Complex sentence: GTS-21 (DMXB-A) is a drug which acts as a subtype-selective neural nicotinic acetylcholine receptor partial agonist, binding to both the α4β2 and α7 subtypes, but only activating the α7 to any significant extent.
Split into simpler sentences: GTS-21 (DMXB-A) is a drug which acts as a partial agonist at neural nicotinic acetylcholine receptors. It binds to both the α4β2 and α7 subtypes, but only activates the α7 to any significant extent.