title: Biophysical characterization and molecular modeling of the coordinative-intercalative DNA monoadduct of a platinum-acridinylthiourea agent in a site-specifically modified dodecamer.
abstract: The guanine- N7 monoadduct of [Pt(en)Cl(ACRAMTU)](NO(3))(2) (PT-ACRAMTU; en=ethane-1,2-diamine, ACRAMTU=1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea), a dual metalating/intercalating cytotoxic agent, was generated in a double-stranded dodecamer, d(CCTCTCG*TCTCC/GGAGACGAGAGG) (III*), and isolated by preparative reverse-phase high-performance liquid chromatography (HPLC). The adduct was characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), circular-dichroism spectropolarimetry (CD), UV-melting curves, and NMR spectroscopy. In addition, a molecular mechanics/restrained molecular dynamics (MM/rMD) study was performed for this adduct using the AMBER force field. Monoadduction of the sequence leads to a pronounced increase in melting temperature, Delta T(m)= T(m)(III*)- T(m)(III)=9.7 degrees C. Because there is complete enthalpy-entropy compensation, binding occurs without noticeable thermodynamic destabilization. This feature and the CD (induced-ligand circular dichroism) and NMR (upfield shifts of aromatic acridine proton signals) data are indicative of a unique, nondenaturing dual-binding mode that involves partial intercalation of the acridine chromophore. An energy-minimized AMBER model ofIII* demonstrates that platination of G7- N7 of guanine in the major groove and partial insertion of the acridine moiety into the C6G19/G7C18 base step on the 5' face of the modified purine base is feasible and supportive of the experimental results. Differences in the biophysical properties betweenIII* and duplexes containing adducts of the clinical-drug cisplatin are outlined, and possible biological consequences are discussed.
authors.affiliation: Department of Chemistry, Wake Forest University, PO Box 7486 Reynolda Station, Winston-Salem, NC 27109, USA.
authors.forename: Hemanta
authors.initials: H
authors.lastname: Baruah
authors.forename: Ulrich
authors.initials: U
authors.lastname: Bierbach
mesh_terms: D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002942:Circular Dichroism; D018736:DNA Adducts / Q000737:chemistry*; D007364:Intercalating Agents / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry; D017671:Platinum Compounds / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013890:Thiourea / Q000737:chemistry*; D014508:Urea / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: C471910:1-(2-(acridin-9-ylamino)ethyl)-1,3-dimethylthiourea; D018736:DNA Adducts; D007364:Intercalating Agents; D009692:Nucleic Acid Heteroduplexes; D017671:Platinum Compounds; D014508:Urea; D013890:Thiourea