Host dihydrofolate reductase (DHFR)-directed cycloguanil analogues endowed with activity against influenza virus and respiratory syncytial virus

Abstract

We have identified a series of 1-aryl-4,6-diamino-1,2-dihydrotriazines, structurally related to the antimalarial drug cycloguanil, as new inhibitors of influenza A and B virus and respiratory syncytial virus (RSV) via targeting of the host dihydrofolate reductase (DHFR) enzyme. Most analogues proved active against influenza B virus in the low micromolar range, and the best compounds (11, 13, 14 and 16) even reached the sub-micromolar potency of zanamivir (EC₅₀ = 0.060 μM), and markedly exceeded (up to 327 times) the antiviral efficacy of ribavirin. Activity was also observed for two influenza A strains, including a virus with the S31N mutant form of M2 proton channel, which is the most prevalent resistance mutation for amantadine. Importantly, the compounds displayed nanomolar activity against RSV and a superior selectivity index, since the ratio of cytotoxic to antiviral concentration was >10,000 for the three most active compounds 11, 14 and 16 (EC₅₀ ∼0.008 μM), far surpassing the potency and safety profile of the licensed drug ribavirin (EC₅₀ = 5.8 μM, SI > 43).

Keywords: 1-Aryl-4,6-diamino-1,2-dihydrotriazine derivatives; Anti-RSV activity; Anti-influenza A and B viruses activity; Host (human) DHFR inhibition.

Graphical abstract

Fig. 1

Chemical structure of the reference hDHFR inhibitor I and of the investigated series of 1-aryl-4,6-diamino-1,2-dihydrotriazines.

Fig. 2

Structures of the investigated compounds 1–33.

Scheme 1

^aReagents and conditions: a) 1 equiv. conc. HCl, r.t., 24 h, 34–68%.

Fig. 3

Scatter Plot of Ki values (hDHFR) versus EC₅₀ towards Influenza B virus and Respiratory Syncytial Virus. Data plotted are reported in Table 1, Table 2. All the values are expressed in logarithm scale.

Fig. 4

A) details of the X-ray crystallographic complex hDHFR - inhibitor I (C atom; yellow); B) Docking pose of cycloguanil (1) (C atom; white) within the X-ray crystallographic structure of the human DHFR in complex with the inhibitor I (C atom; yellow). The most important residues are labelled and coloured by atom type. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

A) Docking pose of compound 13 (C atom; pink) within the X-ray crystallographic structure of the human DHFR in complex with the inhibitor I (C atom; yellow); B) Docking pose of compound 25 (C atom; tan) within the X-ray crystallographic structure of the human DHFR in complex with the inhibitor I (C atom; yellow). The most important residues are labelled and coloured by atom type. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)