A summary of second-line randomized studies of aromatase inhibitors

An overview of letrozole in postmenopausal women with hormone-responsive breast cancer

Third-generation aromatase inhibitors (AIs) have proven to be superior to tamoxifen in terms of time to disease progression in patients with hormone receptor (HR) positive (HR+) status and, nowadays, are used in the adjuvant and neoadjuvant settings, and first-line therapy for advanced breast cancer. Letrozole is a third generation AI, as are anastrozole and exemestane. In the past, clinical studies had demonstrated that letrozole was effective as a second-line treatment of metastatic breast cancer. In this paper, pharmacokinetic and pharmacodynamic properties of letrozole are reviewed along with its activity in preclinical and clinical settings. Additionally, the results of important clinical trials such as Breast International Group (BIG) 1-98, which tested the optimal initial adjuvant endocrine treatment and the sequential therapy with letrozole and tamoxifen, MA-17 that evaluates the benefits of extended adjuvant therapy, and other important studies in advanced and neoadjuvant disease, are reviewed. Safety comparisons of treatments are also addressed. Interestingly, about 50% of human epidermal growth factor receptor 2-positive (HER2+) breast cancers are HR+. However, HER2 positivity is a marker of antiestrogen treatment resistance. Because of this, a dual treatment is a logical approach when both receptors are overexpressed. The combination of lapatinib and letrozole leads to a significant improvement in the overall disease outcome. Also, the combination of everolimus plus letrozole has been tested in this setting. In fact, the coadministration of both agents seems to increase the efficacy of letrozole in newly-diagnosed HR+ patients. Once resistance to sequential trastuzumab and AI as monotherapy has been found, trastuzumab and letrozole combined in HR+ and HER2+ patients with advanced breast cancer can overcome resistance to both drugs administered as single agents, according to recently reported results.

B-Type natriuretic peptide inhibited angiotensin II-stimulated cholesterol biosynthesis, cholesterol transfer, and steroidogenesis in primary human adrenocortical cells

In this study, we demonstrate that B-type natriuretic peptide (BNP) opposed angiotensin II (Ang II)-stimulated de novo cholesterol biosynthesis, cellular cholesterol uptake, cholesterol transfer to the inner mitochondrial membrane, and steroidogenesis, which are required for biosynthesis of steroid hormones such as aldosterone and cortisol in primary human adrenocortical cells. BNP dose-dependently stimulated intracellular cGMP production with an EC(50) of 11 nm, implying that human adrenocortical cells express the guanylyl cyclase A receptor. cDNA microarray and real-time RT-PCR analyses revealed that BNP inhibited Ang II-stimulated genes related to cholesterol biosynthesis (acetoacetyl coenzyme A thiolase, HMG coenzyme A synthase 1, HMG coenzyme A reductase, isopentenyl-diphosphate Delta-isomerase, lanosterol synthase, sterol-4C-methyl oxidase, and emopamil binding protein/sterol isomerase), cholesterol uptake from circulating lipoproteins (scavenger receptor class B type I and low-density lipoprotein receptor), cholesterol transfer to the inner mitochondrial membrane (steroidogenic acute regulatory protein), and steroidogenesis (ferredoxin 1,3beta-hydroxysteroid dehydrogenase, glutathione transferase A3, CYP19A1, CYP11B1, and CYP11B2). Consistent with the microarray and real-time PCR results, BNP also blocked Ang II-induced binding of (125)I-labeled low-density lipoprotein and (125)I-labeled high-density lipoprotein to human adrenocortical cells. Furthermore, BNP markedly inhibited Ang II-stimulated release of estradiol, aldosterone, and cortisol from cultured primary human adrenocortical cells. These findings demonstrate that BNP opposes Ang II-induced steroidogenesis via multiple steps from cholesterol supply and transfer to the final formation of steroid hormones. This study provides new insights into the cellular mechanisms by which BNP modulates Ang II-induced steroidogenesis in the adrenal gland.

Use of an aromatase inhibitor in patients with polycystic ovary syndrome: a prospective randomized trial

OBJECTIVE

To compare the use of an aromatase inhibitor (letrozole) with the use of clomiphene citrate (CC).

DESIGN

Prospective randomized study.

SETTING

An infertility clinic in a university hospital.

PATIENT(S)

Seventy-four consecutive infertile patients with polycystic ovary syndrome were recruited. Thirty-eight patients were randomized to the letrozole group (99 cycles), and the remaining patients were recruited to the CC group (95 cycles).

