CYP2D6 and tamoxifen: DNA matters in breast cancer

Overcoming endocrine resistance in hormone receptor-positive breast cancer

Endocrine therapy, a major modality in the treatment of hormone receptor (hr)-positive breast cancer (bca), has improved outcomes in metastatic and nonmetastatic disease. However, a limiting factor to the use of endocrine therapy in bca is resistance resulting from the development of escape pathways that promote the survival of cancer cells despite estrogen receptor (er)-targeted therapy. The resistance pathways involve extensive cross-talk between er and receptor tyrosine kinase growth factors [epidermal growth factor receptor, human epidermal growth factor receptor 2 (her2), and insulin-like growth factor 1 receptor] and their downstream signalling pathways-most notably pi3k/akt/mtor and mapk. In some cases, resistance develops as a result of genetic or epigenetic alterations in various components of the signalling pathways, such as overexpression of her2 and erα co-activators, aberrant expression of cell-cycle regulators, and PIK3CA mutations. By combining endocrine therapy with various molecularly targeted agents and signal transduction inhibitors, some success has been achieved in overcoming and modulating endocrine resistance in hr-positive bca. Established strategies include selective er downregulators, anti-her2 agents, mtor (mechanistic target of rapamycin) inhibitors, and inhibitors of cyclin-dependent kinases 4 and 6. Inhibitors of pi3ka are not currently a treatment option for women with hr-positive bca outside the context of clinical trial. Ongoing clinical trials are exploring more agents that could be combined with endocrine therapy, and biomarkers that would help to guide decision-making and maximize clinical efficacy. In this review article, we address current treatment strategies for endocrine resistance, and we highlight future therapeutic targets in the endocrine pathway of bca.

Anticancer effect of acid ceramidase inhibitor ceranib-2 in human breast cancer cell lines MCF-7, MDA MB-231 by the activation of SAPK/JNK, p38 MAPK apoptotic pathways, inhibition of the Akt pathway, downregulation of ERα

Acid ceramidase is the key enzyme of the ceramide metabolic pathway, which plays a vital role in regulating ceramide - sphingosine-1-phosphate rheostat. Ceramide acts as a proapoptotic molecule, but its metabolite sphingosine-1-phosphate, in contrast, signals for cell proliferation, cell survival, and angiogenesis. Acid ceramidase is highly upregulated in breast tumors and treatment with an acid ceramidase inhibitor, ceranib-2, significantly induced apoptosis in human breast cancer cell lines. However, the mechanisms underlying the induction of apoptosis remain ambiguous to date. Hence, in the present study, we have explored ceranib-2-mediated apoptotic signaling pathways in human breast cancer cell lines. MCF-7 and MDA MB-231 cells were treated with IC50 doses of ceranib-2 and tamoxifen. Nuclear changes showed the apoptotic effect of ceranib-2 in both the cell lines. Loss in the mitochondrial membrane potential was observed only in ceranib-2-treated MCF-7 cells. Ceranib-2 activated intrinsic and extrinsic apoptotic pathways in MCF-7 cells, but only the extrinsic apoptotic pathway was activated in MDA MB-231 cells. Further, ceranib-2 induced apoptosis by activating SAPK/JNK (stress-activated protein kinase/c-Jun N-terminal kinase), p38 MAPK (mitogen-activated protein kinase) apoptotic pathways and by inhibiting the Akt (antiapoptotic) pathway in both the cell lines. Most importantly, ERα (estrogen receptor-α) expression was highly downregulated after ceranib-2 treatment and a docking study predicted the highest binding affinity of ceranib-2 than tamoxifen with ERα in MCF-7 cells. Hence, ceranib-2 may have potential as a chemotherapeutic drug of breast cancer.

Cytochrome P450 Genetic Variation Associated with Tamoxifen Biotransformation in American Indian and Alaska Native People

Despite evidence that pharmacogenetics can improve tamoxifen pharmacotherapy, there are few studies with American Indian and Alaska Native (AIAN) people. We examined variation in cytochrome P450 (CYP) genes (CYP2D6, CYP3A4, CYP3A5, and CYP2C9) and tamoxifen biotransformation in AIAN patients with breast cancer (n = 42) from the Southcentral Foundation in Alaska and the Confederated Salish and Kootenai Tribes in Montana. We tested for associations between CYP diplotypes and plasma concentrations of tamoxifen and metabolites. Only the CYP2D6 variation was significantly associated with concentrations of endoxifen (P = 0.0008) and 4-hydroxytamoxifen (P = 0.0074), tamoxifen's principal active metabolites, as well as key metabolic ratios. The CYP2D6 was also the most significant predictor of active metabolites and metabolic ratios in a multivariate regression model, including all four genes as predictors, with minor roles for other CYP genes. In AIAN populations, CYP2D6 is the largest contributor to tamoxifen bioactivation, illustrating the importance of validating pharmacogenetic testing for therapy optimization in an understudied population.

A multi-gram-scale stereoselective synthesis of Z-endoxifen

Z-Endoxifen is widely regarded as the most active metabolite of tamoxifen, and has recently demonstrated a 26.3% clinical benefit in a phase I clinical trial to treat metastatic breast cancer after the failure of standard endocrine therapy. Future pharmacological and pre-clinical studies of Z-endoxifen would benefit from reliable and efficient synthetic access to the drug. Here, we describe a short and efficient, stereoselective synthesis of Z-endoxifen capable of delivering multi-gram (37 g) quantities of the drug in >97% purity with a Z/E ratio >99% after trituration.

Detection of Cytochrome P450 Polymorphisms in Breast Cancer Patients May Impact on Tamoxifen Therapy

Background:

Breast cancer is the most common cancer among women worldwide. Tamoxifen (TAM), a selective estrogen receptor modulator, is widely used in its treatment. TAM is metabolized by cytochrome P450 (CYP450) enzymes, including CYP2D6, CYP3A5 and CYP2C19, whose genetic variations may have clinicopathological importance. However, reports on the association of various P450 polymorphisms with certain cancers are contradictory.

Methods:

We here investigated whether the prevalence of the four most common polymorphism in the CYP2D6*4 (G1934A), CYP2D6*10 (C188T), CYP3A5*3 and CYP2C19*2 alleles has any link with breast cancer using genomic DNA and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis.

Results:

Prevalences of CYP2D6*4, CYP2D6*10 and CYP2C19*2 genotypes were differed significantly (P = 0.01 and P = 0.004) between breast cancer patients and controls. The CYP3A5*3 genotype did not demonstrate statistically significant variation.

Conclusion:

Polymorphisms in CYP2 appear to be associated with breast cancer risk. Our data taken together with other reports indicates that drug resistance gene polymorphisms might be indicators of response to tamoxifen therapy in breast cancer cases.

Pharmacogenetic Analysis of the UK MRC (Medical Research Council) MAGIC Trial: Association of Polymorphisms with Toxicity and Survival in Patients Treated with Perioperative Epirubicin, Cisplatin, and 5-fluorouracil (ECF) Chemotherapy

Purpose: Germline polymorphisms may affect chemotherapy efficacy and toxicity. We examined the effect of polymorphisms in drug metabolism and DNA repair genes on pathologic response rates, survival, and toxicity for patients randomized to surgery alone or perioperative ECF chemotherapy in the MRC MAGIC trial.Experimental Design: DNA was extracted from nontumor resection formalin-fixed paraffin-embedded (FFPE) blocks. ERCC1, ERCC2, XRCC1, DYPD, and OPRT SNPs were evaluated using Sequenom, GSTP1, GSTT1 deletion, and TYMS (TS) 5' 2R/3R using multiplex PCR. Post PCR amplification, TS 2R/3R and GSTT1 samples underwent gel electrophoresis.Results: Polymorphism data were available for 289 of 456 (63.4%) operated patients. No polymorphism was statistically significantly associated with pathologic response to chemotherapy. Median overall survival (OS) for patients treated with surgery alone with any TS genotype was not different (1.76 years 2R/2R, 1.68 years 2R/3R, 2.09 years 3R/3R). Median OS for patients with a TS 2R/2R genotype treated with chemotherapy was not reached, whereas median OS for 2R/3R and 3R/3R patients were 1.44 and 1.60 years, respectively (log rank P value = 0.0053). The P value for the interaction between treatment arm and genotype (3R/3R and 3R/2R vs. 2R/2R) was 0.029. No polymorphism was statistically significantly associated with chemotherapy toxicity.Conclusions: In MAGIC, patients with a TS 2R/2R genotype appeared to derive a larger benefit from perioperative ECF chemotherapy than patients with 3R containing genotypes. Further exploration of this potential predictive biomarker in this patient population is warranted. Clin Cancer Res; 23(24); 7543-9. ©2017 AACR.

