Synthesis, biodistribution and effects of farnesyltransferase inhibitor therapy on tumour uptake in mice of 99mTc labelled epidermal growth factor

OBJECTIVE: The goal of this study was to develop a 99mTc labelled human epidermal growth factor (hEGF) for the in-vivo prediction of cancer cell response to farnesyltransferase inhibitor (FTI) therapy. This is based on the observation that internalization of EGF receptors is inhibited by FTIs. METHODS: We describe the radiolabelling of 99mTc-hEGF using the hydrazinonicotinamide (HYNIC) linker. Binding characteristics of 99mTc-HYNIC-hEGF to the EGF receptor are explored using an in-vitro binding assay. Biodistribution data of the compound in mice and tumour uptake in LoVo tumour bearing athymic mice before and after farnesyltransferase inhibitor therapy are presented. RESULTS: No colloid formation was observed. Binding parameters and LoVo tumour uptake of 99mTc-HYNIC-hEGF did not differ significantly from directly labelled 123I-hEGF values. However, the biodistribution data of the 99mTc-HYNIC-hEGF showed higher uptake in liver and intestines and decreased stomach uptake compared to its 123I analogue. Eight hours after farnesyltransferase inhibitor therapy with R115777, LoVo tumour uptake of 99mTc-HYNIC-hEGF decreased significantly, as shown using planar gamma scintigraphy (the ratio tumour vs. thigh dropped from 2.54+/-0.83 to 0.99+/-0.18). These data confirm the results obtained using 123I-hEGF. CONCLUSION: These data suggest that 99mTc-HYNIC-hEGF is a promising and selective new radiotracer for in-vivo monitoring of the EGF receptor with SPECT. Moreover, 99mTc-HYNIC-hEGF is a possible tool for early therapy response prediction of farnesyltransferase inhibitors.