Influence of aminoglutethimide on the metabolism of medroxyprogesterone acetate and megestrol acetate in postmenopausal patients with advanced breast cancer

Canadian Contraception Consensus (Part 3 of 4): Chapter 8 - Progestin-Only Contraception

OBJECTIVE

To provide guidelines for health care providers on the use of contraceptive methods to prevent pregnancy and on the promotion of healthy sexuality.

OUTCOMES

Overall efficacy of cited contraceptive methods, assessing reduction in pregnancy rate, safety, ease of use, and side effects; the effect of cited contraceptive methods on sexual health and general well-being; and the relative cost and availability of cited contraceptive methods in Canada.

EVIDENCE

Published literature was retrieved through searches of Medline and The Cochrane Database from January 1994 to January 2015 using appropriate controlled vocabulary (e.g., contraception, sexuality, sexual health) and key words (e.g., contraception, family planning, hormonal contraception, emergency contraception). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies published in English from January 1994 to January 2015. Searches were updated on a regular basis in incorporated in the guideline to June 2015. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The quality of the evidence in this document was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1). CHAPTER 8: PROGESTIN-ONLY CONTRACEPTION: Summary Statements Recommendations.

Pharmacokinetic interactions between depot medroxyprogesterone acetate and combination antiretroviral therapy

OBJECTIVE

To evaluate the effect of an antiretroviral (ARV) therapy regimen containing zidovudine (AZT), lamivudine (3TC), and efavirenz (EFV) on the pharmacokinetics of depot medroxyprogesterone acetate (DMPA).

DESIGN

Open-label, nonrandomized, clinical trial.

SETTING

University hospital clinic.

PATIENT(S)

Thirty HIV-infected women; 15 using ARV therapy (AZT, 3TC, and EFV) and 15 non-users of ARV therapy, followed biweekly for 12 weeks.

INTERVENTION(S)

Single injection of DMPA (150 mg IM) for both groups.

MAIN OUTCOME MEASURE(S)

Pharmacokinetic parameters of DMPA by liquid chromatography with mass spectrometry, and ovulation by serum P.

RESULT(S)

Maximum serum concentrations of DMPA were reached at 14 days after injection. The area under the curve was similar in both groups, as were the minimum concentration, half-life, and clearance. Only 1 woman, not using ARV therapy, ovulated at 11 weeks after DMPA.

CONCLUSION(S)

Pharmacokinetics of DMPA were similar in HIV-infected women, regardless of ARV therapy use, suggesting that triple therapy with AZT, 3TC, and EFV is not likely to interfere with the contraceptive effectiveness of DMPA.

Effects of megestrol acetate on pituitary function and end-organ hormone secretion: A post hoc analysis of serum samples from a 12-week study in healthy older men

BACKGROUND

Megestrol acetate (MA) is a synthetic progestin commonly used to promote weight gain in malnourished older individuals. In small studies, MA administration has been associated with reduced serum cortisol concentrations in patients with cancer or AIDS. The impact of MA on the pituitary secretion of adrenocorticotropic hormone (ACTH) and other hormones is unclear, and the prevalence and extent of hypocortisolemia in older individuals after MA treatment is unknown. A randomized, placebo-controlled study of the effects of testosterone (T) and resistance training (RT) on body composition after MA administration in older men has been reported previously.

OBJECTIVE

The purpose of this post hoc analysis was to examine the effect of 12 weeks of MA on pituitary function and end-organ hormone secretion in healthy older individuals using frozen serum samples from that study.

METHODS

The previous study was conducted at the Department of Geriatrics, Donald W. Reynolds Center on Aging and the General Clinical Research Center at The University of Arkansas for Medical Sciences, Little Rock, Arkansas. Healthy male volunteers aged 60 to 85 years were recruited from the center and were randomly assigned to 1 of 4 study groups: RT + T, T, RT + placebo (P), or P. Subjects enrolled in the RT groups underwent supervised upper- and lower-body strength-training exercises 3 d/wk at 80% of 1 repetition maximum. Subjects in the groups to receive T received injections of testosterone enanthate 100 mg i.m. QW for 12 weeks. Subjects receiving P were given 1-mL saline injections i.m. QW for 12 weeks. All subjects received MA 800 mg p.o. QD concurrently for 12 weeks. For the present analysis, serum concentrations of the pituitary hormones follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), ACTH, prolactin (PRL), and luteinizing hormone (LH), as well as the end-organ hormones estradiol (E2), cortisol, free T4, and T, were measured in samples obtained at baseline (week 0) and after 12 weeks of MA treatment.

