Interaction of small molecules with nucleic acid targets: from RNA secondary structure to the riobosome
Canzoneri, Joshua Craig
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Nucleic acids have proven to be viable targets for small molecule drugs. While many examples of such drugs are detailed in the literature, only a select few have found practical use in a clinical setting. These currently employed nucleic acid targeting therapies suffer from either debilitating off-target side effects or succumb to a resistance mechanism of the target. The need for new small molecules that target nucleic acids is evident. However, designing a novel drug to bind to DNA or RNA requires a detailed understanding of exactly what binding environments each nucleic acid presents. In an effort to broaden this knowledge, the work presented in this thesis details the binding location and affinity of known and novel nucleic acid binding small molecules with targets ranging from simple RNA secondary structure all the way to the complex structure of ribosomal RNA. Specifically, it is shown that the anthracycline class of antineoplastics prefer to bind at or near mismatch base pairs in both physiologically relevant iron responsive element RNA hairpin constructs as well as DNA hairpin constructs presenting mismatched base pairs. Also characterized in this thesis is a novel class of topoisomerase II / histone deacetylase inhibitor conjugates that display a unique affinity for DNA over RNA. Finally, the novel class of macrolide-peptide conjugates, known as peptolides, are shown to retain potent translation inhibition of the prokaryotic ribosome. The binding pocket of the peptolides, including a crevice previously unreachable by macrolides that extends away from the peptidyl transferase center toward the subunit interface, is confirmed in detail via chemical footprinting of the 70S ribosome. Overall, the identification of a novel binding site for the anthracycline class of drugs and the characterization of the two novel drug designs presented in this thesis will undoubtedly aid in the effort to design and discover new molecules that aim for nucleic acid targets. For example, the anthracycline derivative topoisomerase II / histone deacetylase inhibitor conjugates, with their differential mode of nucleic acid binding, may prove to have a unique side effect profile in a therapeutic application. The peptolide compounds also have the potential to be applied as novel antibiotics as they bind to an area of the prokaryotic ribosome unrelated to known macrolide resistance mutations. Furthermore, as a result of the observation of this thesis work that some peptolides also posses eukaryotic translation inhibition capabilities, they could prove to be useful in preventing the growth of rapidly proliferating eukaryotic cells such as plasmodium, leishmania, or tumor cells. Additionally, different head groups could be utilized in creating new peptolides; for example, an oxazolidinone antibiotic could be employed to sample a different binding area of the ribosome.