Anthracyclines are common antitumor antibiotics for cancer treatments characterized by a conjugated four ring system. Doxorubicin, a marketed anthracycline, intercalates into the DNA double helix, preventing cellular replication in tumors. A positively charged sugar moiety attached to the anthracycline base interacts with the negatively charged phosphate backbone of DNA, leading to a strong DNA/drug interaction. The binding mechanism of doxorubicin has been extensively studied due to its high toxicity and aims towards improving its specificity. A doxorubicin analogue, doxorubicinone, does not have the sugar moiety, has the potential for a unique binding profile that could reduce toxicity. Preliminary circular dichroism data show that, despite the lack of favorable charge interactions between the drug and DNA, doxorubicinone intercalates into DNA. It is suspected, that the decreased solubility of doxorbucinone will enhance the hydrophobic effect and may give insights into the role of water in drug-DNA binding interactions. We will use the osmotic stress method to determine if water is released or taken-up during binding. Fluorescence titrations with increasing concentrations of triethylene glycol (TEG) yield binding constants that are plotted against osmolality to determine the number of water molecules exchange during the binding event. TEG was selected as the osmolyte following extensive studies on DNA osmolyte interactions using circular dichroism and viscosity. This osmolyte showed the least disruption to the DNA helix, making it an ideal osmolyte that only dehydrates DNA. Previously, it has been reported that most intercalators have a net uptake of 10 water molecules in the binding event. Doxorubicinone in fact has a net uptake of 65 water molecules when binding to genomic DNA that is 42% GC base pairs, while weakly binding to poly(dA-dT) DNA, suggesting that there is sequence specificity for GC base pairs. The Van’t Hoff method will be used to calculate the changes in enthalpy and entropy. Intercalators typically have large negative enthalpy values and very small changes in entropy. If the hydrophobic effect is enhanced, the entropy change may increase accordingly.

Thermodynamic characterization of a novel anthracycline/DNA binding mechanism

253rd National Meeting (2017)

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