Dougan H, Lyster D M, Vo C V, Stafford A, Weitz J I, Hobbs J B
TRIUMF,., Vancouver, B.C, Canada.
Nucl Med Biol. 2000 Apr;27(3):289-97. doi: 10.1016/s0969-8051(99)00103-1.
We have investigated (123)I and (125)I DNA aptamer analogs of anticoagulant DNA aptamers to thrombin exosite 1 and exosite 2 for thrombus imaging potential. Two severe problems are rapid clearance from circulating blood and blood nuclease. With aptamers (unlike antisense) the nucleotide analogs used in polymerase chain reaction-selection cycles also must be used in the radiotracer. We investigated 3'-biotin-streptavidin (SA) bioconjugates of the aptamers to alleviate these problems. Blood nuclease assays and biodistribution analysis were used in the mouse and rabbit. We found that 3'-biotin protected the aptamers significantly from blood nuclease in vitro, but it did not slow in vivo clearance. In contrast, the 3'-biotin-SA bioconjugates were resistant to blood nuclease in vitro and were also longer-lived (10-20 times) in vivo. Bioconjugate aptamers retained affinity for thrombin. Two solutions emerge: 1) In noncirculating blood (within a thrombus) 3'-biotin extends aptamer lifetime, whereas 2) in circulating blood (the transport medium), where more aggressive clearance is encountered, 3'-SA extends aptamer lifetime.
我们已经研究了针对凝血酶外位点1和外位点2的抗凝DNA适配体的（123）I和（125）I DNA适配体类似物的血栓成像潜力。存在两个严重问题，即从循环血液中快速清除以及血液核酸酶的作用。对于适配体（与反义核酸不同），聚合酶链反应筛选循环中使用的核苷酸类似物也必须用于放射性示踪剂中。我们研究了适配体的3'-生物素-链霉亲和素（SA）生物共轭物以缓解这些问题。在小鼠和兔子身上进行了血液核酸酶测定和生物分布分析。我们发现，3'-生物素在体外能显著保护适配体免受血液核酸酶的影响，但并未减缓其在体内的清除速度。相比之下，3'-生物素-SA生物共轭物在体外对血液核酸酶具有抗性，并且在体内的寿命也更长（延长了10至20倍）。生物共轭适配体保留了对凝血酶的亲和力。由此产生了两种解决方案：1）在非循环血液（血栓内）中，3'-生物素可延长适配体的寿命，而2）在循环血液（运输介质）中，由于遇到更积极的清除作用，3'-SA可延长适配体的寿命。
