Preparation and preclinical evaluation of radioiodinated secnidazole as a possible tumor imaging agent

To develop a radiopharmaceutical localizing in tumor hypoxic tissues, secnidazole (SECN) was labeled with ¹²⁵I. The labeled product was prepared with the radiochemical yield higher than 96% when performing the reaction at 45°C for 30 min. The electrophilic radioiodination of SECN was done using different oxidizing agents. Iodogen appeared to be more effective than chloramine-T (CAT) and N-bromosuccinimide (NBS). ¹²⁵I-SECN was tested in vivo with a tumor model prepared by the intramuscular injection of Ehrlich cell line into the thigh muscle of mice. ¹²⁵I-SECN showed high accumulation in tumor hypoxic tissue (3.6% of injected dose per gram of organ at 2 h post injection). The target/nontarget (T/NT) ratio was high (T/NT = 6 at 24 h post injection). Thus, radioiodinated SECN shows promise as a selective imaging agent for diagnosis of tumor hypoxia.