We report here data showing that CLQ is an effective antiviral agent for DENV-2 under cell culture condition. The inhibitory effect was observed when the drug was added 1
h after the initiation of infection, probably due to the increase of the endosomes pH and thus subverting the ongoing fusion events between virus envelope and endosome membranes. These results suggest that CLQ could have a potential for therapeutic use against dengue virus and even against other viruses that penetrate cells by endocytosis. In that sense, some studies have shown that CLQ inhibits SARS coronavirus (SARS-CoV) replication in vitro [6
]. In addition, di Trani et al. [8
] tested the antiviral effects of CLQ in vitro against selected human and avian viruses belonging to different subtypes and displaying different pH requirements. Those authors found that CLQ had inhibitory effect against the viruses when the drug had been added at the time of infection and the effect was lost after 2-hour postinfection. Finally, Eng et al. [9
] reported that CLQ is able to inhibit influenza A virus replication in vitro.
CLQ is a safe drug with over half a century of use in the treatment of malaria; therefore, the implementation of a protocol to use it in dengue treatment would not be a problem. Since there is a correlation between high viral load and development of DHF/DSS [10
], the use of CLQ to treat dengue virus infection as soon as the patients present the dengue symptoms could prevent the development of the severe forms of the disease due to the reduction of dengue viremia. Furthermore, due to its interference with TNF-α
], CLQ would probably reduce the inflammatory symptoms, such as high fever and backache, associated with dengue.
The inhibitory effect of CLQ on virus replication in mammalian cells has already been studied with other viruses. This drug has been used to control infection with coronavirus (SARS-CV), the etiologic agent of severe acute respiratory syndrome (SARS) in nonhuman primate cells (Vero) [7
]. It was also used to inhibit the replication of human immunodeficiency virus (HIV-1) in lineages of monocytes and lymphocytes [12
] and lineages of H9 cells [13
]. Furthermore, CLQ has been used to inhibit Kunjin virus replication in cells of nonhuman primates (Vero) [14
Dengue viruses replicate well in C6/36 cells and in other mosquito lines, they are presently used as sensitive assays for virus isolation from patients, and Vero are also permissive cell lines [15
]. In the present study, we observed that in experiments carried out with C6/36 cells infected with DENV-2 and treated with CLQ did not reduce the viral load. In 1981, Coombs et al. [16
] observed also that CLQ did not reduce the viral load in experiments carried out with the Sindbis virus in cells of the mosquito Aedes albopictus
. Hernandez et al. [17
] obtained similar results when they used CLQ to inhibit replication of the Sindbis virus. Two explanations are possible for these findings: (i) CLQ does not block endosome acidification in the cells of the mosquito Aedes albopictus
, or (ii) CLQ blocks endosome acidification but not the infection of mosquito cells with the Sindbis virus. These facts suggest that the replication of DENV-2 used in our experiments in Aedes albopictus
cells occurs possibly by a pathway of intracytoplasmic penetration other than the endosomal one, which was not blocked by CLQ.
Taken together with the data obtained in these studies, our results suggest that CLQ interferes in DENV-2 virus replication in Vero cells culture but not in C6/36 cells.
Thus, as chloroquine is considered a safe and effective drug, used to treatment many diseases, including malaria, their therapeutic use is promising because it was shown in this study that the drug has significant antiviral effect on the replication of dengue-2 virus in cells culture.