Johns Hopkins University PS-OC
Johns Hopkins Physical Sciences-Oncology Center (PS-OC)
This PS-OC is developing an integrated approach for a systematic, quantitative understanding of the physical and chemical cues mediating local invasion from the hypoxic primary tumor to distant organs, through single and collective invasion into the stromal matrix, and confined migration along confining tracks (which represent some of the early critical steps in the metastatic cascade).
To address the complexity of the combined effects of hypoxia, extracellular matrix microstructure, and confinement on tumor cell invasion, the PS-OC is working on inter-related projects. Additionally, computational biophysicists in a computational core are systematically developing a quantitative understanding of physical cues in the metastatic cascade.
This PS-OC takes a trans-disciplinary, integrated approach, combining the fields of physics, biomedical engineering, cancer biology, ecology, and clinical medicine, to transform the understanding of metastatic cancer, opening new paradigms for prognosis and treatment.
Project 1: The Role of Physical Cues in Collective Cell Invasion
The ability of tumors to invade adjacent tissues, leading to local or distant metastasis, is a hallmark of cancer. Cancer cells frequently invade as groups of adherent cells in a process termed collective invasion. Previous studies have primarily focused on single cell or semi-collective (multicellular streaming) cell invasion. Single cell models for metastasis have direct implications for tumors whose cells migrate constitutively as individual cells, such as leukemias and lymphomas, or after cell detachment from a primary tumor via epithelial-to- mesenchymal transition (EMT).
However, EMT has long been controversial among pathologists as breast tumors at metastatic sites typically display epithelial features. While EMT-like gene signatures can be observed in specific mouse models and breast cancer subtypes, the majority of breast tumors do not exhibit clear molecular features of EMT. Intravital microscopy studies reveal that tumor cells preferentially migrate collectively along pre-existing channels that are defined by various anatomical structures in vivo. Yet, it is currently unknown how the physical properties of the microenvironment, such as confinement and compliance, regulate the molecular mechanisms of collective cell invasion.
Intriguing preliminary data reveal that cancer cells migrate through wide tracks as a collective unit. However, as confinement increases, the cancer cells spontaneously disseminate, first as clusters of 2-5 cells and eventually, in very narrow tracks, as single cells. PS-OC investigators hypothesize that the physical microenvironment induces a signaling cascade of events that transforms the classical collective to single cell invasion.
To test this hypothesis, the PS-OC is employing a multidisciplinary approach combining novel bioengineering tools and mathematical modeling with sophisticated molecular cell biology and imaging techniques and in vivo models:
- Developing an integrated experimental and computational model of collective cell movement in confined geometries modeling primary tumor invasion, and dissecting the mechanisms by which cell-cell contact is released during mechanically-induced transitions to single cell movement
- Delineating the relative contributions of actomyosin contractility, small GTPases and osmotic engine model to locomotion in rigid versus compliant confined microenvironments
- Validating the in vitro understanding of the dissemination and locomotion of cancer cells in more complex microenvironments characteristic of in vivo breast tumors using an organotypic 3D culture system and genetically engineered mouse models.
Elucidation of the underlying mechanisms of collective cancer cell invasion will offer insights into our understanding of how cancer cells spread through the body, and it could shift the currently prevailing single cell paradigm in cancer to incorporate concepts of mechanical signaling, cell-cell adhesion, and cell-cell cooperation.
Project 2: The Effects of Cell-ECM and Cell-Cell Interactions on Tumor Collective Cell Migration
The majority of cancer mortality arises because tumors cells leave their primary site, giving rise to metastatic tumors in other organs. While there are many and complex biologic aspects of tumor progression leading to cancer metastasis, local invasion through the basement membrane of epithelia and migration of primary tumor cells through the extracellular matrix (ECM) to access lymphatic and vascular channels is clearly a critical early step. Tumor cells can invade and migrate individually or as groups.
Accumulating pathologic and in vivo experimental evidence now indicates that the most common form of tumor cell migration is likely as a collective group. While researchers have learned a great deal about the cell biologic, biochemical, and biophysical mechanisms underlying the migration of individual cells in 2D, 3D and in vivo, the understanding about the regulation of collective cell migration in cancer metastasis is at an early stage.
Organization of cells into collective groups and their migration of cells is governed by a number of forces:
- Passive (elastic and adhesive forces)
- Frictional (resistance to cells sliding past one another and cells sliding across a substrate)
- Active (protrusive and contractile forces)
- Traction (forces upon the underlying or surrounding ECM)
However, which forces are critical for the collective migration of tumor cells, and how, is not understood.
The overarching hypothesis of this project is that cell-ECM and cell-cell interactions will combine through adhesion crosstalk to modulate tumor collective cell migration by altering cooperativity of motion and force generation. PS-OC investigators are testing this hypothesis by developing computational tools, as well as 2D and in vivo 3D experimental models that measure various physical forces within and around a group of tumor cells as they organize to migrate in a collective through the tumor stroma and within the tumor epithelium.