Enhancement of the bioavailability of a novel anticancer compound (acetyltanshinone IIA) by encapsulation within mPEG-PLGA nanoparticles: a study of formulation optimization, toxicity, and pharmacokinetics

The Poly (ethylene glycol) methyl ether-block-poly (lactide-co-glycolide) (mPEG-PLGA) nanoparticles carrying acetyltanshinone IIA (ATA), a novel anti-breast cancer agent, were prepared by ultrasonic emulsion method to enhance the bioavailability and reduce the toxicity. Systematic optimization of encapsulation process was achieved using an orthogonal design. Drug efficacy analysis showed that ATA nanoparticles were as effective as free ATA against estrogen receptor positive breast cancer cells, but much less toxic towards human endothelial cells. Furthermore, in zebrafish, ATA nanoparticles displayed much lower toxicity than free ATA. More importantly, the blood concentration of ATA nanoparticles indicated by 24 hour-area under the curve (AUC_0-24h) was 10 times higher than free ATA. These results indicated the potential of ATA-loaded mPEG-PLGA nanoparticles for the delivery of ATA in a clinical formulation, and their potential for use in tumor therapy in the future.

Pharmacogenetics of UGT1A4, UGT2B7 and UGT2B15 and Their Influence on Tamoxifen Disposition in Asian Breast Cancer Patients

Tamoxifen (TAM) is an established endocrine treatment for all stages of oestrogen receptor (ER)-positive breast cancer. Its complex metabolism leads to the formation of multiple active and inactive metabolites. One of the main detoxification and elimination pathways of tamoxifen and its active metabolites, 4-hydroxytamoxifen (4-OHT) and endoxifen, is via glucuronidation catalysed by uridine 5'-diphospho-glucuronosyltransferases (UGTs). However, few studies have comprehensively examined the impact of variations in the genes encoding the major hepatic UGTs on the disposition of tamoxifen and its metabolites. In the present study, we systematically sequenced exons, exon/intron boundaries, and flanking regions of UGT1A4, UGT2B7 and UGT2B15 in 240 healthy subjects of different Asian ethnicities (Chinese, Malays and Indians) to identify haplotype tagging single nucleotide polymorphisms. Subsequently, 202 Asian breast cancer patients receiving tamoxifen were genotyped for 50 selected variants in the three UGT genes to comprehensively investigate their associations with steady-state plasma levels of tamoxifen, its active metabolites and their conjugated counterparts. The UGT1A4 haplotype (containing variant 142T>G, L48 V defining the *3 allele) was strongly associated with higher plasma levels of TAM-N-glucuronide, with a twofold higher metabolic ratio of TAM-N-glucuronide/TAM observed in carriers of this haplotype upon covariate adjustment (P < 0.0001). Variants in UGT2B7 were not associated with altered O-glucuronidation of both 4-OHT and endoxifen, while UGT2B15 haplotypes had a modest effect on (E)-endoxifen plasma levels after adjustment for CYP2D6 genotypes. Our findings highlight the influence of UGT1A4 haplotypes on tamoxifen disposition in Asian breast cancer patients, while genetic variants in UGT2B7 and UGT2B15 appear to be of minor importance.

Exploring public genomics data for population pharmacogenomics

Racial and ethnic differences in drug responses are now well studied and documented. Pharmacogenomics research seeks to unravel the genetic underpinnings of inter-individual variability with the aim of tailored-made theranostics and therapeutics. Taking into account the differential expression of pharmacogenes coding for key metabolic enzymes and transporters that affect drug pharmacokinetics and pharmacodynamics, we advise that data interpretation and analysis need to occur in light of geographical ancestry, if implications for drug development and global health are to be considered. Herein, we exploit ePGA, a web-based electronic Pharmacogenomics Assistant and publicly available genetic data from the 1000 Genomes Project to explore genotype to phenotype associations among the 1000 Genomes Project populations.

CYP2D6 polymorphisms may predict occurrence of adverse effects to tamoxifen: a preliminary retrospective study

INTRODUCTION AND AIMS

Tamoxifen is an adjuvant drug effective in treating hormone receptor - positive breast cancer. However, 30%-50% of patients relapse and many develop adverse effects, such as hot flashes and fatty liver. Allelic variations altering the activity of cytochrome P450-2D6 enzyme affect response to tamoxifen by modulating metabolism of tamoxifen into its pharmacologically active metabolite endoxifen. Although association between CYP2D6 polymorphisms and recurrence of breast cancer in patients on tamoxifen had been reported, little evidence exists on association between these polymorphisms and adverse effects to tamoxifen. This study explored the association between CYP2D6 polymorphisms and tamoxifen effects, hitherto not studied in Sri Lanka.

METHODS

A retrospective preliminary study was carried out on 24 breast cancer patients on tamoxifen for minimally 3 months attending National Cancer Institute, Maharagama, Sri Lanka. They were not on CYP2D6-inhibiting drugs, chemotherapy or other endocrine therapy, and had no conditions that could occur as adverse effects to tamoxifen before starting the therapy. Their blood samples were collected, DNA was extracted and genotyped using SNaPshot Multiplex sequencing based single-nucleotide polymorphism (SNP) assay.

RESULTS

SNP/allele frequencies detected: 1846G>A (confirmatory of *4 null allele)=8.3%; 2549delA (confirmatory of *3 null allele)=50%; 100C>T (suggestive of *10 reduced functional allele, in addition to other alleles)=0%; combination of 2988G>A, -1584C and 2850C>T (strongly suggestive of *41 or other reduced functional allele)=4.8%. Occurrence of heterozygous 2988G>A SNP with -1584C and 2850C>T was significantly higher among those with ultrasound-diagnosed fatty liver following the commencement of tamoxifen therapy (P=0.029). Adverse effects occurred at a significantly higher frequency among postmenopausal women (P=0.041). Three patients who developed recurrence of breast cancer had no association with SNPs tested.

CONCLUSIONS

CYP2D6 SNP combination 2988G>A, -1584C and 2850C>T, strongly suggestive of *41 reduced functional allele, is likely to be useful in predicting occurrence of adverse effect fatty liver in breast cancer patients on tamoxifen, thereby alternative treatment can be considered and lifestyle modifications implemented. Larger sample studies are recommended with the measurement of tamoxifen and metabolite levels. Alternative therapy should be considered for postmenopausal patients.

CYP2D6 polymorphisms may predict occurrence of adverse effects to tamoxifen: a preliminary retrospective study

INTRODUCTION AND AIMS

Tamoxifen is an adjuvant drug effective in treating hormone receptor - positive breast cancer. However, 30%-50% of patients relapse and many develop adverse effects, such as hot flashes and fatty liver. Allelic variations altering the activity of cytochrome P450-2D6 enzyme affect response to tamoxifen by modulating metabolism of tamoxifen into its pharmacologically active metabolite endoxifen. Although association between CYP2D6 polymorphisms and recurrence of breast cancer in patients on tamoxifen had been reported, little evidence exists on association between these polymorphisms and adverse effects to tamoxifen. This study explored the association between CYP2D6 polymorphisms and tamoxifen effects, hitherto not studied in Sri Lanka.

METHODS

A retrospective preliminary study was carried out on 24 breast cancer patients on tamoxifen for minimally 3 months attending National Cancer Institute, Maharagama, Sri Lanka. They were not on CYP2D6-inhibiting drugs, chemotherapy or other endocrine therapy, and had no conditions that could occur as adverse effects to tamoxifen before starting the therapy. Their blood samples were collected, DNA was extracted and genotyped using SNaPshot Multiplex sequencing based single-nucleotide polymorphism (SNP) assay.

