Investigating the Effects of Tissue Stiffness on Cancer Cell Dormancy

Restricted (Penn State Only)
- Author:
- Pirog, Angelica
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Esther Gomez, Thesis Supervisor
Darrell Velegol, Thesis Honors Advisor - Keywords:
- matrix stiffness
proliferation
apoptosis
Ki67
caspase-3
breast cancer
dormancy
hydrogel
Young's Modulus - Abstract:
- Cancer cells can be dormant and then reawakened to cause cancer progression with new mutations and resistance. The stiffness associated with the extracellular matrix regulates many cellular functions, such as proliferation, apoptosis, and tumor development. Typically, an increased extracellular matrix stiffness is associated with breast cancer. We synthesized hydrogels that mimic the extracellular matrix stiffness of healthy and diseased breast tissue. The soft hydrogels have a Young’s modulus of ~470 Pa, similar to healthy mammary tissue, and the stiffened hydrogels have a Young’s modulus of ~3600 Pa, similar to breast tumor tissue. MDA-MB-231 breast cancer cells were plated onto soft hydrogels, and the hydrogels were then stiffened using light irradiation and a photoinitiator to form hydrogels with a stiffness mimicking mammary tumors. Ki67, a protein marker of proliferation, was monitored using immunofluorescence staining, microscopy, and image analysis. The activity of caspase-3, a protein that measures apoptosis, was analyzed using an activity kit and a plate reader. The static soft hydrogels were seen to have rounded cells, while the stiffened hydrogels were seen to have cells that were elongated. Quantitively, there was an increase in the percentage of Ki67-positive cells following stiffening of the hydrogels in comparison to when the cells were cultured on the soft hydrogels, indicating the cells waking up from their dormant state. When monitoring caspase-3 activity, cells cultured on the soft hydrogels had higher levels of caspase-3 activity than cells cultured on the stiffened hydrogels. Less caspase-3 activity on the stiffened hydrogels suggests less apoptosis.