Cucurbitacin R

Activated kRas protects colon cancer cells from cucurbitacin-induced apoptosis: the role of p53 and p21.[Pubmed:18561895]

Biochem Pharmacol. 2008 Jul 15;76(2):198-207.

Cucurbitacins have been shown to inhibit proliferation in a variety of cancer cell lines. The aim of this study was to determine their biological activity in colon cancer cell lines that do not harbor activated STAT3, the key target of cucurbitacin. In order to establish the role of activated kRas in the responsiveness of cells to cucurbitacins, we performed experiments in isogenic colon cancer cell lines, HCT116 and Hke-3, which differ only by the presence of an activated kRas allele. We compared the activity of 23, 24-dihydrocucurbitacin B (DHCB) and Cucurbitacin R (CCR), two cucurbitacins that we recently isolated, with cucurbitacin I (CCI), a cucurbitacin with established antitumorigenic activity. We showed that cucurbitacins induced dramatic changes in the cytoskeleton (collapse of actin and bundling of tubulin microfilaments), inhibited proliferation and finally induced apoptosis of both HCT116 and Hke-3 cells. However, the presence of oncogenic kRas significantly decreased the sensitivity of cells to the three cucurbitacins tested, CCR, DHCB and CCI. We confirmed that mutational activation of kRas protects cells from cucurbitacin-induced apoptosis using nontransformed intestinal epithelial cells with inducible expression of kRasV12. Cucurbitacins induced the expression of p53 and p21 predominantly in HCT116 cells that harbor mutant Ras. Using HCT116 cells with targeted deletion of p53 or p21 we confirmed that p53 and p21 protect cells from apoptosis induced by cucurbitacins. These results demonstrated that sensitivity of human colon cancer cell lines to cucurbitacins depends on the kRas and p53/p21 status, and established that cucurbitacins can exert antitumorigenic activity in the absence of activated STAT3.

Bcl-2 is a negative regulator of interleukin-1beta secretion in murine macrophages in pharmacological-induced apoptosis.[Pubmed:20649584]

Br J Pharmacol. 2010 Aug;160(7):1844-56.

BACKGROUND AND PURPOSE: Cucurbitacin R, a natural anti-inflammatory product, has been shown to exhibit activity against both adjuvant-induced arthritis and delayed-type hypersensitivity reactions induced by various agents. Previous studies have demonstrated that the effects of Cucurbitacin R stem from its inhibition of both cytokine production and lymphocyte proliferation. EXPERIMENTAL APPROACHES: Effects of Cucurbitacin R were investigated on lipopolysaccharide-stimulated RAW 264.7 cells. Cell cycle evolution was analysed by flow cytometry, detection of apoptosis by DNA ladder, Bcl-2, p21, p53, Bax, cleaved caspase-1 (p10), caspase-9, and caspase-3, cleaved caspase (p17) and interleukin-1beta detection was followed by Western blot analysis and mRNA expression with quantitative real time reverse transcription-polymerase chain reaction (qRT-PCR). KEY RESULTS: Cucurbitacin R was found to induce apoptosis in lipopolysaccharide-stimulated RAW 264.7 macrophages through the inhibition of Bcl-2 expression, which regulates pro-inflammatory caspase-1 activation and interleukin-1beta release. Also, Cucurbitacin R arrested the cell cycle in the G(2)/M phase and increased the subG(0) population in lipopolysaccharide-stimulated RAW 264.7 macrophages. Moreover, it increased the expression of proteins p53 and p21, down-regulated the expression of Bcl-2, activated the activity of caspase-1 and augmented the production of interleukin-1beta. Finally, the transfection of RAW 264.7 macrophages with a Bcl-2 expression plasmid produced the inhibition of apoptosis and caspase-1 activation/interleukin-1beta release induced by Cucurbitacin R in RAW 264.7 cells. CONCLUSIONS AND IMPLICATIONS: Taken together, these results point to a new apoptotic process in which interleukin-1beta release is directly regulated by Bcl-2 status; this contributes to the evidence that apoptotic processes do not induce inflammation.

Cucurbitacin R reduces the inflammation and bone damage associated with adjuvant arthritis in lewis rats by suppression of tumor necrosis factor-alpha in T lymphocytes and macrophages.[Pubmed:17065367]

J Pharmacol Exp Ther. 2007 Feb;320(2):581-90.

The aim of this study was to investigate the effects of Cucurbitacin R on an experimental model of adjuvant-induced arthritis in rats. The treatment of arthritic rats with Cucurbitacin R (1 mg/kg p.o. daily) modified the evolution of the clinical symptoms, whereas the histopathology of paws demonstrated a reduction in the signs of arthritis. Compared with the control group, radiography of the tibiotarsal joints of Cucurbitacin R-treated rats showed a decrease in joint damage and soft tissue swelling of the footpad. The in vivo study of the expression of proinflammatory enzymes (nitric-oxide synthase-2 and cyclooxygenase-2) with the aid of the Western blot technique, and that of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E(2) by means of enzyme-linked immunosorbent assays demonstrated a clear decrease in both the enzymes and the mediators in paw homogenates. The analysis for prostaglandin E(2), nitric oxide, and TNF-alpha production in RAW 264.7 macrophages, as well as that for TNF-alpha in human lymphocytes, indicated a reduction of all mediators. The expression of cyclooxygenase-2 was not modified in RAW 264.7 macrophages, whereas the expression of nitric-oxide synthase-2 was clearly diminished. Moreover, Cucurbitacin R was found to inhibit signal transducer and activator of transcription 3 activation in the lymphocytes of both healthy and arthritic men. These experimental data on the chronic model, together with previously reported activity on acute and subchronic experimental models, justify the anti-inflammatory activity of Cucurbitacin R and provide further evidence for the therapeutic potential of a group of natural products as anti-inflammatory agents.

Inhibition of delayed-type hypersensitivity by Cucurbitacin R through the curbing of lymphocyte proliferation and cytokine expression by means of nuclear factor AT translocation to the nucleus.[Pubmed:19846588]

J Pharmacol Exp Ther. 2010 Feb;332(2):352-63.

Cucurbitacin R is known to exhibit an anti-inflammatory effect in different experimental models of inflammation. In this article, we outline the effect of Cucurbitacin R on T lymphocyte proliferation, cytokine production, and nuclear factor activation, as well as its influence on various experimental models of delayed-type hypersensitivity (DTH) in mice. Cucurbitacin R reduced the proliferation of phytohemagglutinin A-stimulated human T lymphocytes (IC(50), 18 microM), modifying the cell cycle, as well as the production of cytokines [interleukin (IL)-2, IL-4, IL-10, and especially interferon-gamma] and the induction of the principal cyclins implicated in the cell cycle (A(1), B(1), D(2), and E). These effects are brought on by a novel, selective inhibition of nuclear factor AT (NFAT) by Cucurbitacin R, with no concomitant effect on other transcription factors such as activator protein-1. In addition, we tested the in vivo effects of Cucurbitacin R in three experimental models of DTH, as well as its effects on T lymphocyte proliferation, the cell cycle, cytokines, and cyclins. Although Cucurbitacin R was found to reduce the inflammatory response brought on by both oxazolone and dinitrofluorobenzene, its activity was even more pronounced against sheep red blood cell-induced edema in mouse paws, with a clear reduction in the production of IL-1beta, IL-4, and tumor necrosis factor alpha in the inflamed paw. In conclusion, Cucurbitacin R has the potential to be a new immunosuppressive agent with antiproliferative effects through the inhibition of the NFAT with anti-inflammatory activity in DTH reactions.