The influence of thyroid hormone analogues on an isotransplanted spontaneous mammary adenocarcinoma in mice

Effect of altered thyroid status on lysosomal enzymes and thymidylate synthetase activity in tumors and livers of host animals

The purpose of this study was to determine whether or not alternations in tumor growth induced by changes in thyroid status were mediated through changes in key enzymes, whose activity is known to be influenced by thyroid hormones. The activities of three lysosomal enzymes (cathepsin B1, cathepsin D, and acid phosphatase) and thymidylate synthetase were measured in implanted mammary tumors as well as in the livers of host animals that were either euthyroid, hypothyroid, or hyperthyroid. Hypothyroidism produced no significant change in enzyme activity in the tumors. Hyperthyroidism, on the other hand, did cause a significant increase in the activity of all lysosomal enzymes in the tumors, but did not affect thymidylate synthetase levels. In the livers of the host animals, hypothyroidism produced a significant decrease in cathepsin B1 and a significant increase in acid phosphatase but did not change cathepsin D or thymidylate synthetase levels. Hyperthyroidism produced a significant increase in all enzymes measured in the livers of the host animals. The significant decrease in tumor weight with hypothyroidism did not correlate with the insignificant changes in the enzymes tested. Similarly, there was no correlation between the significant increase in the enzymes levels found with hyperthyroidism and the insignificant change in tumor weight.

Potency of thyroid hormone analogues in suppressing prolactin-mediated mammary growth in thyroidectomized rats

An antagonism between prolactin and thyroxine, similar to that found in amphibian tissues at metamorphosis, has been recently shown to occur at the level of the rat mammary epithelium. This phenomenon may be implicated in the pathogenesis of human breast cancer. This experiment demonstrates that two analogues of thyroid hormone, triiodothyropropionic acid and triiodothyroacetic acid, which are relatively very weak in their calorigenic action, are as potent as thyroxine and triiodothyronine in inhibiting the prolactin-mediated mammary growth in thyroidectomized rats. The possible implication of this finding in the treatment of mammary cancer is discussed.

The influence of thyroactive substances on the induction of cervico-vaginal tumours in intact and castrate rats

The effect of the administration of L-thyroxine and of methylthiouracil alone, together, in combination with stilboestrol or in the perinatal period on the induction of cervico-vaginal tumours by weekly local applications of DMBA was investigated in intact and castrate rats and compared with carcinogenesis in animals not additionally treated.In intact rats the rate of sarcoma induction is accelerated by methylthiouracil, delayed and reduced by methylthiouracil plus L-thyroxine and delayed by perinatal injection of either L-thyroxine or methylthiouracil. In castrates sarcoma induction is accelerated and increased by L-thyroxine, methylthiouracil and by combination of either substance with stilboestrol; it is accelerated but not significantly increased by combined treatment with the thyroactive compounds.The incidence of epithelial neoplasms is accelerated and increased in intacts and in castrates by methylthiouracil. This effect is slightly reduced in intacts but potentiated in castrates by additional stilboestrol treatment as well as by administration of L-thyroxine plus methylthiouracil.The incidence of sarcomas is significantly greater in intact than in spayed rats not additionally treated, greater in castrates than in intacts given L-thyroxine ± stilboestrol and not significantly different in intacts and castrates with any of the other additional medications. For epithelial tumours the incidence is low and similar in both groups without additional treatment, greater in spayed than intact animals given methylthiouracil plus stilboestrol or plus L-thyroxine.The influence of the thyroactive compounds on the induction of epithelial and sarcomatous tumours is not correlated with their effect on gain in body weight nor on growth of the stroma and of the epithelium of the vagina, cervix and uterus. Changes induced in the thyroid gland and the hypophysis are not correlated with those on carcinogenesis.Central and local factors may account for the differential response in carcinogenesis of intacts and castrates as well as of the epithelial and connective tissue of the cervico-vaginal tract to medication with thyroactive compounds.