Synthetic ozonide drug candidate OZ439 offers new hope for a single-dose cure of uncomplicated malaria

Abstract

Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate designed to provide a single-dose oral cure in humans. OZ439 has successfully completed Phase I clinical trials, where it was shown to be safe at doses up to 1,600 mg and is currently undergoing Phase IIa trials in malaria patients. Herein, we describe the discovery of OZ439 and the exceptional antimalarial and pharmacokinetic properties that led to its selection as a clinical drug development candidate. In vitro, OZ439 is fast-acting against all asexual erythrocytic Plasmodium falciparum stages with IC(50) values comparable to those for the clinically used artemisinin derivatives. Unlike all other synthetic peroxides and semisynthetic artemisinin derivatives, OZ439 completely cures Plasmodium berghei-infected mice with a single oral dose of 20 mg/kg and exhibits prophylactic activity superior to that of the benchmark chemoprophylactic agent, mefloquine. Compared with other peroxide-containing antimalarial agents, such as the artemisinin derivatives and the first-generation ozonide OZ277, OZ439 exhibits a substantial increase in the pharmacokinetic half-life and blood concentration versus time profile in three preclinical species. The outstanding efficacy and prolonged blood concentrations of OZ439 are the result of a design strategy that stabilizes the intrinsically unstable pharmacophoric peroxide bond, thereby reducing clearance yet maintaining the necessary Fe(II)-reactivity to elicit parasite death.

Fig. 1.

Structures of artemisinin derivatives and synthetic ozonides. (A) Artemisinin (ART), dihydroartemisinin (DHA), artemether (AM), and artesunate (AS); (B) OZ277; and (C) OZ439.

Fig. 2.

Fe(II) and blood stability profiles for OZ277 and OZ439. (A) Stability of OZ277 (●) and OZ439 (◇) in the presence of aqueous ferrous sulfate at 37 °C (mean ± SD, n = 3). (B) Stability of OZ277 (●) and OZ439 (◆) in noninfected and P. falciparum-infected (OZ277 ○, OZ439 ◇) human RBCs suspended in plasma and incubated at 37 °C (mean ± SD, n = 3–5).

Fig. 3.

Blood concentration versus time profiles for OZ439 (○) and OZ277 (●) following a single 3-mg/kg oral dose to rats (mean ± SD, n = 3–4). For OZ277, concentrations were below the analytical limit of quantitation (~1 ng/mL) by 7.5 h.

Fig. 4.

In vivo efficacy of OZ439 in P. berghei infected mice. (A) Average survival time postinfection (mean ± SEM, n = 5 at each dose level) following single oral doses of OZ439 on day 1 postinfection. The filled circles represent doses for which no parasites could be detected at day 30 postinfection in any mice; at 15 mg/kg (▲), four of five mice were parasite-free at day 30. (B) Onset of action and recrudescence for control (●), AS (○), OZ277 (■), MF (▼), and OZ439 (△) following a single oral dose of 100 mg/kg on day 3 postinfection (n = 5 for each).