Multiple Administrations of (64)Cu-ATSM as a Novel Therapeutic Option for Glioblastoma: a Translational Study Using Mice with Xenografts

Glioblastoma is the most aggressive malignant brain tumor in humans and is difficult to cure using current treatment options. Hypoxic regions are frequently found in glioblastoma, and increased levels of hypoxia are associated with poor clinical outcomes of glioblastoma patients. Hypoxia plays important roles in the progression and recurrence of glioblastoma because of drug delivery deficiencies and induction of hypoxia-inducible factor-1α in tumor cells, which lead to poor prognosis. We focused on a promising hypoxia-targeted internal radiotherapy agent, (64)Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) ((64)Cu-ATSM), to address the need for additional treatment for glioblastoma. This compound can target the overreduced state under hypoxic conditions within tumors. Clinical positron emission tomography studies using radiolabeled Cu-ATSM have shown that Cu-ATSM accumulates in glioblastoma and its uptake is associated with high hypoxia-inducible factor-1α expression. To evaluate the therapeutic potential of this agent for glioblastoma, we examined the efficacy of (64)Cu-ATSM in mice bearing U87MG glioblastoma tumors. Administration of single dosage (18.5, 37, 74, 111, and 148 MBq) and multiple dosages (37 MBq × 4) of (64)Cu-ATSM was investigated. Single administration of (64)Cu-ATSM in high-dose groups dose-dependently inhibited tumor growth and prolonged survival, with slight and reverse signs of adverse events. Multiple dosages of (64)Cu-ATSM remarkably inhibited tumor growth and prolonged survival. By splitting the dose of (64)Cu-ATSM, no adverse effects were observed. Our findings indicate that multiple administrations of (64)Cu-ATSM have effective antitumor effects in glioblastoma without side effects, indicating its potential for treating this fatal disease.