TABLE 1.

Inhibition of human recombinant PDE4 subtypes by BI 1015550 in comparison to roflumilast and its active metabolite Roflu-N-Ox. IC₅₀ values (nmol/L) are given as means from n independent experiments. Cell extracts containing the active site fragments mediated the conversion of 10 µL [³H]cAMP (0.05 µCi in H₂O) to AMP resulting in the binding of this radiolabeled molecule to the yttrium silicate SPA beads and the subsequent generation of scintillation events determined using a Wallac Microbeta counter. AMP, adenosine monophosphate; IC₅₀, inhibitory concentration (nM) for half-maximal inhibition; PDE, phosphodiesterase; SPA, scintillation proximity assay.

	PDE4A	PDE4B2	PDE4C2	PDE4D2
BI 1015550	248 (n = 3)	10 (n = 2)	8,700 (n = 3)	91 (n = 2)
Roflumilast	1.4 (n = 2)	0.6 (n = 12)	12 (n = 2)	0.8 (n = 12)
Roflu-N-Ox	2.8 (n = 1)	1.4 (n = 6)	15 (n = 1)	1.4 (n = 6)