Poster abstracts

Poster number 145 submitted by Hongkun Zhu

Functional characterization of derivatives of the aminoglycoside tobramycin

Hongkun Zhu (Department of Microbiology, The Ohio State University), Keith D. Green (Department of Pharmaceutical Sciences, University of Kentucky), Sylvie Garneau-Tsodikova (Department of Pharmaceutical Sciences, University of Kentucky), Kurt Fredrick (Department of Microbiology, The Ohio State University)

Abstract:
A major problem in health care today is the emergence of multi-drug resistance in bacterial pathogens. In efforts to find ways to evade these resistance mechanisms, numerous derivatives of the aminoglycoside (AG) tobramycin (TOB) were made and tested for biological activity against a broad spectrum of bacteria (1). Here, these TOB derivatives, with various substitutions at the 6’’-position of ring III, are further characterized with respect to their mode of action. We tested the ability of each to inhibit (i) growth of E. coli strain ∆7 prrn (WT), (ii) growth of aminoglycoside-resistant E. coli ∆7 prrn (A1408G), (iii) translocation in WT ribosomes, and (iv) translocation in A1408G ribosomes. Based on the data obtained, the variants fall into distinct functional classes. Those in class A inhibit growth and translocation in A1408-dependent manner, like the parental TOB, suggesting that act by binding the primary h44 site. These compounds are substituted with similarly-sized groups (tert-butyl, benzyl, p-methyl benzyl, cyclohexyl) at the 6’’-position. Class B variants inhibit translocation in an A1408-dependent manner but fail to inhibit growth, suggesting that they target h44 but bind with low affinity or accumulate to lower levels in the cell. Class C variants inhibit both translocation and growth, but only the former activity is A1408-dependent. Presumably, these compounds target h44 and something else in the cell. Class D variants inhibit translocation and growth, and neither activity depends on A1408. These compounds may target another ribosomal site and potentially another cellular component. Class E variants inhibit growth in an A1408-independent manner and fail to inhibit translocation, indicating that they target something other than the ribosome. A common feature of most of the class C, D, and E compounds is a linear alkyl chain extending from the 6’’ position. A subset of these compounds cause cell lysis (1), implicating the membrane as a cellular target in these cases. Together these data provide insight into h44 binding and translocation inhibition by AG antibiotics.

References:
1. I. M. Herzog, K. D. Green, Y. Berkov-Zrihen, M. Feldman, R. R. Vidavski, A. Eldar-Boock, R. Satchi-Fainaro, A. Eldar, S. Garneau-Tsodikova, and M. Fridman, Angew. Chem. Int. Ed. 2012, 51, 5652.

Keywords: Aminoglycoside, h44, ribosome