Effect of the extent of substitution on the immunoreactivity of 21T-BAT-LYM-1 immunoconjugate
- Univ. of California, Davis, CA (United States); and others
Pilot therapy of lymphoma with the radioimmunopharmaceutical Cu-67-21T-BAT-Lym-1 has been promising. 2IT-BAT-Lym-1 is prepared by conjugating the bifunctional macrocyclic chealting agent 6-[p-(bromoacetamido)benzyl]-TETA (BAT) to murine anti-lymphoma lgG{sub 2a} Lym-1 via 2-iminothiolane (2IT). The specific activity of Cu-67 used for radiolabeling is as low as 1 mCi/{mu}g, or 1 Cu-67 atom per 800 total copper atoms; hence as few as 1 in 800 ligands are occupied by radiometal. Increasing the ratio of ligands per antibody will increase the specific activity of the radiopharmaceutical, reducing the amount of immunoconjugate that must be administered for therapy. Conjugation of 4 or more ligands per antibody has been associated with substantial loss of immunoreactivity of other conjugates. Here we examine the effect of the extent of substitution on the immunoreactivity of 2IT-BAT-Lym-1. 19 lots of 2IT-BAT-Lym-1 with 1.3 to 19 ligands per antibody were prepared in conjugation reactions conducted at 37 {degrees}C, pH 9.0, for 30 min with varying concentrations of 2IT and BAT. The conjugates were radiolabeled with Co-57 and examined by fixed plate binding assay to antigenic RAJI cell homogenate. all 17 lots prepared with 11 ligands per antibody or fewer exhibited immunoreactivity of 80% of more vs. unmodified Lym-1. Greater loss of immunoreactivity was observed with higher substitution. Scatchard studies corroborate these results and suggest that binding avidity decreases with increasing substitution. We conclude that 2IT-BAT-Lym-1 can be prepared with up to 11 ligands per antibody with retention of immunoreactivity acceptable for therapeutic use. When radiolabeled with Cu-67 with a specific activity of 1 mCi/{mu}g, the radioimmunopharmaceutical will have a specific activity of 4.5 {mu}Ci/{mu}g, suitable for therapeutic use.
- DOE Contract Number:
- FG03-84ER60233
- OSTI ID:
- 214534
- Report Number(s):
- CONF-940605-; ISSN 0161-5505; TRN: 95:007029-0261
- Journal Information:
- Journal of Nuclear Medicine, Vol. 35, Issue Suppl.5; Conference: 41. annual meeting of the Society of Nuclear Medicine, Orlando, FL (United States), 5-8 Jun 1994; Other Information: PBD: May 1994
- Country of Publication:
- United States
- Language:
- English
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