Biological dosimetry with peripheral blood lymphocytes for targeted alpha therapy of cancer

Full text: Ionizing radiation causes structural chromosomal aberrations, a proportion of which give rise to chromosome fragments without spindle attachment organelles. When a cell divides, some of these fragments are excluded from the main daughter nuclei and form small nuclei within the cytoplasm. The cytokinesis-block micronucleus (MN) assay allows these micronuclei to be counted, providing an in situ biological dosimeter. In this study, we evaluated the micronucleus frequency in peripheral blood lymphocytes after in vitro incubation with the alpha conjugates 213Bi-PAI2, 213BiI3, and 213Bi-9.2.27. Lymphocytes were inoculated in vitro with each alpha conjugate for 3 hours. Further, we report the first MN measurements in melanoma patients after targeted alpha therapy (TAT) with 213Bi-9.2.27. Patient blood was taken at 3 hours, 2 weeks and 4 weeks post-treatment with 240 - 350 MBq. The MN frequency in lymphocytes was similar for equal in vitro doses of Bi, Bi-PAI2, and 213Bi-9.2.27 (P 0.5), indicating that there is no selective targeting of lymphocytes by the alpha conjugates. The base line MN frequency in lymphocytes was significantly different (P < 0.001) compared to that for 15 kBq/mL (1 x 106 cells/mL) of 213Bi inoculated cells. Immediately after inoculation with 15 to 1200 kBq/mL of AC, there was a substantial dose-related increase in MN. The average frequency of MN (60 ± 7) at 2-3 hours post-TAT of melanoma patients with 240 - 350 MBq was similar to the in vitro result with 10 MBq/mL at 3 hours. The number of MN in the blood of treated patients peaked at 2-3 h post-TAT, slowly returning to base line levels by 4 weeks. If the MN are measured at the same post-inoculation time, then the MN assay after Bi inoculation could be used as a biological radiation dosimeter