RESULTS

Serum samples from 21 men (mean [SD]age, 67.0 [7.3]years; mean [SD] body mass index, 23.1 [10.4] kg/m2; mean [SD] percentage of body fat, 22.5% [8.8%]; RT + T, T, RT + P, and P groups, n = 4, 5, 6, and 6 subjects, respectively) were available from the original study. The mean percentage changes from baseline in serum pituitary hormone concentrations after 12 weeks of MA administration were as follows: TSH, -14.7%; ACTH, -89.5%; PRL, 162.2%; and LH, -49.0%; (P = 0.03, <0.001, <0.001, and <0.001, respectively). The mean (SD) percentage changes from baseline in serum end-organ hormone concentrations with MA at 12 weeks were as follows: E2, 181.6%; and cortisol, -90.8% (both, P < 0.001). In the P and RT + P groups, the mean percentage changes from baseline in T were -84% and -85%, respectively (both, P < 0.001). FSH and free T4 concentrations were not significantly changed.

CONCLUSIONS

This analysis of serum samples from healthy older men suggests that MA administration significantly affected the secretion of several pituitary hormones and end-organ hormone synthesis. Most notably, ACTH secretion and serum cortisol levels were statistically significantly suppressed in 20 of 21 subjects, without the development of clinically significant adrenal suppression.

The therapeutic potential of novel aromatase inhibitors in breast cancer

For over 20 years, aromatase inhibitors have played a role in the treatment of breast cancer. However, until relatively recently, their utility has been limited by a lack of selectivity and significant toxicity. Several second and third generation aromatase inhibitors which are highly selective for the aromatase enzyme have reached clinical trials this decade. As a result of these initial studies, aromatase inhibitors are now established as second line agents in the treatment of postmenopausal women with advanced breast cancer. They are now under evaluation in several other settings, including adjuvant and neoadjuvant therapy, and as part of combination treatment in premenopausal women. This review focuses on recent and ongoing clinical trials and the effect these have had on the clinical use of aromatase inhibitors.

Resistance to endocrine therapy of breast cancer: recent advances and tomorrow's challenges

The role of endocrine therapy in early as well as advanced breast cancer cannot be overrated. Long-term tamoxifen exposure (5 years) in the adjuvant setting has been shown to be effective not only in improving relapse-free and overall survival but also in reducing the incidence of contralateral cancers. Promising results have been achieved in breast cancer prevention with use of antiestrogens. Novel aromatase inhibitors and inactivators have been found superior to conventional treatment in metastatic disease and are currently being evaluated in the adjuvant setting to improve relapse-free and overall survival. If potential health hazards from estrogen deprivation with regard to cardiovascular disease as well as bone metabolism can be addressed, adjuvant endocrine therapy may include such drugs in the future. However, while endocrine therapy of breast cancer has become more and more important in the clinic, the major problems in hormonal therapy are primary and acquired resistance to endocrine manipulations. The causes for endocrine resistance and possible ways to delay or avoid this phenomenon are only allusively understood. Elucidation of the mechanisms underlying endocrine resistance in vivo represents the key to improve our treatment strategies. Due to intense use of in vitro models and animal systems, many potential mechanisms of endocrine resistance have been described; however, our understanding of the problem of drug resistance in vivo remains limited. Hopefully, ongoing programs on translational research in the neoadjuvant, adjuvant, and palliative settings will provide information that will improve our understanding of the biology of endocrine resistance in vivo and, thus, provide us with a better rationale to improve early as well as late endocrine therapy in breast cancer patients. The present publication summarizes the state of the art with respect to endocrine resistance.

Selective oestrogen receptor modifiers (SERMs) and breast cancer therapy

Antioestrogen therapy is currently receiving renewed interest for several reasons. Tamoxifen was introduced in the treatment of metastatic breast cancer more than three decades ago. The drug significantly reduces long term mortality and also reduces the risk of contralateral tumours when administered in early breast cancer. Five years of tamoxifen is now standard in adjuvant endocrine therapy, and the drug is currently being evaluated for breast cancer prevention. Despite this, several aspects regarding the pharmacology of the drug are still unclear, and the scientific rationale for dose selection has recently been challenged. Several novel antioestrogen compounds, called selective oestrogen receptor modifiers (SERMs), express selective oestrogen agonistic or antagonistic properties depending on the organ or test system evaluated. Some of these drugs, like raloxifene, do not seem to promote the development of endometrial cancer, although they still have selected oestrogen-like beneficial effects. This paper reviews the pharmacologic and the pharmacokinetic aspects of the different SERMs with particular emphasis on their potential use in therapy and prevention of breast cancer.

