Radiolabelled somatostatin analogue(s) for peptide receptor scintigraphy and radionuclide therapy

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Abstract
Background : Peptide receptor scintigraphy with the radioactive somatostatin analogue, [ 111 In-DTPA 0 ]octreotide, is a sensitive and specific technique to show in vivo the presence and abundance of somatostatin receptors on various tumours. Aim : With this technique primary tumours and metastases of neuroendocrine cancers as well as of many other cancer-types can be localised. This technique is currently used to assess the possibility of peptide receptor radionuclide therapy (PRRT) with repeated administrations of high doses of [ 111 In-DTPA 0 ]octreotide. 111 In emits Auger and conversion electrons having a tissue penetration of 0.02–10 μm and 200 to 500 μm, respectively. Patients and methods : Thirty end-stage patients with mostly neuroendocrine progressing tumours were treated with [ 111 In-DTPA 0 ]octreotide, up to a maximal cumulative patient dose of about 74 GBq, in a phase I trial. Results : There were no major clinical side effects after up to two years treatment, except that in a few patients a transient decline in platelets counts and lymphocyte subsets occurred. Promising beneficial effects on clinical symptoms, hormone production and tumour proliferation were found. Of the 21 patients who received a cumulative dose of more than 20 GBq, eight patients showed stabilisation of disease and six other patients a reduction in size of tumours. There is a tendency towards better results in patients whose tumours have a higher accumulation of the radioligand. Conclusions : PRRT is feasible, also with 111 In as radionuclide. Depending on the homogeneity of distribution of tumour cells expressing peptide receptors and the size of the tumour, β-emitting radionuclides, e.g., 90 Y, labelled to DOTA-chelated peptides, are also attractive candidates for PRRT. The first PRRT trials with [ 90 Y-DOTA 0 ,Tyr 3 ]octreotide started recently.

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