Abstract 3162: Assessing the therapeutic and diagnostic potential of human thymidine kinase 1 in leukemia

Abstract

Abstract Thymidine Kinase 1 (TK1), a salvage pathway enzyme responsible for recycling thymine in cells for use in DNA replication and repair, is normally tightly regulated by the cell cycle; however research studies have shown that it is over-expressed and unregulated in cancer cells. Studies linking TK1 localization to the plasma membrane of lymphoma cells have suggested that this enzyme could also be used as a molecular target for cancer diagnosis and therapy. Previous research in our laboratory showed that TK1 located on the plasma membrane of different cancer cell lines had high enzymatic activity. This study was performed to support the eventual possibility of targeting TK1 for cancer diagnosis and immunotherapy in leukemias expressing high levels of TK1 on their plasma membrane. TK1 levels on plasma membrane were analyzed using a BD FACSCanto flow cytometry on lymphoblastoid cells derived from Burkitt's lymphoma (Raji cells), acute T cell leukemia (Jurkat cells), myeloblastic cells derived from promyelocytic leukemia (HL-60 cells), and normal lymphocytes from healthy individuals. Analysis was performed on unpermeabilized cells in exponential growth phase using both a mouse monoclonal anti-TK1 Ab and a rabbit polyclonal anti TK-1 Ab. Cells were incubated with human FcR blocking reagent to eliminate non-specific binding to Fc receptors. Permeabilized cells were excluded using propidium iodide staining. Using an IgG Isotype control we were able to select proper gating (0% binding). TK1 surface expression was compared to expression of sodium potassium ATPase, a common plasma membrane marker, and pan-leukocyte marker CD45. Results confirmed high levels of TK1 expression on cancer cell lines analyzed. Flow cytometry analysis showed that binding of the mouse monoclonal anti-TK1 Ab and rabbit polyclonal anti-TK1 Ab were 93.4% (SEM=1.05, N = 19) and 99.5 % (SEM=0.67, N=19) in Raji cells; 71.1% (SEM=3.41, N=19) and 89.4 % (SEM=2.74, N=19) in HL-60 cells; 63% (SEM=1.23, N=26) and 88.6% (SEM=1.81, N=27) in Jurkat cells. Lymphoblastoid cells showed significantly higher TK1 expression when compared to that of lymphocytes obtained from healthy individuals 9.9% (SEM=2.39, N=7) and 14.9% (SEM=2.43, N=3). When induced with pokeweed mitogen there was no increase in TK1 expression on the plasma membrane of normal dividing lymphocytes 7.9% (SEM=0.54, N=3) and 10.63% (SEM=2.89, N=3). Fluorescence microscopy observations provided more evidence of TK1 association with the plasma membrane of cancer cells. These results suggest that membrane-bound TK1 has potential for both diagnosis and immunotherapy in human leukemia. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3162. doi:10.1158/1538-7445.AM2011-3162