1. SPECIFIC AIMS 
To apply gene therapy to intracranial tumors we propose a method 
for in vivo gene transfer of the Herpes simplex thymidine kinase (HS- 
tk) gene using GlTkSvNa.29 vector-producing cells. Insertion of the HS- 
tk gene confers a sensitivity to the anti-Herpes drug ganciclovir (GCV) . 
The direct injection of HS-tk vector-producer cells (VPC) into growing 
tumors in animals can result in the complete destruction of the tumor 
with GCV therapy. This selective destruction of growing tumors in situ 
is thought to result from the transfer of the HS-tk gene into the 
surrounding tumor cells where the production of toxic GCV metabolites 
within the tumors result from the interaction of HS-tk and GCV. This 
procedure can result in the cure of some experimental animals with 
limited toxicity due to selective gene transfer into tumors. Therefore 
we propose to apply this technique for the treatment of recurrent 
primary pediatric brain tumors. 
This clinical trial will establish the efficacy of single and 
repeated treatment of pediatric brain tumors with HS-tk VPC. Pediatric 
patients (ages 2-18 years) with recurrent malignant supratentorial 
astrocytomas will be evaluated for extent and location of their 
recurrence. Patients will be divided into two groups, those with 
resectable tumors and those with unresectable tumors, based on the 
location of the tumor and involvement of critical cerebral structures. 
Patients with resectable tumors will undergo maximal tumor resection. 
The tumor bed will then be injected with HS-tk VPC under direct 
visualization. An Ommaya reservoir will be placed in the tumor cavity. 
Seven days later, additional VPC will be injected into the resection 
cavity via the Ommaya reservoir. One week later, GCV will be 
administered at 5 mg/kg/dose IV BID for 14 days. The patient will 
receive additional cycles of VPC via the Ommaya reservoir followed by 
GCV depending on the tumor response and toxicities observed. Patients 
with unresectable tumors will undergo stereotaxic injection of HS-tk VPC 
directly into their tumor, followed 14 days later by treatment with GCV. 
If an initial response is seen and residual tumor remains with a cystic 
necrotic center, an Ommaya reservoir will be placed into the cyst using 
stereotaxic guidance and VPC will be instilled into the cyst via the 
reservoir. Again, GCV therapy will begin 14 days later. Additional 
cycles of VPC injection and GCV treatment will be considered, based on 
the tumor response and toxicity observed. Throughout treatment, 
patients will be carefully followed with serial MR scan to assess tumor 
response. 
The major differences between this protocol versus the RAC and FDA 
approved protocols is the ages of patients treated and in the surgical 
technique. Therefore, this protocol contains several minor 
modifications of the previously approved protocols. However, we felt 
it most appropriate to present a new protocol for RAC consideration 
primarily because it will be conducted in children at a new institution. 
The NIH protocol focuses on adult patients with the use of a single 
stereotaxic injection of VPC into the tumor. This protocol is aimed at 
pediatric patients and will allow for repeated treatments via an Ommaya 
reservoir, similar to the Iowa protocol. Patients with large tumors or 
those with partial response to the initial cycle of therapy will likely 
benefit from repeated cycles to remaining viable tumor. Because large 
tumors may have a significant component of non-cycling cells, repeated 
Recombinant DNA Research, Volume 18 
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