Effects of Dual Targeting of Tumor Cells and Stroma in Human Glioblastoma Xenografts with a Tyrosine Kinase Inhibitor against c-MET and VEGFR2

Contains fulltext : 118357.pdf (publisher's version ) (Open Access)Anti-angiogenic treatment of glioblastoma with Vascular Endothelial Growth Factor (VEGF)- or VEGF Receptor 2 (VEGFR2) inhibitors normalizes tumor vessels, resulting in a profound radiologic response and improved quality of life. This approach however does not halt tumor progression by diffuse infiltration, as this phenotype is less angiogenesis dependent. Combined inhibition of angiogenesis and diffuse infiltrative growth would therefore be a more effective treatment approach in these tumors. The HGF/c-MET axis is important in both angiogenesis and cell migration in several tumor types including glioma. We therefore analyzed the effects of the c-MET- and VEGFR2 tyrosine kinase inhibitor cabozantinib (XL184, Exelixis) on c-MET positive orthotopic E98 glioblastoma xenografts, which routinely present with angiogenesis-dependent areas of tumor growth, as well as diffuse infiltrative growth. In cultures of E98 cells, cabozantinib effectively inhibited c-MET phosphorylation, concomitant with inhibitory effects on AKT and ERK1/2 phosphorylation, and cell proliferation and migration. VEGFR2 activation in endothelial cells was also effectively inhibited . Treatment of BALB/c nu/nu mice carrying orthotopic E98 xenografts resulted in a significant increase in overall survival. Cabozantinib effectively inhibited angiogenesis, resulting in increased hypoxia in angiogenesis-dependent tumor areas, and induced vessel normalization. Yet, tumors ultimately escaped cabozantinib therapy by diffuse infiltrative outgrowth via vessel co-option. Of importance, in contrast to the results from experiments, blockade of c-MET activation was incomplete, possibly due to multiple factors including restoration of the blood-brain barrier resulting from cabozantinib-induced VEGFR2 inhibition. In conclusion, cabozantinib is a promising therapy for c-MET positive glioma, but improving delivery of the drug to the tumor and/or the surrounding tissue may be needed for full activity

Modifiers of mutant huntingtin aggregation: functional conservation of C. elegans-modifiers of polyglutamine aggregation

Protein aggregation is a common hallmark of a number of age-related neurodegenerative diseases, including Alzheimer’s, Parkinson’s, and polyglutamine-expansion disorders such as Huntington’s disease, but how aggregation-prone proteins lead to pathology is not known. Using a genome-wide RNAi screen in a C. elegans-model for polyglutamine aggregation, we previously identified 186 genes that suppress aggregation. Using an RNAi screen for human orthologs of these genes, we here present 26 human genes that suppress aggregation of mutant huntingtin in a human cell line. Among these are genes that have not been previously linked to mutant huntingtin aggregation. They include those encoding eukaryotic translation initiation, elongation and translation factors, and genes that have been previously associated with other neurodegenerative diseases, like the ATP-ase family gene 3-like 2 (AFG3L2) and ubiquitin-like modifier activating enzyme 1 (UBA1). Unravelling the role of these genes will broaden our understanding of the pathogenesis of Huntington’s disease

c-MET is activated in E98 xenografts.

<p>Panel A shows a Western blot containing protein extracts of different xenografts as indicated (40 µg/lane) and stained with a pan and an Y1234/1235 phosphorylated (P-) c-MET specific antibody. As a loading control, γ-tubulin was included. Immunohistochemical analysis reveals prominent c-MET expression and activation in orthotopic E98 xenografts (C–F). Gross appearances of an E98 tumor are shown in C and E, while D and F show magnifications of the boxed areas in C and E. The H&E section in B illustrates the diffuse nature of these tumors, arrows pointing at white matter tracts and comparison with D shows homogeneous expression of c-MET by tumor cells. Arrow in E points at diffuse infiltrative tumor cells in white matter with activated c-MET, while the arrowhead points at a more compact paraventricular tumor area. The inset in E represents an area with compact leptomeningeal growth partly positive for activated c-MET. The pictures shown are representative for this xenograft model. Size bars: B, D, F 200 µm; C 1 mm and E 500 µm.</p

<i>In vivo</i> effects of cabozantinib treatment in E98 xenografts.

