Development of the Antibiotic Potential of a Unique Family of DNA Polymerase Inhibitors

Abstract

The work in the Brown laboratory has two long-range objectives. Both are derived from an interest in the replication of the genome of Gram-positive eubacteria. One objective is to gain a deeper understanding of the structure and function of DNA polymerase III, the unique species of DNA polymerase which is essential for chromosome replication. The second objective, the one from which this thesis is derived, is to determine whether a selective inhibitor of this DNA polymerase can serve as a basis for producing a new generation of clinically useful Gram-positive-selective antimicrobial agents. The polymerase III-specific inhibitor prototypes investigated in this work are members of a family of simple 6-substituted uracils. The following members of this family, TMAU and EMAU, were used as platforms for the manipulation of the N3 atom (arrow), the only ring component which could be substituted without severe reduction of inhibitory activity. The N3 position was substituted with a series of alkyl groups of increasing size. The resulting structure-activity relationships at the level of the polymerase was consistent with the presence of an N3-specific subdomain within the inhibitor binding site which could accommodate a wide variety of substituents. Although specific alkyl substituents at N3 also significantly enhanced the antibacterial potency of TMAU and EMAU, the respective compounds were found to have insufficient aqueous solubility for successful application in in vivo infection. To increase aqueous solubility, the N3 atom of the EMAU platform was substituted with selected hydroxy- and methoxyalkyl groups. The latter agents retained both anti-polymerase and antibacterial activity, and, as expected, they displayed a combination of lipid and aqueous solubility favorable to efficacy in in vivo infection. Two of the agents, N3-hydroxypropyl- and N3-methoxypropyl-EMAU were examined for their ability to protect mice from lethal staphylococcal infection. Both were found to be active in this model. In sum, the results of this work demonstrated, for the first time, that: (1) the eubacterial replication-specific DNA polymerase III is a valid target for antibiotic development, and (2) the N3-substituted 6-anilinouracil platform has strong potential as a basis for novel antibiotics useful against Gram-positive bacterial infection.