ABSTRACT
<p><b>OBJECTIVE</b>To find out a possible approach to improve the effectiveness of radiotherapy and chemotherapy for Ewing's sarcoma by constructing a eukaryotic expression vector expressing herpes simplex virus-thymidine kinase (HSV-TK) regulated by hypoxia responsive element (HRE) under hypoxia and to evaluate the effects of this HRE regulated HSV-TK system on killing effect of gancyclovir (GCV) on Ewing's sarcoma cell line SK-ES under hypoxic condition.</p><p><b>METHODS</b>The HRE was synthesized according to the literature and cloned into the enhancer site of pIRES(2)-EGFP vector to obtain the pHRE recombinant plasmid. The HSV-TK was amplified by PCR and cloned into the multiple clone site of pIRES(2)-EGFP and pHRE to obtain pTK and pHRE-TK recombinant plasmid. The human Ewing's sarcoma cell line SK-ES was transfected by pTK or pHRE-TK recombinant plasmid with liposome and then was exposed to normoxic (21% oxygen) or hypoxic (3% oxygen) condition. The expression of enhanced green fluorescent protein (EGFP) was monitored by fluorescent microscopy. The sensitivity of human Ewing's sarcoma cell line SK-ES transfected with pTK or pHRE-TK recombinant plasmid to the anti-tumour drug GCV was determined with the method of tetrazolium (MTT) after treating with GCV for five days.</p><p><b>RESULTS</b>(1) The result of sequencing showed that the recombinant plasmid pHRE contained HRE, and that the recombinant plasmid pTK and pHRE-TK contained HSV-TK gene in the sense direction. (2) Comparison of fluorescent optical density (FOD) showed that (1) the EGFP FOD value of pHRE and pHRE-TK group cells exposed to hypoxia was significantly higher than those exposed to normoxia (P < 0.01); (2) when the cells were exposed to hypoxia, the EGFP FOD value of pHRE and pHRE-TK group cells was significantly higher than that of pTK and empty vector group (P < 0.01); (3) there was no significant difference among the four groups of cells when they were exposed to normoxia (P > 0.05). (3) Comparison of the sensitivity of four groups of cells to GCV showed that (1) the cells in pHRE-TK and pTK groups were much more sensitive to GCV than the cells in pHRE group under hypoxia condition (P < 0.01), the higher the GCV concentration, the greater the difference; (2) the cells of pHRE-TK group were more sensitive to GCV than those in pTK group under hypoxic condition (P < 0.01), but was almost equally sensitive under normoxic condition (P > 0.05); (3) the pHRE-TK group cells had higher sensitivity to GCV under hypoxia than normoxia (P < 0.01) while the pTK group cells had almost the same sensitivity to GCV under hypoxia and normoxia (P > 0.05).</p><p><b>CONCLUSION</b>(1) The eukaryotic expression vector expressing herpes simplex virus-thymidine kinase (HSV-TK) regulated by hypoxia responsive element (HRE) under hypoxia was constructed successfully. (2) HRE could up-regulate expression of EGFP by SK-ES cells under hypoxia condition. (3) HRE could enhance the killing effect of HSV-TK/GCV system on human Ewing's sarcoma cell line SK-ES under hypoxic condition.</p>
Subject(s)
Humans , Antiviral Agents , Pharmacology , Cell Hypoxia , Genetics , Cell Line, Tumor , Ganciclovir , Pharmacology , Gene Expression Regulation , Genetic Vectors , Green Fluorescent Proteins , Metabolism , Microscopy, Fluorescence , Plasmids , Polymerase Chain Reaction , Response Elements , Genetics , Sarcoma, Ewing , Drug Therapy , Metabolism , Simplexvirus , Genetics , Metabolism , Thymidine Kinase , Genetics , Metabolism , TransfectionABSTRACT
<p><b>OBJECTIVE</b>To observe the ability of triple helix-forming oligonucleotides (TFO) modified with manganese porphyrin to combine with and cleave HBV DNA fractions.</p><p><b>METHODS</b>The ends of TFO were modified with manganese porphyrin and acridine; At 37 degrees C and pH 7.4 condition in vitro, TFO modified with manganese porphyrin and acridine were bound with 32P labeled HBV DNA fragments, the affinity and specificity binding to target sequence were tested by electrophoretic mobility shift and DNase 1 footprinting assays, the ability to cleave HBV DNA fractions was observed with cleavage experiments.</p><p><b>RESULTS</b>TFO modified with manganese porphyrin and acridine could bind to target sequence in a sequence-dependent manner with Kd values of 3.5 x 10(-7) mol/L and a relative affinity of 0.008. In the presence of KHSO5, TFO modified with manganese porphyrin and acridine could cleave target sequence in the region forming triple DNA.</p><p><b>CONCLUSION</b>In the presence of KHSO5, TFO modified with manganese porphyrin and acridine could cleave target HBV-DNA in sequence-dependent manner.</p>