL in plasma from calves from 1 to 45 wk of age. In contrast, the 34-kDa IGFBP increased from 1 to 12 wk but then gradually decreased from 12 to 45 wk, whereas the 26-kDa IGFBP did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of insulin-like growth factor binding protein secretion by a murine mammary epithelial cell line

The regulation of insulin-like growth factor binding protein (IGFBP) secretion by mammogenic and lactogenic hormones was investigated in a mouse mammary epithelial cell line (COMMA-D/MME). Cells were grown to confluency on plastic culture plates in serum-containing medium. The confluent cells were exposed to the hormonal treatments in serum-free medium for 6 days. Conditioned medium was collected on Days 5 and 6 and analyzed for IGFBPs by 125I-labeled insulin-like growth factor (IGF)-II ligand blotting and quantified by densitometry. IGFBP data were expressed as absorbance units x millimeters (AUxmm) that were corrected for DNA per well. In basal serum-free media, the COMMA-D/MME cells secreted predominantly IGFBP-3, but also some IGFBP-2. The mammogenic growth factors, IGF-I (13.3 nM) and epidermal growth factor (EGF; 1.7 nM), both stimulated DNA synthesis (P < 0.05); however, their effects on IGFBP-3 secretion differed. IGF-I stimulated IGFBP-3 secretion whereas EGF was inhibitory. In addition, EGF inhibited IGFBP-2 secretion and IGF-I tended to increase it. No interaction was observed between IGF-I and EGF for any of the parameters measured. Three lactogenic hormones (insulin, 154 nM; prolactin, 4.3 nM; and cortisol, 1.4 microM) in all combinations were tested to determine their effects on IGFBP secretion. Insulin stimulated IGFBP-3 secretion and DNA synthesis, but had no effect on IGFBP-2 secretion. Cortisol inhibited IGFBP-3 secretion and DNA synthesis, but increased IGFBP-2 secretion. Prolactin had no effect on any of the parameters examined. In summary, the COMMA-D/MME cells secrete IGFBP-2 and IGFBP-3 in serum-free media. Although the secretion of IGFBP-2 and IGFBP-3 in serum-free media. Although the secretion of IGFBP-2 and IGFBP-3 was regulated by several of the hormones and growth factors tested, no clear distinction was observed between the mammogenic and lactogenic treatments.

Changes in insulin-like growth factor-binding proteins in bovine mammary secretions associated with pregnancy and parturition

The bovine mammary gland accumulates large quantities of insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) during late gestation which are secreted at parturition. The present study was conducted to determine the changes in the profiles of IGFBPs secreted by the mammary gland and in blood during late gestation and early lactation in dairy cows. Ligand blotting of serum and mammary secretions showed that IGFBPs of Mr 25,000, 30,000, 34,000, 42,000, 46,000 and greater than 200,000 were present in both fluids. The binding activity of the 42-46,000 Mr IGFBP predominated in prepartum mammary secretions and colostrum but was reduced postpartum. The binding activities of the 30,000 and 34,000 Mr IGFBPs, relative to other IGFBPs, were increased postpartum. Concentrations of IGF-I and IGF-II in mammary secretions declined from 347.1 and 181.1 nmol/litre 1 week prepartum to 0.7 and 0.3 nmol/litre 1.5 weeks postpartum. The volume of mammary secretions obtained was 0.109 litre and 6.690 litres at 1 week prepartum and 1.5 weeks postpartum respectively. In prepartum serum, the greatest binding activity was at Mr 42-46,000. The activity at this Mr decreased at parturition but was restored postpartum. The binding activities of the 30,000 and 34,000 Mr IGFBPs were increased around parturition. The 25,000 Mr IGFBP had minor activity during all periods. IGF-I concentrations decreased from 10.6 nmol/litres 1 week prepartum to 4.7 nmol/litres 1.5 weeks postpartum but IGF-II concentrations remained constant. In conclusion, IGFBP activity secreted by the mammary gland shifts from primarily Mr 42-46,000 prepartum to Mr 30,000 postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor (IGF)-I and -II and IGF binding proteins in serum and mammary secretions during the dry period and early lactation in dairy cows

Concentrations of IGF-I and IGF-II, and IGF binding proteins (IGFBP) in serum and mammary gland secretions were surveyed during the dry period and early lactation of 30 Holstein cows. Although there was a threefold drop in the concentration of IGF-I in serum from the last week of the dry period to parturition (81 +/- 7 to 24 +/- 3 ng/ml, P less than .01), there was no significant change in serum IGF-II concentration during this period (150 +/- 17 vs 173 +/- 13 ng/ml, P greater than .05). Furthermore, a 57% increase in serum IGF-I was observed from the last week of lactation to the second week of drying off (100 +/- 5 to 157 +/- 8 ng/ml, P less than .05). Changes in serum IGF-II were not observed (126 +/- 11 vs 150 +/- 10 ng/ml, respectively; P greater than .05). Although IGF-I, IGF-II, and IGFBP concentrations in mammary secretions peaked 2 wk before parturition (2.95 +/- 1.1, 1.83 +/- .6, and 7.27 +/- .76 micrograms/ml, respectively), total output/quarter was highest in colostrum (394 +/- 119, 295 +/- 132, and 2,680 +/- 1,967 micrograms/quarter, respectively). Weekly milking of two individual quarters during the dry period did not affect (P greater than .05) IGF-I or IGF-II concentration (ng/ml) or total output (microgram/quarter) and milk yield in colostrum and milk (2 wk and 7 wk) compared with the ipsilateral quarter. The data support the hypothesis that IGF-I may be transported by the mammary gland epithelium. Furthermore, the secretion mechanisms of IGF-I, IGF-II, and IGFBP by the gland may be related to each other.

