Discussion

Arboviruses such as CHIKV, ZIKV, and MAYV continue to pose significant public health challenges, particularly in tropical and subtropical regions, due to their rapid spread and the absence of specific antiviral therapies [5, 25]. In this context, the identification of novel small molecules with antiviral activity remains a priority.

In the present study, a series of 4-amino-7-chloroquinoline derivatives was synthesized and evaluated for in vitro antiviral activity. Among the tested compounds, derivative 6 demonstrated selective and potent activity against CHIKV, with a low micromolar EC₅₀ and a selectivity index above the threshold commonly considered acceptable for antiviral candidates [26]. In contrast, compound 4 exhibited only moderate activity against ZIKV and MAYV, with limited selectivity, suggesting a narrower therapeutic potential.

The observed differences in antiviral activity among the derivatives highlight the influence of structural modifications on biological activity. In particular, the presence of a cyclohexyl moiety in compound 6 appears to be associated with enhanced anti-CHIKV activity, whereas other substituents, including halogenated phenyl groups, did not confer significant antiviral effects. These findings reinforce the importance of substituent optimization in quinoline based scaffolds for antiviral drug development.

The absence of virucidal activity indicates that the antiviral effect of compound 6 is unlikely to result from the direct inactivation of viral particles. Instead, the available evidence suggests that derivative 6 interferes with a post-adsorption stage of the viral replication cycle. This interpretation is supported by the cytopathic effect inhibition assay, in which treatment initiated after viral adsorption preserved cell monolayer integrity, together with the marked reduction in viral titers observed in plaque assays. Although these findings are consistent with inhibition of post-adsorption events, additional mechanistic studies are required to identify the precise molecular target and stage of the viral replication cycle affected by the compound.

Furthermore, RT-qPCR analysis confirmed a significant decrease in CHIKV RNA levels in treated cells at different time points post infection, demonstrating that compound 6 effectively suppresses viral replication. These findings are consistent with previous studies reporting antiviral activity of quinoline derivatives against RNA viruses, including CHIKV, and suggest that such compounds may act by targeting viral nonstructural proteins or host dependent pathways involved in replication [27, 28].

Previous reports have indicated that quinoline based compounds may interfere with key viral processes, including endosomal acidification and viral protein function [26]. In the case of CHIKV, potential targets include the nsP2 and nsP3 nonstructural proteins, as well as envelope glycoproteins involved in viral entry [29]. Although the precise mechanism of action of compound 6 was not elucidated in this study, the lack of virucidal effect combined with the observed reduction in intracellular viral RNA supports a post entry mode of action.

Overall, the results demonstrate that 4-amino-7-chloroquinoline derivatives represent a promising class of antiviral agents. In particular, compound 6 emerges as a potential lead candidate for the development of new therapeutics against CHIKV. Further studies, including mechanistic investigations and in vivo evaluations, are warranted to fully characterize its antiviral potential and optimize its pharmacological profile.

Conclusion and Future Directions

In summary, the present study demonstrates that 4-amino-7-chloroquinoline derivatives show antiviral potential against arboviruses. Among the synthesized molecules, compound 6 exhibited selective and potent in vitro activity against CHIKV, significantly reducing viral replication and preserving cell integrity without displaying virucidal effects. These findings suggest compound 6 does not directly inactivate viral particles as demonstrated by the absence of virucidal activity. Furthermore, derivative 6 is unlikely to interfere with viral attachment or adsorption and more likely acts during a subsequent stage of the viral replication cycle.

Given the limited number of 4-amino-7-chloroquinoline derivatives evaluated, the present study does not allow definitive structure–activity relationship conclusions to be drawn. However, the analysis of this small series suggests that the presence of a cyclohexyl moiety may be associated with increased antiviral activity within this chemical class. This preliminary observation provides a rationale for expanding the chemical series and systematically investigating structural modifications of the quinoline scaffold to further improve antiviral activity and selectivity.

Future studies should focus on elucidating the precise molecular mechanism of action of compound 6, including its potential interaction with viral or host targets. In addition, in vivo evaluations, pharmacokinetic profiling, and toxicity studies, will be necessary to assess the potential of this scaffold for further antiviral development. The integration of in silico approaches and structure-based design may further support the rational development of more potent and selective 4-amino-7-chloroquinoline derivatives.

Overall, this work provides a foundation for the continued exploration of quinoline derivatives as candidate antiviral agents and contributes to ongoing efforts to develop effective therapeutic strategies against CHIKV and other medically relevant arboviruses.