Treatment of breast carcinoma with aminoglutethimide

Influence of Aromatase Inhibitors on Plasma Total Homocysteine in Postmenopausal Breast Cancer Patients

In this study, we evaluated the effect of estrogen suppression with three aromatase inhibitors, aminoglutethimide (n = 30), formestane (n = 12), and exemestane (n = 10), and the progestin megestrol acetate (n = 21) on plasma total homocysteine (tHcy) in patients suffering from advanced breast cancer. Treatment with 1 g/day aminoglutethimide for 2 and 3–5 months increased plasma tHcy by a mean value of 24.5% [95% confidence interval, 10.5–40.4%] at 2 months and 35.8% (95% confidence interval, 18.2–55.9%) at 3–5 months, corresponding to increases in the mean plasma tHcy of 1.90 and 3.67 μmol/L, respectively. In contrast, none of the other treatment options influenced plasma tHcy concentrations. The finding that aminoglutethimide, but none of the other aromatase inhibitors or megestrol acetate, influenced plasma tHcy suggests that this effect is achieved by mechanisms not related to suppression of plasma estrogens or to the glucocorticoids administered in concert.

Influence of dexaminoglutethimide, an optical isomer of aminoglutethimide, on the disposition of estrone sulfate in postmenopausal breast cancer patients

Aminoglutethimide (AG) has been the most widely used aromatase inhibitor in breast cancer patients to date. Commercially, AG (Orimeten) is available as a racemate (DL-AG). Previous studies suggested the stereoisomers of AG (D-AG and L-AG) to differ considerably in their affinities and potencies to inhibit different cytochrome P-450-dependent enzymes, with D-AG being the potent aromatase inhibitor. DL-AG, apart from being an aromatase inhibitor, is known to enhance the metabolism of plasma estrone sulfate (E1S). In the present study we compared the effects of D-AG (500 mg daily) and DL-AG (1000 mg daily) on plasma estrogen levels and estrone (E1) and E1S clearance rates, determined after the injection of [14C]E1 and [3H]E1S, in a cross-over study involving 12 postmenopausal breast cancer patients. Treatment with DL-AG and D-AG suppressed plasma E1S to 18.6% and 15.0% of pretreatment levels, whereas E1 and estradiol E2 levels fell to 18.6% and 23.4% of their pretreatment levels during treatment with DL-AG and to 17.7% and 23.4% during treatment with D-AG, respectively. Thus, both treatment options suppressed all estrogens measured to a similar extent. The clearance rate of E1S increased from a mean pretreatment value of 5.9 to 14.0 and 10.0 L/h during treatment with DL-AG and D-AG, respectively (P < 0.05, comparing the two on-treatment situations), whereas the production rate of E1S decreased from a pretreatment value of 1.44 to 0.64 nmol/h with DL-AG and 0.36 nmol/h with D-AG (P < 0.05, comparing on-treatment values). These findings are consistent with the hypothesis that the D- as well as the L-form of AG may enhance the clearance rate of E1S. The finding of a higher estrogen production rate during treatment with DL-AG compared to D-AG probably reflects an increased plasma level of the estrogen precursor androstenedione (mean levels of androstenedione of 2.54 and 1.27 nmol/L during treatment with D-AG and DL-AG, respectively; P < 0.05).

Treatment with formestane alone and in combination with aminoglutethimide in heavily pretreated breast cancer patients: clinical and endocrine effects

We studied the clinical and endocrine effects of the aromatase inhibitor formestane (4-hydroxyandrostenedione, 4-OHA) in heavily pretreated breast cancer patients (median number of previous endocrine treatments 2, range 1-4). Of 30 patients eligible for response evaluation, 3 patients (10%) showed a partial response while 11 patients (36.7%) experienced stable disease over a time period of at least 6 months. Plasma levels of oestrone, oestradiol and oestrone sulphate were found suppressed to a mean of 33.9, 35.6 and 24.2% of control values. 4 of 6 patients experienced a further substantial reduction in plasma oestrone sulphate to < 5% of pretreatment values when aminoglutethimide (AG) was added after relapse on 4-OHA monotherapy. Our findings suggest that these aromatase inhibitors may suppress plasma oestrogen levels by a percentage approaching the percentage inhibition of in vivo aromatisation measured by tracer techniques.

Insulin-like growth factors in breast cancer

Insulin-like growth factor (IGF)-I is one of the most potent mitogens to many breast cancer cell lines in vitro. Effective growth inhibition in vitro may be achieved by antibodies to the type I IGF receptor (IGF-IR) or by using antisense strategies. Most human breast cancers express IGF-IR in vivo. Thus, different therapeutic strategies aimed at inhibiting ligand stimulation of the IGF-IR may be an attractive treatment option against breast cancer. Several drugs commonly used in breast cancer influence the IGF system both in vitro and in vivo. While antioestrogens such as tamoxifen and droloxifene reduce the expression of IGF-IR in vitro and suppress plasma levels of IGF-I but elevate IGF-binding protein-1 in vivo, megestrol acetate may reduce the delivery of IGFs to the tissues by inhibition of IGFBP-3 protease activity.

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.

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.

Megestrol acetate versus aminoglutethimide for metastatic breast cancer

In this prospective, randomized study the clinical response and toxicity of megestrol acetate (MA) and aminoglutethimide (AG) as second-line treatment in patients with metastatic breast cancer was compared. 176 patients were included, and 150 received treatment greater than 8 weeks and are evaluable for treatment response. The two groups did not differ with regard to prognostic factors. Response rate for the AG and MA groups were 34% and 31% respectively, with duration of response of 13.1 and 13.0 months. Stable disease was obtained in 33% and 35% respectively. No difference was observed in survival. Side effects occurred more frequently in the AG group (42%) than in the MA group (18%).

