Mechanisms of collective cell movement lacking a leading or free front edge in vivo

4D pathology: translating dynamic epithelial tubulogenesis to prostate cancer pathology

The Gleason score is the gold standard for grading of prostate cancer (PCa) and is assessed by assigning specific grades to different microscopical growth patterns. Aside from the Gleason grades, individual growth patterns such as cribriform architecture were recently shown to have independent prognostic value for disease outcome. PCa grading is performed on static tissue samples collected at one point in time, whereas in vivo epithelial tumour structures are dynamically invading, branching and expanding into the surrounding stroma. Due to the lack of models that are able to track human PCa microscopical developments over time, our understanding of underlying tissue dynamics is sparse. We postulate that human PCa expansion utilizes embryonic and developmental tubulogenetic pathways. The aim of this study is to provide a comprehensive overview of developmental pathways of normal epithelial tubule formation, elongation, and branching, and relate those to the static microscopical PCa growth patterns observed in daily clinical practise. This study could provide a rationale for the discerned pathological interobserver variability and the clinical outcome differences between PCa growth patterns.

Randomly Distributed K14+ Breast Tumor Cells Polarize to the Leading Edge and Guide Collective Migration in Response to Chemical and Mechanical Environmental Cues

Collective cell migration is an adaptive, coordinated interactive process involving cell-cell and cell-extracellular matrix (ECM) microenvironmental interactions. A critical aspect of collective migration is the sensing and establishment of directional movement. It has been proposed that a subgroup of cells known as leader cells localize at the front edge of a collectively migrating cluster and are responsible for directing migration. However, it is unknown how and when leader cells arrive at the front edge and what environmental cues dictate leader cell development and behavior. Here, we addressed these questions by combining a microfluidic device design that mimics multiple tumor microenvironmental cues concurrently with biologically relevant primary, heterogeneous tumor cell organoids. Prior to migration, breast tumor leader cells (K14⁺) were present throughout a tumor organoid and migrated (polarized) to the leading edge in response to biochemical and biomechanical cues. Impairment of either CXCR4 (biochemical responsive) or the collagen receptor DDR2 (biomechanical responsive) abrogated polarization of leader cells and directed collective migration. This work demonstrates that K14⁺ leader cells utilize both chemical and mechanical cues from the microenvironment to polarize to the leading edge of collectively migrating tumors. SIGNIFICANCE: These findings demonstrate that pre-existing, randomly distributed leader cells within primary tumor organoids use CXCR4 and DDR2 to polarize to the leading edge and direct migration.