Among different cancers, breast cancer is the most common type. A major contributing factor to mortality in cancer patients is the return of the cancer after chemotherapy. Cancer relapse affects 30% of breast cancer patients. Recent observations indicate that cancer relapse may be related to a very small population of slow-growing cancer stem cells (CSCs) in the tumor that are unaffected by chemotherapy. After chemotherapy, the bulk of the tumor shrinks to less than a few percent of the initial size, thus enriching the tumor with CSCs that do not respond to conventional therapies. The enriched CSCs divide, grow and regenerate the tumor volume, leading to cancer relapse or recurrence. Consistent with that notion, the triple negative cancer (TNBC), which is the most aggressive type of breast cancer, has the highest sub-population of CSCs among different breast cancer types with 77% survival rate, compared to 93% for other types, The broader significance of this project is understanding the role of those factors in the tumor environment that contribute the survival of CSCs. One of the factors that play a central role is the tumor tissue stiffness. For example, lumps in the breast that feel stiffer than the rest of the tissue are a sign of possible breast cancer that should be checked. The objective of this project was to determine the role of tissue stiffness on CSC survival and growth in a tissue-like three-dimensional matrix. The importance of this project lies in identifying new agents that target tissue stiffness to destroy CSCs and the development of a kit to test drugs against cancer stem cells. The PI will use several programs to recruit under-represented students and he will work with the South Carolina Children's museum to develop an interactive exhibit titled "hydrogels" for kids. This proposal is co-funded by the Biomedical Engineering Program in the Chemical, Bioengineering, Environmental and Transport Systems Division, and by the Biomaterials Program in the Division of Materials Research.
Cancer relapse is related to a very small population of slow-growing cancer stem cells (CSCs) that do not respond to conventional therapies. Naturally derived matrices are widely used as a matrix to study CSC survival but due to many ligand-receptor interactions, the effect of mechanotransduction on CSC signaling pathways that maintain CSC cannot be investigated. The objective of this work is to engineer a matrix with defined properties to serve as a sieve for selection and enrichment of CSCs and to investigate the effect of matrix stiffness on intracellular pathways that maintain CSCs. The overall hypothesis is that in the absence of receptor-ligand interaction, matrix stiffness is the extracellular activator of YAP/TAZ through GPCR/lipid rafts/Rho/ROCK signaling pathway, leading to CSC survival. It is further hypothesized that in the presence of integrin-binding ligands, focal adhesion is the extracellular activator of Hippo through the FAK/Rac signaling pathway and stress fiber formation in the cell periphery, leading to the expression of LATS1/2 kinases, inhibition of YAP/TAZ transcription factors and loss of CSC maintenance. The following approach is used to test the hypothesis. In Aim 1, cancer cells will be encapsulated in the novel lactide-chain-extended polyethylene glycol (SPELA) hydrogel and cultured in a medium supplemented with Doxorubicin (Dox) and/or Salinomycin (Sal) to select and enrich for the most invasive CSC phenotype in the growing CSC colonies. In Aim 2, the effect of matrix stiffness on the activation of YAP/TAZ transcription factors through GPCR/lipid rafts/Rho/ROCK signaling pathway of CSC will be investigated with the enriched CSC colonies encapsulated in the SPELA hydrogel. And in Aim 3, the effect of conjugated integrin-binding ligands on the activation of Hippo signaling pathway of CSC will be investigated with the enriched CSC colonies encapsulated in the SPELA hydrogel with optimum stiffness. The intellectual merit of this work is a model engineered culture system to screen for the most effective drugs and targeting ligands against the most invasive CSC colonies. The broader impact of this work lies in generating a cancer stem cell-on-a-chip as a more relevant in vitro tumor model in basic research, drug discovery and personalized medicine.