Abstract
Purpose:
The aim of this study was to investigate the therapeutic efficacy of the alpha-radioimmunotherapy of ovarian cancer in mice, using different specific activities. This study was performed by using the monoclonal antibody, MX35 F(ab′)2, labeled with the α-particle-emitter, 211At.
Methods:
Animals were intraperitoneally inoculated with ∼1 × 107 cells of the cell line, NIH:OVCAR-3. Four (4) weeks later, five groups of animals were given 400 kBq of 211At-MX35 F(ab′)2 with specific activities equal to 130, 65, 32, 16, or 4 kBq/μg, respectively (n = 18 in each group). As controls, animals were given unlabeled MX35 F(ab′)2 (n = 12). Eight (8) weeks after treatment, the animals were sacrificed and the presence of macro- and microscopic tumors and ascites was determined.
Results:
The tumor-free fractions (TFFs) of the animals, defined as the fraction of animals with no macro- and microtumors and no ascites, were 0.67, 0.73, 0.50, 0.50, and 0.17 when treated as above. Only the TFF of 0.17, for the specific activity of 4 kBq/μg, was significantly less, compared to that of the specific activity of 130 kBq/μg. The TFF for the specific activity of 4 kBq/μg showed a significant lowering, compared to the specific activity of 130 kBq/μg (p < 0.05). Treatment with unlabeled MX35 F(ab′)2 resulted in a TFF of zero.
Conclusions:
A specific activity-dependent therapeutic outcome could not be shown in the interval of 130– to 16 kBq/μg. For lower specific activities (i.e., 4 kBq/μg), the therapeutic efficacy was significantly lowered.