RESULTS

SNP/allele frequencies detected: 1846G>A (confirmatory of *4 null allele)=8.3%; 2549delA (confirmatory of *3 null allele)=50%; 100C>T (suggestive of *10 reduced functional allele, in addition to other alleles)=0%; combination of 2988G>A, -1584C and 2850C>T (strongly suggestive of *41 or other reduced functional allele)=4.8%. Occurrence of heterozygous 2988G>A SNP with -1584C and 2850C>T was significantly higher among those with ultrasound-diagnosed fatty liver following the commencement of tamoxifen therapy (P=0.029). Adverse effects occurred at a significantly higher frequency among postmenopausal women (P=0.041). Three patients who developed recurrence of breast cancer had no association with SNPs tested.

CONCLUSIONS

CYP2D6 SNP combination 2988G>A, -1584C and 2850C>T, strongly suggestive of *41 reduced functional allele, is likely to be useful in predicting occurrence of adverse effect fatty liver in breast cancer patients on tamoxifen, thereby alternative treatment can be considered and lifestyle modifications implemented. Larger sample studies are recommended with the measurement of tamoxifen and metabolite levels. Alternative therapy should be considered for postmenopausal patients.

Challenges in assigning endocrine-specific modes of action: Recommendations for researchers and regulators

As regulatory programs evaluate substances for their endocrine-disrupting properties, careful study design and data interpretation are needed to distinguish between responses that are truly endocrine specific and those that are not. This is particularly important in regulatory environments where criteria are under development to identify endocrine-disrupting properties to enable hazard-based regulation. Irrespective of these processes, most jurisdictions use the World Health Organization/International Programme on Chemical Safety definition of an endocrine disruptor, requiring that a substance is demonstrated to cause a change in endocrine function that consequently leads to an adverse effect in an intact organism. Such a definition is broad, and at its most cautious might capture many general mechanisms that would not specifically denote an endocrine disruptor. In addition, endocrine responses may be adaptive in nature, designed to maintain homeostasis rather than induce an irreversible adverse effect. The likelihood of indirect effects is increased in (eco)toxicological studies that require the use of maximum tolerated concentrations or doses, which must produce some adverse effect. The misidentification of indirect effects as truly endocrine mediated has serious consequences for prompting animal- and resource-intensive testing and regulatory consequences. To minimize the risk for misidentification, an objective and transparent weight-of-evidence procedure based on biological plausibility, essentiality, and empirical evidence of key events in an adverse outcome pathway is recommended to describe the modes of action that may be involved in toxic responses in nontarget organisms. Confounding factors such as systemic toxicity, general stress, and infection can add complexity to such an evaluation and should be considered in the weight of evidence. A recommended set of questions is proffered to help guide researchers and regulators in discerning endocrine and nonendocrine responses. Although many examples provided in this study are based on ecotoxicology, the majority of the concepts and processes are applicable to both environmental and human health assessments. Integr Environ Assess Manag 2017;13:280-292. © 2016 SETAC.

Complications and thromboembolic events associated with tamoxifen therapy in patients with breast cancer undergoing microvascular breast reconstruction: a systematic review and meta-analysis

PURPOSE

Tamoxifen therapy is integral in the treatment of patients with hormone receptor-positive breast cancer. However, there is an association between tamoxifen and thromboembolic events. Flap and systemic thromboembolic events have devastating consequences in microvascular breast reconstruction. Currently, there are conflicting data on the association between tamoxifen therapy and thromboembolic complications for patients undergoing microvascular breast reconstruction. The objective of this study is to determine if perioperative tamoxifen therapy modifies the risk of complications and thromboembolic events for patients with breast cancer undergoing microvascular breast reconstruction.

METHODS

A comprehensive literature search was performed across six databases from January 2003 to February 2016. Pooled estimates and relative risk (RR) were calculated using a random-effects model, confounding was examined with meta-regression, and risk of bias was evaluated. Primary outcomes were thrombotic flap complications and total flap loss. Study quality was assessed using Downs and Black criteria.

RESULTS

Of 95 studies reviewed, 4 studies comprising 1700 patients and 2245 procedures were included for analysis. Compared to non-recipients, patients on tamoxifen were at increased risk of developing thrombotic flap complications (pooled RR 1.5; 95% CI 1.14-1.98) and total flap loss (pooled RR 3.35; 95% CI 0.95-11.91). There was no significant heterogeneity present in either outcome and no evidence of publication bias.

CONCLUSIONS

Perioperative tamoxifen therapy may increase the risk of thrombotic flap complications and flap loss for patients with breast cancer undergoing microvascular reconstruction. These findings further the ability of providers to make evidence-based recommendations in the perioperative management of patients with breast cancer.

Augmentation of Endoxifen Exposure in Tamoxifen-Treated Women Following SSRI Switch

BACKGROUND AND OBJECTIVE

The anti-oestrogen tamoxifen requires metabolic activation to endoxifen by cytochrome P450 (CYP) enzymes, predominantly CYP2D6. Potent CYP2D6-inhibiting antidepressants can seriously disrupt tamoxifen metabolism, probably influencing the efficacy of tamoxifen. For this reason, paroxetine and fluoxetine are recommended not to be used with tamoxifen in breast cancer patients. We investigated the effects of switching potent CYP2D6-inhibiting antidepressants to weak CYP2D6-inhibiting antidepressants on the plasma pharmacokinetics of tamoxifen.

METHODS

Ten breast cancer patients who were treated with tamoxifen in combination with a potent CYP2D6-inhibiting antidepressant (paroxetine or fluoxetine) for at least 4 weeks were enrolled. Under close supervision by a psychiatrist, patients were switched to treatment with escitalopram or venlafaxine (weak CYP2D6-inhibiting antidepressants). Before and after the switch, pharmacokinetic blood sampling was performed over 24 h. Pharmacokinetic parameters were estimated using noncompartmental analysis. Adverse effects were recorded during the study.

RESULTS

Endoxifen exposure was ~3-fold higher during escitalopram co-administration than during paroxetine or fluoxetine co-administration (median 387 nM·h [range 159-637 nM·h] versus 99.2 nM·h [range 70.0-210 nM·h]; P = 0.012; Wilcoxon signed-rank test). The ratio of endoxifen to N-desmethyltamoxifen and the ratio of 4-hydroxytamoxifen to tamoxifen increased by 3.3- and ~1.5-fold, reflecting increased CYP2D6 activity. Antidepressant switching did not result in psychiatric problems or antidepressant-related adverse effects.

CONCLUSION

In this study, switching to the weak CYP2D6 inhibitor escitalopram was safe and feasible and resulted in clinically relevant rises in endoxifen concentrations. We therefore advise switching paroxetine and fluoxetine to escitalopram in patients using tamoxifen. However, switching should always be weighed in individual patients.

CYP2D6 gene polymorphisms in Brazilian patients with breast cancer treated with adjuvant tamoxifen and its association with disease recurrence

At present, there is controversy regarding the efficacy of tamoxifen in breast cancer patients who are carriers of cytochrome P450 2D6 (CYP2D6) gene polymorphisms, in terms of recurrence and overall survival. Thus, the aim of the present study was to investigate the association of the CYP2D6 *4, *10 and *17 gene polymorphisms with breast cancer recurrence in a Brazilian population. The cohort comprised 40 receptor-positive breast cancer patients without recurrence and 40 with distant recurrence. A 3-ml sample of peripheral blood was collected from each patient to determine the presence of the *4, *10 and *17 single nucleotide polymorphisms of the CYP2D6 gene by quantitative polymerase chain reaction analysis. There was no statistically significant difference between the two groups regarding the polymorphism frequency (P=0.246). The results revealed that intermediate metabolizers occurred in 5% of patients without recurrence and in 15% of those with distant recurrence. Poor metabolizers occurred in only 1 patient (2.5%) per group, and there was no significant difference between the groups (P=0.789). The present study concluded that the CYP2D6 gene polymorphism in women with hormone-sensitive breast cancer treated with tamoxifen was not associated with disease recurrence.

Development of the β-lactam type molecular scaffold for selective estrogen receptor α modulator action: synthesis and cytotoxic effects in MCF-7 breast cancer cells

The estrogen receptors (ERα and ERβ) which are ligand inducible nuclear receptors are recognized as pharmaceutical targets for diseases such as osteoporosis and breast cancer. There is an increasing interest in the discovery of subtype Selective Estrogen Receptor Modulators (SERMs). A series of novel β-lactam compounds with estrogen receptor modulator properties have been synthesized. The antiproliferative effects of these compounds on human MCF-7 breast tumor cells are reported, together with binding affinity for the ERα and ERβ receptors. The most potent compound 15g demonstrated antiproliferative effects on MCF-7 breast tumor cells (IC₅₀=186 nM) and ERα binding (IC₅₀=4.3 nM) with 75-fold ERα/β receptor binding selectivity. The effect of positioning of the characteristic amine containing substituted aryl ring (on C-4 or N-1 of the β-lactam scaffold) on the antiproliferative activity and ER-binding properties of the β-lactam compounds is rationalized in a molecular modeling study.

