Abstract 553: Quantification of the cobalamin (vitamin B12) TCN2 transport protein, cobalamin CD320 cell surface receptor and Ki-67 in naturally occurring canine and feline tumors and comparison to expression in adjacent normal tissues

Abstract

Abstract Introduction: Cobalamin-dependent enzymes such as methionine synthase are critical to DNA synthesis. While all living cells require cobalamin for this purpose, rapidly proliferating cancer cells have an especially high demand. Cancer cells ensure sufficient cobalamin supply through increased production of the serum cobalamin transport protein (transcobalamin II; TCII; TCN2) and through up-regulation of the cobalamin cell surface receptor (transcobalamin II-R; TCII-R; CD320). Previously, we developed a standardized immunohistochemical method to quantify expression of TCII, TCII-R, and Ki-67 in 34 human tumor xenografts. Specific Aim: The purpose of this study was to quantify the expression of TCII, TCII-R, and Ki-67 in naturally occurring tumors, and to compare these results to expression in corresponding adjacent normal tissues. Methods: 30 canine and 36 feline patient-derived, archived tissue samples were utilized. Immunohistochemical staining was performed using rabbit polyclonal antibodies to the cobalamin transport protein (anti-TCN2) and cell surface receptor (anti-CD320), and using a mouse monoclonal antibody to Ki-67 (clone MIB-1). Representative areas of solid tumor were digitally photographed. An Image J color deconvolution plugin was used to quantify TCII and TCII-R positively stained cells, and an Immunoratio plugin was used to calculate percentage of Ki-67 positively stained cells. Results: All canine and feline tumor tissues stained positively for TCII, TCII-R and Ki-67. Expression of these proteins was noted to vary both within and between tumor types. Expression of TCII, TCII-R and Ki-67 was significantly higher in tumor tissues than in corresponding adjacent normal tissues in both canine and feline samples. There was a strong correlation between TCII and TCII-R expression in both canine and feline tissues. A modest correlation was identified between TCII and Ki-67 expression in canine tissues, and between TCII-R and Ki-67 expression in both canine and feline tissues. Conclusion: For the first time since the discovery of cobalamin in 1948, we have quantified on a molecular level the tumor-specific expression of TCII and TCII-R compared to adjacent, histologically normal tissues. These results demonstrate a quantifiable, synchronous up-regulation of TCII and TCII-R expression by proliferating tumors. Results from this study also indicate that cobalamin homology is highly conserved between human, canine and feline species. The potential to utilize these proteins as biomarkers to identify tumor tissues, assess eligibility for cobalamin-based anti-tumor regimes, evaluate response to therapy and monitor for recurrent and metastatic disease has important implications in the management of both human and companion animal cancer patients. Citation Format: Annette M. Sysel, Victor E. Valli, Joseph A. Bauer. Quantification of the cobalamin (vitamin B12) TCN2 transport protein, cobalamin CD320 cell surface receptor and Ki-67 in naturally occurring canine and feline tumors and comparison to expression in adjacent normal tissues. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 553. doi:10.1158/1538-7445.AM2015-553