ECM stiffness regulates glial migration in Drosophila and mammalian glioma models.

Cell migration is an important feature of glial cells. Here, we used the Drosophila eye disc to decipher the molecular network controlling glial migration. We stimulated glial motility by pan-glial PDGF receptor (PVR) activation and identified several genes acting downstream of PVR. Drosophila lox is a non-essential gene encoding a secreted protein that stiffens the extracellular matrix (ECM). Glial-specific knockdown of Integrin results in ECM softening. Moreover, we show that lox expression is regulated by Integrin signaling and vice versa, suggesting that a positive-feedback loop ensures a rigid ECM in the vicinity of migrating cells. The general implication of this model was tested in a mammalian glioma model, where a Lox-specific inhibitor unraveled a clear impact of ECM rigidity in glioma cell migration.

Wound healing complications in brain tumor patients on Bevacizumab.

Bevacizumab (BEV) is commonly used for treating recurrent glioblastoma (GBM), and wound healing is a well-established adverse event. Retrospective analysis of GBM patients with and without wound healing complications while on BEV treatment is reported. 287 patients identified, majority were males (60 %) with median age of 52.5 years. 14 cases identified with wound healing problems, related to either craniotomy (n = 8) or other soft tissue wounds (n = 6). Median duration of BEV treatment to complication was 62 days (range 6-559). Majority received 10 mg/kg (n = 11) and nine (64.3 %) were on corticosteroids, with median daily dose of 6 mg (range 1-16 mg) for median of 473 days before starting BEV. For dehisced craniotomy wounds, median time for starting BEV from last surgery was 29 days (range 27-345). Median time from starting BEV to developing wound complication was 47 days (range 16-173). Seven (87.5 %) had infected wounds requiring antibiotics, hospitalization. Four (50 %) required plastic surgery. BEV stopped and safely resumed in 6 (75 %) patients; median delay was 70 days (range 34-346). Soft tissue wounds included decubitus ulcer, dehisced striae, herpes simplex, trauma to hand and back, and abscess. Median time from starting BEV to wound issues was 72 days (range 6-559). Five (83.3 %) were infected, requiring antibiotics. While three (50 %) required hospitalization, none required plastic surgery. Treatment stopped in five (83.3 %) and restarted in two (median delay 48 days, range 26-69). Wound healing complications are uncommon but associated with significant morbidity. Identifying those at risk and contributing factors warrants further investigation.

Modeling glioma growth and invasion in Drosophila melanogaster.

Glioblastoma is the most common and most malignant intrinsic human brain tumor, characterized by extensive invasion and proliferation of glial (astrocytic) tumor cells, frequent activation of tyrosine kinase receptor signaling pathways, relative resistance to chemotherapy and radiotherapy, and poor prognosis. Using the Gal4-UAS system, we have produced glioma models in Drosophila by overexpressing homologs of human tyrosine kinase receptors under control of the glia-specific promoter reversed polarity (repo). Glial overexpression of activated epidermal growth factor receptor (EGFR) resulted in enhanced proliferation and migration of larval glial cells with increased numbers in the eye imaginal disc, diffuse tumor-like enlargement of the optic stalk, and marked ectopic invasion of glial cells along the optic nerve. Glial overexpression of the downstream kinase PI3K showed similar pathology. Overexpression of activated pvr (platelet-derived growth factor receptor/vascular endothelial growth factor receptor homolog) led to migration of glial cells along the optic nerve, whereas expression of activated htl (fibroblast growth factor receptor 1 homolog) and INR (insulin receptor) showed markedly elevated numbers of glial cells in the optic stalk. The EGFR/phosphatidylinositol 3-phosphate kinase (PI3K) phenotype was partly reverted by the administration of the EGFR tyrosine kinase inhibitor gefitinib and completely rescued by the PI3K inhibitor wortmannin and the Akt inhibitor triciribine. We suggest that Drosophila models will be useful for deciphering signaling cascades underlying abnormal behavior of glioma cells for genetic screens to reveal interacting genes involved in gliomagenesis and for experimental therapy approaches.