Effects of aminoglutethimide on plasma estrone sulfate not caused by aromatase inhibition

Plasma levels of estrone and estrone sulfate were measured in 16 postmenopausal women with advanced breast cancer before and during chronic aminoglutethimide therapy. Aminoglutethimide caused a significant reduction in plasma estrone (mean 36%, P less than 0.025) and estrone sulfate (mean 65%, P less than 0.001). The estrone/estrone sulfate ratio was increased by a mean of 84% (P less than 0.0025). These results suggest that aminoglutethimide influences plasma estrone sulfate by mechanisms unrelated to aromatase inhibition. The findings in this study are consistent with previous results suggesting that aminoglutethimide treatment enhances the rate of estrone sulfate metabolism. This biochemical effect of aminoglutethimide treatment could be a contributory factor to the drugs mechanism of action.

Alterations in the production rate and the metabolism of oestrone and oestrone sulphate in breast cancer patients treated with aminoglutethimide

Plasma level, plasma clearance, production rate and interconversions of oestrone and oestrone sulphate were measured in six breast cancer patients receiving aminoglutethimide therapy. Three additional patients had the production rate of oestrone sulphate investigated. Plasma oestrone and oestrone sulphate levels were reduced by a mean of 46% (P less than 0.05) and 71% (P less than 0.005) respectively. These alterations were due to a combined action of aminoglutethimide inhibiting oestrogen production but also increasing oestrogen metabolism. While oestrone and oestrone sulphate production rate was reduced by a mean of 31% (P less than 0.05) and 41% (P less than 0.005) respectively, the plasma clearance rate of oestrone was found to be increased by a mean of 30% (P less than 0.05), and the plasma clearance rate of oestrone sulphate was increased by a mean of 112% during aminoglutethimide treatment. The fraction of oestrone sulphate converted into plasma oestrone was reduced by 52% (P less than 0.05), the transfer of circulating oestrone into sulphate was non-significantly reduced by a mean of 16%. The findings in this investigation show that aminoglutethimide treatment influences oestrogen disposition by mechanisms unrelated to aromatase inhibition. The possibility that such effects might be partly responsible for the mechanism of action of aminoglutethimide in advanced breast cancer should be considered.

Mechanisms of action of aminoglutethimide as endocrine therapy of breast cancer

During the last decade aminoglutethimide has been recognised as a valuable alternative in endocrine therapy for advanced breast cancer. Although some side effects do occur, most often these are initial effects which subside within a few weeks, and cessation of therapy is not usually indicated. Aminoglutethimide was originally introduced as an inhibitor of steroidogenesis in the adrenal cortex. It was soon recognised, however, that inhibition of the non-glandular aromatase, blocking the conversion of androgenic prohormones to oestrogens, was more important, resulting in decreased blood levels of oestrogens. In this review the role of aromatase inhibition as the only important aspect of the mechanism of action of aminoglutethimide is challenged. Evidence has accumulated during the last few years that aminoglutethimide is a most potent inducer of microsomal enzymes. In addition to the pharmacological implications this has (suggesting important interactions), it also points to the possibility that levels of oestrogens are decreased due to accelerated metabolism of these hormones. Based on new experimental data, and also clinical work with alternative aromatase inhibitors, it appears that the antitumour activity of aminoglutethimide may be due to both aromatase inhibition and accelerated metabolism of oestrogens. This seriously challenges the importance of aromatase inhibition alone as a strategy in endocrine therapy of breast cancer, and furthermore suggests that accelerated metabolism of key hormones is an alternative strategy to be explored.

The influence of a graded dose schedule of aminoglutethimide on the disposition of the optical enantiomers of warfarin in patients with breast cancer

The pharmacokinetics of the optical enantiomers of warfarin (R-warfarin and S-warfarin) were investigated in patients treated for breast cancer with aminoglutethimide (AG). The patients received 125 mg AG b.i.d. (i.e., low-dosage regimen); 250 mg AG q.i.d. together with cortisone acetate (i.e. high-dosage regimen); or an escalating dose schedule was followed (i.e. low-dosage regimen followed by high-dosage regimen). The pharmacokinetics for R-warfarin and S-warfarin were determined before initiation of AG treatment and again after 2, 4, or 8 weeks of continuous AG treatment. The plasma clearance for both enantiomers showed a moderate increase (mean 41.2%) in patients receiving the low AG dose, whereas in patients treated according to the high-dosage regimen a marked increase (mean 90.8%) was observed. There was a corresponding reduction in warfarin half-life, and no alteration in distribution volume. These effects on the warfarin pharmacokinetics appeared after 14 days of AG treatment, and after this time point there was no further increase in warfarin clearance. Notably, the effect of AG on warfarin kinetics was the same for both enantiomeric forms of warfarin. These data show that there is a dose-response relationship between AG dose and induction of warfarin metabolism.

Single-dose and steady-state pharmacokinetics of aminoglutethimide

The oral pharmacokinetics of aminoglutethimide were determined in 17 patients receiving the drug therapeutically. The absorption of aminoglutethimide after oral intake was almost complete as judged by recovery of radio-labelled drug in the urine. The plasma half-life of the drug was markedly reduced (mean 43%) during multiple-dose administration as compared with a single dose, but only a moderate increase in total clearance (mean 26.9%) was observed. This finding was consistent with a significant reduction (mean 29.2%) in apparent volume of distribution (Vd) occurring during prolonged treatment. These alterations in drug distribution could also be demonstrated after a drug-free interval of 96 hours during treatment. The reduction in apparent volume of distribution could not be explained by altered plasma protein binding of aminoglutethimide, as evaluated by equilibrium dialysis experiments.