Jacaric acid and its octadecatrienoic acid geoisomers induce apoptosis selectively in cancerous human prostate cells: a mechanistic and 3-D structure-activity study.

Plant-derived non-essential fatty acids are important dietary nutrients, and some are purported to have chemopreventive properties against various cancers, including that of the prostate. In this study, we determined the ability of seven dietary C-18 fatty acids to cause cytotoxicity and induce apoptosis in various types of human prostate cancer cells. These fatty acids included jacaric and punicic acid found in jacaranda and pomegranate seed oil, respectively, three octadecatrienoic geometric isomers (alpha- and beta-calendic and catalpic acid) and two mono-unsaturated C-18 fatty acids (trans- and cis-vaccenic acid). Jacaric acid and four of its octadecatrienoic geoisomers selectively induced apoptosis in hormone-dependent (LNCaP) and -independent (PC-3) human prostate cancer cells, whilst not affecting the viability of normal human prostate epithelial cells (RWPE-1). Jacaric acid induced concentration- and time-depedent LNCaP cell death through activation of intrinsic and extrinsic apoptotic pathways resulting in cleavage of PARP-1, modulation of pro- and antiapoptotic Bcl-2 family of proteins and increased cleavage of caspase-3, -8 and -9. Moreover, activation of a cell death-inducing signalling cascade involving death receptor 5 was observed. Jacaric acid induced apoptosis in PC-3 cells by activation of the intrinsic pathway only. The spatial conformation cis, trans, cis of jacaric and punicic acid was shown to play a key role in the increased potency and efficacy of these two fatty acids in comparison to the five other C-18 fatty acids tested. Three-dimensional conformational analysis using the PubChem Database (http://pubchem.ncbi.nlm.nih.gov) showed that the cytotoxic potency of the C-18 fatty acids was related to their degree of conformational similarity to our cytotoxic reference compound, punicic acid, based on optimized shape (ST) and feature (CT) similarity scores, with jacaric acid being most 'biosimilar' (ST(ST-opt)=0.81; CT(CT-opt)=0.45). This 3-D analysis of structural similarity enabled us to rank geoisomeric fatty acids according to cytotoxic potency, whereas a 2-D positional assessment of cis/trans structure did not. Our findings provide mechanistic evidence that nutrition-derived non-essential fatty acids have chemopreventive biological activities and Exhibit 3-D structure-activity relationships that could be exploited to develop new strategies for the prevention or treatment of prostate cancer regardless of hormone dependency.

Growth inhibitory, antiandrogenic, and pro-apoptotic effects of punicic acid in LNCaP human prostate cancer cells.

Prostate cancer is a commonly diagnosed cancer in men, and dietary chemoprevention by pomegranate (Punica granatum) extracts has shown noticeable benefits. In this study, we investigated the growth inhibitory, antiandrogenic, and pro-apoptotic effects of 13 pure compounds found in the pomegranate in androgen-dependent LNCaP human prostate cancer cells. Cells deprived of steroid hormones were exposed to increasing concentrations (1-100 µM) of pomegranate compounds in the presence of 0.1 nM dihydrotestosterone (DHT), and the inhibition of cell growth was measured by WST-1 colorimetric assay after a 4 day exposure. Four compounds, epigallocatechin gallate (EGCG), delphinidin chloride, kaempferol, and punicic acid, were found to inhibit DHT-stimulated cell growth at concentrations of 10 µM and above. These four pomegranate compounds inhibited DHT-stimulated androgen receptor nuclear accumulation and the expression of the androgen receptor-dependent genes prostate specific antigen and steroid 5α-reductase type 1 at concentrations ≥10 µM. We determined the possible contribution of apoptosis to the observed decrease in cell growth and found that three compounds, EGCG, kaempferol, and, in particular, punicic acid, induced DNA fragmentation after a 24 h treatment, at concentrations in the 10-100 µM range. Punicic acid, an important fatty acid in pomegranate seeds, was further found to induce intrinsic apoptosis via a caspase-dependent pathway. In conclusion, punicic acid, the main constituent of pomegranate seed (70-80%), exhibited potent growth inhibitory activities in androgen-dependent LNCaP cells, which appear to be mediated by both antiandrogenic and pro-apoptotic mechanisms.