The therapeutic efficacy of various doses and schedules of 131I-labelled anti-
episialin monoclonal antibody (MAb) 139H2 was assessed in the NIH:OVCAR-3 human
ovarian cancer xenograft model.
Radioimmunotherapy was started at the time s.c.
tumors were well established (100 to 300 mm3). The anti-
tumor effects induced by i.v.
injections of 131I-MAb 139H2 were dose- and schedule-dependent. Optimal growth inhibition and long-lasting complete
tumor regressions were obtained with 2
injections of 500, 700 or 750 muCi 131I-MAb 139H2 per mouse given with a 2-week interval. The percentage of
tumors with more than 50% reduction of their initial volume
after treatment with a total dose of 1,000 muCi 131I-MAb 139H2 per mouse, given as 10
injections of 100 muCi (3 x/week), 4
injections of 250 muCi (2 x/week), 10
injections of 100 muCi (5 x/week) within a period of 3 weeks, or 2
injections of 500 muCi with a 2-week interval, was 9%, 40%, 64% and 75% respectively. Unlabelled MAb 139H2 did not affect
tumor growth, while the effects of 131I-control MAb were minor and transient. 131I-MAb 139H2 treatment did not select for outgrowth of
episialin-negative cells in the OVCAR-3 xenografts. Highest absorbed doses of whole-body-radiation were calculated for 2
injections (500 to 750 muCi 131I-MAb 139H2) given with the 2-week interval. The radiation dose to the
tumor after a single injection of 500 muCi 131I-MAb 139H2 was 1,300 cGy over 7 days, which appeared slightly lower than the dose calculated after administration of a tracer dose of iodinated MAb 139H2.