Folate Receptor Targeted Alpha-Therapy Using Terbium-149

Terbium-149 is among the most interesting therapeutic nuclides for medical applications. It decays by emission of short-range alpha-particles (E-alpha = 3.967 MeV) with a half-life of 4.12 h. The goal of this study was to investigate the anticancer efficacy of a Tb-149-labeled DOTA-folate conjugate (cm09) using folate receptor (FR)-positive cancer cells in vitro and in tumor-bearing mice. Tb-149 was produced at the ISOLDE facility at CERN. Radiolabeling of cm09 with purified Tb-149 resulted in a specific activity of similar to 1.2 MBq/nmol. In vitro assays performed with Tb-149-cm09 revealed a reduced KB cell viability in a FR-specific and activity concentration-dependent manner. Tumor-bearing mice were injected with saline only (group A) or with 149 Tb-cm09 (group B: 2.2 MBq; group C: 3.0 MBq). A significant tumor growth delay was found in treated animals resulting in an increased average survival time of mice which received Tb-149-cm09 (B: 30.5 d; C: 43 d) compared to untreated controls (A: 21 d). Analysis of blood parameters revealed no signs of acute toxicity to the kidneys or liver in treated mice over the time of investigation. These results demonstrated the potential of folate-based alpha-radionuclide therapy in tumor-bearing mice.