Inhibition of PDE5A1 guanosine cyclic monophosphate (cGMP) hydrolysing activity by sildenafil analogues that inhibit cellular cGMP efflux

Abstract

Objectives: To determine the ability of 11 sildenafil analogues to discriminate between cyclic nucleotide phosphodiesterases (cnPDEs) and to characterise their inhibitory potencies (K_i values) of PDE5A1-dependent guanosine cyclic monophosphate (cGMP) hydrolysis.

Methods: Sildenafil analogues were identified by virtual ligand screening (VLS) and screened for their ability to inhibit adenosine cyclic monophosphate (cAMP) hydrolysis by PDE1A1, PDE1B1, PDE2A1, PDE3A, PDE10A1 and PDE10A2, and cGMP hydrolysis by PDE5A, PDE6C, PDE9A2 for a low (1 nm) and high concentration (10 μm). Complete IC₅₀ plots for all analogues were performed for PDE5A-dependent cGMP hydrolysis. Docking studies and scoring were made using the ICM molecular modelling software.

Key findings: The analogues in a low concentration showed no or low inhibition of PDE1A1, PDE1B1, PDE2A1, PDE3A, PDE10A1 and PDE10A2. In contrast, PDE5A and PDE6C were markedly inhibited to a similar extent by the analogues in a low concentration, whereas PDE9A2 was much less inhibited. The analogues showed a relative narrow range of K_i values for PDE5A inhibition (1.2-14 nm). The sildenafil molecule was docked in the structure of PDE5A1 co-crystallised with sildenafil. All the analogues had similar binding poses as sildenafil.

Conclusions: Sildenafil analogues that inhibit cellular cGMP efflux are potent inhibitors of PDE5A and PDE6C.

Keywords: PDE5; guanosine cyclic monophosphate; inhibitors; molecular modelling; sildenafil analogues.

Figure 1

The sildenafil analogues were tested for their inhibition of PDE5A‐mediated cGMP hydrolysis as described in methods. The experimental points represent mean ± SE (n = 6). Sildenafil was used as reference substance. Panel a: sildenafil (●), IN‐03 (▲), IN‐08 (×) and IN‐09 (■). Panel b: sildenafil (●), IN‐01 (▲), IN‐02 (×) and IN‐04 (■). Panel c: sildenafil (●), IN‐05 (▲), IN‐11 (×), panel d: sildenafil (●), IN‐06 (▲), IN‐07 (×) and IN‐10 (■).

Figure 2

Docking of sildenafil and sildenafil analogues into the crystal structure of PDE5A. Panel a: Location of sildenafil (red) after self‐docking and that of sildenafil (black) co‐crystallised with PDE5. Panel b: Location and poses of the 11 sildenafil analogues in the sildenafil binding site. Panel c: Location of the salicylic acid moiety of the compounds IN‐01 and 1N‐02. [Colour figure can be viewed at wileyonlinelibrary.com]