Continuous Wave Electron Paramagnetic Resonance Imaging

TH-302是一种二元化疗药物，其2-硝基咪唑片段与DNA烷基化氮芥片段共价连接。2-硝基咪唑部分通过细胞内还原进行生物还原。在氧气存在的情况下，药物被重新氧化到原始状态，但在缺氧条件下，药物经历碎裂并释放烷基化氮芥，造成选择性缺氧细胞毒性。我们利用EPR自旋捕获和DMPO作为自旋陷阱，研究了TH-302在不同浓度的溶解氧存在下的氧化还原循环行为，以监测TH-302暴露于活化酶时产生的超氧自由基。使用超氧化物通量作为TH-302 DNA烷基化效应的正交指标，我们定量地发现该过程可以在pO2水平（5 mmHg）下发生，超过该水平时氧化还原循环占主导地位。细胞研究评估缺氧细胞毒性也与体外EPR研究一致。

TH-302 is a binary chemotherapeutic drug which has a 2-nitroimidazole moiety covalently linked to a DNA alkylating nitrogen mustard moiety. The 2-nitroimidazole moiety undergoes bioreduction by intracellular reduction. In the presence of oxygen, the drug is reoxidized to original state but in hypoxic conditions, the drug undergoes fragmentation and releases the alkylating nitrogen mustard inflicting selective hypoxic cytotoxicity. We studied the redox-cycling behavior of TH-302 using EPR spin trapping with DMPO as the spin trap to monitor the superoxide radical produced during redox cycling of TH-302 when exposed to activating enzymes, in the presence of different concentrations of dissolved oxygen. Using superoxide flux as an orthogonal indicator of DNA alkylating effects of TH-302, we found quantitatively that this process can occur at pO2 levels < 5 mmHg beyond which redox-cycling predominates. The cellular studies evaluating the hypoxic cytotoxicity also were in agreement with the in vitro EPR studies.