Tamoxifen promotes superoxide production in platelets by activation of PI3-kinase and NADPH oxidase pathways

The beneficial effects of tamoxifen on arteries: a key player for cardiovascular health of breast cancer patient

Breast cancer is the most common cancer in women. Over the past few decades, advances in cancer detection and treatment have significantly improved survival rate of breast cancer patients. However, due to the cardiovascular toxicity of cancer treatments (chemotherapy, anti-HER2 antibodies and radiotherapy), cardiovascular diseases (CVD) have become an increasingly important cause of long-term morbidity and mortality in breast cancer survivors. Endocrine therapies are prescribed to reduce the risk of recurrence and specific death in estrogen receptor-positive (ER+) early breast cancer patients, but their impact on CVD is a matter of debate. Whereas aromatase inhibitors and luteinizing hormone-releasing hormone (LHRH) analogs inhibit estrogen synthesis, tamoxifen acts as a selective estrogen receptor modulator (SERM), opposing estrogen action in the breast but mimicking their actions in other tissues, including arteries. This review aims to summarize the main clinical and experimental studies reporting the effects of tamoxifen on CVD. In addition, we will discuss how recent findings on the mechanisms of action of these therapies may contribute to a better understanding and anticipation of CVD risk in breast cancer patients.

Diabetes and Colorectal Cancer Risk: A New Look at Molecular Mechanisms and Potential Role of Novel Antidiabetic Agents

Epidemiological data have demonstrated a significant association between the presence of type 2 diabetes mellitus (T2DM) and the development of colorectal cancer (CRC). Chronic hyperglycemia, insulin resistance, oxidative stress, and inflammation, the processes inherent to T2DM, also play active roles in the onset and progression of CRC. Recently, small dense low-density lipoprotein (LDL) particles, a typical characteristic of diabetic dyslipidemia, emerged as another possible underlying link between T2DM and CRC. Growing evidence suggests that antidiabetic medications may have beneficial effects in CRC prevention. According to findings from a limited number of preclinical and clinical studies, glucagon-like peptide-1 receptor agonists (GLP-1RAs) could be a promising strategy in reducing the incidence of CRC in patients with diabetes. However, available findings are inconclusive, and further studies are required. In this review, novel evidence on molecular mechanisms linking T2DM with CRC development, progression, and survival will be discussed. In addition, the potential role of GLP-1RAs therapies in CRC prevention will also be evaluated.

Cancer Therapy-Associated Thrombosis

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Direct oral anticoagulants in the prevention of stroke in breast cancer patients with atrial fibrillation during adjuvant endocrine therapy: A cohort study

BACKGROUND

Atrial fibrillation (AF) is a frequent comorbidity in malignant patients. Anticancer therapies complicate anticoagulant strategy. We evaluated the safety and efficacy of long-term use of direct oral anticoagulants (DOACs) in breast cancer women.

METHODS

In a prospective cohort study we enrolled 48 consecutive radically treated breast cancer women with AF (median age 63 [interquartile range 56-69] years, CHA₂DS₂-VASc 2 [2,3]) score) and adjuvant hormonal therapy. Thromboembolic complications (stroke, transient ischemic attack [TIA], venous thromboembolism [VTE]) and bleeding events (major and clinically relevant non-major bleeding [CRNMB]) were recorded in follow-up.

RESULTS

During a median follow-up of 40 (interquartile range 28-50.5) months 13 (27%) patients received apixaban, 22 (46%) rivaroxaban, and 13 (27%) dabigatran. One stroke (2.3%/year) and two CRNMBs (4.6%/year) were observed on apixaban. One TIA (1.3%/year), three major bleedings and two CRNMBs (6.7%/year, combined) were reported on rivaroxaban. Three VTE were documented in dabigatran treated individuals (7.8%/year), without any bleeding or cerebrovascular events. Women with thromboembolic events had higher body mass index (32 [29-33]) vs. 26 [24-29]) kg/m², p = 0.02) and CHA₂DS₂-VASc score (3 [3]) vs. 2 [1-3]), p = 0.02). Most thromboembolic complications (n = 4, 80%) and all three major bleedings were observed in tamoxifen users, while three of four CRNMBs occurred on aromatase inhibitors. Mortality rates were low (apixaban, n = 1 [2.3%/year], rivaroxaban, n = 3 [5.22%/ year], and dabigatran, n = 2 [4%/ year]). No death was related to bleeding.