INTERVENTION(S)

The aromatase inhibitor letrozole (2.5 mg/d) and CC (100 mg/d) were administered orally on days 3-7 of menses.

MAIN OUTCOME MEASURE(S)

Number of follicles, endometrial thickness, E(2) levels on hCG day, and pregnancy rates among both groups.

RESULT(S)

Ovulation occurred in 65.7% (65/99) of letrozole cycles and in 74.7% (71/95) of CC cycles. The median (minimum-maximum) number of follicles sized >15 mm in diameter on the day of hCG administration were 1 (0-4) and 1 (0-5) in the letrozole and CC groups, respectively. On the day of hCG administration, median serum E(2) concentrations in the letrozole and CC groups were statistically significantly different: 189 pg/mL (18-1,581 pg/mL) and 386 pg/mL (27-6,190 pg/mL), respectively. The median serum E(2) concentrations per follicle sized >15 mm in diameter on the day of hCG also statistically significantly differed between the letrozole and CC groups: 160 pg/mL (18-808 pg/mL) and 281 pg/mL (27-2,615 pg/mL), respectively. The median endometrial thickness on the day of hCG did not significantly differ between the CC and letrozole groups; it was 8 mm. Pregnancy was achieved in nine cycles (9.1%) of the letrozole group and in seven cycles (7.4%) of the CC group, which also was not a statistically significant difference.

CONCLUSION(S)

The aromatase inhibitor letrozole may be an acceptable alternative to CC as an ovulation-induction drug in patients with PCOS.

Second- and third-generation aromatase inhibitors as first-line endocrine therapy in postmenopausal metastatic breast cancer patients: a pooled analysis of the randomised trials

The purpose of this study was to estimate in all randomised trials the relative risk of overall response rate (ORR), clinical benefit (CB), time to progression (TTP), overall survival (OS), and toxicity of aromatase inhibitors (AI), compared with tamoxifen (Tam) as first-line endocrine therapy in postmenopausal metastatic breast cancer (PMBC) women. Prospective randomised studies were searched through computerised queries of MEDLINE, EMBASE, and the American Society of Clinical Oncology (ASCO) abstract database. Relative risk, 95% confidence interval, and heterogeneity were derived according to the inverse variance and Mantel-Haenszel method and Q statistics. Six phase III prospective randomised trials including 2787 women were gathered. A significant advantage in ORR (P = 0.042), TTP (P = 0.007), and CB (P = 0.001) in favour of AI over Tam was detected at the fixed effects model. These results were not significant at the random effects model, owing to the significant heterogeneity. On the contrary, no difference was registered for OS (P = 0.743) with no significant heterogeneity. Regarding toxicity, Tam caused more frequently thromboembolic events (P = 0.005) and vaginal bleeding (P = 0.001) compared with AI. Aromatase inhibitors appear to be superior to Tam as first-line endocrine option in PMBC women. Owing to a component of variability between the six studies analysed, the random effects estimates differed from corresponding fixed ones. Investigators should assess heterogeneity of trial results before deriving summary estimates of treatment effect.

Can the dextroenantiomer of the aromatase inhibitor fadrozole be useful for clinical investigation of aldosterone-synthase inhibition?

The beneficial effects of spironolactone, eplerenone, amiloride and potassium in preventing cardiovascular damage in various experimental models of salt-induced hypertension can be dissociated from blood pressure effects, and have drawn attention to the direct genomic and non-genomic actions of aldosterone at the level of the vessels, the heart and the kidneys. Exposure to endogenous aldosterone could be decreased by direct and specific aldosterone-synthase inhibition. FAD 286A, the dextroenantiomer of the aromatase inhibitor fadrozole, might be a first candidate to investigate in humans, the physiological impact and therapeutic properties of aldosterone-synthase inhibition, especially in various forms of primary aldosteronism.

Effect of bee venom on aromatase expression and activity in leukaemic FLG 29.1 and primary osteoblastic cells

The effect of bee venom aqua-acupuncture (BVA) (api-toxin), a traditional immunosuppressive Korean aqua-acupuncture, on the bone function in human osteoblastic cells was studied. To provide insights into the effect of BVA on aromatase activity in bone-derived cells, we examined the human leukaemic cell line FLG 29.1, which is induced to differentiate toward the osteoclastic phenotype by TPA and TGF-beta1, and the primary first-passage osteoblastic cells (hOB). Southern blot of RT-PCR products with a 32P-labeled cDNA probe for the human aromatase demonstrated that FLG 29.1 and hOB cells express aromatase mRNA. Gene expression and enzyme activity were stimulated in a time-dependent fashion by 5.0 microl/ml BV and by either 1-50 nM TPA or 0.01-0.5 ng/ml TGF-beta1, with maximal responses after 2-3 h exposure. After 24 h incubation of the cells in the absence of these stimuli the aromatase mRNA and the protein were barely detectable. These findings demonstrate that cells of the osteoclastic lineage synthesize aromatase in vitro by the local cytokine of TGF-beta1 and BVA. These can offer an explanation for the lack of development of osteoarthritis in BVA-treated patients.

