Thymidine kinase, an enzyme essential to function and control of the nucleotide salvage pathway, has been suggested as a potential marker for cancer identification. One of the two forms of human thymidine kinase, TK1, exhibits increased serum levels in patients with leukemias, lymphomas, and many solid tumors, including breast, prostate and colon. It has been suggested that this increase is may be due to increased cellular proliferation. During the G1/S transition of the normal cell cycle, TK1 levels increase and remain elevated until M phase, where it is degraded. Cancer cells, by their nature, are known to lack cell cycle control, which may lead to increased levels of TK1 in these cells. In order to better understand the role of TK1 in cancer, a monoclonal antibody against TK1 was produced and a modified immunofluorescent protocol incorporating an array of antigen retrieval methods was developed. The anti-TK1 monoclonal was used as the primary antibody in a primary/secondary immunofluorescent stain of multiple malignant breast tissue tumors obtained from the Utah Valley Regional Medical Center tissue repository. Normal (non-cancerous) breast tissue was also stained as a negative control. Further studies utilizing arrays of tissue progressing from “normal” to “infiltrating with lymph node metastasis” were conducted to demonstrate the potential of TK1 to specifically designate cancer tissue. Over one hundred individual cancer cases were screened via immunohistochemical array analysis. Normal tissue would be expected to express low levels of TK1, whereas an increase of TK1 expression would theoretically be indicative of malignancy. Results presented in this study show that not only does TK1 exhibit upregulation in cultured breast cancer cells and breast tumor tissue, but that localization is unique and potentially indicative of cancer stage and progression. In fact, the first signs of moderate staining were seen at the “sclerosing adenosis”/“atypical hyperplasia” stages and by the “infiltrating lobular cancer” stage, significant staining was observed. By the more advanced stages, the TK1 levels shown by staining were significantly upregulated. These data were confirmed by both pathologist and an independent third-party laboratory and shown to be statistically significant. As it appears that the monoclonal antibody is specifically staining cancer tissue and can differentiate between fibroadenomas and stage 1 breast tumors, These data indicate that TK1 may be utilized not only for diagnostic use, but possibly therapeutic regimen. Further studies are ongoing to confirm specificity to other tumor types and determine specific treatment options utilizing the thymidine kinase pathway.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA