Serum osteopontin level is elevated in dogs with mammary carcinomas.

The objective of the current research was to assess osteopontin (OPN) as a biomarker of canine mammary tumors (CMT). Twenty CMT tissues were collected post-surgery. Blood samples were also collected from the same dogs as well as healthy tumor free dogs and serum was harvested. Fragment encoding the immunodominant region of canine osteopontin (693 bp) was cloned and expressed as a HISx6 - tagged protein in a prokaryotic expression system using pPROEX-HTa vector. A 26 kDa recombinant osteopontin (rOPN) was expressed, purified by Ni-NTA affinity chromatography and assessed by SDS-PAGE and western blot analysis. In order to optimize a sandwich ELISA for the relative assessment of circulating OPN in the sera of dogs with mammary tumors, hyperimmune sera were produced against the expressed protein in rabbits and mice. The developed sELISA was found to be 90% specific and 85% sensitive with respect to histopathological examination in detecting CMT. The circulating levels of OPN were significantly elevated in dogs with mammary tumors as compared to the healthy animals. The results suggest that OPN can serve as a serum biomarker of CMT.