<p>Panels A and B show representative examples of IHC for the hypoxia marker MCT4 in control and cabozantinib-treated tumor bearing animals. Hypoxia in compact tumor regions is significantly increased after treatment (Students <i>t</i>-test, p = 0.003, panel C). D and E show examples of Ki67 stainings in compact tumor areas. Proliferation indices were significantly different in these regions (Students <i>t-</i>test p = 0.04), but no difference was detected in diffuse tumor areas (panel F). Panels G and H show representative examples of GLUT-1 vessel staining. Automated quantification revealed no differences between vessel densities of diffuse tumor areas in control vs treated mice (I). Numbers of CD34-positive vessels were lower in cabozantinib treated mice (see panels J and K, arrows point at blood vessels), but these data were not quantified because vessels without CD34 expression were also observed in these mice. L: Western blot analysis of protein extracts (50 µg protein/lane), derived from cabozantinib-treated xenografts reveals a substantial, though not complete, reduction of c-MET phosphorylation. As a loading control, γ-tubulin was included. Immunohistochemistry for phospho-c-MET (Y1234/1235) also shows the presence of phosphorylated c-MET in treated animals, as visualized in panel K. Size bars: A–B 2 mm, D–E 100 µm, G, H, J, K 200 µm,</p

Cabozantinib prolongs survival of mice bearing orthotopic E98- xenografts.

<p>Mice were treated with 100 mg/kg cabozantinib from day 12 post tumor inoculation, when tumor was detected via abnormalities in T2 images (see panel A for a representative example). B) Survival curves for placebo (n = 10) and cabozantinib (n = 10) treated animals. Note that, for ethical reasons, mice were sacrificed when excessive weight loss and signs of neurological dysfunction occurred. Median survival was significantly different between the groups (20 and 32 days respectively, log rank test, <i>p</i><0.0001). C) Representative examples of T1-weighted MRI of control (upper row) and treated (lower row) E98 bearing animals before (pre) and 2–3 minutes after (post) Gd-DTPA injection. [Post-pre]/pre represents subtracted images. Note the complete loss of contrast enhancement in treated animals. Panel D shows H&E staining of sections, corresponding to the slices shown in the MR images. Bars: overviews 2 mm, zoom 200 µm.</p

Additional file 4: of Comprehensive protein tyrosine phosphatase mRNA profiling identifies new regulators in the progression of glioma

Immunohistochemical staining for PTPRT on formalin-fixed paraffin-embedded materials. (PDF 303 kb

<i>In vitro</i> effects of Cabozantinib on c-MET and VEGFR2 signaling.

<p>Panel A shows a Western blot of E98NT cell extracts (20 µg per lane) treated for 30 minutes with different concentrations of cabozantinib as indicated. Protein extracts were analyzed for c-MET, phospho-c-MET, AKT, and ERK1/2, using α-tubulin as a loading control. B) MTT assays were done to determine the IC₅₀ concentration of cabozantinib on E98NT cells. Experiments were performed at least in triplicate. C) Effects of cabozantinib on cell migration. Shown are representative examples of DAPI-stained spheroids after 24 hr incubation with indicated concentrations. Number of outgrowing and migrating cells per spheroid are shown in panel D (***: p<0.001). Number of migrating cells were significantly different between groups (one-way ANOVA, p<0.0001). Post-hoc Tukey's Multiple Comparison Test revealed significant differences groups as indicated (***: p<0.001). E) Western blot of cell lysates of E98NT and HUVEC extracts, treated with 10 ng/ml VEGF with or without cabozantinib, and stained for VEGFR2, phospho-VEGFR2 and α-tubulin as an internal control. Note the absence of VEGFR2 in E98NT cells. F) Western blot of treated E98NT cell extracts with the anti-apoptotic antibody U1-70. Control sample consists of Jurkat cells treated with anisomycin.</p