Locoregional alpha-radioimmunotherapy of intraperitoneal tumor cell dissemination using a tumor-specific monoclonal antibody.

PURPOSE: The locoregional application of tumor-specific antibodies conjugated with highly cytotoxic alpha-emitters is a promising new strategy for therapy of i.p. tumor cell dissemination. Using this approach, an antibody specifically targeting diffuse-type gastric cancer cells was coupled to the high linear energy transfer alpha-emitter (213)Bi for treatment of i.p. tumor cell spread in a nude mouse model. EXPERIMENTAL DESIGN: Nude mice were inoculated with HSC45-M2 human gastric cancer cells expressing mutant d9-E-cadherin. Twenty-four h after cell inoculation, mice received i.p. injections of either (213)Bi-d9MAb specifically binding to mutant d9-E-cadherin of HSC45-M2 cells or unspecific (213)Bi-d8MAb (7.4 or 22.2 MBq). Survival of treated animals was monitored compared with controls that had been injected with nonlabeled monoclonal antibody (MAb) or saline. Toxicity was evaluated by WBC counts after injection of 1.85, 7.4, or 22.2 MBq and analysis of chromosomal aberrations of bone marrow cells after injection of 7.4, 14.8, or 22.2 MBq. RESULTS: Survival rates of control mice and of mice treated with (213)Bi-MAbs differed significantly: the mean survival of untreated controls and mice that were given the nonlabeled antibody was 23 and 26 days. After injection of 22.2 MBq of the specific (213)Bi-d9MAb or the unspecific (213)Bi-d8MAb, mean survival was at least 143 or 130 days, respectively. Treatment with 7.4 MBq of (213)Bi-d9MAb increased mean survival to at least 232 days and with (213)Bi-d8MAb to at least 172 days. WBC counts decreased within 2 days after (213)Bi-therapy but reached pretreatment values between day 14 and 21 after activity injection. Chromosomal aberrations in bone marrow cells could only be detected at day 1 after (213)Bi-therapy. The frequency of chromosomal damages increased depending on the applied (213)Bi-activity. CONCLUSIONS: The therapeutic efficacy of the (213)Bi-d9MAb together with a low bone marrow toxicity support the locoregional therapy for that subgroup of diffuse-type gastric carcinoma patients expressing d9-E-cadherin.

Comparison of the radiotoxicity of two alpha-particle-emitting immunoconjugates, terbium-149 and bismuth-213, directed against a tumor-specific, exon 9 deleted (d9) E-cadherin adhesion protein.

We investigated the effects of the alpha-particle emitters (149)Tb and (213)Bi coupled to a tumor-specific antibody targeting the mutated delta 9 E-cadherin (d9 E-Cad) on single cells and cell pellets. The d9 mutation of the adhesion molecule E-cadherin is found in 10% of diffuse-type gastric cancers and is not expressed in normal tissue. Human breast cancer cells (MDA-MB-435S) transfected with d9 E-Cad or the wild-type E-cadherin gene were used to study the effects of anti-d9 E-Cad MAb coupled to (149)Tb and (213)Bi ((149)Tb-d9 MAb and (213)Bi-d9 MAb). The density of binding sites determined on transfected MDA tumor cells by Scatchard analysis and flow cytometry varied from 4 x 10(4) to 6 x 10(4) antigens per cell. Internalization of radioimmunoconjugates by cells expressing d9 E-Cad was less than 10% of bound antibody within 240 min. The effect of the radioimmunoconjugates on cell suspensions and cell pellets was quantified by [(3)H]thymidine incorporation, and the dose to the cell nuclei was determined using microdosimetric calculations. (149)Tb and (213)Bi immunoconjugates affected cells in suspension similarly. Significant differences in the proliferation capacity of d9 E-cadherin- and wild-type E-cadherin-expressing cells were observed at activity concentrations around 185 kBq/ml, corresponding to antibody concentrations between 200 ng/ml and 1000 ng/ml. Proliferation after incubation with (213)Bi-d9 MAb was 50% greater in pelleted wild-type E-Cad-expressing cells compared to wild-type E-Cad cells in suspension. In contrast, the proliferation of pelleted d9 E-Cad cells was similar to that of d9 E-Cad cells in suspension. For (149)Tb-d9 MAb, no significant difference was found between pelleted cells and cells in suspension for low activity concentrations. However, at high activity concentrations, (149)Tb-d9 MAb had only a small effect on pelleted cells. These in vitro studies demonstrate different effects of (149)Tb and (213)Bi conjugated to a tumor-specific antibody toward single cells and tumor cell pellets. Microdosimetric simulation of single cell survival after alpha-particle irradiation modeled the experimental results with reasonable accuracy.