An implantable guide-screw system for brain tumor studies in small animals

Object. To overcome the problems associated with using stereotactic techniques to establish intracranial xenografts in nude mice and to treat engrafted tumors with intratumoral therapies (such as gene or viral therapies), the authors developed an implantable guide-screw system. In this study, they describe the guide-screw system, its method of implantation, and their experience with establishing xenografts and delivering intratumoral therapy. Methods. The system consists of a 2.6-mm guide screw with a central 0.5-mm diameter hole that accepts the 26-gauge needle of a Hamilton syringe. The screw is implanted into a small drill hole made 2.5 mm lateral and 1 mm anterior to the bregma. A stylet is used to cap the screw between treatments. Tumor cells or therapeutic agents are injected in a freehand fashion by using a Hamilton syringe and a 26-gauge needle fitted with a cuff to determine the depth of injection. To test this system, guide screws were successfully implanted in 44 (98%) of 45 nude mice. After 1 to 2 weeks of recovery, 38 mice were inoculated with U87MG cells and killed 5 days later. On histological studies in 37 (97%) of these animals, xenografts were evident within the caudate nucleus (mean diameter 2.5 mm). To determine whether injections into the center of an established xenograft could be reproducibly achieved with the guide-screw system, an adenovirus vector containing the β-galactosidase gene was injected 3 days after cell implantation in 15 of the mice. All of these animals demonstrated transduced cells within the tumor. To demonstrate that engrafted animals have a uniform survival time that is indicative of reproducible tumor growth, the survival of six mice was assessed after engraftment with U87MG cells. All six animals died within 28 to 35 days. Conclusions. The guide-screw system allows a large number of animals to be rapidly and reproducibly engrafted and for intratumoral treatments to be accurately delivered into established xenografts.