Polyamines and Autocrine Control of N-Nitrosomethylurea-induced Rat Mammary Tumor Growth in Vitro by Progesterone

Andrea Manni, Carol Wright, Betty Badger, Laurence Demers, Mary Bartholomew

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Abstract

These experiments were designed to test whether autocrine/paracrine mechanisms are involved in the growth-promoting action of progesterone (Pg) in the N-nitrosomethylurea-induced rat mammary tumor cultured in vitro in soft agar donogenic assay. In support of our hypothesis, we observed that conditioned media obtained from Pg-treated tumors (Pg-CM), consistently stimulated colony formation in our system to the same degree as Pg itself (approximately 140% of control). Treatment with heat, trypsin, and concanavalin A abolished the colony-stimulating effect of Pg-CM, thus suggesting the possible glycoprotein nature of the Pg-indudble growth factor(s). The growth-promoting action of Pg-CM was rather specific since CMs obtained from tumors exposed to a variety of other steroid hormones rarely stimulated colony formation and usually only to a modest degree. Administration of the polyamine biosynthetic inhibitor, a-difluoromethylornithine, abolished the colony-stimulating effect of Pg-CM. The inhibitory effect of α-difluoromethylornithine was reversed in a dose-dependent fashion by exogenous administration of spermidine, which entirely restored the growth-promoting action of Pg-CM. Addition of increasing amounts of spermidine, however, did not potentiate Pg-CM action under our experimental conditions. Our results indicate that autocrine/paracrine mechanisms may mediate, at least in part, the colony-stimulating effect of Pg in our system. The polyamine pathway plays an essential role in the expression of such control of tumor growth by Pg.

Original languageEnglish (US)
Pages (from-to)3058-3061
Number of pages4
JournalCancer Research
Volume48
Issue number11
StatePublished - 1988

All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research

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