Biodistribution studies are essential in drug carrier design and translation, and radiotracing provides a sensitive quantitation for this purpose. Yet, for biodegradable formulations, small amounts of free‐label signal may arise prior to or immediately after injection in animal models, causing potentially confounding biodistribution results. In this study, we refined a method to overcome this obstacle. First, we verified free signal generation in animal samples and then, mimicking it in a controllable setting, we injected mice intravenously with a radiolabeled drug carrier formulation (¹²⁵I‐antibody/3DNA) containing a known amount of free radiolabel (¹²⁵I), or free ¹²⁵I alone as a control. Corrected biodistribution data were obtained by separating the free radiolabel from blood and organs postmortem, using trichloroacetic acid precipitation, and subtracting the confounding signal from each tissue measurement. Control free ¹²⁵I‐radiolabel was detected at ≥85% accuracy in blood and tissues, validating the method. It biodistributed very heterogeneously among organs (0.6–39 %ID/g), indicating that any free ¹²⁵I generated in the body or present in an injected formulation cannot be simply corrected to the free‐label fraction in the original preparation, but the free label must be empirically measured in each organ. Application of this method to the biodistribution of ¹²⁵I‐antibody/3DNA, including formulations directed to endothelial target ICAM‐1, showed accurate classification of free ¹²⁵I species in blood and tissues. In addition, this technique rendered data on the in vivo degradation of the traced agents over time. Thus, this is a valuable technique to obtain accurate measurements of biodistribution using ¹²⁵I and possibly other radiotracers.

中文翻译：

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一种改进基于定量放射性示踪的药物载体体内生物分布分析的方法

生物分布研究在药物载体设计和翻译中必不可少，而放射性示踪为此提供了灵敏的定量方法。然而，对于可生物降解的制剂，在动物模型注射之前或之后可能会立即出现少量的游离标记信号，从而导致潜在的混淆生物分布结果。在这项研究中，我们改进了一种方法来克服这一障碍。首先，我们在动物样本中验证了游离信号的产生，然后，在可控环境中模拟它，我们给小鼠静脉注射含有已知量游离放射性标记 ( ¹²⁵ I)的放射性标记药物载体制剂 ( ¹²⁵ I-抗体/3DNA)，或免费¹²⁵我一个人作为对照。通过从血液和死后器官中分离游离放射性标记、使用三氯乙酸沉淀并从每个组织测量值中减去混杂信号来获得校正的生物分布数据。在血液和组织中以≥85% 的准确度检测到无对照的^{125 I 放射性标记，验证了该方法。}它在器官之间的生物分布非常不均匀（0.6–39 %ID/g），表明体内产生或存在于注射制剂中的任何游离¹²⁵ I 不能简单地校正为原始制剂中的游离标记部分，但游离必须在每个器官中根据经验测量标签。该方法在^{125生物分布中的应用}I-抗体/3DNA，包括针对内皮靶点 ICAM-1 的制剂，显示出对血液和组织中游离^{125 I 物种的准确分类。}此外，该技术还提供了有关示踪剂随时间在体内降解的数据。^{因此，这是一种有价值的技术，可以使用125} I 和可能的其他放射性示踪剂来准确测量生物分布。