PT  - JOURNAL ARTICLE
AU  - Sharkey, Robert M.
AU  - van Rij, Catharina M.
AU  - Karacay, Habibe
AU  - Rossi, Edmund A.
AU  - Frielink, Cathelijne
AU  - Regino, Celeste
AU  - Cardillo, Thomas M.
AU  - McBride, William J.
AU  - Chang, Chien-Hsing
AU  - Boerman, Otto C.
AU  - Goldenberg, David M.
TI  - A New Tri-Fab Bispecific Antibody for Pretargeting Trop-2–Expressing Epithelial Cancers
AID  - 10.2967/jnumed.112.104364
DP  - 2012 Oct 01
TA  - Journal of Nuclear Medicine
PG  - 1625--1632
VI  - 53
IP  - 10
4099  - http://jnm.snmjournals.org/content/53/10/1625.short
4100  - http://jnm.snmjournals.org/content/53/10/1625.full
SO  - J Nucl Med2012 Oct 01; 53
AB  - RS7 is an internalizing anti-Trop-2 pancarcinoma antibody capable of targeting most epithelial cancers. Because pretargeting strategies could improve the tumor localization of radionuclides, a new anti-Trop-2 × antihapten bispecific antibody for pretargeting, based on humanized RS7, was prepared and evaluated with a radiolabeled hapten-peptide in vitro and in vivo to determine whether its internalization properties would interfere with pretargeting. Methods: The anti-Trop-2 × antihapten bispecific antibody, TF12, was prepared using the modular dock-and-lock method. TF12 and humanized RS7 binding was assessed by cell binding assays and fluorescence-activated cell sorting analysis in a variety of human carcinoma cell lines. The internalization of TF12 was evaluated in vitro using a fluorescent TF12 conjugate or hapten-peptide and 111In-labeled TF12 and RS7. The biodistribution of TF12 and its use as a pretargeting agent with an 111In-labeled hapten-peptide were assessed in several human epithelial cancer xenografts. Dose optimization was examined in 2 tumor models. Results: TF12 internalizes, but a substantial fraction remained accessible on the tumor surface. Fluorescence-activated cell sorting analysis showed only a minor change in fluorescent signal when the tumor was probed with a fluorescent hapten-peptide over 4 h, and microscopy showed substantial membrane staining when reassessed at 24 h after TF12 exposure. Only 40.1% of 111In-TF12 was internalized after 24 h. In vivo, excellent tumor localization of the 111In-labeled peptide was observed in several tumor models. Conclusion: TF12 was retained sufficiently on the cell surface in several epithelial cancers, thereby making it suitable for pretargeted imaging and therapy of various Trop-2–expressing carcinomas.