New Negamycin-Based Potent Readthrough Derivative Effective against TGA-Type Nonsense Mutations.

We report a novel negamycin derivative TCP-1109 (13x) which serves as a potent readthrough drug candidate against nonsense-associated diseases. We previously demonstrated that TCP-112 (7), a nor-compound of native 3-epi-deoxynegmaycin, showed a higher readthrough activity than (+)-negamycin. In the present study, we performed a structure-activity relationship (SAR) study of compound 7 focused on its 3-amino group in an effort to develop a more potent readthrough compound. Introduction of a variety of natural or unnatural amino acids to the 3-amino group gave us the more potent derivative 13x which has about four times higher readthrough activity than 7 in a cell-based assay using a premature termination codon of TGA derived from Duchenne muscular dystrophy. The activity was dose-dependent and relatively selective for TGA. However, the activities for TAG and TAA were also higher than those of (+)-negamycin and 7. Moreover, compound 13x showed significant cell-based readthrough activity for several nonsense mutations derived from other nonsense-associated diseases. It is suggested that 13x has the potential to be a readthrough drug useful for the treatment of many kinds of nonsense-associated diseases.

Structure-Activity Relationship Studies of 3-epi-Deoxynegamycin Derivatives as Potent Readthrough Drug Candidates.

(+)-Negamycin (1), a natural dipeptidic antibiotic bearing a hydrazide structure, exhibits a readthrough activity toward the nonsense mutation of the dystrophin gene and restores dystrophin expression in muscles of Duchenne muscular dystrophy model mdx mice. Herein to develop more potent readthrough compounds, we performed a structure-activity relationship (SAR) study of 3-epi-deoxynegamycin (2), which is also another natural readthrough compound with little antimicrobial activity, focusing on the main carbon chain length. We found that one carbon atom shorter derivative 9b shows a higher readthrough activity than 1 and 2. Further derivatization at the carboxylic acid part of 9b demonstrates that its meta-chlorobenzyl ester derivative 17e, which has a higher ClogP value, exhibits a more potent readthrough activity than 9b. Interestingly, in the cell-free protein expression system, the readthrough activity of 17e drastically decreases compared to that in the cell-based assay. These results suggest that benzyl ester-type derivatives enhance the hydrophobicity and function as prodrugs to produce active compound 9b in living cell systems.

Discovery of natural products possessing selective eukaryotic readthrough activity: 3-epi-deoxynegamycin and its leucine adduct.

Herein we report the first discovery of natural readthrough products that do not display antimicrobial activity. Two natural negamycins, 3-epi-deoxynegamycin and its leucine adduct, isolated 37 years ago, were found to be potent readthrough agents against nonsense mutations of eukaryotes, but not prokaryotes, without displaying antimicrobial activity. These results suggest that the compounds are valuable leads for the development of readthrough drugs against nonsense-mediated genetic diseases without the potential for contributing to the emergence of drug-resistant bacteria.