Antiproliferative effects of the histone deacetylase inhibitor FR901228 on small-cell lung cancer lines and drug-resistant sublines

FR901228 is a novel histone deacetylase (HDAC) inhibitor, and its antiproliferative effects on non-small cell lung cancer cells have been shown in vitro. However, there have been no reports concerning the effects on small-cell lung cancer (SCLC). We have recently demonstrated that the HDAC inhibitors trichostatin A and sodium butyrate inhibit expression of the catalytic subunit of telomerase (hTERT) mRNA and telomerase activity in prostate cancer cells. The present study was designed to evaluate the effects of FR901228 on proliferation and telomerase activity in SCLC cells in vitro. FR901228 at 5 to 10 nM increased the fraction of cells in the G(2)/M and sub-G(1) phases of the cell-cycle, and inhibited the growth of H69, H526 and H82 cell lines. The expression of hTERT mRNA was inhibited 6 hr after treatment, prior to obvious inhibition of cell growth or cell-cycle distribution shifts. The inhibition of hTERT mRNA expression and telomerase activity was not a consequence of cell-growth arrest or apoptosis. Cycloheximide blocked the suppression of hTERT mRNA induced by FR901228, and the inhibition of hTERT mRNA by FR901228 required newly synthesized proteins. FR901228 also effectively inhibited growth of etoposide-resistant UMCC-1/VP-16, irinotecan-resistant PC-6/SN2-5H and cisplatin-resistant H526/CDDP cells having decreased expression of hTERT mRNA and telomerase activity, as well as their parental cells. This implies that SCLC resistant to these key drugs are not cross-resistant to FR901228. The present study suggests that FR901228 may be a promising drug for chemotherapy of cancers including SCLC, even for refractory or relapsing tumors after conventional chemotherapy.     

Synergistic growth inhibition of prostate cancer cells by 1 alpha,25 Dihydroxyvitamin D(3) and its 19-nor-hexafluoride analogs in combination with either sodium butyrate or trichostatin A

Prostate cancer is a major cause of male cancer death. In vitro and in vivo data support a role for 1 alpha,25 Dihydroxyvitamin D(3) (1 alpha,25(OH)(2)D(3)) in regulating the growth and differentiation of the normal prostate gland yet prostate cancer cells appear significantly less sensitive to this action. Vitamin D(3) receptor (VDR) content or mutational status do not correlate clearly with the antiproliferative effects of 1 alpha,25(OH)(2)D(3) and therefore it is unclear why prostate cancer cell lines are significantly less sensitive to this action. We hypothesized that the antiproliferative responses of prostate cancer cells to 1 alpha,25(OH)(2)D(3) are suppressed by a process involving histone deacetylation. Sodium butyrate (NaB) and trichostatin A (TSA) are inhibitors of histone deacetylase (HDAC) activity. Low doses of NaB or TSA (300 microM and 15 nM respectively), which alone were relatively inactive, synergized with 1 alpha,25(OH)(2)D(3) in liquid and semi-solid agar to inhibit the growth of LNCaP, PC-3 and DU-145 prostate cancer cells. Still greater synergy was observed between vitamin D(3) hexafluoride analogs and either NaB or TSA. The mechanism appeared to involve neither the cyclin-dependent kinase inhibitor, p21((waf1/cip1)) nor cell cycle arrest, but rather induction of apoptosis. These data suggest that cells dysregulate the normal pro-apoptotic signals of 1 alpha,25(OH)(2)D(3) during prostate cancer development by a mechanism involving histone deacetylation. Combination therapy with potent vitamin D(3) analogs and clinically approved HDAC inhibitors may overcome this lesion and improve the treatment of both androgen-dependent and independent prostate cancer.     

