Zaprinast was an unsuccessful clinical drug candidate that was a precursor to the chemically related PDE5 inhibitors, such as sildenafil (Viagra), which successfully reached the market. It is a phosphodiesterase inhibitor,[1] selective for the subtypes PDE5, PDE6, PDE9 and PDE11. IC50 values are 0.76, 0.15, 29.0, and 12.0 μM, respectively.[2][3]
Zaprinast inhibits the growth of asexual blood-stage malaria parasites (P. falciparum) in vitro with an ED50 value of 35 μM, and inhibits PfPDE1, a P. falciparum cGMP-specific phosphodiesterase, with an IC50 value of 3.8 μM.[4]
^Choi, SH; Choi, DH; Song, KS; Shin, KH; Chun, BG (2002). "Zaprinast, an inhibitor of cGMP-selective phosphodiesterases, enhances the secretion of TNF-alpha and IL-1beta and the expression of iNOS and MHC class II molecules in rat microglial cells". Journal of Neuroscience Research. 67 (3): 411–21. doi:10.1002/jnr.10102. PMID11813247. S2CID24513289.
^Taniguchi, Y.; Tonaikachi, H.; Shinjo, K. (2006). "Zaprinast, a well-known cyclic guanosine monophosphate-specific phosphodiesterase inhibitor, is an agonist for GPR35". FEBS Letters. 580 (21): 5003–5008. doi:10.1016/j.febslet.2006.08.015. PMID16934253. S2CID43142927.