The PS-OC approach to the problem is iterative: using computational simulations to inform experimental testing of how various forces contribute to the organization and motion of collective groups of tumor cells. It is using various tools to address different aims:
- Determine an integrated experimental and computational model of how tumor cell-intrinsic changes in adhesion influence collective migration
- Determine how changes in the tumor environment affect collective migration of tumor cell
- Determine how cell-cell and cell-ECM forces influence the nature of tumor cell collective migration in clinically relevant primary human breast tumor samples
- Develop a computational model of collective cell migration dynamics in tissues
Project 3: Determining Mechanisms of Sarcoma Cell Invasion and Migration
Sarcoma is a malignant cancer derived from transformed cells of mesenchymal origin. Progression and metastasis of sarcomas is regulated by microenvironmental cues. Low intratumoral oxygen (i.e., hypoxia) dramatically increases pulmonary metastasis and poor clinical outcomes. Yet, researchers do not yet completely understand the critical effects of hypoxia on sarcoma cells and the microenvironment. Thus, defining how primary tumor cells respond to oxygen in their microenvironment is essential for understanding metastasis and identification of novel therapeutic targets.
Recent work of PS-OC investigators has shown that hypoxia promotes sarcoma metastasis through induction of HIF1-PLOD2 and the subsequent deposition of aberrant collagen that leads to distant metastasis. However, a number of questions still remain:
- How is cell migration/invasion altered in the presence of the oxygen gradients that occur in tumors?
- Which collagen modifying-enzymes define the ECM?
- How are cells’ motility modified in response to altered collagen structure in the microenvironment?
The PS-OC studies are addressing each of these unknowns. To model the oxygen gradients that develop in tumors as they outgrow their vascular supply, PS-OC investigators developed novel oxygen-controlling hydrogels that can serve as 3D hypoxic microenvironments.
The PS-OC hypothesizes that sarcoma cell invasion and migration is guided by increased oxygen tension and facilitated by hypoxia-induced ECM remodeling. PS-OC investigators are determining if oxygen gradients regulate the direction, speed and distance of migrating sarcoma cells and how these factors depend on hypoxic ECM remodeling (by focusing on collagen microstructure). This approach will integrate mathematical modeling and experimental models, linking oxygen-ECM-cellular invasion and migration in sarcomas.
The specific aims are:
- Determine sarcoma cell and tumor graft responses to spatial oxygen gradients
- Characterize collagen remodeling during sarcoma invasion under hypoxic gradients
- Determine how collagen fiber organization regulates hypoxic invasion and migration.
The results of the project will identify the molecular and physical mechanisms underlying the initial steps of metastasis, invasion and migration, and develop predictive models for these mechanisms, ultimately leading to novel therapeutic targets.
The computational core provides theory and modeling hands-on expertise to the PS-OC. It is also actively developing user-friendly software packages for assisting data collection, as well as Matlab routines and software for running simulations by non-experts. Tutorials on modeling concepts, modeling results, and developed software are conducted at center-wide retreats, as well as center symposia. All of the developed software packages will be made available to researchers in the PS-OC and the larger community.
The aims of the computational core are:
- Develop a 3D computational framework for simulating single-cell migration simultaneously with reaction-diffusion-advection equations for complex biochemical signaling pathways
- Construct a computational platform for simulating discrete numbers of interacting motile cells
- Bridge from discrete models of single cells to 3D continuum algorithms for simulating the migration of multicellular groups
Education and Outreach Unit
The PSOC uses a variety of activities and strategies to support education and outreach initiatives. The center hosts major collaborative events and supports training activities to prepare the next generation of researchers.
Denis Wirtz, Ph.D.
Johns Hopkins University
Dr. Denis Wirtz earned a Physics Engineering degree at the Ecole Polytechnique of the Université Libre de Bruxelles (Belgium) in 1988. With a Hoover fellowship, he moved to Stanford University, where he earned a PhD in 1993 in Chemical Engineering for work in polymer physics. With a “Human Capital Mobility” fellowship of the European Union, he did postdoctoral research at the Ecole Supérieure de Physique et Chimie Industrielles (ESPCI) in Paris, France.
He joined the faculty of the Department of Chemical and Biomolecular Engineering at Johns Hopkins University in 1994 and was promoted to the rank of full professor in 2003. He is currently T.H. Smoot Professor of Engineering Science. Wirtz has made important contributions to molecular and biophysical mechanisms of cell motility and adhesion and nuclear dynamics in health and disease. He pioneered the method of particle-tracking microrheology to probe the rheological properties of complex fluids and living cells and tissues.
Kenneth Pienta, M.D.
Johns Hopkins University
Dr. Kenneth Pienta is a Professor of Urology, Oncology, and Pharmacology and Molecular Sciences and a two-time American Cancer Society Clinical Research Professor Award recipient. Between 1995 and 2013, Dr. Pienta served as the Director of the Prostate Specialized Program of Research Excellence (SPORE) at The University of Michigan, with a proven, peer-reviewed track record in organizing and administering a translational research program that successfully incorporates bench research, agent development, and clinical application.
He has made major contributions in understanding prostate cancer biology and improving diagnosis and treatment. He is the Director of Research for the Brady Urological Institute at Johns Hopkins University School of Medicine and the Program Leader for the Prostate Cancer Program of the Sidney Kimmel Comprehensive Cancer Center. He also serves as the co-Director of the Johns Hopkins University inHealth Signature Initiative, a trans-University, cross-disciplinary effort to coordinate and apply the intelligent use of population health data for individual patients.