The anti-proliferative activity of ursolic acid has been reported in a wide variety of cancer cell lines. The esters inhibited the growth of several lung, colon, breast and renal cancers, melanoma and leukemia cell lines with GI50 values based on sulforhodamine B (SRB) assay of between 1.2 and 11 micro M.
Ursolic acid may also affect migration and colony formation by cancer cells. We used clonogenic assays to assess effects of cranberry constituents on tumor colony formation over a 2 week period, showing that ursolic acid and cranberry proanthocyanidins separately inhibited tumor colony formation in a dose-dependent manner in HT-29 and HCT116 colon tumor models.
The ursolic acid and cranberry proanthocyanidins both induced apoptosis, as detected by DNA fragmentation, but the effect varied with cell line. Both compounds caused a dose-dependent induction of apoptosis in HT-29 cells, whereas in the HCT116 cells, ursolic acid effectively induced apoptosis, but the proanthocyanidins had a weaker effect. Complementary effects of these compounds are likely to play a role in decreased tumor cell proliferation.
Most of the existing bioactivity studies on ursolic acid examine the activity of purified ursolic acid, either isolated from a plant or commercially obtained. The anti-inflammatory actions of pentacyclic triterpenoids are well known and structure-activity relationships have been reviewed. For ursolic acid, several studies report anti-inflammatory activities in vivo, primarily observing reduced inflammation in mouse-ear edema models.
The effects of ursolic acid on proinflammatory pathways observed in vitro include inhibition of COX-2 catalyzed prostaglandin biosynthesis. Ursolic acid inhibited COX-2 transcription in a human mammary oncogenic epithelial cell line (184B5/HER) and the observed suppression of gene expression involved the protein kinase C signal transduction pathway.
Recently, cranberry extracts were evaluated for their anti-inflammatory activity, and a methanol-soluble extract was found to inhibit the activity of COX-2 at 50 micro g/mL based on measuring conversion of arachidonic acid to prostaglandin E2. The most active subfraction in this investigation, which inhibited COX-2 activity by 85% at a concentration of 10 μg/mL, was analyzed by LC-MS and found to contain ursolic acid and its hydroxycinnamate esters. The methanol fraction and active subfractions also inhibited the TNF-induced activation of NF-κB in Jurkat cells as well as NF-κB transcription in human T lymphocytes.
Other possible anti-inflammatory mechanisms for ursolic acid include induction of NF-KB mediated expression of inducible nitric oxide synthase (iNOS) and TNF-alpha in macrophages, implying a possible anti-carcinogenic mechanism involving enhanced NO production.
Cranberry extracts were also evaluated for iNOS activity in RAW 264.7 mouse macrophages. However, the extracts had no effect on iNOS activity at concentrations of 100 micro g/mL or less. Despite its being recognized as an anti-inflammatory, ursolic acid has received relatively little attention as a functional food factor. Data on in vivo anti-cancer effects are quite scarce and most involve mouse paw edema models.
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1. Intravenous injections and hormonal activity
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