Cellular effects of oncolytic viral therapy on the glioblastoma microenvironment.

The objective of the present study was to evaluate the cellular effects of the oncolytic HSV-1 based vector, G207, on the tumor microenvironment. We established progressively growing intracerebral xenografts in athymic nude rats generated from three different human GBM surgical specimens. The lesions were identified by MRI and subsequently injected with a concentrated vector stock. The animals were killed 10 or 30 days after G207 injection and the tumors were quantitatively evaluated for virus-induced changes in proliferation, apoptosis and vascularity. Moreover, we assessed vector spread as well as the infiltration pattern of CD68-positive inflammatory cells. In all G207-injected lesions, immunostaining identified widespread regions of viral infection and replication (plaques). Proliferation indices were significantly lower, whereas apoptotic counts were significantly elevated in plaques as compared with that in non-infected areas of the same lesions, as well as in corresponding control xenografts. Furthermore, there was a significant decline in the number of blood vessels in the plaques and the vascular area fractions were reduced. CD68-positive inflammatory cells accumulated in the plaques. The present study highlights the favorable cellular responses to G207 treatment seen from a clinical viewpoint, such as reduced tumor cell proliferation, more frequent events of tumor cell death and a strongly attenuated tumor vascular compartment. However, our results suggest that transduction of a significant volume of tumor tissue is essential, as these beneficial changes were only observed in areas of active viral replication, leaving non-transduced tumor tissues unaffected.

Intravital microscopy reveals novel antivascular and antitumor effects of endostatin delivered locally by alginate-encapsulated cells.

The current study describes new, antivascular, and antitumor effects of human endostatin. A novel system for continuous, localized delivery of antiangiogenic compounds to brain tumors was used. The delivery system was composed of endostatin-producing 293 cells encapsulated into immuno-isolating sodium alginate. Intravital multifluorescence microscopy was used to assess vascular and antitumor effects of endostatin in C6 glioma spheroids implanted into an ectopic as well as an orthotopic setting. Analysis of total and functional vascular density, microvascular diameters, vessel perfusion, tumor growth, and tumor cell migration were performed repetitively. Tumor growth was reduced by 35% in treated animals. It was of interest that tumor cell invasion into the surrounding tissue was also inhibited. The total vascular density was reduced by 67.6%, perfusion by 67%, and vessel diameters by 37%. This resulted in a significant reduction in tumor perfusion, although the vessel permeability was not influenced. We have demonstrated that human endostatin not only reduces total vascular density, as shown previously, but also greatly reduces the functionality and the diameters of the vessels. Furthermore, we show that this therapeutic approach also inhibits tumor cell invasion, thus supporting the hypothesis that tumor angiogenesis and invasion represent two interrelated processes. Finally, this work further confirms the new therapeutic concept using alginate cell-encapsulation technology for the localized delivery of therapeutic compounds to central nervous system malignancies.