Cancer metastasis is a complex process that culminates in the majority of patient deaths. A key component of the cancer paradigm involves cancer stem cells (CSCs), the primary mediators of cancer progression, resistance to therapy and recurrence of cancer after remission/latency. Although the clinical significance of CSCs is well accepted, the key upstream regulatory mechanisms that define these unique subsets of cancer cells requires further clarification. Previous studies demonstrate that MDA-9/Syntenin or syndecan binding protein (SDCBP) levels are elevated in large spectrum of tumors, including melanoma, breast carcinoma, gastric carcinoma and glioblastoma multiforme (GBM), versus normal cellular counterparts. We now uncover a unique function of MDA-9 as a facilitator of cancer stemness and survival.

Expression profiles of mda-9, Nanog, Oct4, Sox2 and c-myc were studied in different clinical samples and cell lines for correlations. Cells were sorted by FACS into stem and non-stem populations and the same genes were assayed for correlative expression. Stemness gene expression array profile analysis was performed on control and mda-9 silenced CSCs. Genetic (gain-of-function, loss-of-function) approaches were used to modify mda-9 expression in normal human astrocytes and prostate cells, non-stem cancer cells (NSCCs) and CSCs from breast prostate and GBM. Recovery-of-function approaches were also applied to elucidate the pathways responsible for MDA-9-mediated regulation of CSCs. The impact of MDA-9 on CSC-mediated tumorigenicity and progression was evaluated in vivo by intracranial glioma and subcutaneous xenograft mice models. Apoptosis was assayed by caspase activation and Annexin V staining.

A positive and statistically significant correlation was observed between mda-9 and stemness regulating genes (Nanog, Oct4, Sox2 and c-myc), in 50 clinical samples and 3 cell culture systems, including breast, prostate and GBM. CSCs expressed elevated levels of mda-9 vs. non-stem cancer cells or normal stem cells from a total of 11 cell lines including breast, prostate and GBM and two clinical GBM samples. Over-expression of mda-9 in NSCCs increased populations of CSCs as well as expression of stemness regulating genes. Loss of MDA-9 affected 84 genes linked to CSC regulation. Control intracranial glioma xenograft mouse models had large tumors with spongioblastic morphology typical of human gliomas, whereas the loss of mda-9 caused a large decrease in tumor size. Mechanistically, MDA-9 regulated multiple stemness genes and knockdown of MDA-9 caused a loss of stemness and tumorigenicity with initiation of apoptosis.

Our data uncover a previously unidentified relationship between MDA-9 and CSCs. CSCs appear more dependent on MDA-9 expression than normal stem cells. MDA-9 regulates CSCs on multiple levels of stemness and survival, reinforcing the relevance of this gene as a potential therapeutic target.

Citation Format: Sarmistha Talukdar, Swadesh Das, Anjan K. Pradhan, Luni Emdad, Xue-Ning Shen, Jolene J. Windle, Devanand Sarkar, Paul B. Fisher. MDA-9/Syntenin (SDCBP) promotes self renewal and malignancy in cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2527.