Gallotannin is a DNA damaging compound that induces senescence independently of p53 and p21 in human colon cancer cells.

The plant secondary metabolite gallotannin (GT) is the simplest hydrolyzable tannin shown to have anti-carcinogenic properties in several cell lines and to inhibit tumor development in different animal models. Here, we determined if GT induces senescence and DNA damage and investigated the involvement of p53 and p21 in this response. Using HCT116 human colon cancer cells wildtype for p53(+/+) /p21(+/+) and null for p53(+/+) /p21(-/-) or p53(-/-) /p21(+/+) , we found that GT induces senescence independently of p21 and p53. GT was found to increase the production of reactive oxygen species (ROS) by altering the redox balance in the cell, mainly by reducing the levels of glutathione and superoxide dismutase (SOD). Using the key antioxidants N-acetyl cysteine, dithiothreitol, SOD, and catalase, we showed that ROS were partially involved in the senescence response. Furthermore, GT-induced cell cycle arrest in S-phase in all HCT116 cell lines. At later time points, we noticed that p53 and p21 null cells escaped complete arrest and re-entered cell cycle provoking higher rates of multinucleation. The senescence induction by GT was irreversible and was accompanied by significant DNA damage as evidenced by p-H2AX staining. Our findings indicate that GT is an interesting anti colon cancer agent which warrants further study.

Hsp90 inhibition by AUY922 as an effective treatment strategy against myxoid liposarcoma.

Liposarcoma is one of the most common soft tissue sarcomas in adults. Recognized histological subtypes include well differentiated/dedifferentiated liposarcoma (WD/DDLS), myxoid liposarcoma (MLS) and pleomorphic liposarcoma. Currently, there are no proper subtype-specific treatments due to the genetic, histological and clinical heterogeneity of the liposarcoma subentities. In the past decade, the rising understanding of the various genetic and molecular aberrations in liposarcoma led to the development of novel alternative therapeutic strategies. One such therapy is the inhibition of the heat shock protein 90 (Hsp90) which is overexpressed in liposarcomas. In this study, we dissect the functional role of a novel potent Hsp90 inhibitor NVP-AUY922 (AUY922) in different cell lines of myxoid (MLS402, MLS1765) and undifferentiated (SW872) liposarcomas. We show that compared with 17-AAG treatment, lower concentrations of AUY922 achieve markedly cytotoxic effects on tumor cell viability. Combination treatment of AUY922 (20 nM) with Doxorubicin (300 nM) yielded a further reduction in cell viability in comparison to Doxorubicin alone. In vivo, we document an inhibition of tumor growth after AUY922 treatment. Further analyses revealed that Hsp90-inhibition induces apoptotic cell death and cell cycle arrest. In addition, we report striking perturbations of subtype-specific pattern in Raf/MEK/ERK and PI3K signaling after AUY922 application. In conclusion, our results provide evidence that Hsp90-inhibition by AUY922 may be a promising alternative therapeutic strategy for myxoid liposarcoma patients.

Gallotannin inhibits NFĸB signaling and growth of human colon cancer xenografts.

Gallotannin (GT), the polyphenolic hydrolyzable tannin, exhibits anti-inflammatory and anticancer activities through mechanisms that are not fully understood. Several effects modulated by GT have been shown to be linked to interference with inflammatory mediators. Considering the central role of nuclear factor kappa B (NF-ĸB) in inflammation and cancer, we investigated the effect of GT on NF-ĸB signaling in HT-29 and HCT-116 human colon cancer cells. DNA binding assays revealed significant suppression of tumor necrosis factor (TNF-α)-induced NFĸB activation which correlated with the inhibition of IĸBα phosphorylation and degradation. Sequentially, p65 nuclear translocation and DNA binding were inhibited. GT also down-regulated the expression of NFĸB-regulated inflammatory cytokines (IL-8, TNF-α, IL-1α) and caused cell cycle arrest and accumulation of cells in pre-G 1 phase. In vivo, GT (25 mg/kg body weight) injected intraperitoneally (i.p.) prior to or after tumor inoculation significantly decreased the volume of human colon cancer xenografts in NOD/SCID mice. GT-treated xenografts showed significantly lower microvessel density (CD31) as well as lower mRNA expression levels of IL-6, TNF-α and IL-1α and of the proliferation (Ki-67) and angiogenesis (VEGFA) proteins, which may explain GTs in vivo anti-tumorigenic effects. Overall, our results indicate that the anti-inflammatory and antitumor activities of GT may be mediated in part through the suppression of NF-ĸB activation.