Aromatase inhibitors: a safety comparison

Aromatase enzyme: Paving the way for exploring aromatization for cardio-renal protection

Documented male-female differences in the risk of cardiovascular and chronic kidney diseases have been largely attributed to estrogens. The cardiovascular and renal protective effects of estrogens are mediated via the activation of estrogen receptors (ERα and ERβ) and G protein-coupled estrogen receptor, and involve interactions with the renin-angiotensin-aldosterone system. Aromatase, also called estrogen synthase, is a cytochrome P-450 enzyme that plays a pivotal role in the conversion of androgens into estrogens. Estrogens are biosynthesized in gonadal and extra-gonadal sites by the action of aromatase. Evidence suggests that aromatase inhibitors, which are used to treat high estrogen-related pathologies, are associated with the development of cardiovascular events. We review the potential role of aromatization in providing cardio-renal protection and highlight several meta-analysis studies on cardiovascular events associated with aromatase inhibitors. Overall, we present the potential of aromatase enzyme as a fundamental contributor to cardio-renal protection.

Comparison of Changes in the Lipid Profiles of Eastern Chinese Postmenopausal Women With Early-Stage Breast Cancer Treated With Different Aromatase Inhibitors: A Retrospective Study

Cardiovascular morbidity is closely associated with serum lipid level. We aimed to investigate the effects of different aromatase inhibitors, including letrozole, anastrozole, and exemestane, on the lipid profile of eastern Chinese breast cancer patients. We evaluated a retrospective cohort of eastern Chinese postmenopausal women with early-stage breast cancer who received aromatase inhibitors. A total of 116 postmenopausal women with early-stage breast cancer without prior cardiovascular disease were included. Lipid changes at 3, 6, 12, and 24 months were compared across the endocrine therapy categories. Our data demonstrated that exemestane treatment significantly decreased triglyceride level compared with letrozole after 24 months. However, the aromatase inhibitors had almost equivalent impacts on high-density liportein cholesterol, low-density lipoprotein cholesterol, and triglyceride after long-term aromatase inhibitor treatment. As a small-size retrospective study, our data do not support a judgment about whether one AI or another carries more or less risk in terms of lipid disorders in eastern Chinese breast cancer patients. The exact effects need further randomized, controlled trials to investigate.

Aromatase inhibitor-associated bone loss and its management with bisphosphonates in patients with breast cancer

Postmenopausal women have an increased risk of osteopenia and osteoporosis due to loss of the bone-protective effects of estrogen. Disease-related processes may also contribute to the risk of bone loss in postmenopausal women with breast cancer. One of the most common and severe safety issues associated with cancer therapy for patients with breast cancer is bone loss and the associated increase in risk of fractures. This paper reviews the recent literature pertaining to aromatase inhibitor (AI)-associated bone loss, and discusses suggested management and preventative approaches that may help patients remain on therapy to derive maximum clinical benefit. A case study is presented to illustrate the discussion. We observed that AIs are in widespread use for women with hormone receptor-positive breast cancer and are now recommended as adjuvant therapy, either as primary therapy or sequential to tamoxifen, for postmenopausal women. AIs target the estrogen biosynthetic pathway and deprive tumor cells of the growth-promoting effects of estrogen, and AI therapies provide benefits to patients in terms of improved disease-free survival. However, there is a concern regarding the increased risk of bone loss with prolonged AI therapy, which can be managed in many cases with the use of bisphosphonates and other interventions (eg, calcium, vitamin D supplementation, exercise).

Cancer therapy disparity: unequal access to breast cancer therapeutics and drug funding in Canada

Adjuvant therapy has made a significant contribution in reducing breast cancer-specific mortality. Standard chemotherapeutics and tamoxifen have been the mainstay treatment for years, but recent clinical evidence supports the use of novel small-molecule therapy and aromatase inhibitor therapy in selected settings, challenging not only the traditional paradigm of breast cancer treatment, but also provincial funding of oncologic care across Canada. The disparity in access to aromatase inhibitor therapy for postmenopausal women with early-stage hormone-sensitive breast cancer across Canada is highlighted as an example.

