(P 419) BONE MECHANICS INFLUENCE CANCER STEM CELL FORMATION IN OSTEOSARCOMA

Objective: Chemoresistance and recurrence of OS can be attributed to a subpopulation of OS cells known as Osteosarcoma Cancer Stem-like Cells (OS-CSCs). The aim of the study was to identify factors in the physical tumor microenvironment that might participate in OS-CSC development. It was hypothesized that within an OS tumor, spatial localized niches possessing distinct microenvironmental structural and mechanical properties could favor the genesis and survival of different OS cell populations, and certain niches might be more conducive for OS-CSCs formation and maintenance.

Methods: Mineralized collagen scaffolds mimicking heterogenous bone niches with distinct structural and mechanical properties were fabricated by changing collagen content and pore alignment and were cultured with the highly metastatic human OS cell lines. Scaffolds with 47% collagen by weight but different pore alignment were chosen for further analysis because they possessed different stiffness and topographical properties. Cytoskeletal changes, cell stiffness, epigenetic pathways, chemoresistance and chemoresistance-related pathways, and the differential expression of stemness genes were assessed in the 3D scaffold cultures.

Results: A consistent trend of OS-CSC phenotype was observed in OS cells grown within softer bone niches (12 kPa) with aligned pores as compared to stiffer niches (31 kPa) with non-aligned pores. The cell population growing in softer, aligned scaffolds had significantly higher expression of stemness genes (OCT4, NANOG, SOX2, ALDH1A1) and drug efflux gene ABCB1 and increased chemoresistance to doxorubicin and cisplatin. Epigenetic modifications associated with cisplatin resistance in OS including decreased methyl transferase EZH2 and concurrent upregulation of LIF/Notch and PRKCA pathways were observed in OS cells grown within softer, aligned niches. Fluorescent imaging of actin organization and Atomic Force Microscopy showed rounder, softer cells in aligned niches indicative of a CSC phenotype, and stretched, elongated, stiffer cells in the non-aligned niche indicative of a differentiated phenotype.

Conclusion: In summary, our research investigation demonstrates that the mechanical and structural properties of bone niches influence the formation of distinct OS cell populations. A softer niche with an aligned structure is more conducive for maintaining OS-CSCs, and these findings could be translated to designing therapeutic strategies that modify the microarchitecture to potentially reduce CSC-favoring niches.