Telomerase in relation to expression of p53, c-Myc and estrogen receptor in ovarian tumours

Telomerase activity and its subunits (hTERC, hTERT mRNA) were evaluated in ovarian tumours in relation to the expression of p53, c-Myc and estrogen receptor (ER). Furthermore, relations between telomerase activity, hTERC and hTERT with known clinicopathologic prognostic factors and survival in patients with malignant tumours was investigated. Telomerase activity was determined with TRAP, hTERC and hTERT with RT-PCR, while p53, c-Myc and ER expression with immunohistochemistry. Telomerase activity and hTERT mRNA were more frequently observed in malignant ovarian tumours compared to borderline and benign tumours, whereas hTERC was present in all tumour types. p53 and c-Myc were more frequently detected in malignant compared to borderline and benign tumours. Telomerase activity was positively related to hTERT mRNA, p53 and c-Myc expression, but not to hTERC and ER expression. In malignant tumours, hTERC levels were related to tumour stage, while telomerase activity and hTERT mRNA expression were not related to any clinicopathologic feature. Tumour stage, differentiation grade, residual tumour after first laparotomy and presence of ascites were related to (progression free) survival, whereas telomerase activity or its subunits were not. In conclusion, these data suggest that p53 expression (e.g. p53 mutation) as well as c-Myc expression may have a role in regulation of telomerase activity in ovarian tumours.     

Amplification of hTERT and hTERC genes in leukemic cells with high expression and activity of telomerase

Reactivation of telomerase plays an important role in carcinogenesis. Malignant cells almost always possess high activity and expression of telomerase. The aim of this study was to see whether there is any relationship between telomerase activity and expression and hTERT and hTERC gene amplification in acute lymphoblastic leukemia (ALL) and non-lymphoblastic leukemia (ANLL) cells. In addition telomere length was tested in leukemic cells at the time of diagnosis and during remission. Expression of the three components of telomerase (hTERT, hTERC and TP1) as well as telomerase activity was found both in ALL and ANLL cells. Telomerase activity was diminished in patients in remission. The leukemic cells showed considerable heterogeneity of terminal restriction fragments, that is telomere length. ALL cells showed a variable pattern of telomere length in contrast to ANLL cells which produced a predominantly short telomere pattern. Telomere length in the lymphocytes of leukemia patients was shorter in remission as compared to the time of diagnosis. FISH analysis revealed amplification of hTERT and hTERC genes in ALL and ANLL cells. Quantitative analysis showed that leukemic cells possess higher number of hTERT and hTERC copies than the normal PBL. Our results suggest that the activation of telomerase in leukemic cells is connected with amplification of hTERT and hTERC genes. The high expression and activity of telomerase found in leukemic cells may be partially explained by amplified hTERT and hTERC genes. Amplification of the telomerase genes seems to be a common event in carcinogenesis and may play a role in telomerase reactivation leading to cell immortalization.     

hTERT 短发夹状RNA 抑制前列腺癌细胞生长的研究

 目的 研究靶向端粒酶逆转录酶（hTERT）的短发夹状RNA（shRNA）基因转染对前列腺癌细胞体外生长的抑制效应及其促细胞凋亡作用。方法 在脂质体介导下将针对hTERT基因的shRNA表达载体psilencer-TRT转染前列腺癌细胞PC-3m，得到稳定细胞株PC-3m／shRNA-TRT。采用RT-PCR检测hTERT基因表迭情况，western blot分析各组细胞hTERT及c-myc蛋白表达变化，细胞计数并绘制细胞生长曲线，Hoechst33258染色、透射电镜、流式细胞仪检测细胞凋亡情况。结果 重组质粒psilencer-TRT转录生成的shRNA使实验组细胞的hTERT基因表达显著下调，抑制率约为89．02％；同时实验组细胞hTERT及c-myc蛋白水平较对照组有明显下降，细胞的生长增殖能力也显著降低（P〈0．05），生长速率明显变慢，部分细胞呈现凋亡形态学改变，凋亡率为（19．69±4．75）％。结论 hTERT短发夹状RNA能有效抑制前列腺癌细胞中hTERT表达及癌细胞生长，诱导PC-3m细胞凋亡，可望为前列腺癌的基因治疗提供新方法。     

Ectopic expression of c-myc fails to overcome downregulation of telomerase activity induced by herbimycin A, but ectopic hTERT expression overcomes it.

