This soluble VEGFR1 could trap VEGF-A to prevent its binding to VEGFRs

guishable in culture. With respect to U-118 MG, 8-week intermittent induction of HIF1 failed to result in discernible morphological differences in culture but apparently helped tumor maintenance, as indicated by the preserved bioluminescent signals throughout a 7-week period of observation. In contrast, the signals from the -gal control were diminished progressively, resulting in a statistically significant drop in tumor volume. Tumor incidence of the HIF1 cells was 5/6, similar to that of the control. Furthermore, tumors from the HIF1 cells often had multiple lesions, in contrast to mostly single lesions in the -gal control group. Therefore, these results further corroborate the long-lasting effects of HIF-1 on malignant progression and the differential observations between cell culture and animal models. Transient induction of HIF-1 inhibits glioma growth To test whether transient induction of HIF1 would produce similar effects in vivo, we analyzed tumor growth of U-87 MG cells that had been treated with tetracycline in culture for only 2 days before intracranial transplantation. Fig 6A shows that transient induction of HIF1 retarded tumor growth significantly in the brain in reference to that of -gal. To extend this finding, we employed a patient-derived, mesenchymal glioma sphere culture, GSC20. These cells were allowed for constitutive expression of -gal, HIF1, or HIF2 after lentiviral infection and grown in sphere culture medium for adequate expansion prior to 8 / 15 Lasting Effect of HIF-1 on Malignant Progression Fig 5. Intermittent induction of HIF1 facilitated intracranial tumor growth of U-118 MG cells. Bioluminescent imaging analysis of intracranial tumors derived from 8-week treated cells as indicated. Tumor volumes, plotted PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19776696 in a log scale, from -gal cells decreased significantly during the course of 49 days, but those from HIF1 did not. , p-value < 0.01. Representative tumor lesions are shown in hematoxylin and eosin staining from 2 individual mice of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19777456 each group at 25 and 200 magnifications, with scale bars of 1 mm and 100 m, respectively. doi:10.1371/journal.pone.0125125.g005 intracranial injections. It is noteworthy that while the HIF1 population expanded slightly faster than the -gal control and more readily formed tumor spheres, the HIF2 multiplied at an extremely slow rate. Contrary to these in vitro findings, injection of the HIF1 cells led to the development of only small, primarily singular tumors in the mouse brain, whereas the other two cell types yielded much larger, multiple lesions and invasions. Tumor incidence was slightly decreased for HIF1 cells. Strikingly, tumors derived from the -gal and HIF2 cells manifested a multitude of mitoses and multinuclear giant cells, both of which were markedly diminished in HIF1-derived tumors. Furthermore, vascular proliferation and necrosis, common features of glioblastomas, were present in tumors derived from the -gal and HIF2 cells but not the HIF1 cells. Taken together, these results suggest that HIF-1 can also inhibit glioma growth and progression. Discussion We provide evidence in this study that intermittent induction of HIF1 in vitro produced lasting effects on malignant progression of purchase Y27632 dihydrochloride different cancer cell lines, unexpectedly independent of continued expression of the transgene. All these cells eventually lost HIF1 9 / 15 Lasting Effect of HIF-1 on Malignant Progression Fig 6. Transient expression of HIF1 inhibited intracranial tumor growth. U-87 MG cells were indu