particles/cell, 100% of cells expressed p-galactosidase. No difference in vector transduction 
effeciency was detected between glioma and medulloblastoma cell lines. 
The cytotoxicity of H5.010RSVr/C adenovirus-transduced cells to GCV was evaluated by a clonogenic 
assay or MTT assay. LD50 values for GCV in the 4 medulloblastoma cell lines ranged from 5.5 - 16 nM. 
In contrast, cells transduced with a control adenovirus (H5.010CMV/acZ adenovirus) had LD50 values 
of 270-310 nM. Glioma cell lines ranged in sensitivity from 10 - 78 nM. One cell line (G10) had a 
mean LD50 value of 200 nM, probably reflecting the long doubling time (96 hrs) and low growth 
fraction of this tumor. A bystander effect to GCV was demonstrated in selected medulloblastoma (D324) 
and glioma (U251) cell lines. Cytotoxicity to bystander cells was maintained below a 20:1 ratio of 
uninfected to infected cells. Cell contact was not essential for the bystander effect as demonstrated by 
the cytotoxic effects of filtered conditioned media on non-transfected medulloblastoma cells. 
Flank xenograft experiments were performed with human brain tumor cell lines in nude mice. The mice 
were injected with 50 pi of D324 medulloblastoma or U251 glioma tumor homogenate in the right flank 
on day 1 and the size of the tumor was measured daily. When the median tumor volume reached 0.4 cm 3 
the tumors were injected with H5.010RSV77C adenovirus. In addition, one group of nude rats bearing 
medulloblastoma flank xenografts was allowed to grow until the median tumor volume reached 0.8 mm3 
prior to HS.OIORSVTX adenovirus injection. Anesthetized mice were injected slowly over 15 minutes 
with 1 x 10 10 H5.010RSVT/C viral particles in a 100 pi volume. Seventy two hours after viral 
injection, the mice were treated with 15 mg/kg gancyclovir intraperitoneally, twice daily for 14 days. 
Control animals received an intratumoral saline injection (100 pi), followed 72-hours later by 
gancyclovir at the same dose and schedule. Tumor size was measured twice weekly thereafter and tumor 
volume was calculated as: volume = (width 2 x length)/2. All glioma flank xenografts had complete 
resolution of tumor within 50 days after the start of GCV (see figure 1). 
U251 Glioma 
DAYS 
Figure 1. Tumor volume reduction for U251 glioma flank xenografts. All tumors were 
injected with H5.010 RSVTK adenovirus on day 24 and received twice daily GCV from day 
Recombinant DNA Research, Volume 20 
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