Klaus Edvardsen

Neural Progenitor Cell Lines Inhibit Rat Tumor Growth in Vivo

Current therapies for gliomas often fail to address their infiltrative nature. Conventional treatments leave behind small clusters of neoplastic cells, resulting in eventual tumor recurrence. In the present study, we have evaluated the antitumor activity of neural progenitor cells against gliomas when stereotactically injected into nucleus Caudatus of Fisher rats. We show that the rat neural progenitor cell lines HiB5 and ST14A, from embryonic hippocampus and striatum primordium, respectively, are able to prolong animal survival and, in 25% of the cases, completely inhibit the outgrowth of N29 glioma compared with control animals. Delayed tumor outgrowth was also seen when HiB5 cells were inoculated at the site of tumor growth 1 week after tumor inoculation or when a mixture of tumor cells and HiB5 cells were injected s.c. into Fisher rats. HiB5 cells were additionally coinoculated together with two alternative rat gliomas, N32 and N25. N32 was growth inhibited, but rats inoculated with N25 cells did not show a prolonged survival. To evaluate the possibility of the involvement of the immune system in the tumor outgrowth inhibition, we show that HiB5 cells do not evoke an immune response when injected into Fisher rats. Furthermore, the rat neural progenitor cells produce all transforming growth factor β isotypes, which could explain the observed immunosuppressive nature of these cells. Hence, some neural progenitor cells have the ability to inhibit tumor outgrowth when implanted into rats. These results indicate the usefulness of neural stem cells as therapeutically effective cells for the treatment of intracranial tumors.

Combretastatin family member OXI4503 induces tumor vascular collapse through the induction of endothelial apoptosis

The mechanism of tumor cell killing by OXI4503 was investigated by studying vascular functional and morphological changes post drug administration. SCID mice bearing MHEC5‐T hemangioendothelioma were given a single dose of OXI4503 at 100 mg/kg. Tumor blood flow, measured by microsphere fluorescence, was reduced by 50% at 1 hr, and reached a maximum level 6–24 hr post drug treatment. Tumor vascular permeability, measured by Evans blue and hemoglobin, increased significantly from 3 hr and peaked at 18 hr. The elevated tumor vessel permeability was accompanied by an increase in vascular endothelial growth factor (VEGF) from 1 hr post drug treatment. Immunohistochemical staining for CD31 and laminin showed that tumor blood vessels were affected as early as 3 hr but more prominent from 6 hr. From 12 hr, the vessel structure was completely destroyed. Histopathological and double immunohistochemical staining showed morphological change and induction of apoptosis in endothelial cells at 1–3 hr, followed by tumor cell necrosis from 6–72 hr. There were no statistically significant changes of Evans blue and hemoglobin contents in liver tissue over the time course. These results suggest that OXI4503 selectively targets tumor blood vessels, and induces blood flow shutdown while it enhances tumor blood vessel permeability. The early induction of endothelial cell apoptosis leads to functional changes of tumor blood vessels and finally to the collapse of tumor vasculature, resulting in massive tumor cell necrosis. The time course of the tumor vascular response observed with OXI4503 treatment supports this drug for development as a stand alone therapy, and also lends support for the use of the drug in combination with other cancer therapies.

Synthesis, in vitro, and in vivo evaluation of phosphate ester derivatives of combretastatin A-4

Combretastatin A-4 disodiumphosphate (CA4P), a prodrug formulation of the natural product combretastatin A-4 (CA4), is currently in clinical investigation for the treatment of cancer. In vivo, CA4P is rapidly enzymatically converted to CA4, a potent inhibitor of tubulin polymerization (IC(50)=1-2 microM), and rapidly causes bloodflow shutdown in tumor tissues. A variety of alkyl and aryl di- and triesters of CA4P have been synthesized and evaluated as potential CA4 prodrugs and/or stable CA4P analogues.