title: Model platinum nucleobase and nucleoside complexes and antitumor activity: X-ray crystal structure of [PtIV(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-ethylguanine)Cl]NO3.H2O.
abstract: A series of platinum(II) and (IV) monoadducts of the type [Pt(II)(DACH)LCl]NO3 and [Pt(IV)(DACH)trans-(X)2LCl]NO3 (where DACH=trans-1R,2R-diaminocyclohexane, L=adenine, guanine, hypoxanthine, cytosine, adenosine, guanosine, inosine, cytidine, 9-ethylguanine (9-EtGua), or 1-methylcytosine and X=hydroxo or acetato ligand) have been synthesized and characterized by elemental analysis and by 1H and 195Pt nuclear magnetic resonance (NMR) spectroscopy. The crystal structure of the model nucleobase complex [Pt(IV)(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-EtGua)Cl]NO3.H2O was determined using a single crystal X-ray diffraction method. The compound crystallized in the monoclinic space group P2(1), with a=10.446(2) A, b=22.906(5) A, c=10.978(2) A, Z=4, and R=0.0718, based upon the total of 11,724 collected reflections. In this complex, platinum had a slightly distorted octahedron geometry owing to the presence of a geometrically strained five-member ring. The two adjacent corners of the platinum plane were occupied by the two amino nitrogen of DACH, whereas, the other two equatorial positions occupied by chloride ion and 9-ethylguanine. The remaining two axial positions were occupied by the oxygen atoms of acetato ligands. The DACH ring was in a chair configuration. An intricate network of intermolecular hydrogen bonds held the crystal lattice together. Some of these synthesized models of DACH-Pt-DNA adducts have good in vitro cytotoxic activity against the cisplatin-sensitive human cancer ovarian A2780 cell line (IC50=1-8 microM). Interestingly, a substituted nucleobase (9-ethylguanine) adduct was over 6-fold more potent than regular adducts. The cross-resistance factor against the 44-fold cisplatin-resistant 2780CP/clone 16 cells was about 3-9; thus, the cytotoxicity of adducts was indicative of low potency, but the resistance factors were also substantially low. These results suggest that DNA adducts of DACH-Pt are cytotoxic with low cross-resistance.
authors.affiliation: Department of Experimental Therapeutics, P.O. Box 353, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA.
authors.forename: Mohammad S
authors.initials: MS
authors.lastname: Ali
authors.forename: S Rounaq Ali
authors.initials: SR
authors.lastname: Khan
authors.forename: H
authors.initials: H
authors.lastname: Ojima
authors.forename: Ilse Y
authors.initials: IY
authors.lastname: Guzman
authors.forename: Kenton H
authors.initials: KH
authors.lastname: Whitmire
authors.forename: Zahid H
authors.initials: ZH
authors.lastname: Siddik
authors.forename: Abdul R
authors.initials: AR
authors.lastname: Khokhar
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology; D002945:Cisplatin / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods; D003514:Cyclohexylamines / Q000737:chemistry; D006147:Guanine / Q000737:chemistry; D006801:Humans; D020128:Inhibitory Concentration 50; D008958:Models, Molecular; D009566:Nitrates / Q000737:chemistry; D009705:Nucleosides / Q000737:chemistry* / Q000378:metabolism; D009944:Organoplatinum Compounds / Q000737:chemistry* / Q000494:pharmacology; D010984:Platinum / Q000737:chemistry* / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D003514:Cyclohexylamines; D009566:Nitrates; D009705:Nucleosides; D009944:Organoplatinum Compounds; D010984:Platinum; D006147:Guanine; D002945:Cisplatin