Chinese hamster ovary (CHO) cells transfected with the wild-type gene for the human epidermal growth factor-receptor (EGFR) and expressing the receptor in their cell membrane are, together with the receptor negative parent CHO cells, an interesting model system for experimental EGFR-targeting tumour therapy. Comparisons of effects on nearly identical cells with and without receptors can be made. The main purpose of this work was to compare the internalisation and retention of the radioactivity delivered as 125I-EGF or 125I-EGF-dextran in transfected cells (called CHO-EGFR), and human glioma cells U-343 which naturally express wild-type EGFR. We found that radioactivity delivered as 125I-EGF-dextran was retained intracellularly by both cell types to a higher degree than radioactivity delivered as 125I-EGF. Prolonging the cellular exposure time for 125I-EGF-dextran considerably increased postincubation intracellular retention in both cell types. No major differences between the two EGFR expressing cell lines were found and, based on the results in this work, CHO-EGFR cells seem an adequate model for experiments with agents targeting the EGF-receptor.

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