Molecular Determinants for the Activating/Blocking Actions of the 2<i>H</i>-1,4-Benzoxazine Derivatives, a Class of Potassium Channel Modulators Targeting the Skeletal Muscle K<sub>ATP</sub> Channels
作者:Domenico Tricarico、Antonietta Mele、Giulia Maria Camerino、Antonio Laghezza、Giuseppe Carbonara、Giuseppe Fracchiolla、Paolo Tortorella、Fulvio Loiodice、Diana Conte Camerino
DOI:10.1124/mol.108.046615
日期:2008.7
The 2 H -1,4-benzoxazine derivatives are modulators of the skeletal muscle ATP-sensitive-K+ channels (KATP), activating it in the presence of ATP but inhibiting it in the absence of nucleotide. To investigate the molecular determinants for the activating/blocking actions of these compounds, novel molecules with different alkyl or aryl-alkyl substitutes at position 2 of the 1,4-benzoxazine ring were prepared. The effects of the lengthening of the alkyl chain and of branched substitutes, as well as of the introduction of aliphatic/aromatic rings on the activity of the molecules, were investigated on the skeletal muscle KATP channels of the rat, in excised-patch experiments, in the presence or absence of internal ATP (10-4 M). In the presence of ATP, the 2- n -hexyl analog was the most potent activator (DE50 = 1.08 × 10-10 M), whereas the 2-phenylethyl was not effective. The rank order of efficacy of the openers was 2- n -hexyl ≥2-cyclohexylmethyl >2-isopropyl = 2- n -butyl ≥ 2-phenyl ≥ 2-benzyl = 2-isobutyl analogs. In the absence of ATP, the 2-phenyl analog was the most potent inhibitor (IC50 = 2.5 × 10-11 M); the rank order of efficacy of the blockers was 2-phenyl ≥ 2- n -hexyl > 2- n -butyl > 2-cyclohexylmethyl, whereas the 2-phenylethyl, 2-benzyl, and 2-isobutyl 1,4-benzoxazine analogs were not effective; the 2-isopropyl analog activated the KATP channel even in the absence of nucleotide. Therefore, distinct molecular determinants for the activating or blocking actions for these compounds can be found. For example, the replacement of the linear with the branched alkyl substitutes at the position 2 of the 1,4-benzoxazine nucleus determines the molecular switch from blockers to openers. These compounds were 100-fold more potent and effective as openers than other KCO against the muscle KATP channels.
2H-1,4-苯并恶嗪衍生物是骨骼肌ATP敏感性K+通道(KATP)的调节剂,在有ATP存在时激活它,而在无核苷酸存在时抑制它。为了研究这些化合物的激活/阻断作用的分子决定因素,制备了在1,4-苯并恶嗪环的2位上具有不同烷基或芳基-烷基取代基的新型分子。在切除-补丁实验中,在有或无内源性ATP(10-4M)存在的情况下,研究了延长烷基链、引入支链取代基以及引入脂肪/芳香环对这些分子在骨骼肌KATP通道上的活性的影响。在有ATP存在的情况下,2-正己基类似物是最有效的激活剂(DE50 = 1.08 × 10-10 M),而2-苯乙基类似物则无效。开放剂的功效顺序为2-正己基 ≥2-环己基甲基 >2-异丙基 = 2-正丁基 ≥ 2-苯基 ≥ 2-苄基 = 2-异丁基类似物。在没有ATP存在的情况下,2-苯基类似物是最有效的抑制剂(IC50 = 2.5 × 10-11 M);阻断剂的功效顺序为2-苯基 ≥ 2-正己基 > 2-正丁基 > 2-环己基甲基,而2-苯乙基、2-苄基和2-异丁基1,4-苯并恶嗪类似物则无效;即使在无核苷酸存在的情况下,2-异丙基类似物也能激活KATP通道。因此,可以找到这些化合物激活或阻断作用的独特分子决定因素。例如,将1,4-苯并恶嗪核的2位上的线性烷基取代基替换为支链烷基取代基,决定了分子从阻断剂到开放剂的转换。这些化合物作为开放剂,比其他针对骨骼肌KATP通道的KCO具有100倍的更强效力和效果。