BINDING, INTERNALIZATION AND EXCRETION OF TGF-ALPHA-DEXTRAN ASSOCIATED RADIOACTIVITY IN CULTURED HUMAN GLIOMA-CELLS

Conjugates based on transforming growth factor alpha, TGFalpha, or epidermal growth factor, EGF, are candidates for targeted radiotherapy against EGF-receptor rich tumours such as gliomas or squamous carcinomas. In this study, binding, internalization and excretion of radiolabelled TGFalpha and TGFalpha-dextran conjugates was analysed in an EGF-receptor rich human glioma cell line. The binding of I-125-TGFalpha was EGF-receptor specific and the binding pattern was similar to that of I-125-EGF. The TGFalpha-dextran conjugate also bound specifically but gave maximum binding for a longer time during continuous incubation compared to when only TGFalpha was used. The excretion pattern of internalized radioactivity was somewhat slower for I-125-TGFalpha-dextran, with I-125-labelling on the TGFalpha part, as compared to I-125-TGFalpha although most of the radioactivity in both cases was excreted within 4 hours. The fate of the dextran part of the conjugate, as followed by means of I-125-labelling of the dextran, was different since all radioactivity in that case remained cell-associated for at least up to 22 hours. Furthermore, by comparison with previously published results, it was seen that the radioactivity delivered through the TGFalpha part of TGFalpha-dextran was retained for a shorter period of time by the cells than when delivered by EGF in EGF-dextran conjugates. However, when the radioactivity was delivered by the dextran part of the conjugates, the radioactivity seemed to be retained equally well or even better when TGFalpha-dextran was applied It is concluded that TGFalpha-dextran, as well as EGF-dextran, have interesting properties for targeting against EGF-receptors and that the dextran part is well retained in the cells and therefore might be a suitable carrier for toxic agents such as radionuclides. It is of high interest to continue with toxicological and pharmacological in vivo studies of the conjugates.