Pharmacology of Novel Heteroaromatic Polycycle Antibacterials

M Gross

R Bürli

P Jones

M Garcia

U Hoch+3 authors

Pharmacology,^{Chemistry Departments, GeneSoft Pharmaceuticals, South San Francisco, California 94080}²

^{Corresponding author. Mailing address: Department of Pharmacology, GeneSoft Pharmaceuticals, 7300 Shoreline Ct., South San Francisco, CA 94080. Phone: (650) 837-1864. Fax: (650) 827-0479. E-mail:}moc.tfoseneg@nosnhojk.

Received 2003 Jan 22; Revised 2003 Jun 9; Accepted 2003 Jul 17.

Abstract

Heteroaromatic polycycle (HARP) compounds are a novel class of small (M_w, 600 to 650) DNA-binding antibacterials. HARP compounds exhibit a novel mechanism of action by preferentially binding to AT-rich sites commonly found in bacterial promoters and replication origins. Noncovalent binding in the minor groove of DNA results in inhibition of DNA replication and DNA-dependent RNA transcription and subsequent bacterial growth. HARP compounds have previously been shown to have potent in vitro activities against a broad spectrum of gram-positive organisms. The present report describes the extensive profiling of the in vitro and in vivo pharmacology of HARP antibacterials. The efficacies of representative compounds (GSQ-2287, GSQ-10547, and GSQ-11203), which exhibited good MIC activity, were tested in murine lethal peritonitis and neutropenic thigh infection models following intravenous (i.v.) administration. All compounds were efficacious in vivo, with potencies generally correlating with MICs. GSQ-10547 was the most potent compound in vitro and in vivo, with a 50% effective dose in the murine lethal peritonitis model of 7 mg/kg of body weight against methicillin-sensitive Staphylococcus aureus (MSSA) and 13 mg/kg against methicillin-resistant S. aureus (MRSA). In the neutropenic mouse thigh infection model, GSQ-11203 reduced the bacterial load (MRSA and MSSA) 2 log units following administration of a 25-mg/kg i.v. dose. In a murine lung infection model, treatment with GSQ-10547 at a dose of 50 mg/kg resulted in 100% survival. In addition to determination of efficacy in animals, the pharmacokinetic and tissue disposition profiles in animals following administration of an i.v. dose were determined. The compounds were advanced into broad safety screening studies, including screening for safety pharmacology, genotoxicity, and rodent toxicity. The results support further development of this novel class of antibiotics.

Abstract

The increase in the number of infections caused by drug-resistant gram-positive organisms in the clinic represents a medical need and a commercial opportunity for the development of bactericidal agents with new modes of action (10, 14, 16). Such candidates are expected to lack cross-resistance to existing classes and, provided they exhibit efficacy in vivo, might be of great therapeutic utility. The present report provides a proof of concept for novel chemical entities denoted heteroaromatic polycycle (HARP) antibacterials which are thought to act by a unique DNA-binding mode of action.

HARP antibacterials are small (M_w, ∼600) compounds whose design was initially based on the natural product distamycin A, which was recognized to possess weak antibiotic activity in the 1960s (1, 3, 4, 5). The mechanism of action of distamycin A was unclear, although it was postulated to involve interactions with minor-groove, AT-rich sites of DNA (1, 3, 4, 5, 7); and related compounds with in vitro antibacterial activities were shown to bind to an AT-rich dodecamer (9). Despite some intriguing properties, distamycin A was never developed as an antibacterial due to insufficient potency. Beginning 3 years ago, we applied medicinal chemistry approaches to generate novel polyamide-based compounds with improved antibacterial potency in vitro (6, 13). Moreover, we devoted additional efforts at better defining the bactericidal and bacteriostatic modes of action (12; Y. Ge, J. Wu, and S. White, Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. F-1686, p. 241, 2001). We have optimized this class of compounds for reversible nanomolar binding to the minor groove of AT-rich DNA (1; Ge et al., 41st ICAAC) and potent broad-spectrum activity against gram-positive organisms (6, 12, 13; Ge et al., 41st ICAAC). Consistent with the notion that novel chemical entities with novel modes of action might have activities against drug-resistant organisms, it is clear that the optimized HARP compounds are potent against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-insensitive S. aureus, vancomycin-resistant enterococci, and drug-resistant pneumococci (6, 12; Ge et al., 41st ICAAC; data not shown).

The present studies were designed to profile the pharmacology of lead compounds. We selected an early prototype, GSQ-2287, and two more potent derivatives, GSQ-10547 and GSQ-11203, to advance into preclinical animal studies and certain in vitro assays related to selectivity and safety. Herein we present for the first time the pharmacological characterization of HARP antibacterials. In addition to pharmacokinetic and safety profiling, we provide a proof of concept of the broad and potent antibacterial efficacies of these agents in vivo. These studies support the further development of HARP antibacterials as novel therapeutic agents.

The structures of distamycin A and the GSQ compounds are depicted in Fig. Fig.1.1. GSQ-2287 represents a prototype from which the more potent derivatives GSQ-10547 and GSQ-11203 were derived. Optimization of GSQ-2287 led to replacement of the N-terminal chlorothiophene unit by an isoquinoline moiety and the replacement of the central N-methyl-pyrrole by an NH-pyrrole (GSQ-11203) and a benzene moiety in GSQ-10547.

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FIG. 1.

Chemical structures of distamycin A and the HARP compounds.

(This work was presented in part at the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy, 27 to 30 September 2002, San Diego, Calif.)

Acknowledgments

This work was in part funded by a grant (grant N65236-99-1-5427) from DARPA.

We are very appreciative of the excellent technical support provided by Willie Aparicio, Stacey Difuntorum, Lin Lin, Mike Powers, Thamil Annamalai, Mari Iwamoto, Hsiu Chen, James Ge, and Zhijun Ye. Eric Taylor at Bay Bioanalytics is appreciated for scientific contributions. Yuan Chao is acknowledged for excellent patent support and advice. Sandhya Girish and Jackie Gibbons are appreciated for their assistance with data analysis. Finally, we recognize the editorial, scientific, and management contributions of Gary Patou, Ken Drazan, Sarah White, Nick Marini, Denene Lofland, Sofia Touami, and Eldon Baird.

Acknowledgments

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