We evaluated the interaction between oncolytic, replication-competent
adenoviral vectors and the herpes simplex virus-1 thymidine kinase
(HSV1-tk) gene/ganciclovir (GCV) suicide system for the treatment of
malignant gliomas. We constructed a panel of replication-competent
adenoviral vectors in which the luciferase (IG.Ad5E1(+). E3Luc) or HSV1-tk
gene (IG.Ad5E1(+).E3TK) replace the M(r) 19,000 glycoprotein (gp19K)
coding sequence in the E3 region. IG.Ad5E1. IG.Ad5.ClipLuc and IG.AdApt.TK
are E1-deleted viruses that contain the luciferase or the HSV1-tk gene in
the former E1 region driven by the human cytomegalovirus promoter.
IG.Ad5.Sarcoma 1800HSA.E3Luc contains an irrelevant gene in the E1 region,
whereas the gp19K coding sequence in the E3 region is replaced by the
luciferase gene as in the replicating virus IG.Ad5E1(+).E3Luc. For in
vitro experiments, we used a panel of human glioma cell lines (U87 MG,
T98G, A172, LW5, and U251), a rat gliosarcoma cell line (9 L), and human
lung (A549) and prostate carcinoma (P3) cell lines. In vitro, GCV
sensitivity (10 microg/ml) was studied in U87 MG cells after infection at
a multiplicity of infection of 1 and 10. A s.c. U87 MG glioma xenograft
model was established in NIH-bg-nu-xid mice. Tumors of 100-150 mm(3) were
treated with a single injection of adenovirus 10(9) IU suspended in 100
microl of PBS, and GCV 100 mg/kg was administered i.p. twice daily for 7
days. The cytopathic effect of all three replication-competent adenoviral
vectors was similar to the cytopathic effect of wild-type adenovirus 5 on
all human cell lines tested, indicating that deletion of the E3 gp19K
sequences did not affect the oncolytic effect of the vectors. In vitro,
luciferase expression was the same for both E1-deleted vectors
(IG.Ad5.ClipLuc and IG.Ad5.Sarcoma 1800HSA.E3Luc), demonstrating the
strength of the internal E3 promoter even in the absence of E1A. However,
in vitro expression levels obtained with replication-competent
IG.Ad5E1(+). E3Luc were 3 log higher (allowing infection with a