Inhibitory cyclic analogues and chlorambucil derivatives of bombesin-like peptides

Separations of hydrophobic synthetic peptides in counter-current chromatography

Synthetic peptides with many aromatic, aliphatic and especially acidic amino acid residues are not very soluble and require strong solvents for useful partitioning. A chloroform-methanol-acidic solvent system fractionates neutral and basically charged 26-mers to provide high yields. An insoluble 15-mer with 5 Trp residues and 60% overall hydrophobic amino acid content was purified in pyridine-acetic acid and in another basic t-butyl methyl ether-n-butanol-acetonitrile solvent system with high recovery. Two instruments were used, the eccentric-multi-layer hybrid coil planet centrifuge and the new spiral disk planet centrifuge that were able to retain the stationary phase of these solvent systems, some of which have low interfacial tension.

Synthesis, chemical, radiochemical and radiobiological evaluation of a new 99mTc-labelled bombesin-like peptide

A new pentadecapeptide bombesin analogue was prepared by Fmoc synthesis, purified by HPLC and identified by electron ionization mass spectrometry. The biological activity of the new peptide was tested on isolated human colonic muscle cells and compared to native bombesin. Labelling of the new biomolecule with Tc-99m yielded a single radioactive species which remained stable at room temperature for eight hours. In a binding assay, the radiolabelled peptide showed high affinity for oat-cell carcinoma (Kd = 9.8 nM) and colorectal adenocarcinoma (Kd = 27.2 nM). Biodistribution studies, performed in normal rodents, indicated uptake by organs that normally express bombesin receptors, such as liver, intestines and kidneys. Scintigraphic studies, performed in nude mice transplanted with small cell lung carcinoma and colon cancer cells, showed significant tumor uptake two hours p.i. The new synthetic pentadecapeptide appears to have promise for several malignancies, including oat-cell lung carcinoma, colorectal cancer and gastroenteropancreatic (GEP) tumors.

Synthesis and biological evaluation of bombesin constrained analogues

Analogues of bombesin which incorporate dipeptide or turn mimetics have been synthesized. One of them (compound 11) containing a seven-membered lactam ring revealed a good affinity for GRP/BN receptors on rat pancreatic acini (K(i) value of 1.7 +/- 0.4 nM) and on Swiss 3T3 cells (K(i) value of 1.0 +/- 0.2 nM). On the basis of this observation, antagonists containing the same dipeptide mimic were obtained by modification of the C-terminal part of the bombesin analogues. The most potent constrained compounds (15 and 17) were able to antagonize 1 nM bombesin-stimulated amylase secretion from rat pancreatic acini with high potency (K(i) = 21 +/- 3 and 3.3 +/- 1.0 nM, respectively) and 10(-7) M bombesin-stimulated ¿(3)Hthymidine incorporation into Swiss 3T3 cells (K(i) = 7.8 +/- 2. 0 and 0.5 +/- 0.1 nM, respectively).