ABSTRACT
Surface modification of cationic lipoplexes has been carried out by means of a postgrafting reaction. The original lipoplexes described comprise a cationic lipid, a neutral lipid, poly(ethylene glycol)-cholesterol (with or without a targeting ligand) and DNA. Modifying their surface via a chemical, postgrafting reaction did not alter their size (approximately 100 nm) nor their ability to compact DNA, but did give a reduced zeta potential (approximately 0 mV) to afford surface neutral particles. With the modified lipoplexes nonspecific NIH3T3 cell surface binding in vitro was inhibited. Intravenous injection of the neutralized lipoplexes in mice showed decreased accumulation of the particles in the lung as compared to PEGylated cationic lipoplexes. Tumor targeting was also achieved in vivo by the addition of an RGD-PEG-Cholesterol as a lipid-ligand in the postgrafted lipoplex formulation.
Subject(s)
Colloids/chemistry , DNA/administration & dosage , Gene Transfer Techniques/instrumentation , Acetates/chemistry , Acetylation , Animals , Cations/chemistry , Colloids/pharmacokinetics , Colonic Neoplasms/genetics , Colonic Neoplasms/metabolism , DNA/genetics , Female , Genes, Reporter/genetics , Lipids/chemistry , Liposomes , Lung Neoplasms/genetics , Lung Neoplasms/metabolism , Mice , Mice, Inbred C57BL , Microscopy, Electron, Transmission , Molecular Structure , NIH 3T3 Cells , Oligopeptides/chemistry , Polyethylene Glycols/chemistry , Sulfates/chemistryABSTRACT
To improve our knowledge of the bioactive conformation of CCK(1) antagonists, we previously described that replacement of the alpha-MeTrp residue of dipeptoids with the (2S,5S, 11bR)-2-amino-3-oxohexahydroindolizino[8,7-b]indole-5-carbox ylate (IBTM) skeleton, a probed type II' beta-turn mimetic, led to restricted analogues (2S,5S,11bR,1'S)- and (2S,5S,11bR, 1'R)-2-(benzyloxycarbonyl)amino-5-[1'-benzyl-2'-(carboxy)ethyl]carbam oyl-3-oxo-2,3,5,6,11,11b-hexahydro-1H-indolizino[8,7-b]indole, 1a,b, showing high binding affinity and selectivity for CCK(1) receptors. In this report, we describe the synthesis and binding profile of new analogues of compounds 1 designed to explore the importance of the C-terminal residue and of the type of beta-turn on the receptor binding affinity and selectivity. Structure-affinity relationship studies show that a C-terminal free carboxylic acid and an S configuration of the Phe and betaHph residues are favorable for CCK(1) receptor recognition. Moreover, selectivity for this receptor subtype is critically affected by the beta-turn type. Thus, while compounds 15a and 16a, containing the (2S,5S,11bR)- and (2R,5R, 11bS)-IBTM frameworks, respectively, are both endowed with nanomolar affinity for CCK(1) receptors, restricted dipeptoid derivative 15a, incorporating the type II' IBTM mimetic, shows approximately 6-fold higher CCK(1) selectivity than analogue 16a, with the type II mimetic. From these results, we propose that the presence of a beta-turn-like conformation within the peptide backbone of dipeptoids could contribute to their bioactive conformation at the CCK(1) receptor subtype. Concerning functional activity, compounds 15a and 16a behave as CCK(1) receptor antagonists.
Subject(s)
Dipeptides/chemistry , Indoles/chemical synthesis , Indolizines/chemical synthesis , Receptors, Cholecystokinin/antagonists & inhibitors , Animals , Cerebral Cortex/metabolism , In Vitro Techniques , Indoles/chemistry , Indoles/metabolism , Indolizines/chemistry , Indolizines/metabolism , Molecular Conformation , Molecular Mimicry , Pancreas/metabolism , Protein Structure, Secondary , Radioligand Assay , Rats , Receptors, Cholecystokinin/metabolism , StereoisomerismABSTRACT
Conformationally constrained dipeptoid analogues containing the type II' beta-turn mimic (2S,5s,11bR)-2-amino-3-oxohexahydroindolizino[8,7-b]indole-5 -carboxylate framework in place of the alpha-MeTrp residue, show high binding affinity and selectivity for CCK-A receptors, suggesting that a turn-like conformation could contribute to the bioactive conformation at this CCK receptor subtype.
