(P 135) EXPLORING THE ROLE OF CLUSTER OF DIFFERENTIATION 44 IN CHONDROSARCOMA

Objective: Chondrosarcoma is the most common type of primary bone sarcoma in adults with a high risk of local recurrence and metastasis. Most chondrosarcomas are resistant to chemotherapy and radiotherapy meaning surgery is the only effective treatment option for the majority of patients. Therefore, new therapeutic targets are required. Cluster of differentiation 44 (CD44) is a transmembrane protein and is the key receptor for hyaluronic acid. When hyaluronic acid binds to CD44, pathways are regulated which lead to increased cancer cell proliferation, migration and invasion. CD44 has also been shown to be overexpressed in several tumour types. The main objectives of this study were to examine the expression of CD44 across chondrosarcoma patient tissue and to determine the role that CD44 has in chondrosarcoma cell invasion.

Methods: Chondrosarcoma tissue from 46 patients was immunostained for CD44 and the H-score was measured. Survival analysis using Kaplan-Meier analysis and multivariate analysis using Cox regression was then undertaken to determine the effect that CD44 had on the overall survival (OS) and event-free survival (EFS) of the patients. Clustered regularly interspaced short palindromic repeats (CRISPR) – CRISPR associated protein 9 (Cas9) gene editing was used to knockout CD44 from HT1080 dedifferentiated chondrosarcoma cells. To assess the effect of the knockout on the invasion of the cells, a spheroid invasion assay was used. CD44 Wild type (WT) and knockout (KO) spheroids were encased in a collagen hydrogel or a collagen hydrogel with hyaluronic acid added for 72 hours.

Results: Staining of the patient tissue for CD44 showed that CD44 expression was increased in the grade 2 and 3 chondrosarcoma tissues compared to grade 1 (p < 0.05). Multivariate analysis using Cox regression showed that CD44 expression was significant (p < 0.01) in contributing to reduced OS and EFS of the patients. The results of the spheroid invasion assay showed that the CD44 KO cells invaded less than the WT cells when encased in collagen (p < 0.001) and collagen with hyaluronic acid added (p < 0.0001).

Conclusion: The results obtained in this study suggest that CD44 is key for the invasion and progression of chondrosarcoma and could therefore be a future therapeutic or theragnostic target.