Quantum mechanical prediction of the conformational preferences of daunomycins and their relationship to reactivity

Ultrafast Electron Transfer in Complexes of Doxorubicin with Human Telomeric G-Quadruplexes and GC Duplexes Probed by Femtosecond Fluorescence Spectroscopy

Doxorubicin (DOX) is a natural anthracycline widely used in chemotherapy; its combined application as a chemotherapeutic and photodynamic agent has been recently proposed. In this context, understanding the photoinduced properties of DOX complexes with nucleic acids is crucial. Herein, the study of photoinduced electron transfer in DOX-DNA complexes by femtosecond fluorescence spectroscopy is reported. The behaviour of complexes with two model DNA structures, a G-quadruplex (G4) formed by the human telomeric sequence (Tel21) and a d(GC) duplex, is compared. The DOX affinity for these two sequences is similar. Although both 1:1 and 2:1 stoichiometries have been reported for DOX-G4 complexes, only 1:1 complexes form with the duplex. The steady-state absorption indicates a strong binding interaction with the duplex due to drug intercalation between the GC base pairs. In contrast, the interaction of DOX with Tel21 is much weaker and arises from drug binding on the G4 external faces at two independent binding sites. As observed for DOX-d(GC) complexes, fluorescence of the drug in the first binding site of Tel21 exhibits decays within a few picoseconds following a biphasic pattern; this is attributed to the existence of two drug conformations. The fluorescence of the drug in the second binding site of Tel21 shows slower decays within 150 ps. These timescales are consistent with electron transfer from the guanines to the excited drug, as favoured by the lower oxidation potential of the stacked guanines of G4 with respect to those in the duplex.

The anticancer drug-DNA complex: femtosecond primary dynamics for anthracycline antibiotics function

The anthracycline-DNA complex, which is a potent agent for cancer chemotherapy, has a unique intercalating molecular structure with preference to the GC bases of DNA, as shown by Rich's group in studies of single-crystal x-ray diffraction. Understanding cytotoxicity and its photoenhancement requires the unraveling of the dynamics under the solution-phase, physiological condition. Here we report our first study of the primary processes of drug function. In a series of experiments involving the drug (daunomycin and adriamycin) in water, the drug-DNA complexes, the complexes with the four nucleotides (dGTP, dATP, dCTP, and dTTP), and the drug-apo riboflavin-binding protein, we show the direct involvement of molecular oxygen and DNA base-drug charge-separation-the rates for the reduction of the drug and dioxygen indicate the crucial role of drug/base/O(2) in the efficient and catalytic redox cycling. These dynamical steps, and the subsequent reactions of the superoxide product(s), can account for the photoenhanced function of the drug in cells, and potentially for the cell death.

Femtosecond dynamics of a drug-protein complex: daunomycin with Apo riboflavin-binding protein

In this contribution, we report studies of the primary dynamics of the drug-protein complexes of daunomycin with apo riboflavin-binding protein. With femtosecond resolution, we observed the ultrafast charge separation between daunomycin and aromatic amino acid residues of the protein, tryptophan(s). Electron transfer occurs from tryptophan(s) to daunomycin with two reaction times, 1 ps and 6 ps, depending on the local complex structure. The formation of anionic daunomycin radical is crucial for triggering a series of chemical reactions in redox cycling. One of the subsequent reactions is the reduction of dioxygen to form active superoxide by the reduced daunomycin. This catalytic process was found to occur within 10 ps. In the absence of dioxygen, charge recombination takes a much longer time, more than 100 ps. These results, along with similar findings in DNA and nucleotides, elucidate that the ultrafast generation of reduced daunomycin radicals by photoactivation is a primary step for the observed photoenhancement of drug cytotoxicity by several orders of magnitude. We also studied the dependence of the dynamics on protein conformations at different ionic strengths and denaturant concentrations. We observe a sharp transition from the tertiary structure to the unfolding state at 2 M of denaturant concentration.

Circular dichroism studies on anthracycline antitumor compounds. Relationship between the molecular structure and the spectroscopic data

The band assignment of the circular dichroism (CD) spectra of anthracyclines can provide us with the tools to study the interaction of these molecules with biomolecules, such as DNA and membranes, and also with metal ions. This paper reports the CD spectra of 17 anthracycline derivatives and the tentative assignment of the bands to specific electronic transitions. The deprotonation of some anthracyclines, such as doxorubicin, daunorubicin, and idarubicin, have been also studied in order to characterize the electronic transitions involved in the acid-base process. Our evidence suggests the following assignment. The position of the band assigned to pi-->pi transition, polarized along the short axis of the molecule ( approximately 290 nm), does not depend on the hydroxyl group at C(11) (presence and/or ionization state), whereas the position of the band assigned to the pi-->pi transition ( approximately 480 nm), polarized along the long axis, is strongly dependent on it. Concerning the n-->pi transitions, the bands at approximately 320 and approximately 350 nm have a strong contribution of the n-->pi C(12)=O transition and the n-->pi C(5)=O transition, respectively.