Propylthiouracil reduces xenograft tumor growth in an athymic nude mouse prostate cancer model

Methods: Several anecdotal reports indicate that cancer may occasionally re main in a dormant slate for prolonged periods in patients with hypothyroidi sm. Once the hypothyroid state is recognized and supplementation therapy wi th thyroid hormones is initiated, disease progression occurs. In this exper iment, 6-n-propyl-2-thiouracil (PTU) was added to the water of athymic nude mice. The animals were subsequently inoculated with cells from a human pro state cancer cell line. Results: The growth rate of subcutaneously implante d prostate xenografts was significantly slower in mice treated with PTU com pared with mice that did not receive PTU. In a separate experiment, tritiat ed thymidine incorporation assays were performed in DU145 and PC3 human pro state cancer cells with and without PTU. No significant differences were ob served, indicating that PTU did not exert any antitumor effect in vitro. Co nclusions: Our study demonstrates that PTU inhibits the growth of human pro state tumors in nude mice via an indirect effect. This antitumor effect may be caused by hypothyroidism. This is the first in vivo study suggesting po tential therapeutic applications for thyroid hormone manipulations in human cancer of the prostate. Further studies will determine growth kinetics of xenotransplanted prostate cancer in vitro and in vivo. PTU-induced hypothyr oidism may be further explored in conjunction with other antineoplastic the rapy.