Short Communication Dose- and schedule-dependent protective efficacy of celgosivir in a lethal mouse model for dengue virus infection informs dosing regimen for a proof of concept clinical trial Satoru Watanabe a,1 , Abhay P.S. Rathore a,1 , Cynthia Sung a,1 , Fan Lu b , Yok Moi Khoo b , John Connolly c , Jenny Low d , Eng Eong Ooi a , How Sung Lee b , Subhash G. Vasudevan a,⇑ a Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, 8 College Road, Singapore 169857, Singapore b Department of Pharmacology, Yong Loo Lin School of Medicine, Clinical Research Centre 10 Medical Drive, Singapore 117597, Singapore c Singapore Immunology Network (SIgN), 8A Biomedical Grove, Immunos Building, Level 4, Singapore 138648, Singapore d Department of Infectious Diseases, Singapore General Hospital, Singapore 169608, Singapore article info Article history: Received 5 June 2012 Revised 17 July 2012 Accepted 19 July 2012 Available online 31 July 2012 Keywords: Dengue virus Antiviral AG129 lethal infection mouse model Pharmacokinetics abstract Celgosivir (6-O-butanoyl castanospermine), a pro-drug of the naturally occurring castanospermine, is an inhibitor of a-glucosidase I and II that is found to be a potent inhibitor of several enveloped viruses including all four serotypes of dengue virus. We showed previously that the compound fully protected AG129 mice from lethal infection with a mouse adapted dengue virus at a dose of 50 mg/kg twice daily (BID) for 5 days and was effective even after 48 h delayed treatment. Here we show that the protection by celgosivir is dose- and schedule-dependent and that a twice-a-day regimen of 50, 25 or 10 mg/kg is more protective than a single daily dose of 100 mg/kg. Treatment with 50 mg/kg BID castanospermine had comparable efficacy as 25 mg/kg BID celgosivir, suggesting that celgosivir is approximately twice as potent as castanospermine with respect to in vivo antiviral efficacy. Pharmacokinetics (PK) studies of celgosivir in mice showed that it rapidly metabolized to castanospermine. Simulation of the PK data with the survival data for the various doses of celgosivir tested suggests that the steady-state minimum con- centration is a critical parameter to note in choosing dose and schedule. These results influenced the selection of the dose regimen for a proof-of-concept clinical trial of celgosivir as a treatment against den- gue fever. Ó 2012 Elsevier B.V. All rights reserved. Dengue is a global public health threat caused by infection with any of the 4 related viral serotypes (DENV1–4). Clinical manifesta- tions range from self-limiting febrile illness, known as dengue fe- ver (DF), to the life-threatening severe diseases, such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS) (Gubler, 2006; Halstead, 2007). Severe diseases are often accompanied with secondary heterotypic infections, probably due to the phenomenon that is described as antibody-dependent enhanced (ADE) infection (Halstead, 2003). Annually, there are more than 50 million human infections and several hundred thousand cases of DHF/DSS (Hal- stead, 2007). At present, however, there are no approved preven- tive vaccines or antiviral drugs against DENV infection. Celgosivir, also known as 6-O-butanoyl castanospermine (Bu- Cast), is a butyl ester derivative of castanospermine (Cast), a natu- ral product derived from the Moreton Bay chestnut tree (Castano- spermum australae)(Molyneux et al., 1986). It readily crosses cell membranes and is rapidly converted to Cast (Kang, 1996), which acts as an a-glucosidase I and II inhibitor in the endoplasmic retic- ulum (ER). Celgosivir or Cast have been shown to have broad anti- viral effects in cell culture systems and/or in vivo mouse models such as Sindbis virus, CMV, influenza virus, several flaviviruses, HSV, HIV-1 and HBV (Ahmed et al., 1995; Block et al., 1994; Bridges et al., 1995; Saito and Yamaguchi, 2000; Schlesinger et al., 1985; Schul et al., 2007; Sunkara et al., 1989; Taylor et al., 1988; Whitby et al., 2005; Zitzmann et al., 1999). Since the drug target is a host enzyme required for viral maturation, the potential for develop- ment of drug resistance is expected to be lower than a drug direc- ted against a viral target. In a previous study, we demonstrated that celgosivir drastically inhibits the replication of clinical dengue strains of DENV1–4 by impairing proper folding of viral glycopro- teins such as NS1, E and prM (Courageot et al., 2000; Rathore et al., 2011). In a lethal DENV infection mouse model using AG129 mice (Sv/129 mice deficient in type I and II IFN receptors), treatment of 50 mg/kg of celgosivir given twice daily resulted in 100% survival by day 10 after infection (Rathore et al., 2011). These results encouraged further development of celgosivir as a possible 0166-3542/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.antiviral.2012.07.008 ⇑ Corresponding author. Tel.: +65 6516 6718; fax: +65 6221 2529. E-mail address: subhash.vasudevan@duke-nus.edu.sg (S.G. Vasudevan). 1 These authors made equal contribution in this study. Antiviral Research 96 (2012) 32–35 Contents lists available at SciVerse ScienceDirect Antiviral Research journal homepage: www.elsevier.com/locate/antiviral