Tamoxifen metabolite endoxifen interferes with the polyamine pathway in breast cancer

Tamoxifen is the most widely used drug to treat women with estrogen receptor α (ERα)-positive breast cancer. Endoxifen is recognized as the active metabolite of tamoxifen in humans. We studied endoxifen effects on ERα-positive MCF-7 breast cancer cells. Estradiol increased the proliferation of MCF-7 cells by two- to threefold and endoxifen suppressed its effects. Endoxifen suppressed c-myc, c-fos and Tff1 oncogene expression, as revealed by RT-PCR. Estradiol increased the activity of ornithine decarboxylase (ODC) and adenosyl methioninedecarboxylase (AdoMetDC), whereas endoxifen suppressed these enzyme activities. Endoxifen increased activities of spermine oxidase (SMO) and acetyl polyamine oxidase (APAO) significantly, and reduced the levels of putrescine and spermidine. These data suggest a possible mechanism for the antiestrogenic effects of tamoxifen/endoxifen, involving the stimulation of polyamine oxidase enzymes. Therefore, SMO and APAO stimulation might be useful biomarkers for the efficacy of endoxifen treatment of breast cancer.

Profound reduction in tamoxifen active metabolite endoxifen in a breast cancer patient treated with rifampin prior to initiation of an anti-TNFα biologic for ulcerative colitis: a case report

BACKGROUND

Tamoxifen, a common anti-estrogen breast cancer medication, is a prodrug that undergoes bioactivation via cytochrome P450 enzymes, CYP2D6 and to a lesser degree, CYP3A4 to form the active metabolite endoxifen. With an increasing use of oral anti-cancer drugs, the risk for drug-drug interactions mediated by enzyme inhibitors and inducers may also be expected to increase. Here we report the first case demonstrating a potent drug-drug interaction in a real-world clinical setting between tamoxifen and rifampin in a breast cancer patient being treated concurrently for ulcerative colitis.

CASE PRESENTATION

We describe a patient on adjuvant tamoxifen therapy for breast cancer that was prescribed rifampin for TB prophylaxis prior to initiation of an anti-tumor necrosis factor (TNF)-α agent due to worsening ulcerative colitis. This 39 year old Caucasian woman had been followed by our personalized medicine clinic where CYP2D6 genotyping and therapeutic monitoring of tamoxifen and endoxifen levels had been carried out. The patient, known to be a CYP2D6 intermediate metabolizer, had a previous history of therapeutic endoxifen levels. Upon admission to hospital for a major flare of her ulcerative colitis a clinical decision was made to initiate an anti-TNFα biological agent. Due to concerns regarding latent TB, rifampin as an anti-mycobacterial agent was initiated which the patient was only able tolerate for 10 days. Interestingly, her plasma endoxifen concentration measured 2 weeks after cessation of rifampin was sub-therapeutic at 15.8 nM and well below her previous endoxifen levels which exceeded 40 nM.

CONCLUSION

Rifampin should be avoided in patients on tamoxifen therapy for breast cancer unless continued tamoxifen efficacy can be assured through endoxifen monitoring. Drug-drug interactions can pose a significant risk of sub-therapeutic benefit in tamoxifen patients.

ABCB1 and ABCC2 and the risk of distant metastasis in Thai breast cancer patients treated with tamoxifen

BACKGROUND

Genetic polymorphisms of drug-metabolizing enzymes and transporters have been extensively studied with regard to tamoxifen treatment outcomes. However, the results are inconclusive. Analysis of organ-specific metastasis may reveal the association of these pharmacogenetic factors. The aim of this study is to investigate the impact of CYP3A5, CYP2D6, ABCB1, and ABCC2 polymorphisms on the risk of all distant and organ-specific metastases in Thai patients who received tamoxifen adjuvant therapy.

METHODS

Genomic DNA was extracted from blood samples of 73 patients with breast cancer who received tamoxifen adjuvant therapy. CYP3A5 (6986A>G), CYP2D6 (100C>T), ABCB1 (3435C>T), and ABCC2 (-24C>T) were genotyped using allelic discrimination real-time polymerase chain reaction assays. The impacts of prognostic clinical factors and genetic variants on disease-free survival were analyzed using the Kaplan-Meier method and Cox regression analysis.

RESULTS

In the univariate analysis, primary tumor size >5 cm was significantly associated with increased risk of distant metastasis (P=0.004; hazard ratio [HR] =3.05; 95% confidence interval [CI], 1.44-6.47). In the multivariate analysis, tumor size >5 cm remained predictive of distant metastasis (P<0.001; HR=5.49; 95% CI, 2.30-13.10). ABCC2 -24CC were shown to be associated with increased risk of distant metastasis (P=0.040; adjusted HR=2.34; 95% CI, 1.04-5.27). The combined genotype of ABCC2 -24CC - ABCB1 3435 CT+TT was associated with increased risk of distant and bone metastasis (P=0.020; adjusted HR=2.46; 95% CI, 1.15-5.26 and P=0.040; adjusted HR=3.70; 95% CI, 1.06-12.89, respectively).

CONCLUSION

This study indicates that polymorphisms of ABCC2 and ABCB1 are independently associated with bone metastasis. Further prospective studies with larger sample sizes are needed to verify this finding.

OCT-4: a novel estrogen receptor-α collaborator that promotes tamoxifen resistance in breast cancer cells

Tamoxifen has shown great success in the treatment of breast cancer; however, long-term treatment can lead to acquired tamoxifen (TOT) resistance and relapse. TOT classically antagonizes estradiol (E2) -dependent breast cancer cell growth, but exerts partial agonist/antagonist behavior on gene expression. Although both E2 and TOT treatment of breast cancer cells results in recruitment of the estrogen receptor (ER) to common and distinct genomic sites, the mechanisms and proteins underlying TOT preferential recruitment of the ER remains poorly defined. To this end, we performed in silico motif-enrichment analyses within the ER-binding peaks in response to E2 or TOT, to identify factors that would specifically recruit ER to genomic binding sites in the presence of TOT as compared to E2. Intriguingly, we found Nkx3-1 and Oct-transcription factor homodimer motifs to be enriched in TOT preferential binding sites and confirmed the critical role of Oct-3/4 (aka Oct-4) in directing ER recruitment to TOT preferential genomic binding sites, by chromatin immunoprecipitation (ChIP) analyses. Further investigation revealed Oct-4 expression to be basally repressed by Nkx3-1 in MCF-7 cells and TOT treatment appeared to elevate Nkx3-1 degradation through a p38MAPK-dependent phosphorylation of the E3 ligase, Skp2 at serine-64 residue, as observed by quantitative mass-spectrometry analyses. Consistently, Oct-4 upon induction by phospho-Ser64-Skp2-mediated proteasomal degradation of Nkx3-1, participated in ER transcriptional complexes along with p38MAPK and Skp2 in a tamoxifen-dependent manner leading to TOT-dependent gene activation and cell proliferation of the TOT-resistant MCF-7-tam^r breast cancer cells. Notably, Oct-4 levels were highly elevated in MCF-7-tam^r cells, and appeared critical for their TOT sensitivity in cell proliferation assays. Furthermore, overexpression of Oct-4 enhanced tumor growth in the presence of tamoxifen in mice in vivo. Collectively, our work presents a novel mechanism for tamoxifen-specific gene activation by ER, secondary to its TOT preferential recruitment to genomic sites by specific activation of Oct-4, a phenomenon that appears to underlie tamoxifen resistance in breast cancer cells and in xenograft tumor models, and could be useful in designing therapeutic interventions to improve treatment outcome.

Inhibition of breast cancer with transdermal tamoxifen-encapsulated lipoplex

Background

Tamoxifen is currently used for the treatment of both early and advanced estrogen receptor (ER) positive breast cancer in pre- and post-menopausal women. However, using tamoxifen routinely to inhibit endogenous or exogenous estrogen effects is occasionally difficult because of its potential side effects.

