title: Design, synthesis, and in vitro evaluation of cytotoxic analogs of bombesin-like peptides containing doxorubicin or its intensely potent derivative, 2-pyrrolinodoxorubicin.
abstract: Five peptide fragments, based on the C-terminal sequence of bombesin (BN)-(6-14) or BN-(7-14), were selected as carriers for radicals doxorubicin (DOX) and 2-pyrrolino-DOX to create hybrid cytotoxic analogs. All these compounds had a reduced peptide bond (CH2-NH or CH2-N) between positions 13 (Phe or Leu) and 14 (Phe, Leu, or Tac) (Tac = thiazolidine-4-carboxylic acid). Three pseudononapeptide carriers contained N-terminal D-Phe or D-Tpi at position 6 (Tpi = 2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid). Two pseudooctapeptides had Gln7 at the N terminus. The conjugation of N-(9-fluorenylmethoxycarbonyl) doxorubicin (N-Fmoc-DOX)-14-O-hemiglutarate to the peptide carriers at the N terminus resulted in cytotoxic hybrids of BN-like peptides containing DOX. These hybrids could then be converted to analogs with 2-pyrrolino-DOX by a reaction with 4-iodobutyraldehyde. The ability of the carriers and the conjugates to inhibit the binding of 125I-labeled [Tyr4]BN to receptors for BN/gastrin releasing peptide (GRP) on Swiss 3T3 cells was determined. Cytotoxic conjugates of pseudooctapeptide carrier analogs displayed the highest binding affinity (KD approximately 1 nM). The cytotoxic BN analogs and their corresponding cytotoxic radicals exerted similar inhibitory effects on the in vitro growth of CFPAC-1 human pancreatic cancer, DMS-53 human lung cancer, PC-3 human prostate cancer, and MKN-45 human gastric cancer cell lines that have receptors for BN/GRP. In DMS-53 cells, the activity of 2-pyrrolino-DOX and its conjugates was approximately 2500 times higher than that of DOX and its hybrids. These highly potent cytotoxic analogs of BN have been designed as targeted anti-tumor agents for the treatment of various cancers that possess receptors for BN/GRP.
authors.affiliation: Endocrine, Polypeptide and Cancer Institute, Veterans Affairs Medical Center, New Orleans, LA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Nagy
authors.forename: P
authors.initials: P
authors.lastname: Armatis
authors.forename: R Z
authors.initials: RZ
authors.lastname: Cai
authors.forename: K
authors.initials: K
authors.lastname: Szepeshazi
authors.forename: G
authors.initials: G
authors.lastname: Halmos
authors.forename: A V
authors.initials: AV
authors.lastname: Schally
mesh_terms: D001839:Bombesin / Q000737:chemistry*; D002470:Cell Survival / Q000187:drug effects; D003603:Cytotoxins / Q000737:chemistry*; D004317:Doxorubicin / Q000031:analogs & derivatives / Q000737:chemistry; D006801:Humans; D015394:Molecular Structure; D011758:Pyrroles / Q000737:chemistry; D018004:Receptors, Bombesin / Q000378:metabolism; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
chemical_list: D003603:Cytotoxins; D011758:Pyrroles; D018004:Receptors, Bombesin; C098751:AN 204; D004317:Doxorubicin; D001839:Bombesin