Modification of the hTERT promoter by heat shock elements enhances the efficiency and specificity of cancer targeted gene therapy

Cell membrane breakage and triggering T cell infiltration are involved in human telomerase reverse transcriptase (hTERT) promoter-driven novel peptide KK-64 for liver cancer gene therapy

Liver cancer is an aggressive malignancy with exhibits both high mortality and morbidity. The current treatment options are associated with several limitations, novel specific anti-cancer drugs are urgently needed to improve liver cancer treatment. In this study, a new peptide KK-64 was designed, and it showed strong cytotoxicity against liver cancer cells. To obtain the tumor targeting property, a plasmid that contains KK-64 DNA fragment and driven by human telomerase reverse transcriptase (hTERT) promoter was constructed. pcTERT-kk-64 plasmid was found to specifically inhibit the viability of liver cancer cells HepG2, induce substantial apoptosis as well as damage to the cell membranes, but had minimal effects toward normal liver HL-7702 cells. Furthermore, pcTERT-kk-64 plasmids was also noted to significantly attenuate migration and invasion of HepG2 cells. The anti-tumor effect of pcTERT-kk-64 plasmid was also observed in H22 cell-bearing mice, and it appeared to cause significant tumor regression, trigger tumor cell apoptosis, and infiltrate cytotoxicity T cells to the tumor tissues after plasmids injection. Thus, pcTERT-kk-64 plasmids showed both strong cytotoxicity and tumor selectivity in vitro and in tumor-bearing mice in liver cancer models.

Antitumor effects of a dual-specific lentiviral vector carrying the Escherichia coli purine nucleoside phosphorylase gene

The Escherichia coli purine nucleoside phosphorylase/Fludarabine phosphate (ePNP/Fludara) suicide system has several drawbacks, such as side-effects and the low efficiency of ePNP expression. In this study, we evaluated the antitumor effects of the dual-specific 8HSEs-hTERTp-ePNP/Fludara suicide system under hyperthermia in vitro and in vivo. Luciferase activities from the 8HSEs‑hTERT and CMV promoters were compared using the dual luciferase assay in SW480 (high hTERT expression) and MKN74 cells (hTERT-negative) in the presence and absence of hyperthermia. Then, we investigated the effects of overexpressing the suicide gene ePNP using 8HSEs‑hTERT-driven lentiviral vectors with Fludara on in vitro cell viability, side-effects, apoptosis, cycle distribution, colony formation and in vivo xenograft tumor growth. At 43˚C, luciferase activity from the 8HSEs‑hTERT promoter was significantly increased in SW480 cells, but not in MKN74 cells. Importantly, luciferase activities from the 8HSEs‑hTERT promoter were much higher than from the CMV promoter in hTERT-expressing SW480 cells under heated conditions. The in vitro quantitative analysis showed a 4-fold higher ePNP protein expression from the 8HSEs‑hTERT promoter at 43˚C than at 37˚C in SW480 cells and the ePNP mRNA expression in SW480 cells at 43˚C was also higher than at 37˚C. Conversely, ePNP mRNA and protein expression were low, almost absent, in hTERT-negative MKN74 cells with or without hyperthermia. After Fludara addition, cell cytotoxicity assays showed that the significant inhibitory effect of the 8HSEs‑hTERTp-ePNP on SW480 cells was dose- and time-dependent with hyperthermia. The 8HSEs‑hTERTp-ePNP/Fludara suicide system significantly inhibited SW480 cell viability, colony formation, cell cycle progression and induced apoptosis in vitro, but also induced significant bystander effects, especially under the heated conditions. At the protein level, the suicide system significantly promoted Bax, caspase-3 and p53 expression and suppressed Bcl-2 expression. In sections from mouse xenografts, TUNEL assays showed that the suicide system reduced xenograft growth and induced SW480 apoptosis. These results indicated that the combinatorial cancer- and heat-specific promoter system has great potential for improving the efficacy of cancer treatment with hyperthermia. The 8HSEs‑hTERTp-ePNP/Fludara system may serve as a powerful strategy for cancer gene therapy combined with hyperthermia.

Co-delivery of doxorubicin and recombinant plasmid pHSP70-Plk1-shRNA by bacterial magnetosomes for osteosarcoma therapy

To explore a novel combination of chemotherapy, gene therapy, and thermotherapy for osteosarcoma, a targeted heat-sensitive co-delivery system based on bacterial magnetosomes (BMs) was developed. The optimal culture conditions of magnetotactic bacteria (MTB) AMB-1 and characterization of BMs were achieved. A recombinant eukaryotic plasmid heat shock protein 70-polo-like kinase 1-short hairpin RNA (pHSP70-Plk1-shRNA) under transcriptional control of a thermosensitive promoter (human HSP70 promoter) was constructed for gene therapy. Doxorubicin (DOX) and pHSP70-Plk1-shRNA were included in the targeted thermosensitive co-delivery system, and in vitro DOX release activity, targeted gene silencing efficiency and in vitro antitumor efficacy were investigated. The results showed that the optimal culture conditions of MTB AMB-1 are an oxygen concentration of 4.0%, a pH value of 7.0, 20 μmol/L of ferrous sulfate, 800 mg/L of sodium nitrate, and 200 mg/L of succinic acid. The temperature of BMs reached 43°C within 3 minutes and could be maintained for 30 minutes by adjusting the magnitude of the alternating magnetic field (AMF). The diameters of BMs, BM-DOX, BM-recombinant eukaryotic plasmid pHSP70-Plk1-shRNA (shPlk1), and BM-DOX-shPlk1 were 43.7±4.6, 79.2±5.4, 88.9±7.8, and 133.5±11.4 nm, respectively. The zeta potentials of BMs, BM-DOX, BM-shPlk1, and BM-DOX-shPlk1 were -29.4±6.9, -9.5±5.6, -16.7±4.8, and -10.3±3.1 mV, respectively. Besides, the system exhibited good release behavior. DOX release rate from BM-DOX-shPlk1 was 54% after incubation with phosphate-buffered saline at 43°C and 37% after incubation with 50% fetal bovine serum, which was significantly higher than that at 37°C (P<0.05). In addition, the expressions of Plk1 mRNA and protein were significantly suppressed in cells treated with BM-DOX-shPlk1 following hyperthermia treatment under the influence of an AMF compared to other groups (P<0.05). Furthermore, evaluation of the effect of in vitro antitumor revealed that BM-DOX-shPlk1 following hyperthermia treatment under the influence of an AMF was significantly more effective than others in tumor inhibition. In conclusion, the new heat-sensitive co-delivery system represents a promising approach for the treatment of cancer.