Objectives

The aim of this study is to design a local drug delivery system to encapsulate tamoxifen for observing their efficacy of skin penetration, drug accumulation and cancer therapy.

Methods

A cationic liposome-PEG-PEI complex (LPPC) was used as a carrier for the encapsulation of tamoxifen and forming ‘LPPC/TAM’ for transdermal release. The cytotoxicity of LPPC/TAM was analyzed by MTT. The skin penetration, tumor growth inhibition and organ damages were measured in xenograft mice following transdermal treatment.

Results

LPPC/TAM had an average size less than 270 nm and a zeta-potential of approximately 40 mV. LPPC/TAM displayed dramatically increased the cytotoxic activity in all breast cancer cells, especially in ER-positive breast cancer cells. In vivo, LPPC drug delivery helped the fluorescent dye penetrating across the skim and accumulating rapidly in tumor area. Administration of LPPC/TAM by transdermal route inhibited about 86 % of tumor growth in mice bearing BT474 tumors. This local treatment of LPPC/TAM did not injury skin and any organs.

Conclusion

LPPC-delivery system provided a better skin penetration and drug accumulation and therapeutic efficacy. Therefore, LPPC/TAM drug delivery maybe a useful transdermal tool of drugs utilization for breast cancer therapy.

Tamoxifen promotes differentiation of oligodendrocyte progenitors in vitro

The most promising therapeutic approach to finding the cure for devastating demyelinating conditions is the identification of clinically safe pharmacological agents that can promote differentiation of endogenous oligodendrocyte precursor cells (OPCs). Here we show that the breast cancer medication tamoxifen (TMX), with well-documented clinical safety and confirmed beneficial effects in various models of demyelinating conditions, stimulates differentiation of rat glial progenitors to mature oligodendrocytes in vitro. Clinically applicable doses of TMX significantly increased both the number of CNPase-positive oligodendrocytes and protein levels of myelin basic protein, measured with Western blots. Furthermore, we also found that OPC differentiation was stimulated, not only by the pro-drug TMX-citrate (TMXC), but also by two main TMX metabolites, 4-hydroxy-TMX and endoxifen. Differentiating effects of TMXC and its metabolites were completely abolished in the presence of estrogen receptor (ER) antagonist, ICI182780. In contrast to TMXC and 4-hydroxy-TMX, endoxifen also induced astrogliogenesis, but independent of the ER activation. In sum, we showed that the TMX prodrug and its two main metabolites (4-hydroxy-TMX and endoxifen) promote ER-dependent oligodendrogenesis in vitro, not reported before. Given that differentiating effects of TMX were achieved with clinically safe doses, TMX is likely one of the most promising FDA-approved drugs for the possible treatment of demyelinating diseases.

The Role of MicroRNAs as Predictors of Response to Tamoxifen Treatment in Breast Cancer Patients

Endocrine therapy is a key treatment strategy to control or eradicate hormone-responsive breast cancer. However, resistance to endocrine therapy leads to breast cancer relapse. The recent extension of adjuvant tamoxifen treatment up to 10 years actualizes the need for identifying biological markers that may be used to monitor predictors of treatment response. MicroRNAs are promising biomarkers that may fill the gap between preclinical knowledge and clinical observations regarding endocrine resistance. MicroRNAs regulate gene expression by posttranscriptional repression or degradation of mRNA, most often leading to gene silencing. MicroRNAs have been identified directly in the primary tumor, but also in the circulation of breast cancer patients. The few available studies investigating microRNA in patients suggest that seven microRNAs (miR-10a, miR-26, miR-30c, miR-126a, miR-210, miR-342 and miR-519a) play a role in tamoxifen resistance. Ingenuity Pathway Analysis (IPA) reveals that these seven microRNAs interact more readily with estrogen receptor (ER)-independent pathways than ER-related signaling pathways. Some of these pathways are targetable (e.g., PIK3CA), suggesting that microRNAs as biomarkers of endocrine resistance may have clinical value. Validation of the role of these candidate microRNAs in large prospective studies is warranted.

Polymorphism at 19q13.41 Predicts Breast Cancer Survival Specifically after Endocrine Therapy

PURPOSE

Although most patients with estrogen receptor (ER)-positive breast cancer benefit from endocrine therapies, a significant proportion do not. Our aim was to identify inherited genetic variations that might predict survival among patients receiving adjuvant endocrine therapies.

EXPERIMENTAL DESIGN

We performed a meta-analysis of two genome-wide studies; Helsinki Breast Cancer Study, 805 patients, with 240 receiving endocrine therapy and Prospective study of Outcomes in Sporadic versus Hereditary breast cancer, 536 patients, with 155 endocrine therapy patients, evaluating 486,478 single-nucleotide polymorphisms (SNP). The top four associations from the endocrine treatment subgroup were further investigated in two independent datasets totaling 5,011 patients, with 3,485 receiving endocrine therapy.

RESULTS

A meta-analysis identified a common SNP rs8113308, mapped to 19q13.41, associating with reduced survival among endocrine-treated patients [hazard ratio (HR), 1.69; 95% confidence interval (CI), 1.37-2.07; P = 6.34 × 10(-7)] and improved survival among ER-negative patients, with a similar trend in ER-positive cases not receiving endocrine therapy. In a multivariate analysis adjusted for conventional prognostic factors, we found a significant interaction between the rs8113308 and endocrine treatment, indicating a predictive, treatment-specific effect of the SNP rs8113308 on breast cancer survival, with the per-allele HR for interaction 2.16 (95% CI, 1.30-3.60; Pinteraction = 0.003) and HR = 7.77 (95% CI, 0.93-64.71) for the homozygous genotype carriers. A biologic rationale is suggested by in silico functional analyses.

CONCLUSIONS

Our findings suggest carrying the rs8113308 rare allele may identify patients who will not benefit from adjuvant endocrine treatment.

Boronic prodrug of 4-hydroxytamoxifen is more efficacious than tamoxifen with enhanced bioavailability independent of CYP2D6 status

Background

Poor initial response to tamoxifen due to CYP2D6 polymorphism and adverse side effects are two clinical challenges in tamoxifen therapy. We report the development and preclinical testing of a boronic prodrug to orally deliver 4-OHT at therapeutically effective concentrations but at a fraction of the standard tamoxifen dose.

Methods

A mouse xenograft tumor model was used to investigate the efficacy of ZB497 in comparison with tamoxifen. Pharmacokinetic studies were conducted to evaluate the metabolism and bioavailability of the drug in mice. Drug and metabolites distribution in xenograft tumor tissues was determined by high performance liquid chromatography-tandem mass spectrometry.

Results

The boronic prodrug, ZB497, can not only be efficiently converted to 4-OHT in mice, but also afforded over 30 fold higher plasma concentrations of 4-OHT than in mice given either the same dose of 4-OHT or tamoxifen. Further, ZB497 was more effective than tamoxifen at lowered dosage in inhibiting the growth of xenograft tumors in mice. Consistent with these observations, ZB497 treated mice accumulated over 6 times higher total drug concentrations than tamoxifen treated mice.

Conclusions

Our study demonstrates that ZB497 effectively delivers a markedly increased plasma concentration of 4-OHT in mice. The boronic prodrug was shown to have far superior bioavailability of 4-OHT compared to tamoxifen or 4-OHT administration as measured by the area under the plasma concentration time curve (AUC), plasma peak concentrations, and drug accumulation in tumor tissues. Further, ZB497 proves to be a more efficacious hormone therapy than tamoxifen administered at a reduced dose in mice.

