Preparation of alpha-emitting Bi-213-labeled antibody constructs for clinical use

Preclinical evaluation of alpha particle-emitting Bi-213-labeled antibody c onstructs have demonstrated the specificity and potency of these agents in a variety of cancer systems. The transition of a Bi-213-radiolabeled antibo dy from a preclinical construct to a clinical drug represented a difficult task that involved development of reliable and validated methods to provide multiple MBq quantities of a pure, immunoreactive agent that met pharmaceu tical standards to treat patients. Methods: The methods used for the prepar ation of (Bi-213)CHX-A-diethylenetriamine pentaacetic acid (DTPA)-HuM195, a n alpha particle-emitting anti-CD33 antibody construct for therapy of myelo id leukemias, is used as a specific example. This article describes methods for reagent purification, drug labeling, radioprotection and chromatograph ic purification. Quality of the drug is evaluated using radiochemical incor poration and purity assays with instant thin-layer chromatography (ITLC) an d high-performance liquid chromatography (HPLC), determination of cell-base d antibody total immunoreactivity, small animal safety, pyrogen level, ster ility and radionuclidic purity. Results: Sixty-seven doses were prepared. I ndividual doses ranged from 148 to 814 MBq. Specific activities ranged from 329 to 766 MBq/mg. The radiolabeling efficiency (median +/- SD) of CHX-A-D TPA-HuM195 with Bi-213 was 81% +/- 9% (n = 67) after 9 min. The construct w as purified by size-exclusion chromatography and was found to be 99% +/- 2% pure (n = 67) by either ITLC or HPLC methods. The immunoreactivity of (Bi- 213)CHX-A-DTPA-HuM195 was 89% +/- 9% (n = 44) and was independent of the sp ecific activity. The formulated pharmaceutical was found to contain less th an or equal to 4 +/- 1 EU/mL pyrogens (n = 66); all samples examined were s terile. An Ac-225 radionuclidic impurity was present at a level of 0.04 +/- 0.03 x 10(-6)/mL (n = 10) in a product volume of 7.4 +/- 0.5 mL (n = 67). Each of the 67 doses was injected intravenously into patients without compl ication as part of a phase I clinical trial. Conclusion: These data show th at Bi-213-labeled antibody constructs can be prepared and administered safe ly to humans at a wide range of therapeutic levels.