DOE OSTI2014
Use of the highly toxic and easily prepared rodenticide tetramethylenedisulfotetramine (TETS) was banned after thousands of accidental or intentional human poisonings, but it is of continued concern as a chemical threat agent. TETS is a noncompetitive blocker of the GABA type A receptor (GABA A R), but its molecular interaction has not been directly established for lack of a suitable radioligand to localize the binding site. We synthesized [ 14 C]TETS (14 mCi/mmol, radiochemical purity >99%) by reacting sulfamide with H 14 CHO and $s$-trioxane then completion of the sequential cyclization with excess HCHO. The outstanding radiocarbon sensitivity of accelerator mass spectrometry (AMS) allowed the use of [ 14 C]TETS in neuroreceptor binding studies with rat brain membranes in comparison with the standard GABA A R radioligand 4'-ethynyl-4-$n$-[ 3 H]propylbicycloorthobenzoate ([ 3 H]EBOB) (46 Ci/mmol), illustrating the use of AMS for characterizing the binding sites of high-affinity 14 C radioligands. Fourteen noncompetitive antagonists of widely diverse chemotypes assayed at 1 or 10 µM inhibited [ 14 C]TETS and [ 3 H]EBOB binding to a similar extent (r 2 = 0.71). Molecular dynamics simulations of these 14 toxicants in the pore region of the α1β2γ2 GABA A R predict unique and significant polar interactions for TETS with α 1 T1' and γ 2 S2', which are not observed for EBOB or the GABAergic insecticides. Several GABA A R modulators similarly inhibited [ 14 C]TETS and [ 3 H]EBOB binding, including midazolam, flurazepam, avermectin Ba1, baclofen, isoguvacine, and propofol, at 1 or 10 μM, providing an in vitro system for recognizing candidate antidotes.
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