Abstract 3551: CD44 expression in Ewing sarcoma is associated with reduced chemosensitivity in vitro.

CD44 is the primary hyaluronate (HA) receptor in a variety of cell types and has been implicated in several processes, such as cell-to-cell and cell-to-extracellular matrix interactions, cell migration and invasion, as well as metastasis and drug resistance. Even though CD44 expression has been studied in various types of cancer, such as prostate and lung cancer, little is known about its role in Ewing sarcoma, the second most common malignancy of bone and soft tissue in children and adolescents. We assessed the expression of CD44 in 25 cases of Ewing sarcoma by immunohistochemistry and found that CD44 is expressed in 40% of them. Furthermore, we noticed that in 4 out of 10 patients CD44 expression increased in one or more subsequent recurrent or metastatic biopsy samples. Therefore, we hypothesized that CD44+ cells in Ewing sarcoma represent cell clones, which are resistant to treatment and lead to tumor relapses. In order to study the role of CD44 in Ewing sarcoma, we cultured tumor cells for 24 to 72 hours in anchorage-independent sphere forming culture conditions, (low attachment plates), which are known to induce CD44 expression and compared them to adherent cells. CD44 mRNA and protein expression was induced in the anchorage-independent group as early as 24h in all 7 Ewing sarcoma cell lines. We then measured mRNA levels of ABCB5 and ABCC1, members of the superfamily of ATP-binding cassette (ABC) transporters related to drug resistance by real time PCR and found them increased. These data were corroborated by our finding of significantly increased efflux of the fluorescent DNA binding dye, Hoechst 33342, in the anchorage-independent group, indicating that the cells that overexpress CD44 are more effective in effluxing the chemotherapeutic drugs, thus becoming more resistant to chemotherapy. Finally, changes in the expression of efflux proteins were associated with increased resistance to doxorubicin-induced apoptotic cell death documented by increased expression of annexin V. In summary, our data indicate that CD44 is involved in drug resistance in Ewing sarcoma and may be clinically useful in making therapeutic decisions. Citation Format: Nikolina Dioufa, Guang Li, Maria Tsokos. CD44 expression in Ewing sarcoma is associated with reduced chemosensitivity in vitro. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3551. doi:10.1158/1538-7445.AM2013-3551