CONCLUSIONS

This study suggests that DOACs are an effective and safe therapeutic option in breast cancer patients with AF during adjuvant hormonal therapy.

Resistance to Acetylsalicylic Acid in Patients with Coronary Heart Disease Is the Result of Metabolic Activity of Platelets

Sensitivity to acetylsalicylic acid (ASA) is important in the treatment of patients with coronary heart disease (CHD) after coronary artery bypass grafting (CABG). Patients were divided into ASA sensitive (sASA) and ASA resistant (rASA) by the activity of platelet aggregation induced arachidonic acid (ARA) together with ASA. Induced platelet aggregation activity was studied in sASA and rASA patients with CHD before and after CABG. The level of synthesis of primary and secondary reactive oxygen species (ROS) by platelets was determined using chemiluminescent analysis. The activity of NAD- and NADP-dependent dehydrogenases in platelets was determined by the bioluminescent method. It was found that the aggregation activity of platelets depended on the sensitivity of CHD patients to ASA and decreased during postoperative ASA therapy. The most pronounced differences in metabolic parameters of platelets in sASA and rASA patients were detected by Nox2 activity. The synthesis of secondary ROS by platelets of CHD patients did not depend on the sensitivity of patients to ASA but increased during postoperative treatment with ASA. The activity of NAD(P)-dependent dehydrogenases in platelets did not differ in sASA and rASA patients with CHD.

Correlation of the tamoxifen use with the increased risk of deep vein thrombosis and pulmonary embolism in elderly women with breast cancer: A case-control study

The association between tamoxifen use and risk of deep vein thrombosis or pulmonary embolism in women with breast cancer has been reported in the Western population. The study aimed to evaluate the association between tamoxifen use and deep vein thrombosis or pulmonary embolism in older women with breast cancer in Taiwan.We conducted a retrospective case-control study using the database of the Taiwan National Health Insurance Program. A total of 281 women subjects with breast cancer aged ≥65 years with newly diagnosed deep vein thrombosis/or pulmonary embolism from 2000 to 2011 were identified as the cases. Additionally, 907 women subjects with breast cancer aged ≥65 years without deep vein thrombosis or pulmonary embolism were randomly selected as the controls. The cases and the controls were matched with age and comorbidities. Ever use of tamoxifen was defined as subjects who had at least a prescription for tamoxifen before index date. Never use of tamoxifen was defined as subjects who never had a prescription for tamoxifen before index date. We used the multivariable logistic regression model to calculate the odds ratio (OR) and the 95% confidence interval (CI) of deep vein thrombosis or pulmonary embolism associated with tamoxifen use.After adjustment for confounding variables, the adjusted OR of deep vein thrombosis or pulmonary embolism was 1.95 for subjects with ever use of tamoxifen (95% CI 1.45, 2.62), as compared with never use of tamoxifen. In addition, atrial fibrillation (adjusted OR 3.73, 95% CI 1.89, 7.35) and chronic kidney disease (adjusted OR 1.72, 95% CI 1.06, 2.80) were also associated with deep vein thrombosis or pulmonary embolism.Tamoxifen use is associated with 1.95-fold increased odds of deep vein thrombosis or pulmonary embolism among older women with breast cancer in Taiwan.

Antiplatelet Therapy in Breast Cancer Patients Using Hormonal Therapy: Myths, Evidence and Potentialities - Systematic Review

Breast cancer is the most frequently diagnosed tumor in women worldwide, with a significant impact on morbidity and mortality. Chemotherapy and hormone therapy have significantly reduced mortality; however, the adverse effects are significant. Aspirin has been incorporated into clinical practice for over 100 years at a low cost, making it particularly attractive as a potential agent in breast cancer prevention and as an adjunct treatment to endocrine therapy in the prophylaxis of cardiovascular complications. The objective of this study was to evaluate the role of aspirin in reducing the incidence of breast cancer and to evaluate the impact of its use on morbidity and mortality and reduction of cardiovascular events as adjuvant therapy during breast cancer treatment with selective estrogen receptor modulators. A systematic review was performed using the PRISMA methodology and PICO criteria, based on the MEDLINE, EMBASE and LILACS databases. The original articles of clinical trials, cohort, case-control studies and meta-analyses published from January 1998 to June 2017, were considered. Most studies showed an association between the use of selective estrogen receptor modulators and the increase in thromboembolic events. The studies suggest a protective effect of aspirin for cardiovascular events during its concomitant use with selective estrogen receptor modulators and in the prevention of breast cancer. This systematic review suggests that aspirin therapy combines the benefit of protection against cardiovascular events with the potential reduction in breast cancer risk, and that the evaluation of the benefits of the interaction of endocrine therapy with aspirin should be further investigated.

