ABSTRACT
OBJECTIVES: The secretory enzyme lysyl oxidase like 2 (LOXL2) is speculated to contribute to tumor progression through its functions in the remodeling of extracellular matrix and epithelial-mesenchymal transition. We previously identified elevated expression of LOXL2 in metastatic human head and neck squamous cell carcinoma (HNSCC) cells in a mouse lymph node metastases model. Here we performed a case series study examining LOXL2 expression levels in human serum from HNSCC patients to evaluate whether LOXL2 is worth evaluation in a large cohort study. METHODS: LOXL2 protein levels in three serum samples from HNSCC patients were assessed by immunoblotting and LOXL2 tissue expression was examined in one human tongue squamous cell carcinoma (SCC) tissue by immunohistochemistry as a representative of HNSCC tissue. Serum samples were further fractionated in exosomes and supernatants by ultracentrifugation, which were then subjected to immunoblot and in vitro LOX activity analyses. Exosomal LOXL2 levels of 36 serum samples from HNSCC patients and seven healthy volunteers were measured using polymer sedimentation exosome preparation followed by ELISA measurement and subjected to statistical analyses. RESULTS: Immunoblot analyses revealed that LOXL2 was present in serum exosomal fractions from three HNSCC patients, and we observed approximately threefold higher levels of LOXL2 in HNSCC patients compared with three healthy volunteers. Immunohistochemical LOXL2 staining was detected in HNSCC cells in addition to non-cancerous lipid tissues and some muscles in human tongue HNSCC tissue. Further measurements of exosomal LOXL2 by ELISA showed over ninefold higher mean LOXL2 levels in patients compared with controls. Statistical analysis revealed a correlation between elevated serum exosomal LOXL2 levels and low-grade, but not high-grade, HNSCC. CONCLUSIONS: Our case series study that elevated serum exosomal LOXL2 levels exhibited a correlation with low-grade HNSCCs. A follow-up large cohort clinical study will be required to determine the potential clinical utility of LOXL2 as a new biomarker and/or therapy target for HNSCCs. LEVEL OF EVIDENCE: 4 Laryngoscope, 130:E327-E334, 2020.
