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 results in a high incidence of metastasizing dorsolateral prostate tumors. In previous studies, a high frequency (> or = 70%) of a G35 --> A transition mutation at the second position of codon 12 of the Ki-ras oncogene 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 among these strains to the induction of prostate cancers by MNU and testosterone: Wistar Furth (62% incidence of grossly visible prostate tumors) > Lobund Wistar (55%) > Fisher 344 (40%) > Copenhagen (37%). A method was developed to isolate and separately culture epithelial and stromal cells from these rat prostate carcinomas. Of 20 primary cell cultures established from histologically confirmed rat prostate carcinomas, 19 (95%) displayed one or more of the following characteristics: the Ki-ras mutation (17 of 20; 85%), anchorage-independent growth in soft agar at early passage (12 of 20; 60%), or tumorigenicity at later passage (eight of eight; 100%). One epithelial cell culture and all five stromal cell cultures established from prostate tumors had none of these characteristics. Epithelial cultures that had the Ki-ras mutation and grew in soft agar constitute the predominant genotype/phenotype (55%), cultures with the mutation that did not grow in soft agar were less frequent (30%), 10% of the cultures had neither characteristic, and only one grew in soft agar but did not have the mutation. These findings suggest that there are at least two and perhaps more different molecular pathways of prostate carcinogenesis in rats treated with MNU plus testosterone. Furthermore, these data suggest that these pathways and the mechanisms determining strain differences in sensitivity to prostate cancer induction are unrelated.

The role of stromal cells in prostate cancer development and progression.

Prostate cancer is one of the most common malignancies in males, and tumor progression critically determines its clinical significance. Prostatic stromal cells may be critically involved in growth and progression of prostate cancer. There is substantial evidence that the stromal component of the embryological tissue of origin, the urogenital sinus, is essential in directing outgrowth and prostatic differentiation of the epithelial anlage of the prostate. The presence of a stromal androgen receptor is required for this effect, and humoral factors, such as keratinocyte growth factor, have been shown to be able to mediate it in a paracrine fashion. The adult prostate is also under control of multiple steroid hormone and paracrine peptide factors, and there is evidence that the prostatic stroma plays a major role in mediation of androgen effects on prostatic epithelium. Normal seminal vesicle mesenchyme can cause differentiation of the Dunning R3327H prostate carcinoma. Normal rat prostatic fibroblasts influence the in vivo and soft agar growth of epithelial cells derived from chemically/hormonally induced rat prostate carcinomas, as do fibroblasts that are isolated from these tumors. Both growth-enhancing and growth-inhibiting effects were observed, apparently depending on the stage of progression of both cell types as well as on whether fibroblasts were derived from the same or a different tumor than the epithelial cells. These findings indicate that stromal cells critically influence epithelial prostate cancer growth, and they suggest that these effects can significantly vary in different tumors as well as in different stages of tumor progression.