Scintigraphy and radionuclide therapy with [indium-111-labelled-diethyl triamine penta-acetic acid-D-Phe(1)]-octreotide

Peptide receptor scintigraphy with [In-111-DTPA-D-Phe(1)]-octreotide is a s ensitive and specific technique to show in vivo the presence and abundance of somatostatin receptors on various tumours. With this technique primary t umours and metastases of neuroendocrine cancers as well as of many other ca ncer types cart be localised. This technique is currently used to assess th e possibility of peptide receptor radionuclide therapy with repeated admini strations of high doses of [In-111-DTPA-D-Phe(1)]-octreotide. In-111 emits Auger and conversion electrons having a tissue penetration of 0.02 to 10 mu m and 200 to 500 mu m, respectively. Twenty end-stage patients, mostly wit h neuroendocrine progressing tumours, were treated with [In-111-DTPA-D-Phe( 1)]-octreotide, up to a maximal cumulative patient dose of about 74 GBq, in a phase I trial. Results showed there were no major clinical side-effects after up to 2 years treatment except that in a few patients a transient dec line in platelet counts and lymphocyte subsets occurred. Promising benefici al effects on clinical symptoms, hormone production and tumour proliferatio n were found. Of the 16 patients who received a cumulative dose of more tha n 20 GBq, 5 patients showed stabilisation of disease and 5 other patients a reduction in size of tumours. There is a tendency towards better results i n patients whose tumours have a higher accumulation of the radioligand. In conclusion, peptide receptor radionuclide therapy is feasible, also with In -111 as radionuclide. Theoretically, depending on the homogeneity of distri bution of tumour cells expressing peptide receptors, beta-emitting radionuc lides, e.g. Y-90, labelled to DOTA-chelated peptides may be more effective than In-111 for peptide receptor radionuclide therapy The first peptide rec eptor radionuclide therapy trials with [Y-90-DOTA-Tyr(3)]-octreotide starte d recently.