Table 1.

Effect of different compounds on T. brucei PDEs

Inhibitor	PDE selectivity (IC50)*	TbPDE2A† IC50 (μM)	TbPDE2B‡ IC50 (μM)
IBMX	Nonselective (2–50 μM)	545	>1,000
Papaverine	Nonselective (5–25 μM)	ND	304 ± 19
Pentoxifylline	Nonselective (45–150 μM)	ND	>800
Rolipram	PDE 4 (2 μM)	>100	>300
Ro 20-1724	PDE 4 (2 μM)	ND	>300
Etazolate	PDE 4 (1.2 μM)	30.3	127 ± 4
Enoximone	PDE 3 (1 μM)	ND	>100
cGMP§	PDE 3	>100	>200
Zaprinast	PDE 5 (0.76 μM)	42.5	>50
	PDE 6 (0.15 μM)
Sildenafil	PDE 5 (0.0039 μM)	9.4	>100
EHNA	PDE 2 (1 μM)	ND	>180
Dipyridamole	PDE 5 (0.9 μM)	5.9	27 ± 3
	PDE 6 (0.38 μM)
	PDE 8 (4.5 μM)
	PDE 10 (1.1 μM)

ND, not determined. IBMX, 3-isobutyl-1-methylxanthine. EHNA, erythro-9-[3-(2-hydroxynonyl)]-adenine. 

^*From ref. 24. 

^† From ref. 19. 

^‡ Substrate concentration 1 μM [³H]-cAMP, mean ± SD, n = 3. 

^§ No inhibition or activation was observed.