Background Telomerase activity is found in 85%—90% of all human cancers but not in their adjacent normal cells.Human telomerase reverse transcriptase (hTERT) is an essential component in the telomerase complex that plays animportant role in telomerase activity.This study investigated the effect of the telomerase inhibition with an hTERTantisense oligodeoxynucleotide (ODN) in bladder cancer cells (T24) on tumor necrosis factor-α (TNF-α)-inducedapoptosis.Methods Antisense phosphorothioate oligodeoxynucleotide (AS PS-ODN) was synthesized and purified.Telomeraseactivity was measured by polymerase chain reaction enzyme-linked immunoassay (PCR-ELISA).hTERT mRNAexpression was measured by reverse transcription polymerase chain reaction (RT-PCR) assay and a gel-image system.hTERT protein was detected by immunochemistry and flow cytometry.Cell viability was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium (MTT) assay.Cell apoptosis was observed by a morphological methodand determined by flow cytometry.Results AS PS-ODN significantly inhibited telomerase activity and decreased the levels of hTERT mRNA whichpreceded the decline in the telomerase activity.AS PS-ODN significantly reduced the percentage of positive cellsexpressing hTERT protein following the decline of hTERT mRNA levels.There was no difference seen in the telomeraseactivity,hTERT mRNA expression or the protein levels between the sense phosphorothioate oligodeoxynucleotide(SPS-ODN) and the control group.AS PS-ODN treatment significantly decreased the cell viability and enhanced theapoptotic rate of T24 cells in response to TNF-α while there was no difference in cell viability and apoptotic rate betweenthe S PS-ODN and the control group.Conclusions AS PS-ODN can significantly inhibit telomerase activity by downregulating the hTERT mRNA andprotein expression.Treatment with AS PS-ODN may be a potential and most promising strategy for bladder cancer withtelomerase activity. Background Telomerase activity is found in 85% -90% of all human cancers but not in their adjacent normal cells. Human telomerase reverse transcriptase (hTERT) is an essential component in the telomerase complex that plays animportant role in telomerase activity. This study investigated the effect of the telomerase inhibition with an hTERTantisense oligodeoxynucleotide (ODN) in bladder cancer cells (T24) on tumor necrosis factor-α (TNF-α) -inducedapoptosis. Methods Antisense phosphorothioate oligodeoxynucleotide (AS PS- ODN) was synthesized and purified. measured by polymerase chain reaction enzyme-linked immunoassay (PCR-ELISA). hTERT mRNA expression was measured by reverse transcription polymerase chain reaction (RT-PCR) assay and a gel-image system. HTTERT was detected by immunochemistry and flow cytometry. Cell viability was measured by the 3- (4,5-dimethylthiazol-2-yl) -2,5-Diphenyltetrazolium (MTT) assay. Cell apoptosis was observed by a morphological methodan d determined by flow cytometry. Results AS PS-ODN significantly reduced telomerase activity and decreased the levels of hTERT mRNA whichpreceded the decline in the telomerase activity. AS PS-ODN significantly reduced the percentage of positive cellsexpressing hTERT protein following the decline of hTERT mRNA levels . There was no difference seen in the telomerase activity, hTERT mRNA expression or the protein levels between the sense phosphorothioate oligodeoxynucleotide (SPS-ODN) and the control group. AS PS-ODN treatment significantly decreased the cell viability and enhanced the apoptotic rate of T24 cells in response to TNF-α while there was no difference in cell viability and apoptotic rate betweenthe S PS-ODN and the control group. Conclusions AS PS-ODN can significantly inhibit telomerase activity by downregulating the hTERT mRNA and protein expression. Treatment with AS PS-ODN may be a potential and most promising strategy for bladder cancer withtelomerase activity.