Funded Grants

Endothelial Cell Mediated Therapeutic Gene Transfer

Therapeutic gene transfer, or "gene therapy" offers a potentially promising new treatment strategy for malignant gliomas. We have recently developed retroviral and adenoviral vectors that transduce a number of new prodrug activating/suicide genes and demonstrated the ability of these vectors to efficiently kill glioma cells in vitro and eradicate intracerebral tumors in vivo. Additionally, we have developed adenoviral and retroviral vectors that transduce genes that encode potent inhibitors of angiogenesis, and demonstrated dramatic inhibition of localized tumor growth following treatment with these vectors. Such approaches, however, require efficient gene transfer to all (or almost all) tumor/target cells to mediate the desired anti-tumor effect. Unfortunately, the current generation of viral and non-viral vectors have efficiencies far below that necessary for in vivo transduction of all glioma cells within a human brain given the infiltrative nature of these tumors. Thus, a major obstacle to successful gene therapy of malignant gliomas remains our inability to deliver these novel vectors to areas of deeply infiltrative tumor in normal cerebral cortex. 'We now propose an endothelial cell-based gene delivery strategy that may make it possible to efficiently and selectively target therapeutic genes to areas of infiltrating glioma cells.

The growth of most solid tumors including gliomas, is highly dependent of the development of vascular structures to support the increasing need of the tumor for nutrients and oxygen, a process called angiogenesis. In adults, physiologic angiogenesis occurs only during limited times thus making angiogenesis a rather tumor-selective process, and therefore, a promising therapeutic target for cancer therapy. It has been recently demonstrated that endothelial progenitor cells (EPCs), or angioblasts, can be easily detected and isolated from the peripheral blood of adult mice and humans. It can be shown that following systemic injection into the circulation of an animal, EPCs can migrate to areas of angiogenesis. We, therefore, hypothesize that EPCs, first transduced in vitro with a prodrug activating or anti angiogenic gene and then re-injected back into the host, can be utilized as a selective tumor targeting "vector" by migrating into, and delivering the therapeutic gene to areas of tumor-associated angiogenesis.

In this proposal we will describe experiments designed to answer three basic questions;

1.) Can EPCs migrate to sites of tumor-mediated angiogenesis following in vitro expansion and re-injection into the systemic circulation;

2.) Can EPCs be transduced by retroviral and/or adenoviral vectors in vitro, and what are the optimal conditions for efficient transduction;

3.) Can EPCs transduced with prodrug activating/suicide or antiangiogenic genes mediate a selective anti-tumor effect following systemic delivery.

It is our expectation that the proposed experiments will generate the requisite data necessary to determine whether endothelial cell-mediated gene targeting is promising enough to move forward toward clinical development.