title: Modulation of melphalan resistance in glioma cells with a peripheral benzodiazepine receptor ligand-melphalan conjugate.
abstract: Peripheral benzodiazepine receptors (PBRs) are located on the outer membrane of mitochondria, and their density is increased in brain tumors. Thus, they may serve as a unique intracellular and selective target for antineoplastic agents. A PBR ligand-melphalan conjugate (PBR-MEL) was synthesized and evaluated for cytotoxicity and affinity for PBRs. PBR-MEL (9) (i.e., 670 amu) was synthesized by coupling of two key intermediates: 4-[bis(2-chloroethyl)-amino]-L-phenylalanine ethyl ester trifluoroacetate (6) and 1-(3'-carboxylpropyl)-7-chloro-1,3- dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one (8). On the basis of receptor-binding displacement assays in rat brain and glioma cells, 9 had appreciable binding affinity and displaced a prototypical PBR ligand, Ro 5-4864, with IC50 values between 289 and 390 nM. 9 displayed differential cytotoxicity to a variety of rat and human brain tumor cell lines. In some of the cell lines tested including rat and human melphalan-resistant cell lines, 9 demonstrated appreciable cytotoxicity with IC50 values in the micromolar range, lower than that of melphalan alone. The enhanced activity of 9 may reflect increased membrane permeability, increased intracellular retention, or modulation of melphalan's mechanisms of resistance. The combined data support additional studies to determine how 9 may modulate melphalan resistance, its mechanisms of action, and if target selectivity can be achieved in in vivo glioma models.
authors.affiliation: Department of Pharmaceutical Chemistry, Simons Laboratories, University of Kansas, Lawrence 66047, USA.
authors.forename: L
authors.initials: L
authors.lastname: Kupczyk-Subotkowska
authors.forename: T J
authors.initials: TJ
authors.lastname: Siahaan
authors.forename: A S
authors.initials: AS
authors.lastname: Basile
authors.forename: H S
authors.initials: HS
authors.lastname: Friedman
authors.forename: P E
authors.initials: PE
authors.lastname: Higgins
authors.forename: D
authors.initials: D
authors.lastname: Song
authors.forename: J M
authors.initials: JM
authors.lastname: Gallo
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D001570:Benzodiazepinones / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology*; D001921:Brain / Q000378:metabolism; D001932:Brain Neoplasms / Q000378:metabolism / Q000473:pathology; D016923:Cell Death; D019008:Drug Resistance, Neoplasm; D005910:Glioma / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008558:Melphalan / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: C106279:1-(4-butanoyl-(4-bis(2-chloroethyl)amino)phenylalanine ethyl ester)-7-chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one; D018906:Antineoplastic Agents, Alkylating; D001570:Benzodiazepinones; D011963:Receptors, GABA-A; C028513:4'-chlorodiazepam; D008558:Melphalan