Guidelines for Osteoprotection in Breast Cancer Patients on an Aromatase Inhibitor

Postmenopausal women are at an increased risk of osteopenia and osteoporosis due to the physiologic loss of the bone protective effects of estrogen. Additionally, disease-related risk factors also contribute to the increased fracture risk. To further complicate matters, one of the most common and severe safety issues associated with cancer therapies for breast cancer patients is bone loss and the associated increased risk of fractures. These facts underscore the need to carefully monitor bone mineral density in patients with endocrine-responsive breast cancer, and to consider adjuvant therapy that may help manage and/or prevent bone loss and fracture. Aromatase inhibitors (AIs) are now in widespread clinical use for women with hormone receptor-positive breast cancer and have replaced tamoxifen as the gold standard of care. AIs target the estrogen biosynthetic pathway and deprive tumor cells of the growth-promoting effects of estrogen. These treatments provide significant benefit to patients in terms of improved disease-free and overall survival. Adversely, there is a concern of an increased risk of bone loss with prolonged therapy consequently leading to an increased fracture risk. This manuscript will review the recent literature pertaining to AI-associated bone loss and discuss suggested management and preventative approaches that may help patients remain on therapy to derive the most clinical benefits.

Adjuvant aromatase inhibitor therapy: outcomes and safety

Adjuvant therapy with the third-generation aromatase inhibitors (AIs) anastrozole, letrozole, and exemestane has largely replaced the use of tamoxifen (TAM) as standard adjuvant endocrine treatment for postmenopausal women with hormone-sensitive early breast cancer. Treatment strategies investigated in large, randomized, well-controlled clinical studies include the use of an AI as an upfront replacement for TAM, as an alternative to continued treatment with TAM, and in the extended adjuvant setting after at least 5 years of TAM. The efficacy of AIs over TAM has been demonstrated, particularly in terms of improving disease-free survival (DFS), and reductions in early distant metastasis with AIs may ultimately translate into improved overall survival. As AI therapy offers prolonged DFS, safety is an important concern over the long term. The AIs are better tolerated than TAM in terms of troublesome gynecologic adverse events such as vaginal bleeding and discharge, as well as life-threatening complications such as venous thromboembolic events and endometrial cancer. On the other hand, AI therapy has been associated with losses in bone density and a potential effect on lipids and cardiovascular risk. In trials comparing AIs with TAM, only limited conclusions can be made because of the putative cardioprotective, lipid-lowering, and bone-sparing effects of TAM. Studies comparing AIs with placebo, and/or in healthy women, may be more useful in understanding the long-term safety of adjuvant AI therapy. Results of ongoing safety analyses within some of the large AI trials should provide further insight into the long-term tolerability of AI therapy in the adjuvant setting.

Tamoxifen and ICI 182,780 increase Bcl-2 levels and inhibit growth of breast carcinoma cells by modulating PI3K/AKT, ERK and IGF-1R pathways independent of ERalpha

We recently showed that estrogen withdrawal from the ERalpha(+), high Bcl-2-expressing breast carcinoma cells (MCF-7B) reduced Bcl-2 protein levels while increasing cell-cell adhesion, and junction formation. Here we compared these cells with the ERalpha(+) and low Bcl-2-expressing MCF-7 cells and with the normal mammary epithelial cell line MCF-10-2A not expressing ERalpha or Bcl-2. All cell lines expressed normal HER2. Antiestrogen (Tamoxifen and ICI 182,780) treatment increased Bcl-2 levels in both MCF-7 and -7B cells and led to the formation of acinar structures. This treatment led to the dissociation of junctions and redistribution of junctional components to the cytoplasm in MCF-10-2A and -7 cells, while in MCF-7B cells junctional proteins redistributed to membranes. Antiestrogen treatment decreased PI3K/Akt activation and increased ERK activation regardless of ERalpha status. IGF-1R was inactivated in the antiestrogen-treated MCF-7 cells while it was activated in MCF-7B cells. Our data show that Tamoxifen and ICI 182,780 can induce growth inhibitory effects via the sustained activation/inactivation of signaling pathways that regulate cell survival, cell death and differentiation in the absence of ERalpha. Furthermore, Bcl-2 overexpression may alter the functional interactions among these pathways in response to antiestrogens, which also may provide a potential explanation for the observation that Bcl-2 overexpressing tumors have a better prognosis.

Inhibition of Cytochromes P450: Existing and New Promising Therapeutic Targets

Mammalian cytochromes P450 have been shown to play highly important roles in the metabolism of drugs and xenobiotics as well as in the biosynthesis of a variety of endogenous compounds, many of them displaying hormonal function. The role of P450s as therapeutic targets is still inadequately recognized although several P450 inhibitors became efficient drugs that even reached blockbuster status. Here, we try to give a comprehensive overview on cytochromes P450s, which are already well-established targets - particularly focussing on the treatment of infectious diseases, metabolic disorders and cancer - and on those, which have a high potential to become successful targets. In addition, the design of inhibitors of cytochromes P450 will be discussed.