Does Hormone Therapy Use Increase Perioperative Complications in Abdominally Based Microsurgical Breast Reconstruction?

BACKGROUND

The use of hormone therapy (tamoxifen and aromatase inhibitors) has been shown to increase venous thromboembolism. As breast cancer patients undergoing microsurgical breast reconstruction are often receiving hormone therapy, it is unclear whether this increased thrombotic risk is associated with increased flap loss.

METHODS

A retrospective review was performed on patients undergoing abdominally based microsurgical breast reconstruction at an academic institution from 2004 to 2015. Patients were divided by use of hormone therapy at the time of surgery. Complication rates, including complete or partial flap loss and overall complications, were compared and analyzed using univariate and logistic regression models.

RESULTS

Among a total of 853 patients (1253 flaps), 193 patients (269 flaps) were receiving hormone therapy and 660 patients (984 flaps) were not. Patients on hormone therapy had higher rates of previous breast surgery, advanced cancer stage, chemoradiation before reconstruction, and delayed and unilateral reconstruction. There were no statistically significant differences between hormone therapy patients and nontherapy patients in complete flap loss (1.0 percent versus 1.1 percent) and partial flap loss (2.2 percent versus 1.5 percent). Hypertension and previous breast surgery were the only independent risk factors for minor complications (adjusted OR, 2.1; 95 percent CI, 1.3 to 3.6; p = 0.005; and adjusted OR, 1.8; 95 percent CI, 1.2 to 2.7; p = 0.009, respectively) and overall complications (adjusted OR, 2.2; 95 percent CI, 1.3 to 3.7; p = 0.004; and adjusted OR, 1.9; 95 percent CI, 1.3 to 3.0; p = 0.003, respectively).

CONCLUSIONS

Hormone therapy was not associated with a higher incidence of complete or partial flap loss or overall complications. The authors propose an individualized approach to the preoperative cessation of tamoxifen or aromatase inhibitors.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Tamoxifen-Related Thrombosis: An Experimental Study in Rat Venous Microvascular Anastomosis Model

Tamoxifen is an estrogen receptor modulator and has been shown to increase risk for microvascular flap complications. This study aimed to investigate the clinical and histopathological effects of tamoxifen use in venous microvascular anastomosis model in rats. The role of vitamin E combination therapy and discontinuing tamoxifen therapy preoperatively were also evaluated.Forty rats were equally divided into 4 groups as follows: group 1 was given saline by oral gavage, group 2 was given tamoxifen citrate, group 3 was given tamoxifen citrate and vitamin E, and in group 4, tamoxifen citrate was given everyday except between days 12 and 16. In each group, femoral veins were dissected in each side and end-to-end anastomosis was performed in one side. Clinical and histopathological evaluations were performed. The ratio of total endothelial area to total vein area in a cross-sectional view of the vein was evaluated and compared.All veins with anastomosis in postoperative 15 minutes were found to be patent. In postoperative 1 week in groups 1 to 4, visible thrombus were present in 1, 3, 2, and 3 samples, respectively. Vitamin E group showed similar histopathological findings with control group. The ratio of endothelial layer to total vein cross-sectional area was increased in groups 2 and 4 in all samples. The increase was statistically significant between groups 2NA and 3NA (P = 0.023) and 2A and 1A (P = 0.006).Chronic tamoxifen consumption in the presence of anastomosis have led to prominent endothelial proliferation in rat femoral veins. Vitamin E combination therapy reversed this endothelial proliferation and should be focused in future studies.

Redox Imbalance in the Development of Colorectal Cancer

Redox imbalance is resulted from the destruction of balance between oxidants and antioxidants. The dominant oxidants are reactive oxygen species (ROS), which are involved in multiple cellular processes by physiologically transporting signal as a second messenger or pathologically oxidizing DNA, lipids, and proteins. Generally speaking, low concentration of ROS is indispensable for cell survival and proliferation. However, high concentration of ROS is cytotoxic. Additionally, ROS are now known to induce the oxidative modification of macromolecules especially proteins. The redox modification of proteins is involved in numerous biological processes related to diseases including CRC. Herein, we attempt to afford an overview that highlights the crosstalk between redox imbalance and CRC.

