Radiosynthesis of new radio neurotensin (8-13) analogues

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

Parameters ruling optimization of radiolabelling of polyamino polycarboxylated functionalized peptide derivatives: a case study report

Parameters studies revealed that successful labeling of DTPA-Neurotensin(8-13) analogues depend on several physico-chemical parameters. The pH of the reaction mixture seemed to be the most critical parameter for obtaining high labeling yields; quantitative radiolabelling was only guaranteed at a pH between 4.2 and 5.5. At a pH of 4.5, metal ion contaminants originating from peptide synthesis and purification procedures were shown not to effect radiolabelling. Nevertheless, proper reducing agents were included in a proposed Kit labeling procedure in order to avoid potential competition from trivalent metal ion contamination, and thus guarantee successful 111In-complexation. The complexing capacity of DTPA for radioactive In(3+) strongly depends upon the pH. As a consequence, labeling yields must be expressed as [[K(ass) x alpha(4) x [DTPA-NT](0)/(1+ K(ass) x alpha(4) x [DTPA-NT](0))], to where K(ass) is the association constant and alpha(4) is a pH dependent correction factor of the association constant.

Neurotensin receptors in human neoplasms: high incidence in Ewing's sarcomas

Receptors for regulatory peptides, such as somatostatin or vasoactive intestinal peptide (VIP), expressed at high density by neoplastic cells, can be instrumental for tumor diagnosis and therapy. Little is known about the expression of neurotensin receptors in human tumors. In the present study, 464 human neoplasms of various types were investigated for their neurotensin receptor content by in vitro receptor autoradiography on tissue sections using 125I-[Tyr3]-neurotensin as radioligand. Neurotensin receptors were identified and localized in tumor cells of 11/17 Ewing's sarcomas, 21/40 meningiomas, 10/23 astrocytomas, 5/13 medulloblastomas, 7/24 medullary thyroid cancers and 2/8 small cell lung cancers. They were rarely found in non-small cell lung cancers and breast carcinomas; they were absent in prostate, ovarian, renal cell and hepatocellular carcinomas, neuroendocrine gut tumors, pituitary adenomas, schwannomas, neuroblastomas and lymphomas. When present, the receptors bound with nanomolar affinity neurotensin and acetyl-neurotensin-(8-13), with lower affinity neuromedin N, diethylenetriamine penta-acetic acidneurotensin-(8-13) and SR 48692, but not neurotensin-(1-11). They were all of the NT1 type, without high affinity for levocabastine. Further, in 2 receptor-positive Ewing's sarcomas, neurotensin mRNA was detected by in situ hybridization techniques. Since neurotensin is known to stimulate cell proliferation, the presence of neurotensin receptors in human neoplasia may be of biological relevance, possibly as an integrative part of an autocrine feedback mechanism of tumor growth stimulation.