Secretion of insulin-like growth factor-I (IGF-I) and IGF-binding proteins from bovine mammary tissue in vitro

In vitro, insulin-like growth factor-I (IGF-I) promotes both growth and development of bovine mammary tissue. In vivo, the effects of IGF-I may encompass endocrine, paracrine or autocrine mediation. We addressed the possibility of paracrine/autocrine effects of IGF-I in the mammary gland by examining the in-vitro secretion of IGF-I and IGF-binding proteins (IGFBPs) from bovine mammary tissue. Bovine mammary explants from pregnant non-lactating and lactating non-pregnant animals were found to synthesize and secrete IGF-I and IGFBPs. Mammary acini cultures, representative of mammary secretory epithelia, secreted both IGF-I and IGFBP, but synthesized only IGFBP. Concentrations of IGF-I in conditioned media from explants were 1.54 and 0.72 fmol/micrograms DNA for pregnant and lactating animals respectively. Concentrations of IGFBPs in conditioned media from explants were similar for both physiological states at 2529 pmol 125I-labelled IGF-I bound/micrograms DNA. Ligand/Western blotting procedures identified four IGFBPs of 29, 33, 37 and 44 kDa for acini cultures and five IGFBPs of 28, 31, 36, 44 and 46 kDa for explant cultures. Similar affinities for IGF-I and IGF-II were shown by IGFBP, using 125I-labelled recombinant human IGF-I as the competing ligand (median effective dose (ED50) of 0.085 pmol). When 125I-labelled bovine IGF-II was used as the ligand, only bovine IGF-II (ED50 of 0.25 pmol) inhibited binding. The addition of prolactin, insulin and cortisol, with or without GH, did not affect secretion of either IGF-I or IGFBP. This report describes the ability of normal mammary tissue to synthesize and secrete IGF-I and IGFBPs.

Effects of energy balance on hepatic capacity for oleate and propionate metabolism and triglyceride secretion

The purpose of this study was to identify conditions that could decrease accumulation of triglyceride in liver, preferably by increasing hepatic secretion of triglyceride-rich lipoproteins. Hepatocytes isolated from lactating goats were incubated in vitro, and the fate of [1-14C]oleate was measured to determine hepatic capacity for various routes of long-chain fatty acid metabolism. The effect of in vivo energy balance and modifications of the nutrients present in the culture media were tested. Addition of linoleic acid, isovalerate, niacin, propionate, or propylene glycol did not affect triglyceride accumulation or secretion. Pyruvate decreased intracellular triglyceride accumulation. Changes in oxidation of oleate through manipulation of carnitine acyl transferase activity did not influence oleate esterification rate. Livers and hepatocytes isolated from goats in negative energy balance contained more lipid and triglyceride. Liver cells from goats in negative energy balance had decreased capacity for converting propionate to glucose with no change in ketogenic capacity as judged by acid soluble product formation from oleate. Hepatocytes from goats in negative energy balance retained less oleate as cell triglyceride with no change in triglyceride export, indicating a decreased net rate of esterification. Lactating goats, either in negative or positive energy balance, demonstrated the same low capacity for export of newly synthesized triglyceride as previously reported for fed wethers.

Seasonal effects of prepartum and postpartum fat and niacin feeding on lactation performance and lipid metabolism

Control, prilled fat (5% of ration DM), niacin (12 g/d), or fat and niacin treatments were fed to 39 Holstein cows beginning 17 d prior to expected calving through 15 wk postpartum to determine effects on hepatic lipid content, plasma ketone concentration, and lactation performance. Cows were blocked according to season of calving (cool = November 1 through April 1; warm = April 2 through August 1). Fat supplementation tended to increase milk yield but only for cows that calved in the warm season. Milk composition was not affected by treatments. Fat supplementation did not decrease BW loss in early lactation but increased rate of BW gain af ter 8 wk postpartum. Dry matter intake and glucose, nonesterified fatty acid, and beta-hydroxybutyrate concentrations in plasma were not different among treatments. Fat and niacin supplementation tended to increase hepatic total lipid and triglyceride content. Between 17 d prior to expected calving and 1 to 2 d postpartum, hepatic lipid content increased approximately 2-fold and triglyceride content increased 6- to 10-fold. Hepatic lipid and triglyceride contents were greater postpartum during the warm season than the cool season and were greater at 5 wk than at freshening during the warm season but lower at 5 wk than at freshening during the cool season. The cause of the dramatic increase in hepatic lipid and triglyceride content prepartum is unknown.

Distribution of lipid in hepatic tissue of dairy goats in positive and negative energy balance

Liver biopsies are commonly used to obtain tissue to determine hepatic lipid content in ruminants, particularly the dairy cow. The location of the biopsy is unknown and it is assumed that the sample is representative of the entire organ. This study investigated the distribution of lipid in the caudate, left, right, and quadrate lobes of goat livers having normal or elevated lipid content. Goats that experienced negative energy balance for 4 days had significantly greater hepatic total lipids, primarily due to a 4-fold increase in triglycerides, than goats in positive energy balance. Triglyceride concentrations were similar among lobes within energy balance groups. Within the positive energy balance treatment, the caudate lobe had a significantly greater total lipid concentration than the other lobes, which had a similar lipid concentration. Total lipid concentrations were similar among lobes obtained from goats in negative energy balance.