Shoara Aron A, Churcher Zachary R, Slavkovic Sladjana, Johnson Philip E
Department of Chemistry & Centre for Research on Biomolecular Interactions, York University, 4700 Keele St., Toronto, Ontario M3J 1P3, Canada.
ACS Omega. 2021 Sep 10;6(37):24209-24217. doi: 10.1021/acsomega.1c03781. eCollection 2021 Sep 21.
Levamisole is a common and harmful adulterant of street samples of cocaine and can cause electrochemical tests for cocaine to give false negative results. To see if levamisole would interfere with aptamer-based bioassays, we analyzed the binding of levamisole to the cocaine-binding DNA aptamer. At low aptamer concentrations (0.5 to 20 μM) using isothermal titration calorimetry methods and thermal stability measurements, no binding of levamisole to the cocaine-binding aptamer was observed. At higher levamisole concentrations (500 μM), weak binding to the cocaine-binding aptamer was detected using nuclear magnetic resonance (NMR) spectroscopy chemical shift perturbations. NMR-detected titrations show that levamisole binding is competitive with cocaine binding, indicating that both ligands share a common binding site. Finally, we show that the presence of levamisole does not interfere with the photochrome aptamer switch binding assay for cocaine. We conclude that assays using low concentrations of cocaine, and consequently low concentration of levamisole as an adulterant, should be unaffected by the weak binding of levamisole.
左旋咪唑是可卡因街头样本中常见的有害掺杂物，可导致可卡因的电化学测试产生假阴性结果。为了探究左旋咪唑是否会干扰基于适配体的生物测定，我们分析了左旋咪唑与可卡因结合DNA适配体的结合情况。使用等温滴定量热法和热稳定性测量方法，在低适配体浓度（0.5至20 μM）下，未观察到左旋咪唑与可卡因结合适配体的结合。在较高的左旋咪唑浓度（500 μM）下，使用核磁共振（NMR）光谱化学位移扰动检测到其与可卡因结合适配体的弱结合。NMR检测的滴定表明，左旋咪唑的结合与可卡因的结合具有竞争性，这表明两种配体共享一个共同的结合位点。最后，我们表明左旋咪唑的存在不会干扰用于检测可卡因的光致变色适配体开关结合测定。我们得出结论，使用低浓度可卡因以及因此作为掺杂物的低浓度左旋咪唑的测定，不应受到左旋咪唑弱结合的影响。
