Synthetic Ozonide Drug Candidate OZ439 Offers New Hope for a Single-Dose Cure of Uncomplicated Malaria
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Synthetic ozonide drug candidate OZ439 offers new hope for a single-dose cure of uncomplicated malaria Susan A. Charmana, Sarah Arbe-Barnesb, Ian C. Bathurstc, Reto Brund,e, Michael Campbella, William N. Charmana, Francis C. K. Chiua, Jacques Cholletd,e, J. Carl Craftc, Darren J. Creeka, Yuxiang Dongf, Hugues Matileg, Melanie Maurerd,e, Julia Morizzia, Tien Nguyena, Petros Papastogiannidisd,e, Christian Scheurerd,e, David M. Shackleforda, Kamaraj Sriraghavanf, Lukas Stingelina, Yuanqing Tangf, Heinrich Urwylerh, Xiaofang Wangf, Karen L. Whitea, Sergio Wittlind,e, Lin Zhouf, and Jonathan L. Vennerstromf,1 aCentre for Drug Candidate Optimisation, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia; bFulcrum Pharma Developments Ltd., Hemel Hempstead, Hertfordshire HP1 1JY, United Kingdom; cMedicines for Malaria Venture, CH-1215 Geneva, Switzerland; dSwiss Tropical and Public Health Institute, CH-4002 Basel, Switzerland; eUniversity of Basel, CH-4051 Basel, Switzerland; fCollege of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025; gF. Hoffmann-La Roche Ltd., CH-4070 Basel, Switzerland; and hBasilea Pharmaceutica Ltd., CH-4058 Basel, Switzerland Edited by Thomas E. Wellems, National Institutes of Health, Bethesda, MD, and approved January 11, 2011 (received for review October 21, 2010) Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate Thai-Cambodian border, and more recently, increased parasite designed to provide a single-dose oral cure in humans. OZ439 has clearance times with artesunate (AS) monotherapy, have raised successfully completed Phase I clinical trials, where it was shown to significant concerns that resistance to these agents may be be safe at doses up to 1,600 mg and is currently undergoing Phase emerging (2, 3). IIa trials in malaria patients. Herein, we describe the discovery of Over the past several years, we have been working in con- OZ439 and the exceptional antimalarial and pharmacokinetic junction with the Medicines for Malaria Venture (www.mmv.org) properties that led to its selection as a clinical drug development to design and optimize a completely synthetic ozonide antima- candidate. In vitro, OZ439 is fast-acting against all asexual eryth- larial based upon the 1,2,4-trioxolane pharmacophore, which rocytic Plasmodium falciparum stages with IC50 values comparable exhibits a rapid onset of action, potent activity against all blood to those for the clinically used artemisinin derivatives. Unlike all stages of P. falciparum and Plasmodium vivax, high oral bio- other synthetic peroxides and semisynthetic artemisinin deriva- availability, a good safety profile, low projected cost of goods, and MICROBIOLOGY tives, OZ439 completely cures Plasmodium berghei-infected mice most importantly, the potential for a single-dose oral cure. The with a single oral dose of 20 mg/kg and exhibits prophylactic ac- availability of such a drug would have a profound and positive tivity superior to that of the benchmark chemoprophylactic agent, impact on patient access, treatment, and compliance, and would mefloquine. Compared with other peroxide-containing antimalarial contribute to the goal of malaria eradication. Importantly, as the agents, such as the artemisinin derivatives and the first-generation ozonides are structurally dissimilar to the ART derivatives, they ozonide OZ277, OZ439 exhibits a substantial increase in the phar- may offer an alternative if ART resistance becomes more wide- macokinetic half-life and blood concentration versus time profile in spread (3). Currently, sulfadoxine-pyrimethamine is the only three preclinical species. The outstanding efficacy and prolonged available antimalarial effective when given as a single dose; blood concentrations of OZ439 are the result of a design strategy however, its clinical utility is threatened by resistance in many that stabilizes the intrinsically unstable pharmacophoric peroxide parts of the world (1). bond, thereby reducing clearance yet maintaining the necessary Fe Ozonide OZ277 (11) (Fig. 1B), also known as RBx11160 or (II)-reactivity to elicit parasite death. arterolane maleate, was the first synthetic ozonide to be evalu- ated clinically and is now in Phase III clinical trials as a combi- 1,2,4-trioxolane | antimalarial drug discovery nation product with piperaquine phosphate (12). Like the artemisinins, OZ277 contains a pharmacophoric peroxide bond, he need for new, fast acting, and effective antimalarial drugs which is essential for activity (13, 14), exhibits antimalarial ac- Thas never been greater; drug resistance continues to threaten tivity against all asexual blood stages of P. falciparum (15, 16) conventional therapy (1), there are new reports of resistance to and has a rapid onset of action in an established murine model of the artemisinin derivatives (2, 3), and the global aspiration of malaria (11). However, in Phase I clinical trials, the half-life in malaria