| Summary: | Ya-Lan Zhou,1 Qiu-Mei Yao,1 Jiao Zhou,1 Yan Chang,1 Jin-Lan Li,1 Ya-Zhe Wang,1 Hong-Ping Wu,2 Yu-Hong Chen,1 Yan-Rong Liu,1 Xiao-Jun Huang,1 Guo-Rui Ruan1 1Beijing Key Laboratory of Hematopoietic Stem Cell Transplantation, Peking University People’s Hospital and Institute of Hematology, Beijing, China; 2Laboratory of Viral and Gene Therapy, Eastern Hepatobiliary Surgical Hospital, Second Military Medical University, Shanghai, China Background: Daunorubicin is a traditional chemotherapeutic agent that plays a pivotal role in leukemia therapy. However, the dose-related toxicity remains a considerable challenge. The apoptosis-regulating gene, PDCD5, is downregulated in various tumors, including leukemias, and may provide a potential target for the diagnosis and treatment of leukemia. The purpose of this study was to construct a triple-regulated oncolytic adenovirus carrying a PDCD5 gene expression cassette (SG611-PDCD5) and explore the combined antitumor efficacy of SG611-PDCD5 in combination with low dose daunorubicin on leukemic cells. Materials and methods: A variety of leukemic cell lines, including K562, MEG-01, KG-1a, HL-60, SUP-B15, and BV-173, were cultured according to the providers’ instructions. The insertion and orientation of all recombined plasmids were confirmed by restriction enzyme digestion and PCR. The tumor-selective replication of the constructed conditionally replicating SG611-PDCD5 and its antitumor efficacy in combination with daunorubicin were characterized in leukemic cell lines in vitro and in a nude mouse xenograft model. Cell viability was detected using cell-counting kit-8. Apoptosis was detected in whole living cells using flow cytometry and in paraffin-embedded tumor tissues using a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Results: The triple-regulated CRAd carrying SG611-PDCD5 and nude mouse xenograft models of K562 cells were successfully constructed. In vitro treatment with SG611-PDCD5 in combination with low-dose daunorubicin elicited more potent anti-proliferative and proapoptotic effects in leukemic cells in a dose-dependent manner. The Chou-Talalay analysis revealed synergistic anti-proliferative effects in all of the above cell lines. In the nude mice xenograft model, the tumor size in the control, daunorubicin, SG611-PDCD5, and combined treatment groups on day 10 were 170.1±47.8, 111.9±81.1, 60.7±12.3, and 33.2±17.5 mm3, respectively (all P<0.05). The results of the TUNEL assay showed significantly more apoptotic cells in the SG611-PDCD5 plus daunorubicin group than in the SG611-PDCD5 or daunorubicin groups alone (25±0.82, 12.5±2.27, and 7.8±2.67 apoptotic cells/field, respectively) (P<0.05). Conclusion: The findings suggest that combined treatment with SG611-PDCD5 and daunorubicin may be a promising strategy for enhancing chemosensitivity and thus lowering the dose-related toxicity of daunorubicin in leukemia therapy. Keywords: PDCD5 gene, oncolytic adenovirus, leukemia, gene therapy
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