Inhibition of Circulating Dipeptidyl Peptidase 4 Activity in Patients with Metastatic Prostate Cancer

Abstract

Cancer is responsible for many deaths and is a major source of healthcare expenditures. The identification of new, non-invasive biomarkers might allow improvement of the direct diagnostic or prognostic ability of already available tools. Here, we took the innovative approach of interrogating the activity of exopeptidases in the serum of cancer patients with the aim of establishing a distinction based on enzymatic function, instead of simple protein levels, as a means to biomarker discovery. We first analyzed two well-characterized mouse models of prostate cancer, each with a distinct genetic lesion, and established that broad exopeptidase and targeted aminopeptidase activity tests reveal proteolytic changes associated with tumor development. We also describe new peptidebased freeze-frame reagents uniquely suited to probe the altered balance of selected aminopeptidases, as opposed to the full array of exopeptidases, and/or their modulators in patient serum or plasma. One particular proteolytic activity was impaired in animals with aggressive disease relative to cancer-free littermates. We identified the protease in question as dipeptidyl peptidase 4 (DPP4) by analyzing selected knockout mice and evaluating the effect of specific inhibitors. DPP4 activity was also reduced in the sera of patients with metastatic prostate cancer relative to patients with localized disease or healthy controls. However, no significant differences in DPP4 serum levels were observed, which established the loss of activity as the result of impaired enzymatic function. Biochemical analysis indicated that reduced activity was the result not of post-translational modifications or allosteric changes, but instead of a low-molecular-weight inhibitor. After we adjusted for age and total prostatespecific antigen, reduced DPP4 activity remained a significant predictor of cancer status. The results of this proofof-principle study suggest that DPP4 activity might be a potential blood-based indicator of the presence of metastatic cancer of prostatic origin, either by itself or, more likely, as a means to improve the sensitivity and specificity of existing markers. Molecular & Cellular Proteomics

Hepatocyte-secreted DPP4 in obesity promotes adipose inflammation and insulin resistance

“…DPP-4 was immunodepleted from obese mouse plasma using bead-immobilized anti-DPP-4 antibody (R&D Systems, AF954) as previously described 37 . In brief, 10 µg of anti-DPP-4 antibody was conjugated with 1.5 mg of Protein-G Dynabeads (Invitrogen, 10004D) in 200 µl of binding buffer.…”

CD26-Related Serum Biomarkers: sCD26 Protein, DPP4 Activity, and Anti-CD26 Isotype Levels in a Colorectal Cancer-Screening Context

“…Several possible arguments could explain the complex relationship between both measures. For example, a low-molecularweight inhibitor of DPP4 activity was found in sera from patients with metastatic prostate cancer [13], perhaps related to glypican-3, recently reported as a natural inhibitor of CD26/DPP4 enzymatic activity [14], usually absent in adult tissues though expressed in many tumours. Likewise, the variable correlations might be explained by the presence of serum autoantibodies against CD26 [15] we have recently studied [16] and the possibility of Ag-Ab complexes that affect both measures.…”

Discovery of a putative blood-based protein signature associated with response to ALK tyrosine kinase inhibition

“…Higher plasma level of DPP4 has been found to be associated to better survival in multiple cancer types combined [28]. Furthermore, soluble low DPP4 level has been suggested to be a prognostic biomarker for colorectal and prostate cancers as well as NSCLC malignant pleural effusions [29][30][31]. The last candidate is c-KIT transmembrane receptor tyrosine kinase in soluble form.…”