A targeted glycoproteomic approach identifies cadherin-5 as a novel biomarker of metastatic breast cancer

Aberrant glycosylation has long been recognised as a hallmark of cancer, and is increasingly being exploited in biomarker discovery studies. Helix pomatia agglutinin (HPA) is known to bind aberrant glycans associated with metastatic breast cancer, and was used here to isolate glycoproteins from pooled breast cancer serum samples of (i) patients with recurrent breast cancer and (ii) patients with no sign of recurrence 5 years after diagnosis of their primary tumour. Pregnancy zone protein, the polymeric immunoglobulin receptor and cadherin-5 emerged as potential markers of metastasis following proteomic identification of HPA binding glycoproteins. ELISAs were developed to verify these findings, and to assess protein glycosylation, in individual patient sera. The cadherin-5 ELISA discriminated serum samples of patients with recurrent breast cancer from those with no sign of recurrence, and analysis of cadherin-5 glycosylation by HPA also showed a significant difference between the two sample groups. The targeted glycoproteomic and validatory approach developed here has shown that when taking into account both the protein levels and HPA binding, serum cadherin-5 discriminated patients with recurrent breast cancer from those with no sign of recurrence with 90% specificity.

► HPA binding breast cancer serum proteins underwent proteomic identification. ► Pregnancy zone protein, polymeric immunoglobulin receptor and cadherin-5 emerged as potential markers of metastatic breast cancer. ► Proteomic analysis was verified by ELISAs. The cadherin-5 ELISA discriminated recurrent breast cancers from those with no sign of recurrence. ► Analysis of cadherin-5 glycosylation also showed a significantdifference between the two sample groups. ► Serum cadherin-5 discriminated patients with recurrent breast cancerfrom those with no sign of recurrence with 90% specificity.