Anti-Lewis Y Humanized Monoclonal Antibody hu3S193 and Paclitaxel Combined-Modality Radioimmunotherapy in a Breast Cancer Model

Radioimmunotherapy (RIT) of solid tumor is often limited in efficacy because of restrictions in achieved tumor dose. In an effort to overcome this, the combination of RIT with other therapeutic modalities was investigated in an animal model of breast carcinoma. The rationale for this combined-modality RIT (CMRIT) was to increase the therapeutic efficacy of RIT through the use of paclitaxel to arrest cells in the radiosensitive G2/M phase of the cell cycle. Methods: In this study, the biodistribution and therapeutic efficacy of 90Y-radiolabeled humanized anti-Lewis Y hu3S193 monoclonal antibody (90Y-hu3S193) RIT in combination with paclitaxel chemotherapy was explored in a Lewis Y–expressing MCF-7 tumor xenografted BALB/c nude mouse model of breast cancer. Results: Biodistribution studies demonstrated excellent tumor targeting and limited normal tissue uptake by 90Y-hu3S193. A therapeutic study with established tumors assessed 90Y-hu3S193 as a single agent and demonstrated significant antitumor effects in all animals receiving a single intravenous 1.85 or 3.70 MBq dose of this treatment compared with phosphate-buffered saline placebo controls (P 5 0.0008 vs. P , 0.0001). Complete responses were observed in all animals in the 3.70 MBq study arm for the duration of the study. Single-dose 90Y-hu3S193 plus paclitaxel (600 mg) CMRIT displayed improved efficacy over single-modality therapies, with a significant difference (P, 0.0001) between the mean percentage change in tumor volume in mice receiving 0.46 MBq 90Yhu3S193 alone and when combined with 600 mg paclitaxel. Conclusion: The significant efficacy of 90Y-hu3S193 and paclitaxel CMRIT at low radiation doses in this model of breast carcinoma indicates its therapeutic potential and warrants further investigation into this promising therapeutic approach.