Nasopharyngeal carcinoma (NPC), which occurs with a high incidence in southern China and southeast Asia, is of epithelial origin with overexpression of EGF receptor. To study the effect of inhibition of EGFR signaling on nasopharyngeal carcinoma cell proliferation and cell cycle distribution, EGFR tyrosine kinase inhibitor AG1478 was employed to treat Nasopharyngeal Carcinoma CNE2 cells. The results showed that AG1478 inhibited proliferation of CNE2 cells. Immunoblot showed that AG1478 inhibited EGFR phosphorylation in CNE2 cells without reduced expression of EGFR protein. The activation of Akt and MAPK which are downstream molecules of EGFR signaling pathway, were also inhibited by AG1478. AG1478 induced cell cycle arrest in G1 phase, and the levels of protein p27 were signi®cantly up-regulated. We concluded that inhibition of the EGFR signaling induced cell cycle arrest in G1 phase in CNE2 cells and p27 up-regulation was involved in this process. The EGFR kinase speci®c inhibitor is of potential to be developed into drugs for NPC treatment. q 2001 Elsevier Science Ireland Ltd. All rights reserved.

Annonaceous acetogenins have potent antitumor effect in vitro and in vivo. Squamocin is one of the annonaceous acetogenins and has been reported to have antiproliferative effect on cancer cells. Our results from this study showed that squamocin inhibited proliferation of HL-60 cells with IC 50 value of 0.17 m g/ml and induced apoptosis of HL-60 cells. Investigation of the mechanism of squamocininduced apoptosis revealed that treatment of HL-60 cells with squamocin resulted in extensive nuclear condensation, DNA fragmentation, cleavage of the death substrate poly (ADP-ribose) polymerase (PARP) and induction of caspase-3 activity. Pretreatment of HL-60 cells with caspase-3 specific inhibitor DEVD-CHO prevented squamocin-induced DNA fragmentation, PARP cleavage and cell death. The expression levels of protein bcl-2, bax have no change in response to squamocin treatment in HL-60 cells, whereas stress-activated protein kinase (SAPK/JNK) was activated after treatment with squamocin in HL-60 cells. These results suggest that apoptosis of HL-60 cells induced by squamocin requires caspase-3 activation and is related to SAPK activation. © 2002 Elsevier Science Inc. All rights reserved.

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.

Polysaccharides from aloe are always considered an effective radioprotector on irradiation-induced skin damage. The aim of this study was to determine if aloe polysaccharides (AP) have radioprotective effects on normal human cells in vitro and mouse survival in vivo and to explore the mechanism. Pretreatment with 50 m g/ml AP could improve the surviving fraction at 2 Gy (SF 2) of three normal cell lines 293, ECV304, and C. liver from 41.5%, 46.5%, and 40.9% to 49.4%, 72.1%, and 89.1%, respectively. AP could also reduce the apoptotic rate of C. liver cells from 9.5% and 43.0% to 2.2% and 10.9% 48 h and 72 h after 2 Gy irradiation, respectively. Western blot analysis showed that pretreatment with AP could block the upregulation of pro-apoptotic p53, Bax, and Bad and the downregulation of Bcl-2 by irradiation. AP could lower thymocyte apoptosis of mice in vivo after 6 Gy irradiation and abrogate the cell cycle perturbation. Fifty mg/kg of AP treatment for 30 min before 7.5 Gy irradiation provided the best radioprotective effect and improved the 30-day survival rate of mice to 86.0%, from 10.0%. AP exerted radioprotective effects in vitro and in vivo through an inhibition of apoptosis.

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.