Site-specific conjugation of bifunctional chelator BAT to mouse IgG1 Fab' fragment
Abstract
Aim: To perform a site-specific conjugation of Fab' fragments of a mouse monoclonal
antibody(MoAb) B43(of IgG1 subtype) to a bifunctional chelator 6-[p-
(bromoacetamido) benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-
tetraacetic acid (BAT) via the thiol groups in the hinge distal to the antigenbinding
site of the Fab'. Methods: B43 was cleaved using a simple 2-step method.
First, stable F(ab')2 was produced by pepsin treatment. Fab' with free thiol in the
hinge region was then obtained by cysteine reduction of F(ab')2. Second, a sitespecific
conjugation of Fab' to thiol-specific BAT was performed in a one-step
reaction. Results: The Fab' fragment had approximately 1.8 free thiol groups per
molecule after cysteine reduction. The conjugation efficiency and the chemical
yield were approximately 1.28 moles chelator/Fab' and 74% of the initial concentration
of Fab', respectively. The F(ab')2, Fab' and Fab'-BAT all maintained reasonable
antigen-binding properties. 67Cu labeling of the conjugate under standard
conditions did not impair the immunoreactivity of Fab'-BAT. Conclusion: This is
a simple and efficient method for producing immunoreactive conjugates of Fab'-
BAT, which can be used to make radiometal-labeled conjugates for further diagnostic
and therapeutic applications.
Keywords:
antibody(MoAb) B43(of IgG1 subtype) to a bifunctional chelator 6-[p-
(bromoacetamido) benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-
tetraacetic acid (BAT) via the thiol groups in the hinge distal to the antigenbinding
site of the Fab'. Methods: B43 was cleaved using a simple 2-step method.
First, stable F(ab')2 was produced by pepsin treatment. Fab' with free thiol in the
hinge region was then obtained by cysteine reduction of F(ab')2. Second, a sitespecific
conjugation of Fab' to thiol-specific BAT was performed in a one-step
reaction. Results: The Fab' fragment had approximately 1.8 free thiol groups per
molecule after cysteine reduction. The conjugation efficiency and the chemical
yield were approximately 1.28 moles chelator/Fab' and 74% of the initial concentration
of Fab', respectively. The F(ab')2, Fab' and Fab'-BAT all maintained reasonable
antigen-binding properties. 67Cu labeling of the conjugate under standard
conditions did not impair the immunoreactivity of Fab'-BAT. Conclusion: This is
a simple and efficient method for producing immunoreactive conjugates of Fab'-
BAT, which can be used to make radiometal-labeled conjugates for further diagnostic
and therapeutic applications.