Enhanced visible light photoelectrocatalytic degradation of tetracycline hydrochloride by I and P co-doped TiO2 photoelectrode.

Elimination of antibiotics such as tetracycline hydrochloride (TC) from wastewater is of great significance, but still faces challenges. Herein, for the first time, I and P co-doped TiO2 catalysts were prepared via a hydrolysis method. We also reported a simple method to prepare I and P co-doped TiO2 photoelectrodes, which exhibited preeminent photoelectrocatalytic (PEC) performance for the decomposition of TC. The synergistic effect of I and P co-doping could significantly improve the charge separation rate and enhance the light absorption capacity of TiO2, leading to an enhancement of PEC activity. The main factors affecting the PEC performance were investigated, and the highest degradation rate constant (4.20 × 10-2 min-1) was achieved when the doping content of P was 4 at% (ITP-4 photoelectrode) at pH 11.02 under visible light. The Langmuir-Hinshelwood kinetic model and active species trapping experiments were selected to investigate the degradation mechanism of TC. The results suggest that the hydroxyl radicals and photogenerated holes were the main active species that were responsible for the decomposition of TC. Moreover, the degradation pathways of TC based on the intermediates also demonstrated that the hydroxyl radicals and holes showed a principal role in degrading TC.

HSVtk/GCV system on hepatoma carcinoma cells: Construction of the plasmid pcDNA3.1­pAFP-TK and targeted killing effect.

Previous studies demonstrated that herpes simplex virus thymidine kinase (HSVtk) could phosphorylate non­toxic gancyclovir (GCV) efficiently to produce phosphorylated products that result in cell apoptosis, to kill tumor cells. The present study aimed to construct a plasmid vector, pcDNA3.1­pAFP­TK, carrying the suicide gene driven by the alpha­fetoprotein (AFP) promoter, to investigate the cytotoxicity of HSVtk/GCV suicide gene system on hepatoma carcinoma cells. Reverse transcription­polymerase chain reaction and western blotting results demonstrated that the HSVtk gene was effectively expressed in HepG2 hepatoma carcinoma cells transfected with pcDNA3.1­pAFP­TK plasmid, whereas HSVtk gene expression was not detected in normal HL­7702 liver cells. In addition, MTT assays indicated that cell viability of HepG2 cells with the plasmid pcDNA3.1­pAFP­TK decreased in a dose­dependent manner following treatment with GCV for 48 h. Flow cytometry also revealed that the cell apoptosis rate and mitochondrial membrane potential reduction rate in the HepG2 cells treated with HSVtk/GCV suicide gene system were significantly higher than in the control group. Apoptosis rates in the control group and the pcDNA3.1­pAFP­TK group were (1.00±0.62%) and (38.70±6.03%), respectively. Mitochondrial membrane potential reduction rates in the control group and the pcDNA3.1-pAFP-TK group were (0.57±0.11%) and (22.84±5.79%), respectively. Caspase­3 staining demonstrated that activated caspase­3 increased significantly in the HepG2 cells treated with HSVtk/GCV suicide gene system, whereas in the control group activated caspase­3 increase was not observed. The results of the present study, therefore, indicated that HSVtk suicide gene was obviously expressed in the HepG2 cells and that the HSVtk/GCV system was effective at killing HepG2 hepatoma carcinoma cells.

Construction of plasmid vector pAFP-HSVtk-IRES2-EGFP and its effect on the cytotoxicity of ganciclovir to hepatocellular carcinoma.

BACKGROUND: Herpes simplex virus thymidine kinase phosphorylates ganciclovir to ganciclovir monophosphate, which is then converted to ganciclovir triphosphate by endogenous cellular nucleoside kinases. The ganciclovir triphosphate acts as a DNA chain terminator due to the lack of a functional 3'-OH group and terminates the process of DNA replication, hence leading to cell apoptosis. At present, HSVtk gene usually acts as suicide gene to kill tumor cells. The aim of this study was to investigate the selective cytotoxicity of the herpes simplex virus thymidine kinase/ganciclovir (HSVtK/GCV) suicide gene system controlled by the a-fetoprotein (AFP) promoter on hepatocellular carcinoma (HCC) cells in vitro. METHODS: pAFP-HSVtk-IRES2-EGFP recombinant plasmid vectors driven by the AFP promoter were constructed. HL-7702 liver cells, HUH-7 HCC, and HepG2 HCC were transfected with the recombinant plasmids. HSVtK gene expression was detected using Western blotting analysis. HepG2 cells line stably expressing HSVtk gene was selected by G418 reagent. The cytotoxicity of HSVtK/GCV suicide gene system on hepatoma cells was measured by CCK-8 reagents when different doses of ganciclovir were added. RESULTS: Plasmid pAFP-TK-IRES2-EGFP-expressed HSVtk gene was constructed successfully. HSVtk gene expression level was significantly higher in AFP-positive hepatoma cells than in AFP-negative liver cells. After G418 selection, a HepG2 cells line stably expressing HSVtk gene was acquired. With the increase of the dose of ganciclovir the optical density at 450 nm of HepG2 cells stably expressing HSVtk gene gradually decreased (P < 0.05). CONCLUSION: The HSVtK gene-specific expression in hepatoma cells as well as the cytotoxicity of the suicide gene system in HepG2 cells provided the basis for the targeted gene therapy of HCC.