Regression of Schwannomas Induced by Adeno-Associated Virus-Mediated Delivery of Caspase-1

Abstract

Schwannomas are tumors formed by proliferation of dedifferentiated Schwann cells. Patients with neurofibromatosis 2 (NF2) and schwannomatosis develop multiple schwannomas in peripheral and cranial nerves. Although benign, these tumors can cause extreme pain and compromise sensory/motor functions, including hearing and vision. At present, surgical resection is the main treatment modality, but it can be problematic because of tumor inaccessibility and risk of nerve damage. We have explored gene therapy for schwannomas, using a model in which immortalized human NF2 schwannoma cells expressing a fluorescent protein and luciferase are implanted in the sciatic nerve of nude mice. Direct injection of an adeno-associated virus (AAV) serotype 1 vector encoding caspase-1 (ICE) under the Schwann-cell specific promoter, P0, leads to regression of these tumors with essentially no vector-mediated neuropathology, and no changes in sensory or motor function. In a related NF2 xenograft model designed to cause measurable pain behavior, the same gene therapy leads to tumor regression and concordant resolution of tumor-associated pain. This AAV1-P0-ICE vector holds promise for clinical treatment of schwannomas by direct intratumoral injection to achieve reduction in tumor size and normalization of neuronal function.

Developing myelin specific promoters for schwannoma gene therapy

“…Our previously published data have shown that Schwannoma treatment is amenable to a gene therapy approach. That work demonstrated that intra-tumoral injection of an adeno-associated viral serotype 1 vector (AAV1) encoding the pro-apoptotic and pro-inflammatory enzyme caspase-1 under control of the rat Schwann-cell specific promoter, rP0, conferring cell-type specificity to NF2 cells resulted in significant reduction in tumor growth in a xenograft human schwannoma model in nude mice (Prabhakar et al 2013). In the present study, we compared three myelin specific promoters with an overriding goal of identifying the most efficient and selective promoter for use in a schwannoma gene therapy construct.…”

A novel alternative splicing isoform of NF2 identified in human Schwann cells

“…The schwannomas of the patient were resected and the tumor cells were immortalized using the human papilloma virus E6-E7 genes (18). NF2-deficient cells and animal models have contributed significantly to the understanding of the function of the merlin protein.…”

Delivery of Therapeutic Proteins via Extracellular Vesicles: Review and Potential Treatments for Parkinson’s Disease, Glioma, and Schwannoma

“…Direct intratumoral injection of an adeno-associated virus (AAV) vector was used to induce regression of a human NF2 xenograft schwannoma in a mouse sciatic nerve model (Prabhakar et al 2013). The AAV vector encoded caspase-1 (ICE), which can trigger cell death (Croker et al 2015), under the control of a P0 promoter, which is active in myelinating Schwann cells (Shen et al 2011).…”

“…Considering that only a fraction (i.e. about 20%) of schwannoma cells were transduced by the vector injection, it was surprising to achieve almost complete regression of the tumors (Prabhakar et al 2013). One explanation for this may be found in studies showing that ICE is incorporated into EVs, or travel by nanotubes, which can then be taken up by and kill surrounding cells (Sakar et al 2009).…”

“…To test this hypothesis, the DNA expression construct encoding P0-ICE (Prabhakar et al 2013) was transfected into human NF2 schwannoma cells (HEI-193; Hung et al 2002) or human embryonic kidney 293T fibroblastic cells as a negative control. Twelve hrs after transfection, cells were rinsed to remove free plasmid DNA and the media was replaced with DMEM (5% EV depleted FBS, 1% P/S) (Corning Life Sciences, Tewksbury, MA).…”