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.

Tamoxifen Directly Inhibits Platelet Angiogenic Potential and Platelet-Mediated Metastasis

OBJECTIVE

Platelets, which are mainly known for their role in hemostasis, are now known to play a crucial role in metastasis. Tamoxifen is a selective estrogen receptor modulator that is widely used for the treatment of breast cancer. Tamoxifen and its metabolites have been shown to directly impact platelet function, suggesting that this drug has additional mechanisms of action. The purpose of this study was to determine whether tamoxifen exerts antitumor effects through direct platelet inhibition.

APPROACH AND RESULTS

This study found that pretreatment with tamoxifen leads to a significant inhibition of platelet activation. Platelets exposed to tamoxifen released significantly lower amounts of proangiogenic regulator vascular endothelial growth factor. In vitro angiogenesis assays confirmed that tamoxifen pretreatment led to diminished capillary tube formation and decreased endothelial migration. Tamoxifen and its metabolite, 4-hydroxytamoxifen, also significantly inhibited the ability of platelets to promote metastasis in vitro. Using a membrane-based array, we identified several proteins associated with angiogenesis metastasis that were lower in activated releasate from tamoxifen-treated platelets, including angiogenin, chemokine (C-X-C motif) ligand 1, chemokine (C-C motif) ligand 5, epidermal growth factor, chemokine (C-X-C motif) ligand 5, platelet-derived growth factor dimeric isoform BB, whereas antiangiogenic angiopoietin-1 was elevated. Platelets isolated from patients on tamoxifen maintenance therapy were also found to have decreased activation responses, diminished vascular endothelial growth factor release, and lower angiogenic and metastatic potential.

CONCLUSIONS

We demonstrate that tamoxifen and its metabolite 4-hydroxytamoxifen directly alter platelet function leading to decreased angiogenic and metastatic potential. Furthermore, this study supports the idea of utilizing targeted platelet therapies to inhibit the platelet's role in angiogenesis and malignancy.

Drug-Induced Thrombophilic or Prothrombotic States: An Underestimated Clinical Problem That Involves Both Legal and Illegal Compounds

Vascular thrombosis, both arterial and venous, is a condition associated with significant morbidity and mortality. There are multiple risk factors for thrombosis, both congenital and acquired, and in the majority of cases, these risk factors are not modifiable. Over the past 2 decades, multiple drugs (both illegal and legal) have been associated with increased risk of thrombosis. However, due to limited scientific literature regarding the prothrombotic tendencies of these drugs, there is a concomitant limited understanding of the pathophysiology of drug-induced thrombosis. As drugs are one of the few modifiable risk factors for thrombosis, further study and dissemination of knowledge regarding drug-associated and drug-induced thrombosis are essential and have the potential to lead to decreased future incidence of thrombosis. The mechanisms at the basis of the thrombophilic activity of these drugs are variable and sometimes still ill recognized. Increased levels of clotting factors, reduction in coagulation natural inhibitors, decreased fibrinolysis, activated clotting factors, increased blood viscosity, endothelial damage, and increased platelet number and activation are the most frequent causes. Arterial steal or coronary arteries no flow has also been implicated. In some cases due to the intake of several drugs, more than one mechanism is present in a given patient. The purpose of the present review is to analyze all the drugs demonstrated to be potentially thrombotic. It is hoped that a prudent use or nonuse of these drugs might result in a reduction of thrombosis-associated diseases.

Effects of tamoxifen on autosomal genes regulating ovary maintenance in adult mice

