Shanta M. Messerli

In vivo tracking of neural progenitor cell migration to glioblastomas

The ability to noninvasively track the migration, engraftment, and proliferation of neural progenitor cells (NPCs) has significant clinical and research implications. The purpose of our study was to explore the macroscopic migratory capabilities of NPCs toward brain tumors after implantation into nude mice. We stably transfected C17.2 NPCs with the firefly luciferase gene (F-luc) and implanted cells into (1) the contralateral brain parenchyma (2 x 10(6) cells), (2) the ventricles (2 x 10(6) cells), (3) the vasculature (1 x 10(5) cells), or (4) the intraperitoneal cavity (5 x 10(6) cells) of mice bearing intracranial gliomas (Gli36). Using serial bioluminescence imaging, migration of parenchymally injected cells was observed across the corpus callosum, first detected at 1 week, with maximal density at the tumor site 2-3 weeks after implantation. Similar patterns were also observed with intraventricular injections; however, tumors were populated earlier, presumably because of the shorter distance to travel. Intravenous injections resulted in more modest tumoral NPC populations, whereas virtually no cells could be identified in tumors after intraperitoneal injection. These results confirm the migratory capability of NPCs over considerable distances and their preferential accumulation in brain tumors on CNS rather than peripheral injection.

Comparative Pathology of Nerve Sheath Tumors in Mouse Models and Humans

Despite the progress made in our understanding of the biology of neurofibromatosis (NF), the long-term clinical outcome for affected patients has not changed significantly in the past decades, and both NF1 and NF2 are still associated with a significant morbidity and a decreased life span. A number of NF1 and NF2 murine models have been generated to aid in the study of NF tumor biology and in the development of targeted therapies for NF patients. A single, universal pathological classification of the lesions generated in these murine models is essential for the validation of the models, for their analysis and comparison with other models, and for their future effective use in preclinical treatment trials. For the formulation of a pathological classification of these lesions, the WHO classification of human tumors was used as a reference. However, it was not adopted for the classification of the GEM lesions because of some important differences between the human and murine lesions. A novel classification scheme for peripheral nerve sheath tumors in murine models was therefore devised.

Treatment of Implantable NF2 Schwannoma Tumor Models with Oncolytic Herpes Simplex Virus G47Δ

Schwannomas are benign tumors composed of dedifferentiated Schwann cells that form along peripheral nerves causing nerve compression often associated with pain and loss of function. Current surgical therapy involves total or subtotal surgical removal of the tumor, which may cause permanent nerve damage. In the present study, we explore an alternate means of therapy in which schwannomas are injected with a replication-conditional herpes simplex virus (HSV) vector to shrink the tumor through cell lysis during virus propagation. The oncolytic vector used, G47Δ, has deletions in HSV genes, which allow it to replicate selectively in dividing cells, sparing neurons. Two schwannoma cell lines were used to generate subcutaneous tumors in nude mice: HEI193, an immortalized human line previously established from an NF2 patient and NF2S-1, a newly generated spontaneous mouse line. Subcutaneous HEI193 tumors grew about ten times as fast as NF2S-1 tumors, and both regressed substantially following injection of G47Δ. Complete regression of HEI193 tumors was achieved in most animals, whereas all NF2S-1 tumors resumed growth within 2 weeks after vector injection. These studies provide a new schwannoma model for testing therapeutic strategies and demonstrate that oncolytic HSV vectors can be successfully used to shrink growing schwannomas.

Imaging and therapy of experimental schwannomas using HSV amplicon vector-encoding apoptotic protein under Schwann cell promoter.

Schwannomas are benign tumors forming along peripheral nerves that can cause deafness, pain and paralysis. Current treatment involves surgical resection, which can damage associated nerves. To achieve tumor regression without damage to nerve fibers, we generated an HSV amplicon vector in which the apoptosis-inducing enzyme, caspase-1 (ICE), was placed under the Schwann cell-specific P0 promoter. Infection of schwannoma, neuroblastoma and fibroblastic cells in culture with ICE under the P0 promoter showed selective toxicity to schwannoma cells, while ICE under a constitutive promoter was toxic to all cell types. After direct intratumoral injection of the P0-ICE amplicon vector, we achieved marked regression of schwannoma tumors in an experimental xenograft mouse model. Injection of this amplicon vector into the sciatic nerve produced no apparent injury to the associated dorsal root ganglia neurons or myelinated nerve fibers. The P0-ICE amplicon vector provides a potential means of ‘knifeless resection’ of schwannoma tumors by injection of the vector into the tumor with low risk of damage to associated nerve fibers.