Background: Cancer is one of the major threatening factors of human health worldwide. Unfortunately, chemotherapy, the powerful arm of cancer therapy, is accompanied with many side effects, so alternative treatments with greater specificities and fewer side effects are highly required. Methods: Human cancer cell lines including SW-742, HCT116, HepG2, Hep2, MKN45 and LNcap were selected and the anti-cancer potential of Cyrtopodion scabrum extract (CsE) on their growth was studied. Vero cells were used to study the potential cytotoxicity on the normal cells. Cell cycle analysis and DNA fragmentation assay were also performed. Results: CsE was toxic (30% - 78%) to all the cell lines, with the highest cytotoxicity on SW742, MKN45 and HepG2, respectively. A high selectivity index (> 2) was observed for the extract on SW742 and MKN45. DNA laddering pattern, as well as a significant increase in the number of the cells accumulated in sub-G1 and G2-phase of the cell cycle compared to the control untreated cells, was also observed. Conclusions: CsE suppressed the human cancer cells selectively and probably through apoptosis and G2 arrest mechanism. It could suggest a promising alternative/complementary treatment for cancer patients, especially those who suffer from digestive tract cancer. Keywords: Gecko (Gekko) Extract; MTT Assay; DNA Fragmentation Assay; Flow Cytometery; Cyrtopodion Scabrum

The p53 tumor suppressor protein is a principal mediator of growth arrest, senescence, and apoptosis in response to a broad array of cellular damage. p53 is a substrate for the ubiquitin-proteasome system, however, the ubiquitin-conjugating enzymes (E2s) involved in p53 ubiquitination have not been well studied. UBE2Q1 is a novel E2 ubiquitin conjugating enzyme gene. Here, we investigated the effect of UBE2Q1 overexpression on the level of p53 in the MDA-MB-468 breast cancer cell line as well as the interaction between UBE2Q1 and p53. By using a lipofection method, the p53 mutated breast cancer cell line, MDA-MB-468, was transfected with the vector pCMV6-AN-GFP, containing UBE2Q1 ORF. Western blot analysis was employed to verify the overexpression of UBE2Q1 in MDA-MB-468 cells and to evaluate the expression level of p53 before and after cell transfection. Immunoprecipitation and GST pull-down protocols were used to investigate the binding of UBE2Q1 to p53. We established MDA-MB-468 cells that transiently expressed a GFP fusion proteins containing UBE2Q1 (GFP-UBE2Q1). Western blot analysis revealed that levels of p53 were markedly lower in UBE2Q1 transfected MDA-MB-468 cells as compared with control MDA-MB-468 cells. Both in vivo and in vitro data showed that UBE2Q1 co-precipitated with p53 protein. Our data for the first time showed that overexpression of UBE2Q1can lead to the repression of p53 in MDA-MB-468 cells. This repression of p53 may be due to its UBE2Q1 mediated ubiquitination and subsequent proteasome degradation, a process that may involve direct interaction of UBE2Q1with p53.