| This dissertation addresses with the DNA interactions of a novel cytotoxic acridine derivative, 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea (ACRAMTU) and the corresponding platinum conjugate, [PtCl(en)(ACRAMTU)](NO 3)2 (PT-ACRAMTU; en = enthane-1,2-diamine). The introduction (Chapter 1) provides an overview of the different types of small-molecule DNA binders and their interactions with this important biomolecule. The methods used to study these interactions are also discussed.; The DNA binding affinity and sequence and groove specificity of ACRAMTU and an inactive derivative, 1-acridin-9-yl-1,3-dimethylthiourea (DMACRTU), were studied using physico-chemical and biophysical techniques. ACRAMTU (p Ka ≈ 9.8) exhibited a high DNA binding affinity of Ki = 106 M-1 (von Hippel-McGhee model), while DMACRTU (pKa = 3.4) did not bind to DNA. PT-ACRAMTU unwinds pUC19 plasmid by 21°/adduct, suggesting a combination of coordinative and intercalative interactions, while PT-DMACRTU showed only a minor unwinding effect (&phis; = 7°/adduct). Structure-activity and "unwinding-activity" relationships are discussed (Chapter 2).; A high-resolution nuclear magnetic resonance spectroscopy/restrained molecular dynamics (NMR/rMD) study of ACRAMTU with several self-complementary oligonucleotide sequences was performed to explore the base step selectivity of the acridine chromophore and the groove specificity of the thiourea residue. ACRAMTU shows a dual preference for 5'-TA/TA and 5 '-CG/CG, and, most unusually, tolerates 5'-GA/TC sites (relative affinities were confirmed by equilibrium dialysis experiments). In all cases the non-intercalating thiourea residue lies in the minor groove.; Chapter 4 presents the crystal structure and NMR characterization ( 1H, 195Pt) of the major PT-ACRAMTU DNA adduct, [Pt(en)(ACRAMTU-S)(dGuo)] 3+ (dGuo*), identified in enzymatic digests. The structure confirms guanine-N7 coordination of platinum. The adduct exists as dimers both in the solid state and in solution with the guanine bases forming a rare GG - base pair. The acridine-GG- pi-pi stacking in this structure resembles DNA intercalation. (Abstract shortened by UMI.)... |
