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This study demonstrates that silibinin as well as silymarin induce growth inhibition and apoptosis in rat PCA cells. These results form a strong rationale for PCA prevention and therapeutic intervention studies with silibinin and silymarin in animal models, such as the MNU-testosterone rat PCA model, to establish their efficacy and to further define their mechanisms of action under in vivo conditions.

The role of cyclooxygenase-2 (COX-2) and the mechanism by which it influences the development and behavior of prostate cancer is unclear. Selective COX-2 inhibitors may be effective against prostate cancer via COX-2-independent mechanisms. But administration of high doses of COX-2 inhibitors over longer period of time may not be devoid of side effects. There is increasing interest in using COX-2 inhibitors in combination with other chemopreventive agents to overcome the issue of toxicity. However, the molecular mechanisms underlying their combined actions are not well understood. Therefore, the present study was designed to determine the effects of low doses of docosahexaenoic acid (DHA) in combination with celecoxib on the molecular targets at the proteins level in rat prostate cancer cells. Two-dimensional gel electrophoresis, in combination with mass spectrometry analysis, was used for protein identification. Western blot analysis confirmed the proteins identified. Paraffin-embedded tissue sections from the rat prostate tumor were used to detect base level expression of heat shock protein 70 (HSP70) and p53. The rate of cancer cell growth was inhibited more effectively (p < 0.01) by DHA in combination with celecoxib at lower doses (2.5 lM each). A total number of twelve proteins were differentially expressed by the combined action of DHA and celecoxib at low doses. It was interesting to note that these agents activated both HSP70 and p53 proteins. Activation of HSP70 by the combined actions of DHA and celecoxib in the presence of wild-type p53 reveals a unique COX-2 independent mode of action against prostate cancer. ' 2006 Wiley-Liss, Inc.Key words: n-3 PUFA; docosahexaenoic acid; COX-2 inhibitor; proteomics; prostate cancer Prostate cancer is the most commonly diagnosed cancer in the United States and it is the second leading cause of cancer deaths in men, which accounts for $33% of all cancers. 1 Epidemiological studies have provided evidence that the intake of dietary fish oil rich in omega-3 polyunsaturated fatty acids (n-3 PUFA) reduces the risk of several types of cancers, including prostate cancer. [2][3][4][5][6] Most importantly, the inhibitory effects of docosahexaenoic acid (DHA), an n-3 PUFA, on prostate cancer development and progression are supported by studies using cell culture and animal models. [7][8][9] Experimental evidences indicate that n-3 PUFA may induce terminal differentiation (arrest in G0) and trigger apoptosis against colon cancer. 10,11 However, experimental evidence is lacking on the ability of DHA in mediating protein modifications while inducing anticancer effects.In addition, several reports suggest the connection between inflammation and prostate cancer [12][13][14][15] ; however, the mechanism by which inflammation influences the development and behavior of prostate cancer is unclear. It is evident that the expression pattern of the inducible form of the proinflammatory enzyme, cyclooxygenase-2 (COX-2), is characteristic of most human cancers. Numerous studies have suggest...

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.