Tumor Cell Tumorigenesis Research Articles

Effect of HIF-1α on aggressive malignant traits of tumor cells

Objective To explore the action mechanism of hypoxia inducible factor-1α (HIF-1α)on human osteosarcoma cells. Methods After hypoxic treatment to human osteosarcoma cell line, additional mutations were made by site-directed mutagenesis to create HIF-1α (PP) mutants. CD-1 nude mice were used for bilateral subcutaneous injections to evaluate the tumor cell tumorigenesis. Cells were seeded for 2 weeks, the total number of colonies per well was calculated and the anchorage-independent growth was analyzed. Cell proliferation was assayed by cell viability assay, and cell invasion was determined by the total number of invading cells and presented as mean ± SEM. Results The functions of the HIF-1α-ARNT pathway and the HIF-1α-c-Myc pathway were inactivated respectively by site-directed mutagenesis in the context of a stabilized HIF-1α. In accordance with diminished tumor-suppressing activities, both HIF-1α(PP) and HIF-1α (PP) + RFC cells exhibited a remarkable gain of anchorage-independent growth, and the total number of colonies per well was 1480 ± 8 and 1750 ± 6 respectively. Tumorigenicity of HIF-1α(PP) and HIF-1 α (PP) + RFC was all 100%, but US201 and HIF-1 α (PP) + VAT had no tumorigenicity. They also showed a marked increase in cell proliferation and Matrigel invasion, the cell viability of HIF1 α (PP) and HIF-1 α (PP) + VAT was 11 000 ± 3 and 10 900 ± 5, but the cell viability of HIF-1 α (PP)+ RFC and HIF-1α (PP) + RFC + VAT was only 2210 ± 6 and 1880 ± 8 respectively. Whereas inactivation of the HIF-1α-c-Myc pathway abrogated such increase, and the tumorigenicity was decreased to 20%.Gain of aggressive malignant traits required the HIF-1α-c-Myc pathway. Conclusion HIF-α-c-Myc pathway plays an essential role in mediating hypoxic effects on malignant progression via genetic alterations,resulting in formation of malignant tumors with aggressive local invasion and epithelial-mesenchymal transition. Key words: Hypoxia; Tumor progression; Epithelial-mesenchymal transition

Radiosensitization of mammary carcinoma cells by telomere homolog oligonucleotide pretreatment

IntroductionIonizing radiation (IR) is a widely used approach to cancer therapy, ranking second only to surgery in rate of utilization. Responses of cancer patients to radiotherapy depend in part on the intrinsic radiosensitivity of the tumor cells. Thus, promoting tumor cell sensitivity to IR could significantly enhance the treatment outcome and quality of life for patients.MethodsMammary tumor cells were treated by a 16-base phosphodiester-linked oligonucleotide homologous to the telomere G-rich sequence TTAGGG (T-oligo: GGTTAGGTGTAGGTTT) or a control-oligo (the partial complement, TAACCCTAACCCTAAC) followed by IR. The inhibition of tumor cell growth in vitro was assessed by cell counting and clonogenic cell survival assay. The tumorigenesis of tumor cells after various treatments was measured by tumor growth in mice. The mechanism underlying the radiosensitization by T-oligo was explored by immunofluorescent determination of phosphorylated histone H2AX (γH2AX) foci, β-galactosidase staining, comet and Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assays. The efficacy of the combined treatment was assessed in a spontaneous murine mammary tumor model.ResultsPretreatment of tumor cells with T-oligo for 24 hours in vitro enhanced both senescence and apoptosis of irradiated tumor cells and reduced clonogenic potential. Radiosensitization by T-oligo was associated with increased formation and/or delayed resolution of γH2AX DNA damage foci and fragmented DNA. T-oligo also caused radiosensitization in two in vivo mammary tumor models. Indeed, combined T-oligo and IR-treatment in vivo led to a substantial reduction in tumor growth. Of further significance, treatment with T-oligo and IR led to synergistic inhibition of the growth of spontaneous mammary carcinomas. Despite these profound antitumor properties, T-oligo and IR caused no detectable side effects under our experimental conditions.ConclusionsPretreatment with T-oligo sensitizes mammary tumor cells to radiation in both in vitro and in vivo settings with minimal or no normal tissue side effects.