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An engineered anti-CA19-9 cys-diabody for PET imaging of pancreas cancer and targeting of polymerized liposomal nanoparticles.

198 Background: Antibody-based therapeutics is a rapidly growing field. Small engineered antibody fragments, such as the cys-diabody demonstrate similar antigen affinity compared to the parental antibody but have a shorter serum half-life (4hrs) and possess the ability to be conjugated to nanoparticles. Our goal was to engineer an anti-CA19-9 cys-diabody fragment in hopes of imaging and targeting pancreatic cancer.


METHODS
The anti-CA19-9 cys-diabody was created by cloning the variable region of the parental antibody, engineering a C-terminus cysteine, expressing in NS0 cells followed by protein purification utilizing HPLC. Maleimide chemistry was used to conjugate the cys-diabody to PLNs through the engineered cysteine residues. Immunofluorescence and flow cytometry were used to evaluate targeting of cys-diabody and diabody conjugated PLNs to human pancreatic cancer cell lines. The cys-diabody was evaluated in a mouse xenograft model harboring CA19-9 positive (BxPC3) and negative (MiaPaca) tumors. The cys-diabody was radiolabeled with a positron emitter (I-124) and microPET/CT were performed after tail vein injection. Percent of injected dose per gram (%ID/g) of radioactivity was measured in blood and tumor to provide objective confirmation of the microPET images.


RESULTS
Immunofluorescence and flow cytometry showed specific binding of the anti-CA19-9 cys- diabody. Tumor xenograft imaging of the anti-CA19-9 cys-diabody demonstrated an average tumor:blood (%ID/g) ratio of 3.3 and positive:negative tumor ratio of 7.4. Successful conjugation of the cys-diabody to PLNs was indicated by immunofluorescence showing specific targeting of PLN-cys- diabody conjugate to human pancreatic cancer cells in vitro.


CONCLUSIONS
Our results show that the anti-CA19.9 cys- diabody targets pancreatic cancer providing specific molecular imaging in tumor xenograft models. Furthermore, the PLN-cys-diabody conjugate targets human pancreatic cancer cells with the potential to deliver targeted treatment. Further studies evaluating the in vivo ability of the PLN-cys-diabody conjugate to target pancreatic cancer need to be performed. No significant financial relationships to disclose.