The effect of epidermal growth factor receptor (EGFR) expression on in vivo growth of rat C6 glioma cells

The discovery of EGFR gene amplification in glioblastoma multiforme has prompted interest in experimental therapies to target the receptor on brain tumor cells. To develop an animal model for in vivo study of such strategies, we transfected C6 glioma cells with a plasmid containing the neomycin resistance gene and the human EGFR gene under the control of the glucocorticoid-inducible MMTV promoter. Following selection with G418, individual clones that expressed EGFR at high levels were selected. Kinetics of EGF binding fit a dual site model indicating the presence of both high (K(A) = 2.5 x 10⁹ M^-1) and low (K(A) = 3.3 x 10⁷ M^-1) affinity receptors. To assess growth in vivo, graded numbers of either wild-type or transfected cells were implanted into the brains of CD Fischer 344 rats. No differences in survival were observed between groups of animals injected with either wild-type or transfected cells at inocula of 10³ or 10⁴ respectively. In addition, one-third of animals (7/21) challenged with 10⁵ or 10⁶ transfected cells survived > 50 days compared to O% of animals (0/12) challenged with 10⁵ or 10⁶ wild-type cells. Such an effect suggests greater immunogenicity of transfected cells, but only at the larger inocula. Since C6 glioma cells will grow in both outbred and inbred strains, our model should have a number of applications including the in vivo study of EGFR targeting for glioma therapy.