Binding of [3H]MSX-2 (3-(3-hydroxypropyl)-7-methyl-8-(m-methoxystyryl)-1-propargylxanthine) to rat striatal membranes--a new, selective antagonist radioligand for A(2A) adenosine receptors

Eur J Pharm Sci. 2000;10(4):259-65. doi: 10.1016/s0928-0987(00)00064-6.


The present study describes the preparation and binding properties of a new, potent, and selective A(2A) adenosine receptor (AR) antagonist radioligand, [3H]3-(3-hydroxypropyl)-7-methyl-8-(m-methoxystyryl)-1-propargy lxanth ine ([3H]MSX-2). [3H]MSX-2 binding to rat striatal membranes was saturable and reversible. Saturation experiments showed that [3H]MSX-2 labeled a single class of binding sites with high affinity (K(d)=8.0 nM) and limited capacity (B(max)=1.16 of protein). The presence of 100 microM GTP, or 10 mM magnesium chloride, respectively, had no effect on [3H]MSX-2 binding. AR agonists competed with the binding of 1 nM [3H]MSX-2 with the following order of potency: 5'-N-ethylcarboxamidoadenosine (NECA)>2-[4-(carboxyethyl)phenylethylamino]-5'-N-ethylcarboxami doaden osine (CGS-21680)>2-chloroadenosine (2-CADO)>N(6)-cyclopentyladenosine (CPA). AR antagonists showed the following order of potency: 8-(m-bromostyryl)-3, 7-dimethyl-1-propargylxanthine (BS-DMPX)>1, 3-dipropyl-8-cyclopentylxanthine (DPCPX)>(R)-5, 6-dimethyl-7-(1-phenylethyl)-2-(4-pyridyl)-7H-pyrrolo[2, 3-d]pyrimidine-4-amine (SH-128)>3,7-dimethyl-1-propargylxanthine (DMPX)>caffeine. The K(i) values for antagonists were in accordance with data from binding studies with the agonist radioligand [3H]CGS21680, while agonist affinities were 3-7-fold lower. [3H]MSX-2 is a highly selective A(2A) AR antagonist radioligand exhibiting a selectivity of at least two orders of magnitude versus all other AR subtypes. The new radioligand shows high specific radioactivity (85 Ci/mmol, 3150 GBq/mmol) and acceptable nonspecific binding at rat striatal membranes of 20-30%, at 1 nM.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Corpus Striatum / metabolism*
  • Purinergic P1 Receptor Agonists
  • Purinergic P1 Receptor Antagonists*
  • Rats
  • Receptor, Adenosine A2A
  • Receptors, Purinergic P1 / metabolism*
  • Styrenes / metabolism*
  • Styrenes / pharmacology
  • Xanthines / chemistry
  • Xanthines / metabolism*
  • Xanthines / pharmacology


  • (H(3))3-(3-hydroxypropyl)-7-methyl-8-(m-methoxystyryl)-1-propargylxanthine
  • Purinergic P1 Receptor Agonists
  • Purinergic P1 Receptor Antagonists
  • Receptor, Adenosine A2A
  • Receptors, Purinergic P1
  • Styrenes
  • Xanthines