While schwannoma tumors are typically benign (non-malignant) they can have devastating consequences for patients. As for an individual patient there is often no efficacious treatment. Thus, schwannoma therapy represents a major unmet clinical need. We have developed a new therapeutic approach to these nerve-associated tumors that involves intra-tumoral injection of an adeno-associated virus (AAV) vector carrying the pro-apoptotic gene caspase-1 (ICE) under a Schwann-cell specific promoter (P0); the vector is denoted AAV-P0-ICE. Our pre-clinical studies have shown a remarkable ability of the AAV-P0- ICE vector to produce a prolonged reduction in tumor volume with no nerve damage (manuscript submitted). Our preliminary data suggests that AAV-PO-ICE not only directly kills infected caspase-1-expressing tumor cells (presumably by inducing apoptosis), but also kills non-infected tumor cells through a bystander effect. It is hypothesize that this bystander killin is mediated by both tumor- and host-specific mechanisms that involve humoral- and cell-mediated pathways. The overriding goal is to investigate the biology of AAV-P0-ICE mediated tumor destruction in the human and mouse schwannoma models we have developed in nude and immunocompetent mice, respectively, and to identify the molecular and cellular pathways mediating the killing of non-vector-infected tumor cells that is associated with apoptotic death of infected tumor cells. In brief, the specific aims are to 1) investigate the parameters of tumor regression in two schwannoma models in mice - a human schwannoma in nude mice and a mouse schwannoma in immune competent animals, 2) investigate whether caspase-1 bystander killing involves apoptotic death of uninfected cells, and 3) analyze whether host immune mechanisms are involved in AAV-P0-ICE initiated bystander killing. In vivo tumor growth will be monitored via bioluminescent imaging and MRI for the human and mouse schwannoma models, respectively; both techniques allow serial assessment over time in a given animal. A variety of biochemical and cell biological techniques will be used to determine whether caspase expressing tumor cells produce factors - both humoral and microvesicle contained - that can be transferred to and cause apoptotic death of uninfected tumor cells. Histological analysis and a variety of fundamental immunological assays will be used to investigate host mechanisms of bystander killing after AAV-P0-ICE injection. This application is novel and innovative in that it utilizes the first viral vector we know of that is restrictively expressed in Schwann-lineage cells hence allowing targeting of schwannomas without neurotoxicity, and proposes investigation of the pathways - tumor and host specific - which underlie induction of bystander tumor killing. Mechanistic understanding of the extensive and specific tumor killing induced by AAV-P0-ICE injection into schwannomas has the potential lead to novel treatment strategies for NF1, NF2 and schwannomatosis, as well as, a variety of other neoplasms.

Public Health Relevance

Schwannomas are tumors that form on nerves and cause significant suffering for patients; current treatment of this disease is very limited. Our research group has developed a new treatment for schwannoma in which a virus is used to deliver a cell-death gene specifically to the tumor cells. It appears that the virus kills not only the tumor cell that it infects, but also uninfected tumor cells; the goal of this grant is to understand the mechanisms through which this virus destroys schwannoma cells.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Gene and Drug Delivery Systems Study Section (GDD)
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Morris, Jill A
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Massachusetts General Hospital
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Prabhakar, Shilpa; Taherian, Mehran; Gianni, Davide et al. (2013) Regression of schwannomas induced by adeno-associated virus-mediated delivery of caspase-1. Hum Gene Ther 24:152-62