Abstract 3860: Cisplatin-induced CD24 upregulation in CD44+ stem-like head and neck squamous carcinoma cells: a potential marker for unfavorable cisplatin response

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Introduction: Head and neck cancers are usually detected in its later stages of progression, resulting in a 5-year survival rate of only 30-50%. Chemotherapy is the 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 tumor's response to cisplatin therapy. Therefore, to investigate the extremely low rates of cisplatin response 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. Methodology: Expression of membrane bound CD24 was measured by flow cytometry. Tumor cell viability in response to cisplatin was measured by MTT assay. QPCR was performed using a standard thermocycler program and data was normalized to β-Actin. CD24 RNA interference was done through lentiviral transduction with Puromycin and GFP based selection. Standard Western blot procedures were used to check STAT3 and p-STAT3 expression. Ororsphere formation assay was performed in low attachment dishes with stem cell specific media Results: Four 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 four UM-SCC lines that expressed similar amounts of membrane bound CD44 had variable levels of membrane bound CD24. Levels of CD24 peaked at super high doses of cisplatin that had resulted in a cisplatin resistant tail. To further our study, 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 eliminated the cisplatin resistant tail in a dose response curve. It also showed reduced phosphorylation levels of STAT3. Interestingly, the lone CSC marker in HNSCC, CD44, by itself did not select for a cisplatin resistant population. Conclusion: Our work thus far, indicates that up-regulation of CD24 and the resulting phosphorylation of STAT3 upon cisplatin exposure is a phenomenon that leads to cisplatin resistance, and it could be a crucial EGFR independent STAT3 activating mechanism that needs to be explored further. In case a similar relationship in clinical specimens corroborates these in vitro findings, 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. Cisplatin-induced CD24 upregulation in CD44+ stem-like head and neck squamous carcinoma cells: a potential marker for unfavorable cisplatin response. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3860. doi:10.1158/1538-7445.AM2014-3860