Abstract 1476: Prostate cancer-associated fibroblasts secrete Annexin A1 that facilitates both generation of cancer stem cell-like cells (CSCs) from prostatic malignant epithelial cells and self-renewal/differentiation of CSCs

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Previously we described epithelial cell lines (Hormones & Cancer. 1: 44-54, 2010), primary cultures of cancer-associated fibroblasts (CAFs) (Cancer Res. 68: 198-205, 2008) and a primary cancer stem cell (CSC) subpopulation (Cancer Res. 70: 7294-303, 2010), all derived from the cPten-/-L mouse model of prostate adenocarcinoma (Cancer Res. 67: 7525-33, 2007). Most notably, we described evidence that CAFs secrete factors that enhance both the stemness and growth potentials of the CSCs (Cancer Res. 70: 7294-303, 2010). We have now identified the phospholipid binding Annnexin A1 as one of the pertinent secreted factors. When a malignant epithelial cell line (cE1) derived from castration-resistant prostate cancer (CRPC) from the model was fractionated into three different subpopulations based on the levels of cell surface expression of Sca-1(S) and CD49f (C) antigens: SChi, SCme and SC− (high, medium and low expression of S and C, respectively), we found that SCme cells were preferentially susceptible to epithelial-mesenchymal transition (EMT)-like transformation when treated with conditioned medium (CM) from either CAF cultures or Annexin A1 mimetic peptide (Ac1-25). Furthermore, following EMT induction, these trans-differentiated cells acquired stem cell-like properties similar to the SChi group based on expression of S and C and statistically significant up-regulation of Oct4 (p<0.05), Sox2 (p<0.001) and Nanog (p<0.0001). When transplanted within collagen grafts under the renal capsule of Nod.Scid mice, CM- and Ac1-25-EMT-ed SCme cells were able to form invasive lesions in vivo displaying cells with expression of both basal (p63) and luminal (cytokeratin 8, CK8)) cell-specific markers, as compared to untreated control grafts, which lacked glandular structures and had reduced p63 positive cells. Another effect of Annexin A1 was unraveled when CSCs (Lin− SChi subpopulation) from the primary tumors of the model were exposed to Acl-25. In vitro spheroid formation assays showed that in the presence of Acl-25 single spheroids generated from the CSCs could form multiple substructures potentially resulting from activation of additional stem-like progenitors, each capable of forming a prostasphere while remaining attached to the original spheroid structure. Immunofluorescent staining of cryosectioned spheroids revealed the presence of p63+ basal cells and an expanded population of p63/CK8 double positive transit-amplifying cells. Together these results describe two ways in which Annexin A1 may play a role in the development of a more malignant and stem cell-enriched tumor phenotype, or, to hypothetically take it a step further, possibly two ways in which Annexin A1, present in the tumor microenvironment, can lead to an increase or maintenance of a cancer stem cell(-like) population. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1476. doi:1538-7445.AM2012-1476