Over the last two decades with advancements in research, detection, and treatment of all cancer types in the United States, resulting in an overall 23% decrease in cancer related deaths, liver cancer has gone against this trend possessing an increased death rate. Globally, hepatocellular carcinoma (HCC), the most common form of liver cancer, ranks as the second leading cause of cancer related deaths with approximately 788,000 deaths annually. In recent years much emphasis has been placed on understanding the process of HCC cell invasion;​ however, it has become apparent that the progression of this disease is not solely dependent on just the cancer cells or biological factors, but also their interaction with the tumor microenvironment. A significant number of studies have shown that changes in biomechanical forces within the tumor microenvironment can alter cancer progression. Previous research has demonstrated that interstitial fluid flow (IFF), one of the biomechanical forces that is altered during tumor growth, can promote cancer cell invasion. The findings in this work elucidate the effects of IFF in HCC cell invasion. Using our 3D in vitro flow invasion assay, we demonstrate that IFF increases cellular invasion through autologous gradient formation of chemokines (CXCR4/CXCL12) that promote migration, a mechanism known as autologous chemotaxis.

We also demonstrated that MEK/ERK signaling affects IFF-induced invasion;​ however, this pathway was separate from CXCR4/CXCL12 signaling. Increased matrix metalloproteinase (MMP) expression is a hallmark for cancer progression and poor prognosis. Biomechanical forces have been observed to increase the secretion of these proteolytic enzymes, which promote extracellular matrix degradation and tumor cell invasion. We observed an increase in MMP-9 and MMP-2 activity in HCC cells exposed to IFF. In total these findings indicate multiple mechanisms are at play in HCC flow- induced invasion, further emphasizing the significance biomechanical forces play in disease progression.

Finally, by modifying our 3D in vitro flow invasion assay, we examined IFF in a relevant cell-based disease model where HCC cells are embedded in a stiff matrix. The increase in matrix stiffness is a result of tumor growth, shown to disturb the mechanical forces and biochemical signaling that occurs in the microenvironment, effectively promoting disease progression. HCC also possesses a very unique disease profile and risk factors;​ nearly 80% of HCCs occur from patients who suffer from chronic fibrosis or cirrhosis, where inflammation and hepatic wound-healing response attributes to the hepatocarcinogenesis. Many studies have observed cellular behavior of hepatocytes and HCC cells in a stiff matrix;​ however, none have observed the effect of IFF and a stiff microenvironment in HCC cells. The findings in this chapter confirm a synergistic relationship between IFF and matrix stiffness on HCC cell invasion. Ultimately the findings in this study provide a better foundational and mechanistic understanding of IFF and its effects on HCC cell invasion adding to the mounting evidence of how biomechanical forces in the tumor microenvironment influence cancer progression.