How does cisplatin alter DNA structure? A molecular mechanics study on double-stranded oligonucleotides

Cisplatin adducts of d(CCTCTG*G*TCTCC).d(GGAGACCAGAGG) in aqueous solution by vibrational circular dichroism spectroscopy

The vibrational circular dichroism (VCD) and IR absorption spectra of a dodecamer d(CCTCTGGTCTCC).d(GGAGACCAGAGG) coordinated with cisplatin are distinct compared to those of the dodecamer without cisplatin. Although the intensity of PO(2)/deoxyribose absorptions (1150-850 cm(-1)) increases noticeably relative to those of the carbonyl and ring deformations of the bases (1750-1500 cm(-1)), the VCD spectra differ to a much greater extent. Overlapping positive and negative bands can be assigned relatively easily to individual vibrational modes. The effect of platination on the dodecamer duplex is expressed most prominently in VCD arising solely from the vibrations of the guanines bound to the platinum atom. The effect on the VCD features of other bases leads to minute wavenumber shifts at most. These observations are in agreement with previous NMR and X-ray experiments on the same oligonucleotide. The assignment of the absorption and VCD bands strongly resembles those of the octamer duplex d(CCTGGTCC).d(GGACCAGG) when coordinated with platinum. The spectra of the dodecamer did not indicate any isomerization of the complex with time, as is clearly the case for the octamer.

Interaction of anticancer drug cisplatin with guanine: Density functional theory and surface-enhanced Raman spectroscopy study

Surface-enhanced Raman spectroscopy (SERS) in a silver sol assisted by density functional theory (DFT) calculations is shown to be a promising tool in the characterization of platinum complexes and their interaction with nucleic acid bases. This is demonstrated using cisplatin and guanine as a model. The energies and geometric parameters of cisplatin, guanine, and their reaction products are calculated at Becke's nonlocal three parameter exchange and correlation functional and the Lee-Yang-Parr correlation functional level using the 6-31++G(d,p) basis set on the light elements and the effective core potential by Hay and Wadt on platinum. Available X-ray crystallography data are mostly in agreement with predictions within the experimental precision level, although Pt-N bond lengths tend to be systematically overestimated. The normal Raman spectrum of cisplatin is assigned. The SERS spectra of cisplatin and its reaction product with guanine are measured from 10(-6) M aqueous solution. The observed spectral changes in the SERS spectrum of guanine upon cisplatin binding are modeled by DFT calculations. The best agreement between theory and experiment is achieved when the adsorbed reaction product is assumed to be the 1:1 adduct cis-Pt(NH3)2ClG in which Pt is bound to N7 and guanine is deprotonated at N9.

Unprecedented head-to-head conformers of d(GpG) bound to the antitumor active compound tetrakis (mu-carboxylato)dirhodium(II,II)

The N7/O6 equatorial binding interactions of the antitumor active complex Rh(2)(OAc)(4)(H(2)O)(2) (OAc(-) = CH(3)CO(2)(-)) with the DNA fragment d(GpG) have been unambiguously determined by NMR spectroscopy. Previous X-ray crystallographic determinations of the head-to-head (HH) and head-to-tail (HT) adducts of dirhodium tetraacetate with 9-ethylguanine (9-EtGH) revealed unprecedented bridging N7/O6 guanine nucleobases that span the Rh-Rh bond. The absence of N7 protonation at low pH and the notable increase in the acidity of N1-H (pK(a) approximately 5.7 as compared to 8.5 for N7 only bound platinum adducts), suggested by the pH dependence titrations of the purine H8 (1)H NMR resonances for Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2-)[d(GpG)],are consistent with bidentate N7/O6 binding of the guanine nucleobases. The pK(a) values estimated for N1-H (de)protonation, from the pH dependence studies of the C6 and C2 (13)C NMR resonances for the Rh(2)(OAc)(2)(9-EtG)(2) isomers, concur with those derived from the H8 (1)H NMR resonance titrations. Comparison of the (13)C NMR resonances of C6 and C2 for the dirhodium adducts Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2)[d(GpG)] with the corresponding resonances of the unbound ligands [at pH 7.0 for 9-EtGH and pH 8.0 for d(GpG)], shows substantial downfield shifts of Deltadelta approximately 11.0 and 6.0 ppm for C6 and C2, respectively; the latter shifts reflect the effect of O6 binding to the dirhodium centers and the ensuing enhancement in the acidity of N1-H. Intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum of Rh(2)(OAc)(2)[d(GpG)] indicate head-to-head arrangement of the guanine bases. The Rh(2)(OAc)(2)[d(GpG)] adduct exhibits two major right-handed conformers, HH1 R and HH2 R, with HH1 R being three times more abundant than the unusual HH2 R. Complete characterization of both adducts revealed repuckering of the 5'-G sugar rings to C3'-endo (N-type), retention of C2'-endo (S-type) conformation for the 3'-G sugar rings, and anti orientation with respect to the glycosyl bonds. The structural features obtained for Rh(2)(OAc)(2))[d(GpG)] by means of NMR spectroscopy are very similar to those for cis-[Pt(NH(3))(2))[d(GpG)]] and corroborate molecular modeling studies.

