MSX-2

MSX-2 is a selective adenosine A_2A receptor antagonist used in scientific research. It is a xanthine and a derivative of the non-selective adenosine receptor antagonist caffeine.

The affinities (K_i) of MSX-2 for the human adenosine receptors are 5.38 to 14.5 nM for the adenosine A_2A receptor, 2,500 nM for the adenosine A₁ receptor (172- to 465-fold lower than for the A_2A receptor), and >10,000 nM for the adenosine A_2B and A₃ receptors (>690-fold lower than for the A_2A receptor).

MSX-2 has poor water solubility, which has limited the use of MSX-2 itself. Water-soluble ester prodrugs of MSX-2, including MSX-3 (a phosphate ester prodrug) and MSX-4 (an amino acid ester prodrug), have been developed and used in place of MSX-2. MSX-3 is best-suited for use by intravenous administration, whereas MSX-4 can be administered by oral administration.

MSX-3 and MSX-4 reverse motivational deficits in animals and hence have the capacity to produce pro-motivational effects.

MSX-2 and MSX-3 were first described in the scientific literature by 1998. Subsequently, MSX-4 was developed and described by 2008.

• 3-Chlorostyrylcaffeine
• Istradefylline
• Preladenant