Stem cell therapies for malignant glioma.
The prognosis for patients with malignant glioma, which is the most common primary intracranial neoplasm, remains dismal despite significant progress in neurooncological therapies and technology. This is largely due to the inability of current treatment strategies to address the highly invasive nature of this disease. Malignant glial cells often disseminate throughout the brain, making it exceedingly difficult to target and treat all intracranial neoplastic foci, with the result that tumor recurrence is inevitable despite aggressive surgery and adjuvant radiotherapy and/or chemotherapy. The use of neural stem cells (NSCs) as delivery vehicles for tumor-toxic molecules represents the first experimental strategy aimed specifically at targeting disseminated tumor pockets. Investigators have demonstrated that NSCs possess robust tropism for infiltrating tumor cells, and that they can be used to deliver therapeutic agents directly to tumor satellites, with significant therapeutic benefit. With the aim of developing these findings into a clinically viable technology that would not be hindered by ethical and tissue rejection-related concerns, the use of adult tissue-derived stem cells has recently been explored. These technologies represent important progress in the development of a treatment strategy that can specifically target disseminated neoplastic pockets within the brain. Despite encouraging results in preclinical models, however, there are significant impediments that must be overcome prior to clinical implementation of this strategy. Key among these are an inadequate understanding of the specific tropic mechanisms that govern NSC migration toward invasive tumor, and the need to refine the processes used to generate tumor-tropic stem cells from adult tissues so that this can be accomplished in a clinically practicable fashion. Despite these limitations, the use of stem cell therapies for brain tumors holds significant promise and may emerge as an important therapeutic modality for patients with malignant glioma.