Radioimmunotherapy for breast cancer using indium- 111/yttrium-90 BrE-3 : Results of a phase I clinical trial

BrE-3 is a murine IgG1 monoclonal antibody that binds to 97% of human ductal breast cancer specimens. A previous study documented the ability of 111In-labeled 1,4-methyl-benzyl isothiocyanate diethylenetriamine pentaacetic acid (111In-MX-DTPA) BrE-3 to specifically target breast cancer tissue in patients, and the dosimetry derived from the pharmacokinetics suggested that a useful therapeutic index could be obtained with 90Y-MX-DTPA BrE-3. A Phase I maximum tolerated dose study was, therefore, initiated. Six patients received 111In/90Y-MX-DTPA BrE-3, three of them receiving 6.25 and the other three receiving 9.25 mCi/m2 of 90Y. Pharmacokinetics, dosimetry, human anti-mouse antibody (HAMA), toxicity and clinical responses were evaluated. Three of six patients demonstrated a minor and transient, but objective tumor response, and none of the patients had significant toxicity. Tumor dosimetry ranged from 39 to 167 rad/mCi of 90Y (442-1887 rad/ dose). HAMA response occurred in five of six patients. Minimal toxicity, dosimetric calculations and clinical assessment indicate that a useful therapeutic index can be achieved with this therapy. Indium-111/yttrium-90-MX-DTPA BrE-3 can be safely administered to patients with metastatic breast cancer, and therapy doses yielded pharmacokinetics similar to those of tracer doses. Clinical responses, albeit transient, were achieved with single-dose therapy. Rapid onset of the HAMA response will hinder multicycle therapy, unless it is prevented with immunosuppressive drugs or the use of a "humanized" antibody. Further studies are needed to determine the optimal use of BrE-3 for radioimmunotherapy.