Boronic prodrug of endoxifen as an effective hormone therapy for breast cancer

As a prodrug, tamoxifen is activated by the P450 enzyme CYP2D6 that is responsible for converting it to the active metabolites, 4-hydroxytamoxifen and endoxifen. Patients with genetic polymorphisms of CYP2D6 may not receive the full benefit of tamoxifen therapy. There is increasing evidence that poor metabolizer patients have lower plasma concentrations of endoxifen and suffer worse disease outcome, although some clinical studies reported no correlation between CYP2D6 polymorphism and tamoxifen therapy outcome. Endoxifen is currently undergoing clinical trials as a potentially improved and more potent SERM (Selective Estrogen Receptor Modulator) for endocrine therapy that is independent of CYP2D6 status in patients. However, direct administration of endoxifen may present the problem of low bioavailability due to its rapid first-pass metabolism via O-glucuronidation. We have designed and synthesized ZB483, a boronic prodrug of endoxifen suitable for oral administration with greatly enhanced bioavailability by increasing the concentration of endoxifen in mouse blood. Our study demonstrated that ZB483 potently inhibited growth of ER+ breast cancer cells in vitro and was efficiently converted to endoxifen in cell culture media by oxidative deboronation. This metabolic conversion is equally efficient in vivo as indicated in the pharmacokinetic study in mice. Moreover, when administered at the same dose, oral ZB483 afforded a 30- to 40-fold higher plasma level of endoxifen in mice than oral administration of endoxifen. The significantly enhanced bioavailability of endoxifen conferred by the boronic prodrug was further validated in an in vivo efficacy study. ZB483 was demonstrated to be more efficacious than endoxifen in inhibiting xenograft tumor growth in mice at equal dosage but more so at lower dosage. Together, these preclinical studies demonstrate that ZB483 is a promising endocrine therapy agent with markedly enhanced bioavailability in systemic circulation and superior efficacy compared to endoxifen.

Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients

The anti-estrogen tamoxifen is characterized by a large variability in response, partly due to pharmacokinetic differences. We examined circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients. Pharmacokinetic analysis was performed in mice, dosed at six different times (24-h period). Tissue samples were used for mRNA expression analysis of drug-metabolizing enzymes. In patients, a cross-over study was performed. During three 24-h periods, after tamoxifen dosing at 8 a.m., 1 p.m., and 8 p.m., for at least 4 weeks, blood samples were collected for pharmacokinetic measurements. Differences in tamoxifen pharmacokinetics between administration times were assessed. The mRNA expression of drug-metabolizing enzymes showed circadian variation in mouse tissues. Tamoxifen exposure seemed to be highest after administration at midnight. In humans, marginal differences were observed in pharmacokinetic parameters between morning and evening administration. Tamoxifen C(max )and area under the curve (AUC)0-8 h were 20 % higher (P < 0.001), and tamoxifen t(max) was shorter (2.1 vs. 8.1 h; P = 0.001), indicating variation in absorption. Systemic exposure (AUC0-24 h) to endoxifen was 15 % higher (P < 0.001) following morning administration. The results suggest that dosing time is of marginal influence on tamoxifen pharmacokinetics. Our study was not designed to detect potential changes in clinical outcome or toxicity, based on a difference in the time of administration. Circadian rhythm may be one of the many determinants of the interpatient and intrapatient pharmacokinetic variability of tamoxifen.

Population pharmacokinetic modelling to assess the impact of CYP2D6 and CYP3A metabolic phenotypes on the pharmacokinetics of tamoxifen and endoxifen

AIMS

Tamoxifen is considered a pro-drug of its active metabolite endoxifen. The major metabolic enzymes involved in endoxifen formation are CYP2D6 and CYP3A. There is considerable evidence that variability in activity of these enzymes influences endoxifen exposure and thereby may influence the clinical outcome of tamoxifen treatment. We aimed to quantify the impact of metabolic phenotype on the pharmacokinetics of tamoxifen and endoxifen.

METHODS

We assessed the CYP2D6 and CYP3A metabolic phenotypes in 40 breast cancer patients on tamoxifen treatment with a single dose of dextromethorphan as a dual phenotypic probe for CYP2D6 and CYP3A. The pharmacokinetics of dextromethorphan, tamoxifen and their relevant metabolites were analyzed using non-linear mixed effects modelling.

RESULTS

Population pharmacokinetic models were developed for dextromethorphan, tamoxifen and their metabolites. In the final model for tamoxifen, the dextromethorphan derived metabolic phenotypes for CYP2D6 as well as CYP3A significantly (P < 0.0001) explained 54% of the observed variability in endoxifen formation (inter-individual variability reduced from 55% to 25%).

CONCLUSIONS

We have shown that not only CYP2D6, but also CYP3A enzyme activity influences the tamoxifen to endoxifen conversion in breast cancer patients. Our developed model may be used to assess separately the impact of CYP2D6 and CYP3A mediated drug-drug interactions with tamoxifen without the necessity of administering this anti-oestrogenic drug and to support Bayesian guided therapeutic drug monitoring of tamoxifen in routine clinical practice.

Formulation of Anti-miR-21 and 4-Hydroxytamoxifen Co-loaded Biodegradable Polymer Nanoparticles and Their Antiproliferative Effect on Breast Cancer Cells

Breast cancer is the second leading cause of cancer-related death in women. The majority of breast tumors are estrogen receptor-positive (ER+) and hormone-dependent. Neoadjuvant anti-estrogen therapy has been widely employed to reduce tumor mass prior to surgery. Tamoxifen is a broadly used anti-estrogen for early and advanced ER+ breast cancers in women and the most common hormone treatment for male breast cancer. 4-Hydroxytamoxifen (4-OHT) is an active metabolite of tamoxifen that functions as an estrogen receptor antagonist and displays higher affinity for estrogen receptors than that of tamoxifen and its other metabolites. MicroRNA-21 (miR-21) is a small noncoding RNA of 23 nucleotides that regulates several apoptotic and tumor suppressor genes and contributes to chemoresistance in numerous cancers, including breast cancer. The present study investigated the therapeutic potential of 4-OHT and anti-miR-21 coadministration in an attempt to combat tamoxifen resistance, a common problem often encountered in anti-estrogen therapy. A biodegradable poly(d,l-lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-b-PEG-COOH) copolymer was utilized as a carrier to codeliver 4-OHT and anti-miR-21 to ER+ breast cancer cells. 4-OHT and anti-miR-21 co-loaded PLGA-b-PEG nanoparticles (NPs) were developed using emulsion-diffusion evaporation (EDE) and water-in-oil-in-water (w/o/w) double emulsion methods. The EDE method was found to be best method for 4-OHT loading, and the w/o/w method proved to be more effective for coloading NPs with anti-miR-21 and 4-OHT. The optimal NPs, which were prepared using the double emulsion method, were evaluated for their antiproliferative and apoptotic effects against MCF7, ZR-75-1, and BT-474 human breast cancer cells as well as against 4T1 mouse mammary carcinoma cells. We demonstrated that PLGA-b-PEG NP encapsulation significantly extended 4-OHT’s stability and biological activity compared to that of free 4-OHT. MTT assays indicated that treatment of MCF7 cells with 4-OHT–anti-miR-21 co-loaded NPs resulted in dose-dependent antiproliferative effects at 24 h, which was significantly higher than what was achieved with free 4-OHT at 48 and 72 h post-treatment. Cell proliferation analysis showed that 4-OHT and anti-miR-21 co-loaded NPs significantly inhibited MCF-7 cell growth compared to that of free 4-OHT (1.9-fold) and untreated cells (5.4-fold) at 1 μM concentration. The growth rate of MCF7 cells treated with control NPs or NPs loaded with anti-miR-21 showed no significant difference from that of untreated cells. These findings demonstrate the utility of the PLGA-b-PEG polymer NPs as an effective nanocarrier for co-delivery of anti-miR-21 and 4-OHT as well as the potential of this drug combination for use in the treatment of ER+ breast cancer.

Involvement of multiple cellular pathways in regulating resistance to tamoxifen in BIK-suppressed MCF-7 cells

Majority of women with estrogen receptor (ER)-positive breast cancers initially respond to hormone therapies such as tamoxifen (TAM; antagonist of estrogen). However, many tumors eventually become resistant to TAM. Therefore, understanding the various cellular components involved in causing resistance to TAM is of paramount importance in designing novel entities for efficacious hormone therapy. Previously, we found that suppression of BIK gene expression induced TAM resistance in MCF-7 breast cancer cells. In order to understand the response of these cells to TAM and its association with resistance, a microarray analysis of gene expression was performed in the BIK-suppressed MCF-7 cells and compared it to the TAM-only-treated cells (controls). Several genes participating in various cellular pathways were identified. Molecules identified in the drug resistance pathway were 14-3-3z or YWHAZ, WEE1, PRKACA, NADK, and HSP90AA 1. Further, genes involved in cell cycle control, apoptosis, and cell proliferation were also found differentially expressed in these cells. Transcriptional and translational analysis of key molecules such as STAT2, AKT 3, and 14-3-3z revealed similar changes at the messenger RNA (mRNA) as well as at the protein level. Importantly, there was no cytotoxic effect of TAM on BIK-suppressed MCF-7 cells. Further, these cells were not arrested at the G0-G1 phase of the cell cycle although 30 % of BIK-suppressed cells were arrested at the G2 phase of the cycle on TAM treatment. Furthermore, we found a relevant interaction between 14-3-3z and WEE1, suggesting that the cytotoxic effect of TAM was prevented in BIK-suppressed cells because this interaction leads to transitory arrest in the G2 phase leading to the repair of damaged DNA and allowing the cells to proliferate.

