Exploring the Potential of NO-Independent Stimulators and Activators of Soluble Guanylate Cyclase for the Medical Treatment of Erectile Dysfunction

Nitric oxide (NO)-sensitive soluble guanylyl cyclase (sGC) is the receptor that catalyzes the formation of the intracellular messenger cyclic guanosine monophosphate (cGMP). Binding of the physiological activator, NO, to the reduced heme moiety of sGC increases the conversion of guanosine triphosphate (GTP) to cyclic GMP (cGMP) and engages crucial effector systems such as protein kinases, phosphodiesterases, and ion channels. The development of compounds that activate sGC independent of NO release has therapeutic implications. Recent studies have demonstrated the potential use of heme-dependent sGC stimulators (e.g. YC-1, BAY 41- 2272, BAY 41-8543, BAY 63-2521, CFM-1571 and A-350619) and heme-independent sGC activators (e.g. BAY 58-2667, HMR-1766, S-3448, A-778935) in the treatment of cardiovascular diseases. Erectile dysfunction (ED) affects millions of men. Phosphodiesterase (PDE)-5 inhibitors, producing an NO-dependent increase in intracellular cGMP concentration, have been a successful approach in the treatment of ED. However, >30% of men with ED do not respond to PDE-5 inhibitor therapy, implying that endogenous NO production may be impaired to such an extent that inhibition of cGMP degradation produces no significant therapeutic advantage. Endogenous NO released from nitrergic nerves in the corpora cavernosa is significantly decreased in various conditions (e.g. diabetes, aging, and hypertension) and has reduced activation of the NO-sGC-cGMP pathway. It is conceivable that sGC stimulators and/or activators may be more effective than PDE5 inhibitors in the treatment of ED in such circumstances by improving NO-sGC-cGMP signaling and erectile function. This novel drug therapy approach for the treatment of ED shows promise.