eradication has been rekindled (4) and is supported by healthy volunteers was only about two- to threefold longer than many of the world’s most influential organizations (5). The that of dihydroartemisinin (DHA) (17), the active metabolite of semisynthetic artemisinin (ART) derivatives (Fig. 1A), consid- clinically used semisynthetic ART derivatives. Furthermore, ered an essential component of malaria chemotherapy (6), are when administered to malaria patients as monotherapy (18), the only class of drug effective against multidrug-resistant forms OZ277 displayed reduced plasma exposure compared with that of the parasite, and artemisinin combination therapies (ACT) in volunteers (12). To achieve a single-dose oral cure, we are the recommended first-line treatment for uncomplicated therefore considered that the primary challenge was to sub- fi Plasmodium falciparum malaria in all endemic regions (7). stantially increase the in vivo half-life and blood exposure pro le The clinical effectiveness of the ART derivatives stems from their rapid onset of action and activity against all erythrocytic stages of the parasite, a feature unique among currently available Author contributions: S.A.C., S.A.-B., I.C.B., R.B., W.N.C., J.C., J.C.C., Y.D., H.M., H.U., S.W., and J.L.V. designed research; M.C., F.C.K.C., D.J.C., Y.D., M.M., J.M., T.N., P.P., C.S., K.S., antimalarial drugs (6). Despite their clinical utility, the current L.S., Y.T., X.W., and L.Z. performed research; S.A.C., M.C., F.C.K.C., J.C., D.J.C., Y.D., M.M., ART derivatives suffer from notable disadvantages. First, they J.M., T.N., P.P., C.S., D.M.S., K.S., L.S., Y.T., H.U., X.W., K.L.W., S.W., L.Z., and J.L.V. analyzed have short in vivo half-lives, and require 3-d treatment regimens data; and S.A.C., S.A.-B., W.N.C., H.M., H.U., S.W., and J.L.V. wrote the paper. in combination with longer-acting antimalarials to maximize cure The authors declare no conflict of interest. rates (8, 9). Second, isolation from the plant source is still the This article is a PNAS Direct Submission. only practical means of accessing ART as a starting material, Freely available online through the PNAS open access option. and with harvest and extraction costs being highly variable and 1To whom correspondence should be addressed. E-mail: [email protected]. fl often subsidy-driven, the supply of ART uctuates widely (10). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. Finally, alarming reports of ACT treatment failures along the 1073/pnas.1015762108/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1015762108 PNAS Early Edition | 1of6 Downloaded by guest on September 24, 2021 in vitro heme alkylation (which occurs subsequent to heme electron-transfer to the peroxide bond) and the in vitro IC50 against P. falciparum, suggesting a potential link to antimalarial activity (32). We then conducted investigations to assess the reactivity of selected next-generation ozonides with Fe(II) and heme and compared results with those for first-generation ozonides, such as OZ277. Next-generation ozonides (Fig. S2), such as OZ439 (Fig. 1C), containing a cis-8′-phenyl substituent, were >50-fold more stable to Fe(II)-mediated degradation (Fig. 2A) compared with first-generation ozonides, such as OZ277, which contain a cis-8′- Fig. 1. Structures of artemisinin derivatives and synthetic ozonides. (A) alkyl group. The apparent first-order degradation rate constant for − Artemisinin (ART), dihydroartemisinin (DHA), artemether (AM), and artesu- OZ439 in the presence of ferrous sulfate was 0.011 ± 0.001 h 1 − nate (AS); (B) OZ277; and (C) OZ439. (mean ± SD, n = 3) compared with 0.76 ± 0.03 h 1 for OZ277 (30). Previous quantum mechanical studies with OZ27 (Fig. S2B), a structural precursor of the next-generation ozonides, attributed of a next-generation synthetic ozonide drug candidate compared this enhanced stability to greater steric interactions between the with that of the ART derivatives and OZ277. Herein we describe bound iron complex and the cis-8′-phenyl substituent compared the exceptional pharmacokinetic and antimalarial properties of with the cis-8′-alkyl group (33). Importantly, some Fe(II)-reactivity OZ439 (Fig. 1C) and the studies that led to its selection as a could still be detected for the next-generation ozonides. The cis-8′- clinical development candidate (3, 5, 12). phenyl-containing ozonides effectively and rapidly reacted with Results and Discussion heme (with complete disappearance of the ozonide within min- utes), with the extent of heme alkylation being comparable to that The critical design criteria that led to the selection of OZ439 as a observed with the cis-8′-alkyl–containing compounds [e.g., 84 ± clinical candidate was the relationship between Fe(II)-mediated 1.5% heme alkylation for OZ439 and 83 ±1.5% for OZ277 (32), activation and antimalarial activity, and the competing mecha- mean n =3± SD]. Given that OZ439 and structurally related nisms of in vivo degradation and clearance. The focus of initial ozonides are potent antimalarials both in vitro against P.