Atrophic vaginitis in breast cancer survivors: a difficult survivorship issue

Management of breast cancer includes systematic therapies including chemotherapy and endocrine therapy can lead to a variety of symptoms that can impair the quality of life of many breast cancer survivors. Atrophic vaginitis, caused by decreased levels of circulating estrogen to urinary and vaginal receptors, is commonly experienced by this group. Chemotherapy induced ovarian failure and endocrine therapies including aromatase inhibitors and selective estrogen receptor modulators can trigger the onset of atrophic vaginitis or exacerbate existing symptoms. Symptoms of atrophic vaginitis include vaginal dryness, dyspareunia, and irritation of genital skin, pruritus, burning, vaginal discharge, and soreness. The diagnosis of atrophic vaginitis is confirmed through patient-reported symptoms and gynecological examination of external structures, introitus, and vaginal mucosa. Lifestyle modifications can be helpful but are usually insufficient to significantly improve symptoms. Non-hormonal vaginal therapies may provide additional relief by increasing vaginal moisture and fluid. Systemic estrogen therapy is contraindicated in breast cancer survivors. Continued investigations of various treatments for atrophic vaginitis are necessary. Local estrogen-based therapies, DHEA, testosterone, and pH-balanced gels continue to be evaluated in ongoing studies. Definitive results are needed pertaining to the safety of topical estrogens in breast cancer survivors.

Pharmacogenomics toward personalized tamoxifen therapy for breast cancer

Tamoxifen has been used not only for the treatment or prevention of recurrence in patients with estrogen receptor positive breast cancers but also for recurrent breast cancer. Because CYP2D6 is known to be an important enzyme responsible for the generation of the potent tamoxifen metabolite, ‘endoxifen’, lots of studies reported that genetic variation which reduced its enzyme activity were associated with poor clinical outcome of breast cancer patients treated with tamoxifen. However, there are some discrepant reports questioning the association between CYP2D6 genotype and clinical outcome after tamoxifen therapy. Dose-adjustment study of tamoxifen based on CYP2D6 genotypes provides the evidence that dose adjustment is useful for the patients carrying reduced or null allele of CYP2D6 to maintain the effective endoxifen level. This review describes critical issues in pharmacogenomic studies as well as summarizes the results of the association of CYP2D6 genotype with tamoxifen efficacy.

Endoxifen, the active metabolite of tamoxifen, inhibits cloned hERG potassium channels

The effects of tamoxifen, and its active metabolite endoxifen (4-hydroxy-N-desmethyl-tamoxifen), on hERG currents stably expressed in HEK cells were investigated using the whole-cell patch-clamp technique and an immunoblot assay. Tamoxifen and endoxifen inhibited hERG tail currents at -50mV in a concentration-dependent manner with IC50 values of 1.2 and 1.6μM, respectively. The steady-state activation curve of the hERG currents was shifted to the hyperpolarizing direction in the presence of endoxifen. The voltage-dependent inhibition of hERG currents by endoxifen increased steeply in the voltage range of channel activation. The inhibition by endoxifen displayed a shallow voltage dependence (δ=0.18) in the full activation voltage range. A fast application of endoxifen induced a reversible block of hERG tail currents during repolarization in a concentration-dependent manner, which suggested an interaction with the open state of the channel. Endoxifen also decreased the hERG current elicited by a 5s depolarizing pulse to +60mV to inactivate the hERG currents, suggesting an interaction with the activated (open and/or inactivated) states of the channels. Tamoxifen and endoxifen inhibited the hERG channel protein trafficking to the plasma membrane in a concentration-dependent manner with endoxifen being more potent than tamoxifen. These results indicated that tamoxifen and endoxifen inhibited the hERG current by direct channel blockage and by the disruption of channel trafficking to the plasma membrane in a concentration-dependent manner. A therapeutic concentration of endoxifen inhibited the hERG current by preferentially interacting with the activated (open and/or inactivated) states of the channel.

Personalizing medicine in geriatric oncology

Minimizing toxicity while maximizing efficacy is a common goal in the treatment of any condition but its importance is underscored in the discipline of oncology because of the serious nature of many chemotherapeutic toxicities and the risk of cancer recurrence or disease progression. The challenge of achieving an optimal therapeutic index is especially augmented in the elderly population because of age-related metabolism changes and interacting concurrent medications. Additional factors, such as germline mutations in drug-metabolizing enzymes and other pharmacogenomic alterations, may have more pronounced effects in elderly patients, given their predisposition to altered pharmacokinetics and pharmacodynamics with resulting increased risk of toxicity. Examples of the possible interplay of these factors will be discussed using tamoxifen, paclitaxel, codeine, and fluorouracil as starting points. Limited participation of the elderly in many cancer trials, especially trials assessing drug exposure, makes much knowledge on the interaction of these patient and environmental factors speculative in nature but presents an opportunity for future research to achieve better optimization of chemotherapeutic agents in the elderly.

Prediction of tamoxifen outcome by genetic variation of CYP2D6 in post-menopausal women with early breast cancer

The question of whether genetic polymorphisms of CYP2D6 can affect treatment outcome in patients with early post-menopausal oestrogen receptor (ER)-positive breast cancer has been a matter of debate over the past few years. In this article we revisit the hypothesis of CYP2D6 being a potential tamoxifen outcome predictor and provide detailed insight into the ongoing controversy that prevented the CYP2D6 marker from being accepted by the scientific and clinical community. We summarize the available pharmacokinetic, pharmacodynamic and pharmacogenetic evidence and resolve the controversy based on the recognized methodological and statistical issues. The cumulative evidence suggests that genotyping for CYP2D6 is clinically relevant in post-menopausal women. This is important, because the clarification of this issue has the potential to resolve a clinical management question that is relevant to hundreds of thousands of women diagnosed with ER-positive breast cancer each year, who should not be denied effective endocrine therapy.

Overcoming endocrine resistance in metastatic breast cancer: Current evidence and future directions

About 75% of all breast cancers are estrogen receptor (ER)-positive. They generally have a more favorable clinical behavior, prognosis, and pattern of recurrence, and endocrine therapy forms the backbone of treatment. Anti-estrogens (such as tamoxifen and fulvestrant) and aromatase inhibitors (such as anastrozole, letrozole, and exemestane) can effectively control the disease and induce tumor responses in a large proportion of patients. However, the majority of patients progress during endocrine therapy (acquired resistance) and a proportion of patients may fail to respond to initial therapy (de novo resistance). Endocrine resistance is therefore of clinical concern and there is great interest in strategies that delay or circumvent it. A deeper knowledge of the molecular mechanisms that drive endocrine resistance has recently led to development of new strategies that have the promise to effectively overcome it. Many resistance mechanisms have been described, and the crosstalk between ER and growth factor receptor signaling pathways seems to represent one of the most relevant. Compounds that are able to inhibit key elements of these pathways and restore endocrine sensitivity have been studied and more are currently under development. The aim of this review is to summarize the molecular pathophysiology of endocrine resistance in breast cancer and its impact on current clinical management.

