This thesis reports a study of the chemical stability and coordination chemistry of several antitumour metallocenes Cp2MCl2 (Cp = h5-C5H5; M = Ti 1, V 2, Nb 3, Mo 4), as well as derivatives of Cp2TiCl2 1, with nucleic acids, nucleic acid constituents and proteins. These studies were carried out in order to identify the biologically active species and more fully understand the molecular level mechanism of action of the antitumour metallocenes, in particular Cp2TiCl2 1, which is currently undergoing phase II clinical trials. The interactions of Cp2MoCl2 4 with four oligonucleotides were studied by 1H and 31P NMR spectroscopy. In 50 mM salt solutions of Cp2MoCl2 4, hydrolysis of the halide ligands occurred to give a solution with pD -2, containing a species in which both Cp rings remain metal bound for 24 h. At pD -7, partial hydrolysis of the Cp rings (-30percent) occurred after 24 h. Addition of an aqueous solution of Cp2MoCl2 4 in 50 mM salt to the self-complementary sequence d(CGCATATGCG)2, maintaining the pD at 6.0-7.0, showed no evidence for the formation of a metallocene-oligonucleotide complex and only peaks arising from hydrolysis of Cp2MoCl2 4 were detected. A similar result was obtained in titration experiments with the single stranded sequence d(ATGGTA) at pD 6.5-7.0. However, at pD 3.0, new signals assigned to a molybdocene-oligonucleotide complex(es), which was stable for hours at pD 3.0, were detected; while at pD -7 the complex is destabilised and only peaks arising from hydrolysis of Cp2MoCl2 4 were detected. Titration experiments at low pD with Cp2MoCl2 4 and the dinucleotide dCG were consistent with formation of a complex arising due to coordination of molybdenum to guanine N7 and/or cytosine N3. The results obtained showed that stable oligonucleotide adducts were not formed in 50 mM salt at pD -7 and hence it is highly unlikely that formation of molybdocene-DNA adducts in vivo is the primary action that is responsible for the antitumour properties of Cp2MoCl2 4. The rate of hydrolysis of the aromatic rings of Cp2TiX2 (X equals Cl 1, OCOCH2NH3Cl 27) and the dimethylsubstituted derivatives (MeCp)2TiX2 (X equals Cl 34, OCOCH2NH3Cl 41), in aqueous solutions at pD 2-8 was studied by 1H NMR spectroscopy. Rapid hydrolysis of both the halide/glycine and Cp ligands in Cp2TiX2 (X equals Cl 1, OCOCH2NH3Cl 27) occurred and predominantly gave a precipitate at pD -7. In contrast, under the same experimental conditions, the predominant species present in aqueous solutions of (MeCp)2TiX2 (X equals Cl 34, OCOCH2NH3Cl 41) at pH 2-8 contained both MeCp rings metal bound. At pD < 5, Cp2TiX2 (X equals Cl 1, OCOCH2NH3Cl 27) and (MeCp)2TiX2 (X equals Cl 34, OCOCH2NH3Cl 41) formed similar complex(es) with purine nucleotides. However, at pD >5, stable adducts between nucleotides and Cp2TiX2 (X equals Cl 1, OCOCH2NH3Cl 27) were not formed. In contrast, (MeCp)2TiX2 (X equals Cl 34, OCOCH2NH3Cl 41) formed complex(es) with 5'-dAMP or 5'-dGMP, which were stable for 24 h. These results suggest that formation of stable chelates between (MeCp)2TiX2 (X equals Cl 34, OCOCH2NH3Cl 41) and nucleic acid constituents in vivo is possible. However, the methyl substituted derivatives 34 and 41 did not show any antitumour activity against EAT in mice when administered in either 10percentDMSO/90percentsaline or in water at pH 6.2-6.4, which suggests that the labile Cp-Ti bond present in Cp2TiCl2 1 is required for antitumour activity. The synthesis of a range of Cp substituted titanocene derivatives was investigated in an attempt to prepare derivatives with modified Cp stability in comparison to the methyl substituted derivatives. The synthesis of derivatives (CpCH2Y)2TiCl2 where Y equals ?CHO 43, ?CONMe2 44, ?NO2 45, (RCp)2TiCl2 where R equals ?COMe 46, ?COOMe 47 or ?CONMe2 48, (CpNMe2)2TiCl2 62 and (Cp(CH2)2NMe2)2TiCl2 63 was unsuccessful, due to the presence of coordinating substituents on the Cp rings and poor stability in polar, protic solvents. Hence, these derivatives were excluded from further studies. The rate of hydrolysis of the Cp rings of Cp2TiX2 (X equals Cl 1, OCOCCl3 22 and OCOCH2NH3Cl 27) in aqueous solutions, 10percentDMSO/90percentD2O and 100percent DMSO was monitored by 1H NMR spectroscopy. Rapid hydrolysis of both the carboxylate and Cp ligands of Cp2TiX2 (OCOCCl3 22 and OCOCH2NH3Cl 27) occurred in DMSO to give biologically inactive species. The rate of these reactions were concentration dependent as dilution of these samples with saline or water to give the therapeutic conditions of 10percentDMSO/90percentD2O slowed the hydrolysis chemistry. In contrast, samples of Cp2TiX2 (X equals Cl 1 and OCOCH2NH3Cl 27) dissolved in water, gave solutions containing the presumed antitumour active species in which the halide or glycine ligands have been hydrolysed but the Cp rings remain metal bound. Thus, charged X ligands may be incorporated into Cp2TiX2 and will give comparable activity to Cp2TiCl2 1 provided the samples are administered in water. The antitumour metallocenes Cp2MCl2 (M equals Ti 1, V 2, Nb 3, Mo 4) and the inactive derivative (MeCp)2TiCl2 34 were found to inhibit the relaxation of supercoiled plasmid DNA pBR322 by human topoisomerase II in vitro. These results implicated the inhibition of topoisomerase II in the mechanism of antitumour activity although there was no direct correlation between the in vitro results with biological activity against EAT in vivo. UV spectroscopy confirmed that the metallocenes Cp2MCl2 (M equals Ti 1, Mo 4) became associated with and were stabilised to hydrolysis by calf thymus DNA but not with human serum albumin. ICP-AES was used to measure the amount of metal associated with either DNA or human serum albumin after incubation with Cp2MCl2 (M equals Ti 1, Nb 3, Mo 4) and dialysis of these solution. The results confirmed that DNA stabilises or becomes associated with the metallocenes. However, errors associated with the ICP-AES measurements did not allow these results to be quantified. 1H NMR spectroscopy was used to show that the antitumour metallocene Cp2MoCl2 4 formed an adduct with glutathione 72 in the pH range 3-7 through the sulfur donor group. In comparison, the antitumour metallocenes Cp2MCl2 (M equals Ti 1, Nb 3) showed limited adduct formation with glutathione 72 at pH -3 and no adducts were detected at pH > 5.5.
| Identifer | oai:union.ndltd.org:ADTP/283152 |
| Date | January 2000 |
| Creators | Mokdsi, George |
| Publisher | University of Sydney. Chemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English, en_AU |
| Detected Language | English |
| Rights | Copyright Mokdsi, George;http://www.library.usyd.edu.au/copyright.html |
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