Endocrine approaches for the treatment of early and advanced breast cancer in postmenopausal women

Preventing clinical progression is the major treatment goal for both early and advanced breast cancer. For hormone-responsive cases (about 70% of the total), this can necessitate the use of sequential hormone therapies at various points during the patient's life. Newer hormonal therapies, such as the third-generation aromatase inhibitor anastrozole, are now competing with tamoxifen as first choice endocrine therapy in breast cancer. In addition, a further non-steroidal aromatase inhibitor letrozole has been shown to be beneficial when given at completion of 5 years adjuvant tamoxifen. In light of these new data, current treatment paradigms need to be reviewed. Already well established as second-line treatments for advanced breast cancer, the improved risk:benefit profiles of anastrozole and letrozole compared with tamoxifen mean that these agents are now also recognised alternative treatments in the first-line relapse setting. More recent studies demonstrate that anastrozole may also have an improved risk:benefit profile compared with tamoxifen when used as initial adjuvant therapy in early breast cancer. Anastrozole is also being evaluated as a preventative treatment in women at high risk of developing breast cancer. A new addition to the endocrine treatment armamentarium is the oestrogen receptor antagonist fulvestrant, which, unlike tamoxifen, has no agonist effects. Fulvestrant is at least as effective as anastrozole in the second-line treatment of advanced breast cancer, and provides similar benefits to tamoxifen when used as first-line therapy in patients with advanced, hormone receptor-positive tumours.

Patterns of Relapse and Modalities of Treatment of Breast Cancer: The ‘IRIS’ Project, a Multicenter Observational Study

OBJECTIVES

The aim of this study was to describe the patterns of breast cancer relapse and the factors influencing therapeutic choices in an unselected postmenopausal population.

METHODS

Five hundred and thirty-nine patients were enrolled between October 1999 and March 2001. The majority (92.6%) underwent surgery for the primary tumor: there was no difference between general and university hospitals in terms of the type of mastectomy, but a slight difference was found between Southern and Northern Centers.

RESULTS

At the time of first relapse, 61.6% of the patients had a good Karnofsky performance status. The median disease-free interval (DFI) was 34 months. More than half of the patients (62.3%) presented a single metastasis. Metastatic disease was treated with chemotherapy in 64.8% of cases (alone in 44.1%, and in combination with hormone therapy in 20.1%), hormone therapy alone was given in 30.8% of cases. The main reasons for choosing chemotherapy were age (31%), standard guidelines (19.4%) and the site of metastatic disease (14.3%), and those for selecting hormone therapy were age (26.6%), site of relapse (19.3%), standard guidelines (19.2%), biological tumor characteristics (14.3%) and the DFI (11.1%). Taxane-containing treatments accounted for 46.1% of the chemotherapies, whereas letrozole was the preferred hormone (41.2%).

CONCLUSION

The first relapse of breast cancer is often single, at bone or viscera, and mainly diagnosed by instrumental screening examinations. The preferred chemo- and hormone therapies are taxane-containing regimens and letrozole, respectively.

Multiple structural and functional abnormalities in the p450 aromatase expressing transgenic male mice are ameliorated by a p450 aromatase inhibitor

The present study was undertaken to analyze the effect of a P450 aromatase inhibitor (finrozole) on 4-month-old transgenic mice expressing human P450 aromatase (P450arom) under the human ubiquitin C promoter (AROM+). AROM+ mice present several dysfunctions, such as adrenal and pituitary hyperplasia, cryptorchidism, Leydig cell hypertrophy and hyperplasia, and gynecomastia. The present study demonstrates that these abnormalities were efficiently treated by administration of a P450arom inhibitor, finrozole. The treatment normalized the reduced intratesticular and serum testosterone levels, while those of estradiol were decreased. The body weight and several affected organ weights were normalized with the treatment. Histological analysis revealed that both the pituitary and adrenal hyperplasia were diminished. Furthermore, the cryptorchid testes present in the untreated AROM+ males descended to scrotum, 4 to 15 days after inhibitor treatment. In addition, the disrupted spermatogenesis was recovered and qualitatively complete spermatogenesis appeared with the inhibitor treatment. This was associated with normalized structure of the interstitial tissue, as analyzed by immunohistochemical staining for Leydig cells and macrophages. One of the features was that the Leydig cell hypertrophy was markedly diminished in the treated mice. AROM+ mice also present with severe gynecomastia, while the development and differentiation of the mammary gland in AROM+ males was markedly diminished with the inhibitor treatment. Interestingly, the mammary gland involution was associated with the induction of androgen receptor in the epithelial cells, while estrogen receptors were still detectable in the epithelium. The data show that AROM+ mouse model is a novel tool to further analyze the use of P450arom inhibitors in the treatment of the dysfunctions in males associated with misbalanced estrogen to androgen ratio, such as pituitary adenoma, testicular dysfunction, and gynecomastia.

