MSX-2
MSX-2 is a selective adenosine A2A receptor antagonist used in scientific research. It is a xanthine and a derivative of the non-selective adenosine receptor antagonist caffeine.
The affinities of MSX-2 for the human adenosine receptors are 5.38 to 14.5nM for the adenosine A2A receptor, 2,500nM for the adenosine A1 receptor, and >10,000nM for the adenosine A2B and A3 receptors.
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 and MSX-4, 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.