Activity of SQ641, a Capuramycin Analog, in a Murine Model of Tuberculosis

Abstract

New delivery vehicles and routes of delivery were developed for the capuramycin analogue SQ641. While this compound has remarkable in vitro potency against Mycobacterium tuberculosis, it has low solubility in water and poor intracellular activity. We demonstrate here that SQ641 dissolved in the water-soluble vitamin E analogue ␣-tocopheryl polyethylene glycol 1000 succinate (TPGS) or incorporated into TPGS-micelles has significant activity in a mouse model of tuberculosis.SQ641 is an analogue of capuramycin (CM), a naturally occurring nucleoside-based compound produced by Streptomyces griseus. It was derived from a library of over 7,000 CM analogues created by Daiichi-Sankyo (Japan) and was identified as the most potent of the translocase I (TL1) inhibitors, with good activity against mycobacteria (2-4, 8, 9). The target of CM and its analogues is TL1, an essential enzyme for biosynthesis of bacterial cell walls. It is an ideal drug target because inhibition of TL1 leads to cell death and the enzyme is unique to bacteria, reducing the likelihood of toxicity.Sequella licensed the rights to develop the CM analogue library and extended the studies of SQ641. Following on the work performed by Daiichi-Sankyo, we demonstrated (7, 8) that SQ641 shows good activity against both Mycobacterium tuberculosis (MIC ϭ 1.0 g/ml) and Mycobacterium avium complex (MIC ϭ 0.016 to 16 g/ml) bacteria and kills M. tuberculosis faster than many other antituberculosis (anti-TB) drugs, including isoniazid (INH) and rifampin (rifampicin). The SQ641 compound has an extraordinary postantibiotic effect of 55 h against M. tuberculosis and is active against multidrug-resistant M. tuberculosis. SQ641 is strongly synergistic with ethambutol, streptomycin, and SQ109, Sequella's lead antitubercular drug in clinical trials, and is effective in preventing the development of drug-resistant mutants of M. tuberculosis.Unfortunately, SQ641 has limited water solubility and is rapidly expelled from infected cells via P glycoprotein-mediated rapid efflux (4). These limitations result in only modest intracellular activity against M. tuberculosis and poor in vivo activity. In the rapid mouse TB model (6), SQ641 in aqueous solution did not completely prevent body weight loss, and in the chronic model of TB, SQ641 was only able to reduce CFU in the lungs by 0.7 log, compared to the levels for the infected and untreated control groups (data not shown).We were able to overcome these shortcomings by the addition of ␣-tocopheryl polyethylene glycol 1,000 succinate (TPGS), a water-soluble vitamin E analogue (Eastman, Kingsport, TN). We previously published data demonstrating that formulations of TPGS-solubilized SQ641 and TPGS-based SQ641 micelles improved SQ641 solubility and demonstrated higher intracellular activity than SQ641 in aqueous solution (7). In this study, we investigated the activity of these TPGSbased formulations of SQ641 in the chronic mouse model of TB.

Functional and Kinetic Analysis of the Phosphotransferase CapP Conferring Selective Self-resistance to Capuramycin Antibiotics

“…Capuramycins effectively and rapidly kill several species of mycobacteria in vitro (25,26), and they have recently been demonstrated to be very effective and nontoxic anti-TB drugs using a mouse model (25,27), suggesting that these compounds have clinical promise. Given the exciting potential of this family of antibiotics, it is of significant interest to elucidate the potential mechanism(s) of resistance to capuramycins prior to utilization in the clinic, thus serving as the foundation for limiting the onset of capuramycin-resistant strains that is an inevitable consequence of the selection process.…”

The Biosynthesis of Capuramycin-type Antibiotics

“…Studies into the biological activity of A-500359 A, the major congener isolated from S. griseus SANK 60196, and several semisynthetic analogues have revealed a potential utility of these natural products as anti-tuberculosis antibiotics (9,10). For example, SQ641 and SQ922, two leads under preclinical development by Sequella (Rockville, MD), have been shown to have several clinically desirable attributes, including in vitro activity against multiple-drug-resistant strains of Mycobacterium tuberculosis (the primary causative agent of tuberculosis); high efficacy in a murine model of tuberculosis; rapid kill time in vitro and in vivo; and no toxicity to mice (11)(12)(13)(14)(15)(16)(17). Given the widespread documentation of extensively drug-resistant M. tuberculosis and the recent reality of totally drug-resistant M. tuberculosis (18), the development of drugs with novel targets, such as the capuramycin-type antibiotics, makes them attractive leads for tuberculosis chemotherapy (19,20).…”

Reconsidering Some Approved Antimicrobial Agents for Tuberculosis

“…Other new molecular entities, such as the more recently described benzothiazinones (11) and capuramycin derivatives (13), are supported by in vitro and in vivo data but as yet have not been evaluated in human trials. Nonetheless, more than a decade has elapsed since the first description of PA-824.…”