Peptide receptor imaging: advances in the diagnosis of pulmonary diseases.

Radiolabeled cell-surface peptide receptor-binding molecules are emerging as an important class of radiopharmaceuticals. Their binding to specific cell membrane receptors allows for noninvasive assessment of regional receptor proteomics in vivo. Information thus obtained can be used for diagnostic purposes and for predicting and monitoring response to treatment. This paradigm also applies to pulmonary diseases. In this review, available radiopharmaceuticals of great potential or already in clinical use for imaging of lung cancer, lung inflammation and infection and pulmonary embolism are discussed. In lung cancer, somatostatin receptor imaging by means of technetium-99m (99mTc)-octreotide scintigraphy has proven useful for characterizing malignancy in solitary pulmonary nodules. Additionally, several radiopharmaceuticals targeting tyrosine-kinase, e.g. 99mTc labeled epidermal growth factor and indium-111 (111In)-diethylene triamine penta-acetic acid-trastuzumab, or G-protein coupled receptors, e.g. 99mTc-bombesin, iodine-123-vasoactive intestinal peptide and 111In-tetraazacyclododecane tetra-acetic acid (DOTA)-cholecystokinine-B, are being explored for their diagnostic as well as treatment monitoring potential. With the purpose of better evaluating the source of pulmonary embolism, as well as to differentiate acute from chronic deep venous thrombosis, several radiolabeled peptides targeting the glycoprotein IIb/IIIa fibrinogen receptor found on activated platelets have been developed. Out of these, 99mTc-P280 is now approved by the US Food and Drug Administration for scintigraphic imaging of suspected acute venous thrombosis in the lower extremities of patients. In the field of lung inflammation and infection, non-specific 111In and 99mTc-human polyclonal immunoglobulins have been successfully used to identify the presence and extent of Pneumocystis carinii, cytomegalovirus, Mycobaterium avium and fungal infections in patients with HIV infection. The clinical role of other radiopharmaceuticals such as 99mTc-J001X, a nonpyrogenic acylated polygalactoside isolated from Klebsiella pneumoniae and binding with high affinity to CD11b and CD14 lipopolysaccharide receptors expressed on monocytes/macrophages, and 111In-octreotide, binding to up-regulated somatostatin receptors on activated lymphocytes needs to be further defined.