Radioimmunotherapy of experimental pancreatic cancer with 131I-labeled monoclonal antibody PAM4

We examined the therapeutic efficacy of ¹³¹I-labeled murine monoclonal antibody (MAb) PAM4 against human pancreatic cancers carried as xenografts in athymic nude mice. Animals bearing the CaPanI tumor (0.2 cm³) were either untreated or were given, ¹³¹I-labeled nonspecific Ag8 antibody. By week 7 mean tumor size had grown 16.5 ± 8.4-fold and 4.2 ± 2.5-fold for the untreated and ¹³¹I-Ag8-treated animals, respectively. In contrast, animals administered ¹³¹I-PAM4 exhibited marked regression of tumors to an average of 15% of initial tumor volume. Since most pancreatic cancer patients present with large tumor burdens, the limitation of ¹³¹I-PAM4 treatment with respect to initial tumor size was investigated in animals bearing tumors of approximately 0.5 cm³, 1.0 cm³ and 2.0 cm³. Significant extension of survival time (>3-fold increase) was noted for both the 0.5 cm³ and 1.0 cm^{3 131}I-PAM4-treated groups, compared to their respective untreated controls. Even in the group bearing large 2.0-cm³ tumors, survival was increased 2-fold over the control group. To further improve anti-tumor effects in large tumors, 2 injections of ¹³¹I-PAM4 were administered at a 4-week interval to animals bearing tumors of approximately 1.0 cm³. Significant extended survival was noted for the group receiving 2 doses when compared to the group receiving only 1 dose. Int. J. Cancer 71:660-667, 1997. © 1997 Wiley-Liss, Inc.