Abstract 1211: Killing cancer one cell at a time: Development and characterization of a novel antibody drug conjugate

Abstract

Abstract Thymidine Kinase 1 (TK1) is a protein that we have established to be present on the surface of cancer cells and absent on the surface of normal cells. Various methods have been used to confirm the presence of TK1 using localization methods such as scanning electron microscopy gold labeling, fluorescence imaging, and flow cytometry analysis. In this project, we explored the potential of using the TK1 marker as a therapeutic target by conjugating an anti-TK1 antibody to the toxin saporin, a ribosome inhibiting protein derived from the seeds of Saponaria officinalis. The toxin is widely used in the biological and neurological fields due to its stability and adaptability. An additional benefit to using this particular toxin is the inability of saporin to transverse the cell membrane without an antibody or other agent mediating internalization into the cell. We expressed a cysteine mutated form of saporin in the BL21(DE3) E. coli strain. Saporin from the expressed protein was subsequently isolated with a cation exchange cellulose column before verification on a non-reducing SDS-PAGE gel. A single band was observed at approximately 30 kD, indicating purity of the protein. After thiolation of the amine groups in the anti-TK1 antibody, the cysteine residues on the mutated saporin toxin was linked to the antibody through the formation of disulfide bonds. Further purification of the conjugate was achieved by eliminating unconjugated saporin and antibody, and high molecular weight aggregates using a Sephacryl S-200 column. Over 90% cancer cell death was observed in the Burkitt's Lymphoma Raji cell line when exposed to conjugate concentrations of 10 nM. Complete cell death was observed with exposure to 100 nM concentrations. In addition, there was a significant difference between the saporin conjugated treated and untreated samples (p < 0.001). Further tests are underway to determine the effectiveness of the conjugate in other cancer cell lines. These promising results suggest the use of saporin in an effective antibody drug conjugate therapeutic that could influence the way we treat cancer: a drug that will selectively target cancer cells. Citation Format: Michael Xiao, Roger Chu, Jayson Pagaduan, Richard A. Robison, Kim L. O’Neill. Killing cancer one cell at a time: Development and characterization of a novel antibody drug conjugate. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1211.