Harnessing pharmacological knowledge for personalized medicine and pharmacotyping: Challenges and lessons learned

The contribution of the genetic make-up to an individual’s capacity has long been recognized in modern pharmacology as a crucial factor leading to therapy inefficiency and toxicity, negatively impacting the economic burden of healthcare and restricting the monitoring of diseases. In practical terms, and in order for drug prescription to be improved toward meeting the personalized medicine concept in drug delivery, the maximum clinical outcome for most, if not all, patients must be achieved, i.e., pharmacotyping. Such a direction although promising and of high expectation from the society, it is however hardly to be afforded for healthcare worldwide. To overcome any existed hurdles, this means that practical clinical utility of personalized medicine decisions have to be documented and validated in the clinical setting. The latter implies for drug delivery the efficient implementation of previously gained in vivo pharmacology experience with pharmacogenomics knowledge. As an approach to work faster and in a more productive way, the elaboration of advanced physiologically based pharmacokinetics models is discussed. And in better clarifying this topic, the example of tamoxifen is thoroughly presented. Overall, pharmacotyping represents a major challenge in modern therapeutics for which pharmacologists need to work in successfully fulfilling this task.

The influence of the environment on the development of thyroid tumors: a new appraisal

Most epidemiological studies concerning differentiated thyroid cancers (DTC) indicate an increasing incidence over the last two decades. This increase might be partially explained by the better access to health services worldwide, but clinicopathological analyses do not fully support this hypothesis, indicating that there are carcinogenetic factors behind this noticeable increasing incidence. Although we have undoubtedly understood the biology and molecular pathways underlying thyroid carcinogenesis in a better way, we have made very little progresses in identifying a risk profile for DTC, and our knowledge of risk factors is very similar to what we knew 30-40 years ago. In addition to ionizing radiation exposure, the most documented and established risk factor for DTC, we also investigated the role of other factors, including eating habits, tobacco smoking, living in a volcanic area, xenobiotics, and viruses, which could be involved in thyroid carcinogenesis, thus, contributing to the increase in DTC incidence rates observed.

Determination of CYP2D6 *3, *4, and *10 frequency in women with breast cancer in São Luís, Brazil, and its association with prognostic factors and disease-free survival

The CYP2D6 enzyme is crucial for the metabolism of tamoxifen. The CYP2D6 gene is highly polymorphic, and individuals can be extensive, intermediate, or poor tamoxifen metabolizers. The aim of this study was to determine the frequencies of the CYP2D6 *3, *4, and *10 alleles in women with breast cancer who were treated with tamoxifen and analyze the association of enzyme activity with prognostic factors and disease-free survival. We observed a high frequency of CYP2D6 *10, with an allelic frequency of 0.14 (14.4%). The *3 allele was not present in the studied population, and *4 had an allelic frequency of 0.13 (13.8%). We conclude that patients with reduced CYP2D6 activity did not present worse tumor characteristics or decreased disease-free survival than women with normal enzyme activity, as the difference was not statistically significant. We also observed a high frequency of CYP2D6 *10, which had not been previously described in this specific population. This study is the first in north-northeastern Brazil that aimed to contribute to the knowledge of the Brazilian regional profile for CYP2D6 polymorphisms and their phenotypes. These findings add to the knowledge of the distribution of different polymorphic CYP2D6 alleles and the potential role of CYP2D6 genotyping in clinical practice prior to choosing therapeutic protocols.

Breast health in developing countries

Breast cancer is one of the leading cancers world-wide. While the incidence in developing countries is lower than in developed countries, the mortality is much higher. Of the estimated 1 600 000 new cases of breast cancer globally in 2012, 794 000 were in the more developed world compared to 883 000 in the less developed world; however, there were 198 000 deaths in the more developed world compared to 324 000 in the less developed world (data from Globocan 2012, IARC). Survival from breast cancer depends on two main factors--early detection and optimal treatment. In developing countries, women present with late stages of disease. The barriers to early detection are physical, such as geographical isolation, financial as well as psychosocial, including lack of education, belief in traditional medicine and lack of autonomous decision-making in the male-dominated societies that prevail in the developing world. There are virtually no population-based breast cancer screening programs in developing countries. However, before any screening program can be implemented, there must be facilities to treat the cancers that are detected. Inadequate access to optimal treatment of breast cancer remains a problem. Lack of specialist manpower, facilities and anticancer drugs contribute to the suboptimal care that a woman with breast cancer in a low-income country receives. International groups such as the Breast Health Global Initiative were set up to develop economically feasible, clinical practice guidelines for breast cancer management to improve breast health outcomes in countries with limited resources.

Mechanisms and therapeutic advances in the management of endocrine-resistant breast cancer

The estrogen receptor (ER) pathway plays a critical role in breast cancer development and progression. Endocrine therapy targeting estrogen action is the most important systemic therapy for ER positive breast cancer. However its efficacy is limited by intrinsic and acquired resistance. Mechanisms responsible for endocrine resistance include deregulation of the ER pathway itself, including loss of ER expression, post-translational modification of ER, deregulation of ER co-activators; increased receptor tyrosine kinase signaling leading to activation of various intracellular pathways involved in signal transduction, proliferation and cell survival, including growth factor receptor tyrosine kinases human epidermal growth factor receptor-2, epidermal growth factor receptor, PI3K/AKT/mammalian target of rapamycin (mTOR), Mitogen activated kinase (MAPK)/ERK, fibroblast growth factor receptor, insulin-like growth factor-1 receptor; alterations in cell cycle and apoptotic machinery; Epigenetic modification including dysregulation of DNA methylation, histone modification, and nucleosome remodeling; and altered expression of specific microRNAs. Functional genomics has helped us identify a catalog of genetic and epigenetic alterations that may be exploited as potential therapeutic targets and biomarkers of response. New treatment combinations targeting ER and such oncogenic signaling pathways which block the crosstalk between these pathways have been proven effective in preclinical models. Results of recent clinical studies suggest that subsets of patients benefit from the combination of inhibitor targeting certain oncogenic signaling pathway with endocrine therapy. Especially, inhibition of the mTOR signaling pathway, a key component implicated in mediating multiple signaling cascades, offers a promising approach to restore sensitivity to endocrine therapy in breast cancer. We systematically reviewed important publications cited in PubMed, recent abstracts from ASCO annual meetings and San Antonio Breast Cancer Symposium, and relevant trials registered at ClinicalTrials.gov. We present the molecular mechanisms contributing to endocrine resistance, in particular focusing on the biological rationale for the clinical development of novel targeted agents in endocrine resistant breast cancer. We summarize clinical trials utilizing novel strategies to overcome therapeutic resistance, highlighting the need to better identify the appropriate patients whose diseases are most likely to benefit from these specific strategies.

A potential role for human UDP-glucuronosyltransferase 1A4 promoter single nucleotide polymorphisms in the pharmacogenomics of tamoxifen and its derivatives

Tamoxifen (Tam) is a selective estrogen receptor modulator used to inhibit breast tumor growth. Tam can be directly N-glucuronidated via the tertiary amine group or O-glucuronidated after cytochrome P450-mediated hydroxylation. In this study, the glucuronidation of Tam and its hydroxylated and/or chlorinated derivatives [4-hydroxytamoxifen (4OHTam), toremifene (Tor), and 4-hydroxytoremifene (4OHTor)] was examined using recombinant human UDP-glucuronosyltransferases (UGTs) from the 1A subfamily and human hepatic microsomes. Recombinant UGT1A4 catalyzed the formation of N-glucuronides of Tam and its derivatives and was the most active UGT enzyme toward these compounds. Therefore, it was hypothesized that single nucleotide polymorphisms (SNPs) in the promoter region of UGT1A4 have the ability to significantly decrease the glucuronidation rates of Tam metabolites in the human liver. In vitro activity of 64 genotyped human liver microsomes was used to determine the association between the UGT1A4 promoter and coding region SNPs and the glucuronidation rates of Tam, 4OHTam, Tor, and 4OHTor. Significant decreases in enzymatic activity were observed in microsomes for individuals heterozygous for -163G/A and -217T/G. These alterations in glucuronidation may lead to prolonged circulating half-lives and may potentially modify the effectiveness of these drugs in the treatment of breast cancer.

Drug resistance to targeted therapies: déjà vu all over again

A major limitation of targeted anticancer therapies is intrinsic or acquired resistance. This review emphasizes similarities in the mechanisms of resistance to endocrine therapies in breast cancer and those seen with the new generation of targeted cancer therapeutics. Resistance to single-agent cancer therapeutics is frequently the result of reactivation of the signaling pathway, indicating that a major limitation of targeted agents lies in their inability to fully block the cancer-relevant signaling pathway. The development of mechanism-based combinations of targeted therapies together with non-invasive molecular disease monitoring is a logical way forward to delay and ultimately overcome drug resistance development.