Convection-enhanced delivery: targeted toxin treatment of malignant glioma

Historically, malignant gliomas are perhaps the most difficult intracranial neoplasms to treat. Surgery, radiation therapy, and traditional chemotherapy have not been able to significantly alter the course of this disease. By definition, these tumors are located in the protected space of the cranial vault, where the blood-brain barrier prevents most therapies from gaining access. Because of the difficulty in treating this disease, new, innovative treatments and alternative delivery techniques for those therapies are needed. Targeted toxins are fusion proteins that represent a novel medical treatment for these cancers that is under development. However, the efficacy of these agents is dependent on the method of delivery to the tumor. The administration of targeted toxins requires image-guided placement of catheters, either within the tumor or into the adjacent infiltrated brain, and positive pressure infusion. The term that has been applied to this microinfusion technique is convection-enhanced delivery (CED). This infusion method was first attempted via direct intratumoral infusion in nude mouse flank tumor models of human malignant glioma. After significant development of this delivery technique in animal models, the successful demonstration of in vivo efficacy of targeted toxins in Phase I and II clinical trials was reported. Currently, ongoing targeted toxin trials are being conducted at academic health centers to define the best clinical practice for CED. This work involves refining the details of delivery such as infusion rate, duration of treatment, and drug dosing. The early results of CED of targeted toxins supports their continued investigation, as few other treatment modalities have produced durable results in the fight against gliomas.