Tumour therapy with radiolabelled peptides: Current status and future directions

On their plasma membranes, cells express receptor proteins with high affinity for regulatory peptides such as somatostatin. Changes in the density of these receptors during disease, e.g. overexpression in many tumours, provide the basis for new imaging methods. The first peptide analogues successfully applied for visualisation of receptor-positive tumours were the radiolabelled somatostatin analogues. The next step was to label these analogues with therapeutic radionuclides for peptide receptor radionuclide therapy. Results from preclinical and clinical multicentre studies have already shown an effective therapeutic response when using radiolabelled somatostatin analogues to treat receptor-positive tumours. Infusion of positively charged amino acids reduces kidney uptake, enlarging the therapeutic window. For peptide receptor radionuclide therapy of cholecystokinin-B receptor-positive tumours, such as medullary thyroid carcinoma, radiolabelled minigastrin analogues are currently being successfully applied. The combination of different therapy modalities holds interest as a means of improving the clinical therapeutic effects of radiolabelled peptides. In order to reach a wider tumour region of high curability, the combination of different radionuclides, such as 177Lu- and 90Y-labelled somatostatin analogues, has been described. A variety of other peptide-based radioligands, such as bombesin and neuropeptide Y(Y1) analogues, receptors for which are expressed on common cancers, such as prostate and breast cancer, are currently under development and in different phases of (pre)clinical investigation. Multi-receptor tumour targeting using the combination of bombesin and neuropeptide Y(Y1) analogues is promising for scintigraphy and peptide receptor radionuclide therapy of breast carcinomas and their lymph node metastases.

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