A Novel Dietary Triterpene Lupeol Induces Fas-Mediated Apoptotic Death of Androgen-Sensitive Prostate Cancer Cells and Inhibits Tumor Growth in a Xenograft Model

Abstract

In prostate cancer, a fine balance between cell proliferation and apoptotic death is lost, resulting in increased cellular mass and tumor progression. One approach to redress this imbalance and control this malignancy is its preventive intervention through the use of dietary natural agents. Here, we investigated the growth-inhibitory effect and associated mechanisms of Lupeol, a triterpene present in fruits and vegetables, in androgen-sensitive human prostate cancer cells. Lupeol treatment resulted in significant inhibition of cell viability in a dose-dependent manner and caused apoptotic death of prostate cancer cells. Lupeol was found to induce the cleavage of poly(ADP-ribose) polymerase protein and degradation of acinus protein with a significant increase in the expression of FADD protein. Among all death receptor targets examined, Lupeol specifically caused a significant increase in the expression of Fas receptor. The small interfering RNAmediated silencing of the Fas gene and inhibition of caspase-6, caspase-8, and caspase-9 by their specific inhibitors confirmed that Lupeol specifically activates the Fas receptor-mediated apoptotic pathway in androgen-sensitive prostate cancer cells. The treatment of cells with a combination of anti-Fas monoclonal antibody and Lupeol resulted in higher cell death compared with the additive effect of the two compounds alone, suggesting a synergistic effect. Lupeol treatment resulted in a significant inhibition in growth of tumors with concomitant reduction in prostate-specific antigen secretion in athymic nude mice implanted with CWR22RN1 cells. Because early clinical prostate cancer growth is an androgendependent response, the results of the present study suggest that Lupeol may have a potential to be an effective agent against prostate cancer.

Dietary agents for chemoprevention of prostate cancer

“…The small interfering RNA-mediated silencing of the Fas gene and inhibition of caspase-6, caspase-8, and caspase-9 by their specific inhibitors further confirmed that lupeol specifically activates the Fas receptor-mediated apoptotic pathway [41]. Furthermore, combination of anti-Fas monoclonal antibody and lupeol resulted in higher cell death compared with the additive effect of the two compounds alone, suggesting a synergistic effect that can be exploited against CaP.…”

“…It possesses strong anti-inflammatory, antiarthritic, antimutagenic, and antimalarial activity and has been used for the treatment of various diseases [40]. Recent data from our laboratory and others suggest that lupeol possesses potent anti-cancer activities in vitro and in vivo systems [41]. We have shown that lupeol treatment resulted in significant inhibition of cell viability of LNCaP and CWR22Rν1 androgen-sensitive prostate cancer cells with minimal effect on normal prostate epithelial cells [41].…”

“…Recent data from our laboratory and others suggest that lupeol possesses potent anti-cancer activities in vitro and in vivo systems [41]. We have shown that lupeol treatment resulted in significant inhibition of cell viability of LNCaP and CWR22Rν1 androgen-sensitive prostate cancer cells with minimal effect on normal prostate epithelial cells [41]. Lupeol-induced apoptosis in these cells was associated with cleavage of poly(ADP-ribose) polymerase protein and degradation of acinus protein.…”

“…Furthermore, combination of anti-Fas monoclonal antibody and lupeol resulted in higher cell death compared with the additive effect of the two compounds alone, suggesting a synergistic effect that can be exploited against CaP. In mice xenograft model, lupeol treatment significantly inhibited the growth of CWR22Rν1 tumor cells with concomitant reduction in PSA secretion [41].…”

“…Inhibits cell growth, induces apoptosis, increases p21, p53, and Bax [6], inhibits HIF-1α degradation, inhibits biomarkers of invasion, angiogenesis and metastasis, inhibits PSA-triggered basement membrane degradation, and MMP-2 activation [4], inhibits 5α-reductase [15] and ODC activity [19], downregulates CK2 [10], sensitizes CaP cells to TRAIL-mediated apoptosis [11], upregulates eEF1A through laminin receptor [13] Induces clusterin [14], decreases IGF-I and increases IGFBP-3 levels, inhibits tumor growth and PSA secretion [16], reduces CaP progression with decrease in S100A4 and restoration of Ecadherin [20] Reduces risk of CaP [23,26] Shows minimal activity against CaP [24,25] Pomegranate Exerts antiproliferative, antiinvasive, antimetastatic effects [28,29,31], induces apoptosis through modulation of Bcl2 proteins [31], increases p21&p27, downregulates cyclin-cdk network [31] Decreases tumor incidence, tumor growth and serum PSA levels [28,31] Increases PSA doubling time [34] Delphinidin Exerts antiproliferative effects, induces cell cycle arrest, increases p21 and p27, downregulates cyclin-cdk network, modulates Bcl2 poteins in favor of apoptosis, releases cyt c, activates Caspases-3,-6,-8&-9, downregulates PI3K, β-catenin, Notch, and NF-κB signaling [36,37] Lupeol Induces apoptosis, upregulates Fas & FADD, activates Caspase-8 with degradation of acinus and PARP [41], downregulates IGF1-R, myc, cyclin D1, ERBB2, Jun, MMPs -2&7, upregulates IGFBP6, STEAP1, TIMP3, and KLK10, downregulates β-catenin signaling [43] Inhibits tumor growth and PSA secretion [41], inhibits testosterone-induced generation of ROS, depletes antioxidant enzymes [42] Fisetin Exerts antiproliferative effects, induces cell cycle arrest, increases p21& p27, downregulates cyclin-cdk network, induces apoptosis, modulates Bcl2 proteins, releases cyt c, downregulates XIAP, upregulates Smac/DIABLO, activates Caspases-3,-8&-9, induces PARP cleavage …”