title: Locating the binding sites of antitumor drug tamoxifen and its metabolites with DNA.
abstract: We located the binding sites of antitumor drugs tamoxifen, 4-hydroxytamoxifen and endoxifen with calf-thymus DNA. FTIR, CD, UV-vis and fluorescence spectroscopic methods as well as molecular modeling were used to characterize the drug binding sites, binding constant and the effect of drug binding on DNA stability and conformation. Structural analysis showed that tamoxifen and its metabolites bind DNA via hydrophobic and hydrophilic interactions with overall binding constants of K(tam-DNA)=3.5 (±0.2)×10⁴ M⁻¹, K(4-hydroxytam-DNA)=3.3 (±0.4) × 10⁴ M⁻¹ and K(endox)-DNA=2.8 (±0.8)×10⁴ M⁻¹. The number of binding sites occupied by drug is 1 (tamoxifen), 0.8 (4-hydroxitamoxifen) and 1.2 (endoxifen). Docking showed the participation of several nucleobases in drug-DNA complexes with the free binding energy of -3.85 (tamoxifen), -4.18 (4-hydroxtamoxifen) and -3.74 kcal/mol (endoxifen). The order of binding is 4-hydroxy-tamoxen>tamoxifen>endoxifen. Drug binding did not alter DNA conformation from B-family structure, while major biopolymer aggregation occurred at high drug concentrations. The drug binding mode is correlated with the mechanism of action of antitumor activity of tamoxifen and its metabolites.
authors.affiliation: Department of Chemistry-Physics, University of Québec in Trois-Rivières, C. P. 500, Trois-Rivières, Québec G9A 5H7, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Bourassa
authors.affiliation: Department of Medicine, Rutgers Robert Wood Johnson Medical School, and Rutgers Cancer Institute of New Jersey, New Brunswick, NJ 08901, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Thomas
authors.affiliation: Department of Chemistry-Physics, University of Québec in Trois-Rivières, C. P. 500, Trois-Rivières, Québec G9A 5H7, Canada. Electronic address: tajmirri@uqtr.ca.
authors.forename: H A
authors.initials: HA
authors.lastname: Tajmir-Riahi
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D062105:Molecular Docking Simulation; D009690:Nucleic Acid Conformation; D013050:Spectrometry, Fluorescence; D013629:Tamoxifen / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen; D004247:DNA
keywords: Binding site; Conformation; DNA; Endoxifen; Tamoxifen