Abstract P1-06-09: Engineered model matrix to mimic cancer stem cell microenvironment: Effect of integrin and heparin binding peptides

Abstract

Abstract Introduction: It is critical to understand the mechanism of cancer stem cell (CSC) maintenance and its regulation by the microenvironment to prevent and treat cancer. Since cancer takes many years to grow, it is imperative to develop in vitro models to study the molecular basis of tumorigenesis and progression. In an effort to isolate and investigate the effect of individual physical, mechanical, and biological factors in the tumor microenvironment on the fate of cancer cells and maintenance of CSCs, we have developed novel inert synthetic hydroxy acid-chain-extended polyethylene glycol (PEGXA) hydrogels with defined physical, chemical, mechanical, and biological properties. The objective of this work was to investigate the effect of integrin-binding and heparin-binding peptides conjugated to a matrix with defined physiochemical properties and stiffness on tumorsphere formation and CSC maintenance. Methods: Mouse 4T1, human MCF7, and human MDA-MB-231 breast cancer cells were encapsulated in PEGXA gels conjugated with integrin-binding and heparin-binding peptides. Peptides included laminin-derived IKVAV and YIGSR, collagen-IV derived TAGSCLRKFSTMY and GEFYFDLRLKGDKY, and fibronectin-derived WQPPRARI and RGD. Gels without peptide conjugation and those conjugated with laminin-derived CD44 binding RLVSYNGIGGLK peptide were used as positive (CSC forming) and negative controls, respectively. Tumorsphere size and density, and expression of CSC markers were determined with incubation time in tumor CSC culture medium. For in vivo, cell encapsulated gels were inoculated in syngeneic Balb/C mice and tumor formation was determined with time. Results: All tumor cells types encapsulated in PEGXA gels without peptide formed tumorspheres and maintained CSCs. Gel stiffness had a bimodal effect on tumorsphere formation in the 1-50 kPa compressive modulus range. Tumor cells encapsulated in the gel with 5 kPa compressive modulus had the highest expression of CSC markers. Conjugation of CD44 binding peptide eliminated tumorsphere formation by encapsulated tumor cells. Interestingly, integrin-binding peptides (RGD, IKVAV and YIGSR) conjugated to the gel abolished tumorsphere formation by encapsulated cells whereas heparin-binding peptides (TAGSCLRKFSTMY, GEFYFDLRLKGDKY and WQPPRARI) improved rate of tumorsphere growth and the expression of CSC markers. It should be noted that peptides dissolved in the gel (not chemically attached to the gel) or gels conjugated with mutant peptides did not have a noticeable effect compared to the gels without peptide. Similar results were observed with the cell-encapsulated gels were implanted in Balb/C mice. The expression pattern of EMT markers suggested that enhanced EMT contributed to the increased tumorsphere formation in gels conjugated with heparin-binding peptides. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-06-09.