Telomerase plays a key role in the maintenance of chromosomal stability in tumors, but the mechanism regulating telomerase activity is still unclear. Recent studies have suggested that c-myc may be vital for regulation of hTERT mRNA expression and telomerase activity. In this study, we investigated the changes of telomerase activity and telomerase-related genes induced by herbimycin A in K562 human chronic myelogeous leukemic cells. Telomerase activity showed a biphasic pattern in herbimycin A-treated K562 cells. Initially, the telomerase activity decreased along with the decline of cells in S and G2/M phases, but it recovered slightly at the end of treatment. Expression of mRNA for the telomerase catalytic subunit (hTERT) was decreased before the decline of telomerase activity, and increased slightly before the reactivation of telomerase activity. During herbimycin A treatment, both c-myc and cyclin D1 mRNA showed transient downregulation before the increase of G1 cells. Herbimycin A treatment caused the downregulation of both telomerase activity and hTERT mRNA in cyclin D1-transfected K562 cells, while telomerase activity was partially restored in c-Myc-transfected cells. In contrast, hTERT-transfected K562 cells maintained a high level of telomerase activity during herbimycin A treatment. Neither the template RNA component of telomerase (hTERC) nor telomerase-associated protein (TEP-1) were altered in any of the transfected K562 cells. These results indicate that telomerase activity is mainly regulated by hTERT, and that c-Myc protein is one of the positive regulators of hTERT in leukemic cells but is not enough to counteract the downregulation of telomerase activity by herbimycin A completely.     

siRNA-mediated Inhibition of hTERC Enhances Radiosensitivityof Cervical Cancer

Background: To investigate the influence of telomerase activity, apoptosis, radiosensitivity of cervical cancer after siRNA-mediated knockdown of telomerase RNA and evaluate in vivo growth with gene interference.Methods: We studied siRNA-targeting-telomerase RNA transfection into the Hela cell line. Expression of hTERC mRNA was detected by RT-PCR and telomerase activity was measured by the TRAP assay. Growth inhibition was determined by MTT assay and radiosensitivity of the cervical cancer cells was examined by colony formation assay. In addtion, effects of hTERC inhibition in vivo were studied by injection of siRNA-transfected Hela cells into nude mice. Results: The hTERC siRNA effectively downregulated the expression of hTERC mRNA and alsoreduced the telomerase activity to 30% of the untreated control vlaue. The viability of hTERC siRNA transfected Hela cells was reduced by 44.7% after transfection. After radiation treatment, the radiosensitivity of Hela cells with hTERC knockdown was increased. In vivo, the tumors developing from the hTERC siRNA-transfectedcells were of reduced size, indicating that the hTERT siRNA also depressed the tumorigenic potential of the Hela cells. Conclusions: Our results supported the concept of siRNA-mediated inhibition of telomerase mRNA whichcould inhibit the expression of hTERC and telomerase activity. Furthermore, radiosensitivity was upregulated after knockdown the hTERC in vivo and in vitro.     

人端粒酶催化亚基反义核酸对子宫内膜癌细胞的抑制作用

目的 探讨人端粒酶催化亚基(hTERT)基因反义寡核苷酸(AODN)对子宫内膜癌细胞系HEC-1A的生长抑制作用及作用机理。方法 采用四甲基偶氮唑蓝(MTT)法检测AODN对细胞增殖能力及细胞生长的影响;逆转录聚合酶链反应技术(RT-PCR)、定量端粒酶重复扩增法(TRAP)、Westerm blot蛋白免疫印迹法和凋亡相关酶活性测定检测反义核酸对hTERT基因转录、蛋白表达、细胞端粒酶活性以及凋亡相关酶活性的变化。结果 低浓度hTERT基因AODN能够下调HEC-1A细胞HTERT、mRNA含量,抑制细胞hTERT蛋白表达,下调端粒酶活性,并且激活凋亡相关酶Caspase-1和Caspase-3活性;其对细胞的生长抑制作用有明显的时效性和剂量依赖性。结论 hTERT基冈反义核酸能够抑制子宫内膜癌细胞的增殖能力,有望成为内膜癌治疗的新方向。