Karen S. Aboody, M.D. Research
Neural Stem Cells Target Human Primary and Metastatic Tumors in Animal Models: Therapeutic Strategies
 
Introduction and Preliminary Data
Neural Stem Cells (NSCs), by virtue of their inherent migratory and tumor-tropic properties, represent a unique and potentially powerful approach for the treatment of invasive tumors. Utilized as a delivery vehicle to target and disseminate therapeutic gene products to tumor sites, NSCs may meet two major challenges facing current gene therapy strategies: effective delivery and distribution of a therapeutic agent throughout the tumor masses and to aggressive infiltrative tumor cells.  We previously demonstrated that murine C17.CD2 NSCs could deliver a bioactive therapeutically relevant molecule to effect a significant anti-tumor response in experimental intracranial glioma models. Further studies demonstrated retention of tumor-tropic properties when these NSCs were injected into the peripheral vasculature, even when the tumor was established outside the cranial vault, i.e. subcutaneous flank. When injected into the tail vein of animals with intracranial and/or subcutaneous flank tumors, the murine NSCs localized to both tumor sites, with little accumulation in normal tissues.
 
We previously demonstrated that murine C17.CD2 NSCs could deliver a bioactive therapeutically relevant molecule to effect a significant anti-tumor response in experimental intracranial glioma models. Further studies demonstrated retention of tumor-tropic properties when these NSCs were injected into the peripheral vasculature, even when the tumor was established outside the cranial vault, i.e. subcutaneous flank. When injected into the tail vein of animals with intracranial and/or subcutaneous flank tumors, the murine NSCs localized to both tumor sites, with little accumulation in normal tissues.
 
Neural Stem Cells Distribute Efficiently throughout Primary Brain Tumor Mass
CNS-1.GFP invasive rodent glioma cells, were implanted into the frontal lobe of adult nude mice followed 6 days later by transplantation of NSCs directly into the main tumor bed. Note efficient distribution of NSCs throughout main tumor bed, and localizing to invasive tumor islands and cells, and not seen elsewhere in the brain.
 
Neural Stem Cells Selectively Track Infiltrating Tumor Cells
Of note, whether NSCs are injected directly into tumor bed, or at a distance form main tumor (including ventricular or intravascular administration), they are able to localize to main tumor sites, invading tumor islands, and individual tumor cells in the brain.
 
Therapeutic Proof of Concept
The NSCs in the above figures were expressing a reporter gene. These NSCs can also be engineered to stably express therapeutic genes. We can therefore utilize them as cellular delivery vehicles to target therapeutic agents directly to tumor sites. In the following proof-of-concept paradigm, we achieve production of localized chemotherapy to produce a significant therapeutic effect in a metastatic brain tumor model. NSCs are engineered to produce an enzyme, cytosine deaminase, which can convert a systemically administered pro-drug (5-FC) to an active chemotherapeutic agent (5-FU), which diffuses out of the stem cells to selectively kill the surrounding dividing tumor cells. in vivo example shown in Figure 3, schematic representation of paradigm shown below:
 
NSCs expressing cytosine deaminase were injected into brain parenchyma of animals with established melanoma metastasis. After 3 days, in which time NSCs localized specifically to tumor sites, animals received tail vein injections of 5-FC prodrug for eight days. Representative brain tissue sections of untreated vs. treated animals shown. Tumor area is dark purple delineated by red outline.
 
Therapeutic Paradigm Schematic
In this case, stem cells were engineered to express the pro-drug activating enzyme, cytosine deaminase. Once cells are injected into animal tumor models, and localize to tumor sites, the 5-FC pro-drug is given systemically. Result is production of chemotherapeutic agent localized to tumor sites.