Agents stabilizing G-quadruplexes have the potential to interfere with telomere replication by blocking the elongation step catalysed by telomerase or telomerase-independent mechanism and could therefore act as antitumor agents. In this study, we found that quindoline derivatives interacted preferentially with intramolecular G-quadruplex structures and were novel potent telomerase inhibitors. Treatment with quindoline derivatives reproducibly inhibited telomerase activity in human leukemia K562 cells and colon cancer SW620 cells. N0-(10H-Indolo [3,2-b] quinolin-11-yl)-N, Ndimethyl-propane-1,3-diamine (SYUIQ-5), (one of quindoline derivatives), when added to K562 and SW620 cell culture at nonacute cytotoxic concentrations, increased time of population doublings of K562 and SW620 cells, induced a marked cessation in cell growth and cellular senescence phenotype after 35 and 18 days, respectively. Growth cessation was accompanied by a shortening of telomere length, and induction of p16, p21 and p27 protein expression. However, another compound SYUIQ-7 with greater IC50 for telomerase had no obvious cellular effect in nonacute cytotoxic concentrations. These results indicate that quindoline derivatives as novel potent G-quadruplex interactive agents induce senescence and telomere shortening in cancer cells and therefore are promising agents for cancer treatment. Oncogene (2006) 25, 503-511. doi:10.1038/sj.onc.1209067; published online 19 September 2005

Epstein-Barr Virus (EBV) is closely associated with B cell malignancies. However, whether EBV appears to be absolutely required for cell proliferation and survival in lymphoma cells is still unknown. In this study, small interfering RNA (siRNA) targeting LMP1 was employed to investigate the effect of LMP1 on cell proliferation in EBV-positive lymphoblastoid B-cell line. A plasmid stable encoding 21-nt small RNA specifically and efficiently interfering LMP1 was constructed, resulting in a substantial loss of LMP1 mRNA and a significantly decreased LMP1 protein expression. Our data demonstrated that cell proliferation was completely inhibited and apoptosis was induced after knockdown of LMP1 gene in lymphoblastoid B-cell line. Also, we found that suppression of LMP1 caused downregulation of telomerase protein expression and decreased telomerase activity in lymphoma cells. In EBV-negative NPC cell line, transfection of plasmid expressing LMP1 greatly enhanced telomerase protein expression. Our results suggested that siRNA targeting LMP1 can induce apoptosis in EBVpositive lymphoma cells and is associated with inhibition of telomerase activity and expression. siRNA-directed LMP1 silencing may be of the therapeutic value for preventing and treating those EBV-associated tumors.

p33ING1b induces cell cycle arrest and stimulates DNA repair, apoptosis and chemosensitivity. The magnitude of some p33ING1b effects may be due to activation of the tumor suppressor p53. To investigate if the p33ING1b protein affected chemosensitivity of osteosarcoma cells, we overexpressed p33ING1b in p53+/+ U2OS cells or in p53-mutant MG63 cells, and then assessed for growth arrest and apoptosis after treatment with etoposide. p33ING1b increased etoposide-induced growth inhibition and apoptosis to a much greater degree in p53+/+ U2OS cells than in p53-mutant MG63 cells. Moreover, ectopic expression of p33ING1b markedly upregulated p53, p21WAF1 and bax protein levels and activated caspase-3 protein kinase in etoposide-treated U2OS cells. Together, our data indicate that p33ING1b prominently enhances etoposide-induced apoptosis through p53-dependent pathways in human osteosarcoma cells. p33ING1b may be an important marker and/or therapeutic target in the prevention and treatment of metastatic osteosarcoma.

Ceramide mediates differentiation, growth arrest, apoptosis, proliferation, cytokine biosynthesis and secretion, and a variety of other cellular functions. However, little is known regarding ceramide signaling linked to the cell cycle. In the present study, the effect of ceramide on cell cycle in nasopharyngeal carcinoma cell line CNE2 was investigated. The results showed that ceramide inhibited cell proliferation and induced cell cycle arrest in G1 phase in CNE2 cells. Exposure of CNE2 cells to ceramide resulted in a dose-dependent up-regulation of the cyclin-dependent kinase inhibitor p27 and a decrease of phospho-Akt without reduced expression of total AKT protein. The activation of phosphatidylinositol-3-kinase (PI3K) and the protein expression of PTEN were unaffected following ceramide treatment. We concluded that ceramide induced cell cycle arrest in G1 phase in CNE2 cells and p27 up-regulation was involved in this process. In addition, up-regulation of p27 resulting from ceramide treatment may be due to the interruption of Akt, but decrease of phospho-Akt is independent of PI3K function or PTEN protein expression.