Development of a syngeneic rat brain tumor model expressing EGFRvIII and its use for molecular targeting studies with monoclonal antibody L8A4

Abstract

Purpose: The goals of the present study were 2-fold: (a) to develop and characterize a rat brain tumor model that could be used for studies of molecular targeting of EGFRvIII and (b) to study the tumor localizing properties of radiolabeled monoclonal antibody (mAb) L8A4, specifically directed against EGFRvIII, following systemic, i.t., and convection enhanced delivery to brain tumor-bearing rats. Experimental Design and Results: F98 wild-type (F98 WT) rat glioma cells were transfected with a gene encoding human EGFRvIII, and following selection and cloning, a cell line, designated F98 npEGFRvIII, was identified, which expressed a nonconstitutively phosphorylated form of the receptor. As determined by a radioligand binding assay, there were 1.2 × 105 EGFRvIII sites per cell compared with an undetectable number on F98WT cells. The tumorigenicity of the F98npEGFRvIII glioma was studied following i.c. implantation of 103, 104, or 105 cells into CD-Fischer rats. Mean survival times were 23, 17, and 13 days, respectively, which were equivalent to those obtained with F98EGFR and F98WT cells. As determined by magnetic resonance imaging, the mean doubling times for the F98WT and F98npEGFRvIII gliomas were similar (59.8 ± 4.8 versus 52 ± 3.3 hours). Following i.v. administration to glioma-bearing rats, mAb L8A4 specifically targeted the F98npEGFRvIII glioma, and at 24 hours, 7.7% of the injected dose per gram (ID/g) localized in the tumor. This increased 5-fold to 39.5% ID/g following i.t. injection and 7-fold to 59.8% ID/g at 24 hours following convection enhanced delivery. Conclusions: Based on these data, we have concluded that the F98 npEGFRvIII glioma should be a valuable animal model for therapy studies focusing on molecular targeting of EGFRvIII by receptor specific mAbs.