Kinome screening identifies fibroblast PIK3Cδ to be involved in triple-negative breast cancer (TNBC) invasion


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Georgios Giamas1,Teresa Gagliano1,Viviana Vella1,Giulia Bresciani1,Kamila Bienkowska1,Frances Pearl1
1University of Sussex

Abstract

Background

Translational research and clinical trials often focus on targeting epithelial cancer cells. This could diminish the contribution of reciprocal interactions between malignant and stromal cells that can create a local microenvironment, which fosters tumour growth and influences response to treatment.

However, as the prognostic and predictive significance of gene/protein expression signatures of the surrounding stroma has been well-documented, there is an increasing need of identifying novel druggable targets (i.e. kinases) in the TME. Working on triple negative breast cancer (TNBC), a clinically unmet BC subtype, we focused on fibroblasts, the main stroma components in the TME, whose multiplex role in BC initiation, progression and therapy-resistance has been described

Method

  • An experimental pipeline was established consisting of a 3D co-culturing model (cancer/stromal cells) and an invasion assay as a readout tool, to examine the aggressiveness/invasion potential of TNBC cells. 
  • A  kinome siRNA screening was performed in stromal cells, to shed light on kinases involved in stroma-tumour cross-talk.
  • Various molecular, cellular, in vivo techniques were employed including: transwell-assays, secretome/RNA sequencing/bioinformatics analyses, IHC staining and BC in vivo mouse models.

 

Results

  • We identified PIK3Cδ, whose silencing decreased TNBC invasion rate, suggesting a pro-invasive role of this kinase.
  • 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.
  • Pharmacological inhibition (FDA-approved drug) of PIK3Cδ decreased fibroblast-mediated TNBC cells’ invasion in 2D and 3D co-culture experiments.
  • Secretome and RNA sequencing analyses identified specific pathways implicated in the observed phenotype.
  • • IHC staining of TNBC patients as well as in vivo xenograft mouse models revealed a link between PIK3Cδ stromal expression and tumour invasion potential.

Conclusion

Our results suggest that targeting PIK3Cδ in the tumor microenvironment may represent a novel transformative strategy for TNBC therapy.