Use of letrozole as a chemopreventive agent in aromatase overexpressing transgenic mice

Our recent studies have shown that overexpression of aromatase results in increased tissue estrogenic activity and induction of hyperplastic and dysplastic lesions in mammary glands, and gynecomastia and testicular cancer in male aromatase transgenic mice. Our studies also have shown that aromatase overexpression-induced changes in mammary glands can be abrogated with very low concentrations of letrozole, an aromatase inhibitor without any effect on normal physiology. In the present study, we have examined the effect of prior low dose letrozole treatment on pregnancy and lactation. We have also investigated the effect of low dose letrozole treatment on subsequent mammary growth and biochemical changes in these animals. There was no change in the litter size, birth weight and no visible birth defects in letrozole-treated animals. Although, there was an insignificant increase in mammary growth in aged animals after 6 weeks of letrozole treatment, the levels of expression of estrogen receptor, progesterone receptor and genes involved in cell cycle and cell proliferation remained low compared to control untreated animals. These observations indicate that aromatase inhibitors such as letrozole can be used as chemopreventive agents without effecting normal physiology in aromatase transgenic mice.

A comparison of the efficacy of aromatase inhibitors in second-line treatment of metastatic breast cancer

Randomized clinical trials have established the role of third-generation aromatase inhibitors (AIs) (letrozole, anastrozole, and exemestane) as standard treatment for patients with hormone-sensitive metastatic breast cancer who have experienced disease progression with antiestrogen therapy. Significant gains in clinical efficacy and improved tolerability over progestins (megestrol acetate) and the first-generation AI aminoglutethimide have positioned these agents above previous therapies. Estrogen receptor (ER) status remains the best predictive determinant of endocrine response, and further randomized trials with properly selected patient populations may distinguish individual AIs within this class. A recently completed, randomized, head-to-head phase III trial of letrozole versus anastrozole as second-line endocrine therapy demonstrated a significant difference in objective response rate for letrozole compared with anastrozole (19% versus 12%, respectively; P = 0.014), with similar time to progression. The improved efficacy and safety of AIs as second-line endocrine therapies has spawned trials of their use as first-line endocrine therapy versus tamoxifen for patients with metastatic breast cancer. Based on favorable results from these trials, letrozole and anastrozole have also been approved for use as first-line treatment of postmenopausal women with hormone receptor-positive metastatic breast cancer.

Applicability of the intratumor aromatase preclinical model to predict clinical trial results with endocrine therapy

Preclinical models and clinical studies have shown that aromatase inhibitors (AIs) are powerful inhibitors of estrogen synthesis and significantly suppress estrogen in vivo. For more than 20 years, standard first-line treatment for postmenopausal women with metastatic breast cancer has been the antiestrogen tamoxifen, a selective estrogen receptor modulator (SERM) with differential effects on breast, endometrial, bone, and vascular tissues. The estrogenic activity of tamoxifen is associated with deleterious clinical side effects, including vaginal bleeding, endometrial cancer, and thromboembolism. AIs are established second-line treatments in patients who progress with tamoxifen. Compared with progestins, such as megestrol acetate, or the earlier AIs aminoglutethimide and fadrozole, the new AIs, including exemestane, anastrozole, and letrozole, have increased efficacy and clinical benefit and cause fewer side effects in patients with metastatic breast cancer. Letrozole and anastrozole are approved first-line therapy for patients with metastatic breast cancer and as second-line treatment after tamoxifen failure. Studies in the intratumoral aromatase xenograft preclinical model have shown better responses with AIs than with antiestrogens in first-line therapy, and these data are consistent with the results from clinical trials. This model is now being used to assess whether combined or sequential administration of AIs with other agents may provide additional benefit.