oleandrin and Skin-Neoplasms

While certain cardiac glycoside compounds such as oleandrin, bufalin and digitoxin are known to be associated with potent cytotoxicity to human tumor cells, the mechanisms by which this effect is produced are not clear. We now demonstrate that incubation of human malignant melanoma BRO cells with oleandrin results in a time-dependent formation of reactive oxygen species (ROS). Use of Mito-SOX and dihydroethidine dyes revealed the presence of oleandrin-mediated superoxide anions. Formation of superoxide anions correlated with a loss in cellular viability, proliferation and cellular defense mechanisms such as GSH content. Oleandrin also resulted in an unusual time-dependent mitochondrial condensation in BRO cells that could be blocked with use of N-acetyl cysteine (NAC). NAC was also shown to block ROS formation and partially prevent oleandrin-mediated loss of cellular GSH. Taken as a whole, the data suggest that exposure of human tumor cells such as BRO to oleandrin results in the formation of superoxide anion radicals that mediate mitochondrial injury and loss of cellular GSH pools. These mechanisms play a role in cardiac glycoside mediated tumor cell injury. Conversely, incubation of NAC, a precursor to GSH, largely prevents oleandrin-mediated inhibition of proliferation and mitochondria structural changes.

Topics: Cardenolides; Cell Proliferation; Cystine; Humans; Melanoma; Mitochondria; Oxidative Stress; Reactive Oxygen Species; Skin Neoplasms; Tumor Cells, Cultured

Oleandrin, derived from the leaves of Nerium oleander, has been shown to possess anti-inflammatory and tumor cell growth-inhibitory effects. Here, we provide evidence that oleandrin could possess anti-tumor promoting effects. We determined the effect of topical application of oleandrin to CD-1 mice against l2-O-tetradecanoylphorbol-13-acetate (TPA), a widely studied skin tumor promoter, -induced conventional and novel markers of skin tumor promotion. Topical application of oleandrin (2 mg per mouse) 30 min before TPA (3.2 nmol per mouse) application onto the skin afforded significant inhibition, in a time-dependent manner, against TPA-mediated increase in cutaneous edema and hyperplasia, epidermal ornithine decarboxylase (ODC) activity and ODC and cyclooxgenase-2 (COX-2) protein expression. In search for novel markers of skin tumor promotion, we found that TPA application to mouse skin resulted, as an early event, in an increased expression of phosphatidyinositol 3-kinase (PI3K), phosphorylation of Akt at threonine308 and activation of nuclear factor kappa B (NF-kappaB). Topical application of oleandrin before TPA application to mouse skin resulted in significant reduction in TPA-induced expression of PI3K and phosphorylation of Akt, and inhibition of NF-kappaB activation. NF-kappaB is a eukaryotic transcription factor that is critically involved in regulating the expression of specific genes that participate in inflammation, apoptosis and cell proliferation. Employing Western blot analysis, we found that oleandrin application to mouse skin resulted in inhibition of TPA-induced activation of NF-kappaB, IKKalpha and phosphorylation and degradation of IkappaBalpha. Our data suggest that oleandrin could be a useful anti-tumor promoting agent because it inhibits several biomarkers of TPA-induced tumor promotion in an in vivo animal model. One might envision the use of chemopreventive agents such as oleandrin in an emollient or patch for chemoprevention or treatment of skin cancer.

Topics: Administration, Cutaneous; Animals; Anticarcinogenic Agents; Biomarkers, Tumor; Cardenolides; Cyclooxygenase 2; Edema; Female; Hyperplasia; Isoenzymes; Mice; Mice, Inbred Strains; Ornithine Decarboxylase Inhibitors; Phorbol Esters; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Prostaglandin-Endoperoxide Synthases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Skin; Skin Neoplasms