Environmental endocrine-disrupting chemicals (EDCs), known to bind to estrogen/androgen receptors and mimic native estrogens, have been implicated as a main source for increasing human reproductive and developmental deficiencies and diseases. Tamoxifen (TAM) is one of the most well-known antiestrogens with defined adverse effects on the female reproductive tract, but the mechanisms related to autosomal gene regulation governing ovary maintenance in mammals remain unclear. The expression pattern and levels of key genes and proteins involved in maintaining the ovarian phenotype in mice were analyzed. The results showed that TAM induced significant upregulation of Sox9, which is the testis-determining factor gene. The results showed that TAM induced significant upregulation of Sox9, the testis-determining factor gene, and the expression level of Sox9 mRNA in the ovaries of mice exposed to 75 or 225 mg/kg bw TAM was 2- and 10-fold that in the control group, respectively (p < 0.001). Furthermore, the testicular fibroblast growth factor gene, Fgf9, was also elevated in TAM-treated ovaries. Accordingly, expression of the ovary development marker, forkhead transcription factor (FOXL2), and WNT4/FST signaling, were depressed. The levels of protein expression changed consistently with the target genes. Moreover, the detection of platelet/endothelial cell adhesion molecule 1 (PECAM-1) in TAM-treated ovaries suggested the formation of vascular endothelial cells, which is a further evidence for the differentiation of the ovaries to a testis-like phenotype. During this period, the level of 17β-estradiol, progesterone, and luteinizing hormone decreased, while that of testosterone increased by 3.3-fold (p = 0.013). The activation of a testis-specific molecular signaling cascade was a potentially important mechanism contributing to the gender disorder induced by TAM, which resulted in the differentiation of the ovaries to a testis-like phenotype in adult mice. Limited with a relatively higher exposure, the present study provided preliminary molecular insights into the sexual disorder induced by antiestrogens and compounds that interrupted estrogen signaling by other modes of action.

Management of chemotherapy-induced thromboembolism in breast cancer

Thromboembolic events are common in cancer patients and, apart from contributing to significant morbidity, are regarded as the second leading cause of death in this population. Breast cancer patients are considered low risk for venous thromboembolism; however, the presence of advanced disease and use of chemotherapy and/or other adjunct treatments significantly raises this risk by altering the balance of pro- and anti-coagulant proteins. Low molecular weight heparin is central to the management of venous thromboembolism in this context, whether for prophylaxis, acute management or prevention of recurrences. Risk stratification models need to be incorporated to guide decision making where available.

Comparative effects of estrogen, raloxifene and tamoxifen on endothelial dysfunction, inflammatory markers and oxidative stress in ovariectomized rats

AIM

Endothelial dysfunction is considered a premature indication of atherosclerosis and vessel damage and is present in the postmenopausal period. This study compares the influence of estrogen, raloxifene and tamoxifen on factors that affect endothelial function in ovariectomized (OVX) rats.

MAIN METHODS

The rats were divided into: SHAM; OVX; OVX+estrogen (0.5 μg/kg/day); OVX+raloxifene (2 mg/kg/day) and OVX+tamoxifen (1 mg/kg/day) groups. The acetylcholine vasorelaxation response was evaluated in the mesenteric vascular bed. The vascular oxidative stress and serum inflammatory cytokine levels were monitored, and analyses of eNOS and iNOS were performed.

KEY FINDINGS

The acetylcholine-induced responses obtained in the OVX were lower than those obtained in the SHAM, and all treatments restored this response. l-NAME reduced and equalized the acetylcholine-induced response in all groups. The attenuation of the acetylcholine-induced responses by aminoguanidine was greater in the OVX. Endothelial dysfunction in OVX was associated with oxidative stress and an increase in iNOS and decrease in eNOS expression. Except for the production of reactive oxidative species (ROS) in the OVX+tamoxifen, treatments improved the nitric oxide component of the relaxation response and normalized both the oxidative stress and the expression of those signaling pathway enzymes. Serum levels of TNF-α and IL-6 were increased in OVX, and treatments normalized these levels.

SIGNIFICANCE

Raloxifene and tamoxifen have similar anti-inflammatory effects that may be important in improving vascular dysfunction. Tamoxifen did not affect the ROS but improved endothelial dysfunction. The protective effect on endothelial function by these treatments provides evidence of their potential cardiovascular benefits in the postmenopausal period.

Tamoxifen reduces fat mass by boosting reactive oxygen species

As the pandemic of obesity is growing, a variety of animal models have been generated to study the mechanisms underlying the increased adiposity and development of metabolic disorders. Tamoxifen (Tam) is widely used to activate Cre recombinase that spatiotemporally controls target gene expression and regulates adiposity in laboratory animals. However, a critical question remains as to whether Tam itself affects adiposity and possibly confounds the functional study of target genes in adipose tissue. Here we administered Tam to Cre-absent forkhead box O1 (FoxO1) floxed mice (f-FoxO1) and insulin receptor substrate Irs1/Irs2 double floxed mice (df-Irs) and found that Tam induced approximately 30% reduction (P<0.05) in fat mass with insignificant change in body weight. Mechanistically, Tam promoted reactive oxygen species (ROS) production, apoptosis and autophagy, which was associated with downregulation of adipogenic regulator peroxisome proliferator-activated receptor gamma and dedifferentiation of mature adipocytes. However, normalization of ROS potently suppressed Tam-induced apoptosis, autophagy and adipocyte dedifferentiation, suggesting that ROS may account, at least in part, for the changes. Importantly, Tam-induced ROS production and fat mass reduction lasted for 4–5 weeks in the f-FoxO1 and df-Irs mice. Our data suggest that Tam reduces fat mass via boosting ROS, thus making a recovery period crucial for posttreatment study.