Effects of testosterone undecanoate administered alone or in combination with letrozole or dutasteride in female to male transsexuals

INTRODUCTION

Testosterone undecanoate (TU) has potential as androgen therapy for ovariectomized female to male (FtM) transsexual subjects; however, the long-term physiologic effects of TU treatment, the significance of testosterone (T), and the T metabolites dihydrotestosterone (DHT) and estradiol (E) on specific outcome parameters are currently unknown.

AIM

The aim of this study was to investigate the long-term treatment of TU with regard to bone metabolism, body composition, and lipid profile in FtM subjects, and to evaluate the relationship between observed effects and circulating levels of T, E, and DHT.

MAIN OUTCOME MEASURES

Circulating follicle-stimulating hormone, luteinizing hormone, T, E, DHT, and lipid concentrations were measured, as well as bone metabolism, body composition, and insulin resistance.

METHODS

This was a 1-year, randomized treatment, open-label, uncontrolled safety study. Fifteen ovariectomized FtM subjects from an outpatient clinic were divided into three groups to receive TU 1,000 mg alone or in combination with oral administration of letrozole (L) 2.5 mg/die or dutasteride (D) 0.5 mg/die for a period of 54 weeks.

RESULTS

TU alone and TU + D treatments were successful in terms of hormone adjustment, did not result in any adverse effects, and were well-tolerated. Bone mineral density decreased by an average of 0.9 g/cm(2) in the TU + L group, and the addition of D resulted in a failure to gain lean mass.

CONCLUSIONS

This study confirmed that TU is a successful and safe treatment for FtM subjects. These data indicate that E has an important role in bone metabolism and that DHT may play a role in muscle metabolism.

Raloxifene in breast cancer prevention

BACKGROUND

Raloxifene is a benzothiophene, selective estrogen receptor modulator with estrogen-agonist effects in the skeleton and the cardiovascular system but estrogen-antagonist effects in the uterus and the mammary gland. This compound was first approved in different countries for the prevention and treatment of osteoporosis.

OBJECTIVE/METHODS

We performed a literature search to review available preclinical and clinical data that has led to the recent FDA approval of raloxifene as a chemopreventive agent for breast cancer in postmenopausal women.

RESULTS/CONCLUSIONS

Different placebo-controlled trials indicated that raloxifene is effective in reducing invasive breast cancer risk in postmenopausal women. In a recent comparative study, a similar efficacy between raloxifene and tamoxifen for breast cancer prevention was demonstrated, but raloxifene showed a more favorable safety profile.

Methodological issues in evaluating cost effectiveness of adjuvant aromatase inhibitors in early breast cancer: a need for improved modelling to aid decision making

The optimal adjuvant hormonal strategy in post-menopausal women with early breast cancer is a subject of ongoing debate. Aromatase inhibitors (AIs) have been successfully evaluated in clinical trials that have compared them with a standard treatment of 5 years of tamoxifen. However, several options are available in terms of treatment schedule and selected drug. Systematic reviews of clinical trials and health economic evaluations attempt to contribute to the debate. The objective of this paper is to provide a critical review of existing health economic evaluations with a focus on those parameters and assumptions with the largest impact on final outcomes.A wide range of different inputs and assumptions exist, which make a comparison of results difficult, if not impossible. In particular, the modelling of recurrence rates over longer time horizons than those observed in clinical trials, a cornerstone of health economic modelling, is subject to quite different approaches. The practice of indirect comparison of different AIs without sufficiently acknowledging population differences is also bothersome. A list of key features (related to time horizon, clinical data input, patient subtypes, budget impact and model calibration) that an ideal model should have in order to better assist decision makers in this field is proposed.

Aromatase inhibitor-induced arthralgia: clinical experience and treatment recommendations

It is well documented that the aromatase inhibitors (AIs) are superior to tamoxifen as adjuvant endocrine therapy in postmenopausal women with hormone receptor-positive breast cancer. However, compared with tamoxifen, an elevated incidence of arthralgia has been observed during AI treatment. Concerns have been raised that AI-induced arthralgia may dissuade patients from completing their full AI treatment course, and may also deter physicians from prescribing an AI if they feel that patients may be at risk of permanent joint damage. Patient education about the possibility of experiencing arthralgia, and effective management of symptoms if they appear, are important in helping patients adhere to AI treatment, and consequently improving breast cancer outcomes. In this paper, we discuss the potential mechanisms behind AI-induced arthralgia, review the frequency with which arthralgia occurs, and propose for the first time an algorithm specifically for the treatment of AI-induced arthralgia. As with joint pain in non-breast cancer patients, a sequential approach to disease management is recommended, involving modifying the patient's lifestyle in addition to taking a stratified approach to pharmacological intervention with analgesia and anti-inflammatory medication. Knowing that joint symptoms can be managed in most patients may encourage patient-physician communication and treatment compliance.