Abstract 585: Elevated levels of CD24 in head and neck squamous carcinoma cells: A potential marker for unfavorable cisplatin response

Introduction: Head and neck cancers are usually detected in their later stages of progression, resulting in a 5-year survival rate of only 30-50%. Chemotherapy is a treatment of choice for locally advanced head and neck squamous cellular carcinoma (HNSCC), and unfortunately, only a subset of HNSCC responds favorably to cisplatin treatment. Currently, there are no predictive markers of a tumor9s response to cisplatin therapy. Therefore, to investigate the extremely low rates of durable remission in HNSCC, we employed a method of screening membrane bound surface stem cell markers as a means to possibly identify a group of cells that are inherently resistant to high doses of cisplatin treatment. Methods: Flow cytometry, MTT assay, QPCR, CD24 RNA interference, western blot, orosphere formation assay and IHC Results: Three UM-SCC cell lines were taken that had variable degrees of sensitivity to cisplatin, but all the lines formed a pronounced cisplatin resistant tail in a dose response curve. In an effort to screen for the fraction of cells that formed the cisplatin resistant tail, we observed that these three UM-SCC lines that expressed similar amounts of membrane bound CD44 had variable levels of membrane bound CD24 initially; however, all showed higher levels of CD24 with increased cisplatin dosage. Levels of CD24 peaked at the super high doses of cisplatin that had resulted in a cisplatin resistant tail. To further our study on the relationship between CD24 and cisplatin resistance, UM-SCC-10B and UM-SCC-10B/pt15s, a cisplatin sensitive-resistant pair from the larynx that express high amounts of CD24 in normal conditions, were selected. Upon confirmation of CD24 up-regulation at a clinically relevant dose of cisplatin [10uM], a lentiviral vector construct containing a CD24 siRNA was introduced into the model pair. The knockdown of CD24 resulted in increased sensitivity to cisplatin, and it diminished the cisplatin resistant tail in a dose response curve. Also, CD24 knockdown lines had significantly lower cisplatin IC-50 values. Upon treating the CD24 high UM-SCC-10B and UM-SCC-10B/pt15s with a combination of monoclonal CD24 antibody and cisplatin, higher cisplatin sensitivity was achieved. This was followed by screening of CD24 expression in head and neck tumor tissue samples from patients that had undergone cisplatin treatment. The tissue screening further confirmed the correlation between CD24 overexpression and unfavorable cisplatin treatment response. Conclusion: Our work thus far, indicates that higher expression of CD24 in head and neck tumors result in a cisplatin resistant population that may well be the cause of unfavorable response to cisplatin treatment. Overall, CD24 has the potential to be a valuable predictor of response to cisplatin in HNSCC patients as well as a therapeutic target. Citation Format: Vishnu Modur. Elevated levels of CD24 in head and neck squamous carcinoma cells: A potential marker for unfavorable cisplatin response. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 585. doi:10.1158/1538-7445.AM2015-585