Abstract 480: Targeting cancer stem cells through STAT3 inhibition in head and neck cancers

Abstract

Abstract Objectives: There is increasing evidence that cancer stem cells (CSC) are responsible for tumor recurrence and metastasis in head and neck cancer (HNC). The development of therapeutic strategies that preferentially target CSC may decrease cancer cell self-renewal and enhance progenitor apoptosis, potentially halting tumor growth and metastasis. Signal transducer and activator of transcription (STAT) proteins are important in oncogenic signaling pathways including cell cycle control and regulation of apoptosis. We hypothesized that expression of STAT3 would differ in CSC vs. non-CSC and the novel small molecule inhibitor, FLLL32, which blocks STAT3 function, could be used either alone or in combination with cisplatin, to induce cytotoxicity in both groups. We postulated that CSC would be more sensitive to STAT3 inhibition. Methods: CSC were identified and isolated from oral cavity cancer cell lines on the basis of high expression levels of the cell surface marker CD44. UMSCC-74B and UMSCC-47, were each derived from tongue cancers in male patients; UM-SCC-74B from a tumor that recurred after two rounds of treatment with chemotherapy and radiation and UM-SCC-47 from a previously untreated HPV-positive primary cancer. Quantitative RT-PCR analysis was used to determine relative expression values of STAT3 in CSC and non-CSC. Cell growth inhibition by FLLL32 alone and in combination with cisplatin, was then assessed by MTT assay in each cell line. Results: Both cell lines contain CD44high and CD44low expressing cells. In UMSCC-74B, STAT3 expression was increased 20-fold in CD44high relative to CD44low cells whereas for UMSCC-47, STAT3 expression was 3-fold lower in the CD44high cells. FLLL32 treatment induced growth suppression in UMSCC-74B CD44high and CD44low cells by 36% and 52% (p<0.001), respectively. In UMSCC-47, FLLL32 monotherapy induced growth suppression of CD44high and CD44low cells by 54% and 47% (p<0.001), respectively. Both cell lines and their respective CSC subgroups demonstrated enhanced cisplatin sensitivity when FLLL32 was used in combination. Conclusions: STAT3 expression differs between cell lines and between CSC and non-CSC. The aggressive phenotype of some HNC may be related to high levels of STAT3 expression within their CSC. These cancers may be less susceptible to STAT3 inhibition, alone or with cisplatin. Cancers expressing lower STAT3 expression levels in their CSC population may be more sensitive to STAT3 inhibition. By determining the level of STAT3 expression within CSC, we may be able to identify cancers that are more susceptible to STAT3 inhibition. Ongoing work is aimed at identifying the underlying mechanism for differential STAT3 expression and exploring related changes in key mediators of the STAT3 pathway. This work will underlie the development of novel, CSC-targeted treatment strategies that may be more effective than existing therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 480. doi:10.1158/1538-7445.AM2011-480