Claudins-Promising Biomarkers for Selected Gastrointestinal (GI) Malignancies?

Simple Summary Claudins (CLDNs) belong to a family of tetraspan transmembrane proteins of the tight junctions (TJs) which form the paracellular barrier that regulates the flow of molecules in the intercellular space between the cells of the epithelium. Evidence of altered claudin levels in various human malignancies, including GI cancers, has been reported. GI cancers are commonly diagnosed malignancies worldwide and their incidence is still on the increase, particularly in Western countries. Therefore, there is an urgent need for more investigations into early biomarkers of these malignant diseases. In this review, we present the involvement of selected CLDNs in the pathogenesis of the most common GI malignancies. Moreover, the usefulness of these proteins in the diagnosis of GI cancers and patient prognosis has also been evaluated. Our review indicates that selected CLDNs, particularly CLDN1, 2, 4, 7, and 18, play a significant role in the development of GI tumours and in patient prognosis. In addition, selected CLDNs may be of value in the design of therapeutic strategies for the treatment of recurrent tumours.Abstract Despite recent improvements in diagnostic ability and treatment strategies for patients with neoplastic disease, gastrointestinal (GI) cancers, such as colorectal, gastric, pancreatic, and oesophageal cancers, are still common malignancies and the leading cause of cancer deaths worldwide, with a high frequency of recurrence and metastasis as well as poor patient prognosis. There is a link between the secretion of proteolytic enzymes that degrade the extracellular matrix and the pathogenesis of GI tumours. Recent findings have focused on the potential significance of selected claudins (CLDNs) in the pathogenesis and prognosis of GI cancers. Tight junctions (TJs) have been proven to play an important role in maintaining cell polarity and permeability. A number of authors have recently revealed that TJ proteins, particularly selected CLDNs, are related to inflammation and the development of various tumours, including GI malignancies. This review presents general characteristics and the involvement of selected CLDNs in the progression of GI malignancies, with a focus on the potential application of these proteins in the diagnosis and prognosis of colorectal cancer (CRC), gastric cancer (GC), pancreatic cancer (PC), and oesophageal cancer (EC). Our review indicates that selected CLDNs, particularly CLDN1, 2, 4, 7, and 18, play a significant role in the development of GI tumours and in patient prognosis. Furthermore, selected CLDNs may be of value in the design of therapeutic strategies for the treatment of recurrent tumours.