Endocrine Abstracts

Kinases represent a main therapeutic targets in cancer treatment as their impairing is related to tumor growth and progression. Despite the increasing evidence that tumor microenvironment (TME) signaling influences the behavior of surrounding cancer epithelial cells, still little is known about what changes in stromal cells influence tumor cells’ behavior. TNBC patients are still lacking an effective therapy, as not much is known about the biology of this BC tumor subtype. TNBC trials focus mainly on targeting epithelial cancer cells by using a combination of kinase inhibitors and standard chemotherapy however these therapeutic regimens are not considering the action of stromal cells. Our aim is to Identify fibroblasts-expressed kinases that modulate tumor cells’ invasion and Characterize the mechanism by which these kinases promote/reduce tumor invasion.A library of SiRNA targeting 710 Kinases was used to transfect Human Mammary Fibroblast (HMF) and normal lung fibroblast (MRC5). 24h after transfection, fibroblasts were co-cultured with MDA-MB-231 for 3Dspheroids formation. Matrigel and chemoattractants were added to promote invasion that was evaluated by spheroids pictures analysis. kinases silenced spheroids were compared to controls. We identified PIK3Cδ, whose silencing decreased TNBC invasion rate, suggesting a pro-invasive role of this kinase. PIK3Cδ is essential for regulating chemokine production in leukocytes and promotes migration during inflammation. It has been shown that PIK3Cδ inhibitors (CAL -101) interfere in tumour-stroma interactions without directly killing cancer cells. Despite PIK3Cδ being expressed mainly in leucocytes, we detected high PIK3Cδ protein expression in various fibroblast cell lines and in primary fibroblasts derived from TNBC patients; however, PIK3Cδ was hardly detectable in a panel of breast cancer cell lines. Treatment with CAL -101, affected cell viability of fibroblasts cell lines, while it had limited/no effects on breast cancer cells. Fibroblasts treated with CAL -101 showed a decreased AKT phosphorylation, a downstream target of PIK3Cδ. Pretreatment of fibroblasts with CAL -101 significantly decreased TNBC cells’ invasion in both 2D and 3D co-culture experiments. Interestingly, using transwell systems we found that co-culture with TNBC cells increased PIK3Cδ expression in fibroblasts, suggesting a feedback loop that ‘fueled’ tumor progression. Ongoing experiments are suggesting a paracrine signaling mechanism that may lead to the promotion of TNBC via PIK3Cδ fibroblasts expression. Using a novel 3D co-culture invasion assay, we identified stromal PIK3Cδ as a key mediator of TNBC invasion. Our results suggest that targeting PIK3Cδ in the tumor microenvironment may represent a novel strategy for TNBC therapy.