Aminoglutethimide: a toxic object lesson in the endocrine management of cancer

Effect of 3-week treatment with [D-Trp6, des-Gly-NH10(2)]LHRH ethylamide, aminoglutethimide, ketoconazole or flutamide alone or in combination on testicular, serum, adrenal and prostatic steroid levels in the dog

Adult male mongrel dogs were treated with the LHRH agonist [D-Trp6, des-Gly-NH10(2)]LHRH ethylamide, aminoglutethimide, ketoconazole or flutamide alone or in combination for 21 days before measurement of steroid levels in the testes, prostate, adrenals and serum. Ketoconazole alone caused a marked stimulation of the intra-testicular concentration of pregnenolone, 17OH-pregnenolone, progesterone and 17OH-progesterone with no or little change of androstenedione, testosterone and dihydrotestosterone. Aminoglutethimide caused a 30-95% inhibition in the concentration of all steroids in the tests while treatment with the LHRH agonist caused a near complete inhibition of all testicular steroids. When administered concomitantly with the LHRH agonist, ketoconazole partly prevented the inhibitory effect of the LHRH agonist on testicular steroid levels. Serum levels of dehydroepiandrosterone, androst-5-ene-3 beta,17 beta-diol, androstenedione and androstane-3 alpha, 17 beta-diol were 75 to 95% inhibited by the LHRH agonist while serum testosterone and dihydrotestosterone concentrations were reduced below detection limits by the same treatment. Moreover, treatment with the LHRH agonist caused a 70-95% reduction in the intraprostatic concentration of testosterone and dihydrotestosterone in all the groups although maximal effect was observed when the LHRH agonist was combined with any of the three other agents. The present data show that while treatment with ketoconazole, aminoglutethimide or Flutamide alone has only partial inhibitory effects on androgen levels, combination with an LHRH agonist provides maximal inhibition. In addition to its direct blockade of the androgen receptor, some of the effect of Flutamide could be related to its blockade of testicular 3 beta-hydroxy-steroid dehydrogenase activity.

Aminoglutethimide and ketoconazole: historical perspectives and future prospects

Aminoglutethimide and ketoconazole, although originally developed as an anticonvulsant and antifungal agent respectively, have both been used to suppress steroid biosynthesis in patients with hormone-sensitive cancer. Aminoglutethimide inhibits several enzymes involved in the synthesis of corticosteroids as well as the aromatase enzyme which converts androgens to oestrogens. About one third of patients with breast cancer show objective improvement with aminoglutethimide, and it may also be of use in the treatment of adrenal carcinoma. However, its toxicity, and the need for concomitant cortisol replacement, severely limit its usefulness. Ketoconazole also inhibits several steroidogenic enzymes, notably C17,20-lyase, and has been used to treat carcinoma of the prostate. Again however, its toxicity and limited efficacy limit its value, although it may be useful in the treatment of certain endocrine conditions such as precocious puberty. Several aromatase inhibitors similar in structure to aminoglutethimide have been developed in an attempt to create more selective and efficient inhibitors. Some of these compounds have been tested in animals but none have as yet been subjected to clinical trials. Attempts to produce imidazole inhibitors of steroidogenesis are less advanced, although one compound (CGS 16949A) has been reported to be a more selective and potent aromatase inhibitor than aminoglutethimide. Selective and effective compounds could be of great value in the treatment of hormone-sensitive carcinoma.