An inhibition of p38 mitogen activated protein kinase delays the platelet storage lesion

BACKGROUND AND OBJECTIVES

Platelets during storage undergo diverse alterations collectively known as the platelet storage lesion, including metabolic, morphological, functional and structural changes. Some changes correlate with activation of p38 mitogen activated protein kinase (p38 MAPK). Another MAPK, extracellular signal-related kinase (ERK), is involved in PLT activation. The aim of this study was to compare the properties of platelets stored in plasma in the presence or absence of p38 and ERK MAPK inhibitors.

MATERIALS AND METHODS

A single Trima apheresis platelet unit (n = 12) was aliquoted into five CLX storage bags. Two aliquots were continuously agitated with or without MAPK inhibitors. Two aliquots were subjected to 48 hours of interruption of agitation with or without MAPK inhibitors. One aliquot contained the same amount of solvent vehicle used to deliver the inhibitor. Platelets were stored at 20-24°C for 7 days and sampled on Days 1, 4, and 7 for 18 in vitro parameters.

RESULTS

Inhibition of p38 MAPK by VX-702 leads to better maintenance of all platelet in vitro storage parameters including platelet mitochondrial function. Accelerated by interruption of agitation, the platelet storage lesion of units stored with VX-702 was diminished to that of platelets stored with continuous agitation. Inhibition of ERK MAPK did not ameliorate decrements in any in vitro platelet properties.

CONCLUSION

Signaling through p38 MAPK, but not ERK, is associated with platelet deterioration during storage.

5,6-Epoxy-cholesterols contribute to the anticancer pharmacology of tamoxifen in breast cancer cells

Tamoxifen (Tam) is a selective estrogen receptor modulator (SERM) that remains one of the major drugs used in the hormonotherapy of breast cancer (BC). In addition to its SERM activity, we recently showed that the oxidative metabolism of cholesterol plays a role in its anticancer pharmacology. We established that these effects were not regulated by the ER but by the microsomal antiestrogen binding site/cholesterol-5,6-epoxide hydrolase complex (AEBS/ChEH). The present study aimed to identify the oxysterols that are produced under Tam treatment and to define their mechanisms of action. Tam and PBPE (a selective AEBS/ChEH ligand) stimulated the production and the accumulation of 5,6α-epoxy-cholesterol (5,6α-EC), 5,6α-epoxy-cholesterol-3β-sulfate (5,6-ECS), 5,6β-epoxy-cholesterol (5,6β-EC) in MCF-7 cells through a ROS-dependent mechanism, by inhibiting ChEH and inducing sulfation of 5,6α-EC by SULT2B1b. We showed that only 5,6α-EC was responsible for the induction of triacylglycerol (TAG) biosynthesis by Tam and PBPE, through the modulation of the oxysterol receptor LXRβ. The cytotoxicity mediated by Tam and PBPE was triggered by 5,6β-EC through an LXRβ-independent route and by 5,6-ECS through an LXRβ-dependent mechanism. The importance of SULT2B1b was confirmed by its ectopic expression in the SULT2B1b(-) MDA-MB-231 cells, which became sensitive to 5,6α-EC, Tam or PBPE at a comparable level to MCF-7 cells. This study established that 5,6-EC metabolites contribute to the anticancer pharmacology of Tam and highlights a novel signaling pathway that points to a rationale for re-sensitizing BC cells to Tam and AEBS/ChEH ligands.

A Platelet Acquired Storage Pool Disorder Associated with Tamoxifen Therapy

The antiestrogenic drug tamoxifen, used in patients with breast cancer, is associated with an increase in arterial and venous thrombotic events, the mechanism of which is not clearly understood. We report a case of a lady who presented with new bruising and prolonged bleeding following a tooth extraction 4–6 weeks after starting tamoxifen. Investigations were consistent with an acquired platelet storage pool disorder. Repeat platelet function analysis was normal, performed 3 months after discontinuation of tamoxifen. We present a previously clinically unreported effect of tamoxifen on platelet function.