Pharmacokinetically-guided lead optimization of nitrofuranylamide anti-tuberculosis agents

Abstract

In an effort to develop novel and more potent therapies to treat tuberculosis, a new class of chemical agents, nitrofuranylamides, is being developed. The present study examines biopharmaceutic properties and preclinical pharmacokinetics of nitrofuranylamides at early stages of drug discovery to accelerate the optimization of leads into development candidates. The first tested compound, Lee 562, had high anti-tuberculosis activity in vitro, but exhibited poor metabolic stability resulting in a high systemic clearance, a short elimination half-life and low oral bioavailability in vivo in rats. Thus, two follow-up compounds were designed and tested that included structural modifications for increased metabolic stability. Both compounds showed improved metabolic stability compared to Lee 562, with Lee 878 being much more stable than Lee 952. As a consequence, the oral bioavailability of Lee 878 reached approximately 27% compared to 16% for the other two compounds. This observation prompted us to select compounds based on metabolic stability screening and a new set of nine compounds with high in vitro activity were tested for metabolic stability. The most stable compound in the assay, Lee 1106 was selected for further pharmacokinetic evaluation in rats. Surprisingly, Lee 1106 exhibited poor oral bioavailability, 4.6%. Biopharmaceutic evaluation of the compound showed that the compound has poor aqueous solubility and a high clogP. Based on these results, a screening paradigm was developed for optimization of the nitrofuranylamide lead compounds in a timely and cost-effective manner that might also be applicable to other classes of anti-infective drugs.

Fig. 1

Chemical structures of Lee 562, Lee 878, Lee 952 and Lee 1106. The boxes and circles depict important structural differences between the first generation compound Lee 562, the second generation compounds Lee 878 and Lee952, and the third generation compound Lee 1106

Fig. 2

Measured plasma concentration-time profiles (mean ± SD) after intravenous (10 mg/kg; a, c, e, g) or oral (100 mg/kg) (b, d, f, h) administration of nitrofuranylamides to rats (n = 5–6 per group): Lee 562 (a and b), Lee 878 (c and d), Lee 952 (e and f), Lee 1106 (g and h)

Fig. 3

Chemical structures of third generation nitrofuranylamides. The values provided in parenthesis indicate the metabolic stability in an in vitro microsomal preparation assay (percent parent compound remaining stable after 90 min of incubation)

Fig. 4

Correlation between a clogP and aqueous solubility, b clogP and plasma protein binding in the investigated nitrofuranylamides. The plasma protein binding of the compounds Lee 992 and Lee 1053 could not be determined due to instability in plasma

Fig. 5

Screening paradigm for lead optimization of anti-TB compounds