Can we use N-acetyl-L-aspartyl-L-glutamate peptidase-like 2 to target drugs to cancer cells?


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Hayley Luxton1,Ben Simpson1,Michael Brown2,Jonathan Kay1,Suraj Menon3,Noel Clarke4,Hayley Whitaker1
1University College London,2The University of Manchester,3University of Cambridge,4University of Manchester

Abstract

Background

N-acetyl-l-aspartyl-l-glutamate peptidase-like 2 (NAALADL2) is a member of the glutamate carboxypeptidase II family, best characterised by prostate-specific membrane antigen (PSMA/NAALADL1) that is currently being tested in phase II trials for its ability to target drugs to prostate cancer cells. We have shown that NAALADL2 is overexpressed in multiple cancers and can be used in prostate cancer as a marker for relapse following radical prostatectomy. Here we investigate the possibility of exploiting the basal cell membrane localisation of NAALADL2 by validating NAALADL2 as a therapeutic target.

Method

A variety of techniques including immunohistochemistry (IHC), flow cytometry, cell surface biotinylation, Western analysis, RNAseq, cell invasion, migration, colony forming and toxin-delivery assays were used to characterise NAALADL2 expression and function in a range of six prostate cancer stably knocked-down cell lines.

Results

IHC, flow cytometry and cell surface biotinylation with Western analysis have confirmed cell surface localisation of NAALADL2. We have characterised weak or lost NAALADL2 expression in a range of FDA approved normal tissues and in greater detail in normal skin, liver, colon, prostate and eye. This increases our confidence in NAALADL2 as a specific marker for prostate cancer. We have shown NAALADL2 internalises and is capable of delivering a toxic payload within the cell. Using pairs of stable knockdown and non-targeting controls for RNAseq analysis we have seen an effect on actin cytoskeleton stability. Loss of NAALADL2 leads to a changes in the cells ability to adhere to extracellular matrix components, migration and invasion.

Conclusion

NAALADL2 is overexpressed at the cell surface in prostate cancer and interacts with the extracellular matrix. The normal tissue profile of NAALADL2 is low. Overexpression of NAALADL2 in prostate cells can be used to target toxins to prostate cancer cells. NAALADL2 represents an exciting opportunity to develop therapeutics specifically targeted at aggressive prostate cancer.