Mechanical phenotyping of colorectal cancer patient derived organoids based on LGR5 expression
Sefora Conti, Integrative cell and tissue dynamics group
Colorectal cancer (CRC) tumors are composed by heterogeneous cell populations comprising differentiated cells and a small pool of cancer stem cells (CSCs). The link between cancer cell differentiation states and their metastatic potential has been the focus of extensive investigation, with some studies pointing to microenvironmentally defined plasticity as a mechanism indispensable for metastasis formation. Another aspect that might be determinant in tumor cells ability to successfully disseminate, intravasate, survive in the blood stream, extravasate, colonize distant organs and form secondary tumors is their mechanical phenotype.
Adopting a bottom-up approach, we performed a broad biophysical characterization of CRC patient derived organoids (PDOs), engineered to fluorescently label cells expressing LGR5, a well-established marker for CSCs. We show that CRC cells differentiation states are associated with distinct biomechanical phenotypes, with potential repercussions on their metastatic ability.
At the single cell level, LGR5+ cells display a more elongated and polarized shape while the LGR5- cells exhibit higher roundness and a smaller asymmetry in the stress field. LGR5+ are stiffer compared to their differentiated counterparts and more prone to adopt a fast amoeboid-like migration under confinement. At the molecular level, cancer stemness is related to differential expression of the ERM protein family, responsible of tethering the cell membrane to the underlying actin cortex.
These distinct mechanical phenotypes translate to different migratory and morphological phenotypes at a cluster level. Clusters expressing high levels of LGR5 showed a more spread and flattened shape compared to more differentiated clusters. Moreover, LGR5 expression in clusters is negatively correlated with their migration speed and their polarization state. Hence, clusters containing more differentiated cells migrate faster, display higher roundness and higher polarization state.
At higher complexity levels, such as interactions with endothelial cells, LGR5 expression in CRC clusters affects their ability to adhere to an endothelial monolayer and form a gap through which they attach to the underlying collagen coating. Notably, we found that clusters expressing more LGR5 have an advantage while attaching to the endothelium as indicated by higher attachment rate and shorter time to form a gap.
Based on these findings relating distinct mechanical phenotypes to LGR5 expression, we speculate that mechanical adaptability coupled with cancer plasticity may be an indispensable mechanism for cancer progression.