Targeting Article: Basigin-2 (EMMPRIN), a Prognostic Marker, is a Dynamic Portal of Entry into Cancer Cells

by Leonardo R. Ancheta and Douglas A. Lappi, American Association of Cancer Research abstract #5218

Basigin-2 (EMMPRIN) is a marker for prognosis of several tumor types. With the identification of the internalization of basigin-2 in response to antibody binding, we now further explore the possibility of its use as a dynamic portal of entry for molecules into cancer cells. We also wish to identify a correlation between number of basigin-2 on the cell surface and half maximal effective concentration (EC50) of a targeted toxin by examining eleven tumor cell lines which encompass various tumor types such as breast (MCF-7, BT549), leukemia (K562, HL-60), multiple myeloma (RPMI-8226), neuroblastoma (SH-SY5Y), non-small cell lung (A549, NCI-H23, NCI-H522), and prostate (PC3). In this investigation, we employed the use of flow cytometry to characterize each cell line according to mean fluorescence as well as to determine the number of basigin-2 molecules expressed on the cell surface through a surface quantification assay. This was visualized by staining with a monoclonal antibody directed to basigin-2 ECD (Ref. 1; Cat. #AB-42) with comparison of results against a standard with known Antibody Binding Capacity (ABC) and standardizing the results into Molecules of Equivalent Soluble Fluorochromes (MESF; Bangs Labs).

Last year at this meeting we showed the ability of the antibody to basigin-2 ECD to cause internalization of secondary targeted toxins to bring about cell death. We now report on the activity of a primary toxin: the ribosome- inactivating protein saporin attached directly to an antibody to basigin-2 (Cat. #IT-54). Cytotoxicity assays yielded an EC50 range of 3.5-420 pM while surface quantification assays resulted in expression that ranged from 1-4 million basigin-2 molecules per cell. Cell lines showing potent EC50 values were characterized to have higher surface expression of basigin-2 when compared to cell lines with less potent EC50 values. Preliminary results suggest a correlation between EC50 and basigin-2 surface expression such that more basigin-2 available on the cell surface would facilitate greater opportunity for a primary toxin to bind and enter into the cell and cause cell death. These data suggest the use of basigin-2 as an entry system for molecules into cancer cells.