Multiple pathways of prostate carcinogenesis analyzed by using cultured cells isolated from rats treated with N-methyl-N-nitrosourea and testosterone

Treatment of rats with N-methyl-N-nitrosourea (MNU) and testosterone result s in a high incidence of metastasizing dorsolateral prostate tumors. In pre vious studies, a high frequency(greater than or equal to 70%) of a G(35) -- > A transition mutation at the second position of codon 12 of the Ki-ras on cogene was found in these tumors. This was confirmed in the study reported here, and the frequency of this mutation appeared similar in tumors induced in four different rat strains, regardless of differences in sensitivity am ong these strains to the induction of prostate cancers by MNU and testoster one: Wistar Furth (62% incidence of grossly visible prostate tumors) > Lobu nd Wistar (55%) > Fisher 344 (40%) > Copenhagen (37%). A method was develop ed to isolate and separately culture epithelial and stroma cells from these rat prostate carcinomas. Of 20 primary cell cultures established from hist ologically confirmed rat prostate carcinomas, 19 (95%) displayed one or mor e of the following characteristics: the Ki-ras mutation (17 of 20; 85%), an chorage-independent growth in soft agar at early passage (12 of 20; 60%), o r tumorigenicity at later passage (eight of eight; 100%). One epithelial ce ll culture and all five stromal cell cultures established from prostate tum ors had none of these characteristics. Epithelial cultures that had the Ki- ras mutation and grew in soft agar constitute the predominant genotype/phen otype (55%), cultures with the mutation that did not grow in soft agar were less frequent (30%), 10% of the cultures had neither characteristic, and o nly one grew in soft agar but did not have the mutation. These findings sug gest that there are at least two and perhaps more different molecular pathw ays of prostate carcinogenesis in rats treated with MNU plus testosterone. Furthermore, these data suggest that these pathways and the mechanisms dete rmining strain differences in sensitivity to prostate cancer induction are unrelated. (C) 1999 Wiley-Liss, Inc.