Flow cytometric detection of apoptotic bone marrow cells with fractional DNA content after application of WR-2721, cyclophosphamide, cisplatin, and exposure of mice to gamma rays

Little is known about the mechanisms of apoptosis triggered in normal cells of the haemopoietic system by the aminothiol WR-2721 (Amifostine), chemotherapeutic drugs, and ionizing radiation; thus, the present study was undertaken to evaluate the effects of WR-2721, cyclophosphamide (CP), cisplatin (CDDP), and 60Co gamma rays on induction of apoptotic DNA degradation in bone marrow cells. Adult male Swiss mice were treated with WR-2721 (400 mg/kg b.wt.), CP (200 mg/kg b.wt.), and CDDP (10 mg/kg b.wt.), and exposed to 6 Gy 60Co gamma rays. Alterations in the number of apoptotic cells with fractional DNA content and also the cell cycle position of the non-apoptotic cells were determined in the bone marrow at 7 and 24 hours after treatment of mice with these agents, using flow cytometric assay of the controlled extraction of low-MW DNA from apoptotic cells. The chemotherapeutic drugs CP and CDDP and 60Co gamma rays triggered apoptosis and affected the cell cycle position of the non-apoptotic cells in the mouse bone marrow. The pretreatment of mice with WR-2721 resulted in the modulatory action of the aminothiol on induction of apoptotic cell death and changes in the cell cycle distribution of the non-apoptotic cells caused by the DNA-damaging agents. The patterns of changes in the frequency of apoptotic cells and the cell cycle position of the non-apoptotic cells, observed in the bone marrow, were dependent on the agent(s) applied and the time interval after application of the drug(s) and exposure of mice to gamma rays. Understanding of the mechanisms responsible for triggering of apoptotic cell death and disturbing of the cell cycle by the DNA-damaging agents, and modulation of the apoptotic and cell cycle pathways by the aminothiol WR-2721, can lead to more effective therapy and chemo- and radio-protection of normal cells.

WR-2721: inhibitor of cisplatin-induced micronuclei

The modulatory effect of S-2-/3-aminopropylamino/ethyl-phosphorothioic acid, (WR-2721, Amifostine) on induction of micronuclei by cis-diamminedichloroplatinum[II] (CDDP) was studied. The adult, male Swiss mice were treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, and/or with CDDP, at a dose 5 mg/kg or 10 mg/kg body weight. WR-2721 was given alone or 30 min before CDDP administration. The frequency of micronucleated polychromatic erythrocytes (MNPCEs) and also the number of polychromatic erythrocytes (PCEs) in the bone marrow and peripheral blood, at 24 h after the drug application, were determined. After administration of CDDP, the frequency of MNPCEs distinctly increased, and the number of PCEs decreased. As compared with the animals injected with CDDP only, in mice treated with WR-2721 before CDDP application, the number of MNPCEs was reduced and the frequency of PCEs was increased. However, WR-2721 given alone, without subsequent administration of cis-diamminedichloroplatinum[II], caused an increase in the number of micronucleated polychromatic erythrocytes and a decrease in the number of PCEs. The geno- and cyto-toxicity and chemoprotection were dependent on the doses of the agents WR-2721 and CDDP applied. In mice injected with CDDP and/or WR-2721, the patterns of changes in the frequency of MNPCEs and PCEs were similar in the bone marrow and peripheral blood, respectively. The protective effect of the aminothiol compound WR-2721 against induction of micronuclei and apoptotic cell death in the erythropoietic system by CDDP was shown.

DNase I footprinting of cis- or trans-diamminedichloroplatinum(II)-modified DNA

DNase I has been used as an enzymatic probe to visualize the conformational alteration induced in DNA by the binding of either the antitumor drug cis-platinum (cis-DDP) or the therapeutically inactive derivatives, trans-platinum (trans-DDP) and chlorodiethylene-triamineplatinum(II) (dien-Pt). We have constructed double-stranded oligonucleotides (52-mer) containing a single adduct either at the d(GG) site (cis-DDP intrastrand cross-link) or at the d(GC/GC) site (cis-DDP interstrand cross-link) or at the d(G/C) site (trans-DDP interstrand cross-link) or at the d(G) site (dien-Pt adduct). The platinated oligonucleotides are differently recognized by DNase I. As judged by DNase I, the distortions induced in the DNA double helix by the cis-DDP and trans-DDP interstrand cross-links spread over more base-pairs than that induced by the cis-DDP intrastrand cross-link.

