Design and study of artificial nucleases for DNA photocleavage

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Artificial nucleases are molecules capable of inducing single- or double-strand breaks in the DNA backbone.  Molecules that cleave DNA  upon activation with light are especially important in photodynamic therapy (PDT), a strategy that has been applied to the successful treatment of certain cancers and age-related macular degeneration.  Current clinical agents for PDT suffer from three major limitations:  (i) requirement for oxygen to function, (ii) minimum absorption of light at wavelengths most transparent to tissue, and (iii) inability to produce double-strand breaks.  This proposal outlines a research plan that is devoted to overcoming such limitations by introducing new  agents that elicit double-strand breaks in DNA under hypoxic conditions when activated with 700-900 nm light.  The first proposed family of DNA photocleavers is based on dinuclear Ru(II) complexes that absorb light >700 nm.  Extension of this family will include incorporation of Rh(II) to make hybrid multimetallic systems that cleave DNA in the absence of oxygen.  The multimetallic framework will provide two sites of reactivity for DNA cleavage.  Dual reactivity within 15-16 base pairs will introduce double-strand breaks which are more difficult for the cellular machinery to repair.       A related research stream involves  the jadomycins, a family of secondary metabolites that induces DNA strand scissions in the presence of Cu(II) or with light activation.  While  they fall short of the properties outlined for the ideal PDT agent, jadomycins exhibit cytotoxic activity against both Gram positive and Gram negative bacteria as well as some drug-resistant cancer cell lines. This research program will determine whether direct DNA cleavage contributes to the overall cytotoxicity of the jadomycins at intracellular Cu(II) concentrations.  In addition, the DNA photocleaving properties of the jadomycins will be investigated, with particular attention on the mechanism that predominates with Cu(II) activation versus light activation.  The role that L-digitoxose, a structural feature of jadomycin B, plays in DNA cleavage will also be probed to better understand how glycone incorporation aids in DNA recognition.