MBCQ is a cGMP-specific phosphodiesterase PDE5 inhibitor.

The phosphodiesterase type 5 inhibitor (PDE5 inhibitor) is an agent used to inhibit the degradative action of cGMP-specific PDE5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis. PDE5 drugs are used in the treatment of erectile dysfunction and were the first effective oral treatment for this condition. Sinve PDE5 is also present in the arterial wall smooth muscle within the lungs, PDE5 inhibitors have also been applied for the pulmonary hypertension treatment.

In vitro: In previous study, it was found that the addition of MBCQ to the blood vessle samples could lead to an 80 to 85% inhibition of PDE activity, indicating that most of the activity present in these blood vessels could be attributed to PDE5. [1].

In vivo: In animal rat study, tolerance was induced by continuous exposure to glyceryl trinitrate (GTN) for 48 h. Results showed that MBCQ could significantly decrease the EC(50) values for GTN-induced relaxation in both tolerant and nontolerant tissues, but with the greatest relative shift showing in tolerant veins. Moreover, MBCQ could also increase the vasodilator potency of a nitric oxide donor (1,1-diethyl-2-hydroxy-2-nitrosohydrazine). A significant increase in cGMP PDE activity was found in tolerant femoral vein, whereas PDE activity was unchanged in femoral artery [1].

Clinical trial: Up to now, MBCQ is still in the preclinical development stage.

Reference:
[1] MacPherson JD, Gillespie TD, Dunkerley HA, Maurice DH, Bennett BM.  Inhibition of phosphodiesterase 5 selectively reverses nitrate tolerance in the venous circulation. J Pharmacol Exp Ther. 2006 Apr;317(1):188-95.