Identification of DNA--cisplatin adducts in a blind trial of in situ scanning tunneling microscopy

Scanning tunneling microscopy (STM) reveals nanometer scale details of hydrated DNA but the interpretation of the images is controversial because of substrate artifacts and the lack of a theory for image contrast. We demonstrate that we have overcome these problems by identifying five DNA samples by their STM images alone in a blinded trial. The samples were single-stranded and double-stranded DNA with and without covalent modification by the anti-tumor drug cisplatin. The cisplatin adducts were distinguished by substantial kinking at the drug binding site. The oligomers were 20 bases in length, which was too short to permit the kinking angle to be determined with precision. However, models with a 45 degree kink gave a better fit to the images of the duplex adducts than models with a 90 degrees kink. A variety of structures was observed for the single-stranded adducts.

Cisplatin induced cell killing and chromosomal aberrations in CHO cells: treated during G1 or S phase

Variation in sensitivity to cisplatin during the cell cycle was studied in synchronous CHO cells treated during G1 or late S phase. The cells were assayed for cell killing, cell-cycle delay, and chromosomal aberrations after they were treated with cisplatin (1-12 micrograms/ml) for 1 h at 37 degrees C. They were either plated for colony survival, or colcemid was added from 12 to 40 h after plating followed by fixation 4 h later for analysis of chromosomal aberrations after the cells completed 1 or 2 cycles (i.e. first or second mitosis). Cells treated with 6 micrograms/ml exhibited about a 10-h delay during the first cycle after treatment during G1 compared with about 3 h during the first cycle and 6 h during the second cycle after treatment during late S. In both cases, cells entering metaphase exhibited predominantly chromatid-type breaks and exchanges. For both cell killing and chromosomal aberrations, the cells in G1 were 1.5-1.6 times more sensitive than those treated in late S, with 1 aberration per cell corresponding to about 37% survival. However, the exchanges and breaks were observed primarily in the first mitosis when cells were treated in G1 compared with the second mitosis when cells were treated in late S. These results suggest that DNA replication opposite cisplatin cross-links in the DNA results in lethal chromosomal aberrations.

Synthesis and characterization of a d(ApG) platinated nonanucleotide duplex

The nonamer 5'd(CTCAGCCTC) 3' 1 has been reacted with cis-diamminediaquaplatinum(II) in water at pH 4.2. The major reaction product was shown by enzymatic digestion and 1H NMR to be the d(ApG)cis-Pt(NH3)2 chelate [cis-Pt(NH3)2[d(CTCAGCCTC)-N7(4),N7(5)]] 1-Pt. When mixed with its complementary strand 2, 1-Pt forms a B DNA type duplex 3-Pt with a Tm of 35 degrees C (versus 58 degrees C for the unplatinated duplex). The NMR study of the exchangeable protons of 3-Pt revealed that the helix distortion is localized on the CA*G*-CTG moiety (the asterisks indicating the platinum chelation sites) with a strong perturbation of the A*(4)T(15) base pair related to a large tilt of A*(4).

The reaction of platinum(II) complexes with DNA. Kinetics of intrastrand crosslink formation in vitro

The kinetics of the formation of bifunctional DNA platinum(II) adducts (DNA-crosslinks) have been investigated by endonuclease digestion and subsequent HPLC analysis of the soluble nucleotides and nucleotide platinum(II) adducts. The results indicate two waves of crosslinking [rate constants (0.2-0.3) min-1 and (0.015-0.025) min-1] that correlate with changes in ultra violet absorbance and ethidium bromide dependent fluorescence intensity, previously interpreted in terms of two consecutive, local conformational rearrangements of platinum-DNA (Schaller, W., Reisner, H., and Holler, E. (1987) Biochemistry 26, 943-950). The formation of crosslinks at sequences d(GpG) and d(GpNpG) follows identical kinetics. A minimal reaction mechanism is proposed for the binding of cis-diamminedichloroplatinum(II) to DNA under in vitro conditions. The approximately 3-fold higher rate for meso-[1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]diaquaplatinum(II) in comparison to the rate for cis-diamminediaquaplatinum(II) indicates that crosslink formation is affected by the nature of the non-leaving platinum ligand(s).