Mechanisms of action of endocrine treatment in breast cancer

Endocrine treatment plays an important role in the therapy of breast cancer. While the basic mechanisms are understood, additional mechanisms may be of importance to their action and they may also contribute to the mechanism(s) of acquired resistance. Currently, several novel drugs are entering into clinical trials. Observations of the absence or presence of cross resistance to novel 'pure' steroidal antiestrogens and the non-steroidal tamoxifen may add important information to our understanding of the mechanisms of action of both classes of drugs. Similarly, exploration of different aromatase inhibitors in sequence or concert, as well as the combining of different endocrine treatment options may be warranted. Additionally, alterations in different biochemical parameters such as growth factors should not only be carefully explored in relation to treatment options but should also be followed during the course of treatment to asess alterations over time and in relation to the development of drug resistance.

Combined treatment with 4-hydroxyandrostenedione and aminoglutethimide: effects on aromatase inhibition and oestrogen suppression

The effects of a combination of aminoglutethimide (AG) 1,000 mg daily and 4-hydroxy-androstenedione (4OHA) 500 mg i.m. weekly on peripheral aromatase activity as measured by in vivo radioisotopic tracer methodology and serum oestrogen suppression were investigated in ten post-menopausal women with advanced breast cancer. Patients were treated for a minimum of 4 weeks with 4OHA before addition of AG for a minimum of 6 weeks. Aromatase inhibition was found to be nearly identical in the two treatment situations (92.5 +/- 4.7% and 93.8 +/- 3.8% respectively). There was no further significant suppression of plasma oestradiol or plasma oestrone levels when AG was added to 4OHA treatment (mean decrease of 7.6 +/- 12.1% and 2.8 +/- 12.0% respectively). In contrast, adding AG caused a further suppression of plasma oestrone sulphate (Oe1S) compared with 4OHA monotherapy (mean suppression of 35.2 +/- 9.1%, P < 0.025). This effect on Oe1S may be due to an influence of AG on oestrogen metabolism.

Use of endocrine therapy to study the biology of breast cancer

Drug resistance is the main reason for therapeutic failure and death in breast cancer. In vitro investigations have identified some mechanisms that may be responsible for resistance to chemotherapeutic agents in breast cancer, but we know little about the mechanisms responsible for resistance to endocrine treatment in receptor-positive tumors. Accordingly, a major task for future studies is to explore the mechanisms of both primary and acquired resistance to endocrine treatment as well as to chemotherapy in breast cancer. Drug resistance may be related to alterations in endocrine as well as paracrine delivery of certain growth factors or hormones, but it may also be caused by alterations in drug disposition. Primary resistance may be evaluated by comparing the response to drug treatment with the expression of different biochemical parameters in the tumor before treatment. To explore the mechanisms of acquired drug resistance requires study of the changes in biological parameters developing over time during drug therapy. Also, it may be of interest to use certain drugs (like a 'classical' anti-estrogen and a steroidal anti-estrogen) in a particular sequence to explore the possibility of cross-resistance (or lack of it) between particular treatment modalities. Possible implications for the design of future trials in breast cancer treatment are discussed.

Serum elimination half-life of tamoxifen and its metabolites in patients with advanced breast cancer

In breast cancer patients discontinuing chronic tamoxifen therapy, the serum elimination of metabolites X, Y and E paralleled that of tamoxifen, whereas that of metabolite Z did not. The serum elimination of tamoxifen and metabolites X and B was increased by amino-glutethimide treatment, whereas that of metabolites Z, Y, and E was not.

Progestins in breast cancer treatment. A review

The two most widely used synthetic progestins in breast cancer treatment, medroxyprogesterone acetate (MPA) and megestrol acetate (MA), are reviewed with regard to pharmacological, endocrinological and clinical aspects. In high oral doses as second- or first-line endocrine therapy in advanced breast cancer, they give a similar response rate as tamoxifen (TAM) and aminoglutethimide (AG). The mechanism of action is probably complex. Considerable changes in serum levels of different hormones are induced by progestin treatment. The decrease of serum estrone sulfate (E1S) may be part of the therapeutic mechanism. Some studies suggest that the two drugs, MPA and MA, have a different mode of action, and possibly a low cross resistance. Randomized studies using the two progestins with a cross-over design may answer these questions. Further studies on the influence of progestin on different receptors and growth factors are warranted. To determine the most effective clinical dose of the two progestins, studies with increasing therapeutic doses are needed.