本研究旨在开发一种生物相容性血氧测定电子顺磁共振 (EPR) 自旋探针，与参考自旋探针相比，该探针具有降低的自弛豫和对氧的敏感性，可在高氧浓度下实现更高的信噪比和更长的弛豫时间OX071.SOX71 通过 OX071 自旋探针的十二个醇基的琥珀酰化合成，并通过 X 波段 (9.5 GHz) 和低场 (720 MHz) 下的 EPR 进行表征。 SOX71 的生物相容性在小鼠体外和体内进行了测试。进行药代动力学研究以确定 EPR 成像的最佳时间范围。最后，在纤维肉瘤小鼠模型上进行了概念验证 EPR 氧成像。SOX71 是从 OX071 一步合成的。 SOX71 呈现出窄线 EPR 谱，峰峰值线宽为 66 mG，与 OX071 类似。 SOX71 不会与白蛋白结合，在测试浓度高达 5 mM 时也不会表现出细胞毒性。以 EPR 成像所需剂量的两倍对小鼠进行腹腔注射全身给药后，未观察到毒性。注射后，探针很容易被吸收到血流中，注射后半小时血液浓度达到峰值。然后，探针很快被肾脏清除，半衰期为 ~ 45 分钟。 SOX71 在缺氧条件下表现出较长的弛豫时间（T1e = 9.5 µs 和 T2e = 5.1 µs；[SOX71] = 1 mM，PBS 溶液，37 °C，pO2 = 0 mmHg，720 MHz）。弛豫率 R1e 和 R2e 均表现出对 pO2 的敏感性降低，导致室内空气条件下 (pO2 = 159 mmHg) 的弛豫时间比 OX071 长两倍。这是对具有宽范围 pO2 的样品进行氧成像的理想选择。与 OX071 相比，弛豫率 R1e 和 R2e 均显示出对自我弛豫的敏感性降低，探针浓度对 R1e 的影响可以忽略不计。 SOX71 已成功应用于肿瘤中的氧成像。合成、表征了 OX071 的琥珀酰化衍生物 SOX71，并将其应用于体内 EPR 肿瘤氧成像。 SOX71 具有高度生物相容性，并表现出对氧气和自我松弛的敏感性降低。第一份报告表明，在广泛的 pO2 值下，SOX71 的绝对氧分布优于 OX071。© 2023。作者，获得世界分子影像学会的独家许可。

This study aimed to develop a biocompatible oximetric electron paramagnetic resonance (EPR) spin probe with reduced self-relaxation, and sensitivity to oxygen for a higher signal-to-noise ratio and longer relaxation times at high oxygen concentration, compared to the reference spin probe OX071.SOX71 was synthesized by succinylation of the twelve alcohol groups of OX071 spin probe and characterized by EPR at X-Band (9.5 GHz) and at low field (720 MHz). The biocompatibility of SOX71 was tested in vitro and in vivo in mice. A pharmacokinetic study was performed to determine the best time frame for EPR imaging. Finally, a proof-of-concept EPR oxygen imaging was performed on a mouse model of a fibrosarcoma tumor.SOX71 was synthesized in one step from OX071. SOX71 exhibits a narrow line EPR spectrum with a peak-to-peak linewidth of 66 mG, similar to OX071. SOX71 does not bind to albumin nor show cell toxicity for the concentrations tested up to 5 mM. No toxicity was observed after systemic delivery via intraperitoneal injection in mice at twice the dose required for EPR imaging. After the injection, the probe is readily absorbed into the bloodstream, with a peak blood concentration half an hour, post-injection. Then, the probe is quickly cleared by the kidney with a half-life of ~ 45 min. SOX71 shows long relaxation times under anoxic condition (T1e = 9.5 µs and T2e = 5.1 µs; [SOX71] = 1 mM in PBS at 37 °C, pO2 = 0 mmHg, 720 MHz). Both the relaxation rates R1e and R2e show a decreased sensitivity to pO2, leading to twice longer relaxation times under room air conditions (pO2 = 159 mmHg) compared to OX071. This is ideal for oxygen imaging in samples with a wide range of pO2. Both the relaxation rates R1e and R2e show a decreased sensitivity to self-relaxation compared to OX071, with a negligible effect of the probe concentration on R1e. SOX71 was successfully applied to image oxygen in a tumor.SOX71, a succinylated derivative of OX071 was synthesized, characterized, and applied for in vivo EPR tumor oxygen imaging. SOX71 is highly biocompatible, and shows decreased sensitivity to oxygen and self-relaxation. This first report suggests that SOX71 is superior to OX071 for absolute oxygen mapping under a broad range of pO2 values.© 2023. The Author(s), under exclusive licence to World Molecular Imaging Society.