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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HoldCancerBack (What Holds Cancer Cells Back?)

Teaser

Summary

Current cancer research concentrates on the genetic and molecular level of individual cells and tackles with issues like genetic changes, molecular signaling pathways or intracellular mechanisms. To complement this knowledge, the project focuses on the collective behavior of cancer cells and answers the question: When is a cancer cell jammed or when can it overcome the yield stress to actively â€œflowâ€ in a dense microenvironment? The PI has brought forward the basic idea within the concept of Physics of Cancer that changes in a cancer cellâ€™s material properties determine its metastatic potential. The project pursues the next breakthrough in the Physics of Cancer by determining a predictive diagram to mark the conditions for unjamming transitions of cancer cells. Building the exclusive access to two types of carcinomas (mamma, cervix), the will introduce highly innovative techniques such as live cancer cell tracking in biopsies as a ground-breaking alternative to vital imaging. While these approaches are perfect to prove that unjamming transitions are key to tumor progression, the project will investigate to what extent fluid, i.e. unjammed, tissue behavior can be detected by magnetic resonance imaging elastography as an individual predictive marker for metastasis. Moreover, the results may guide surgeons when concerning the local spreading of cancer and thus greatly empower surgery in tumor therapies.

01/08/2017 > 31/01/2019

Despite its importance for cell biology and medicine the lack of understanding cell motility in dense tissues is caused by the lack of adequate approaches to investigate tissues from the subcellular scale to the whole organ scale, the deficiency to track motile cells in vital tissues, and long observation time vital tissue models. I have found unique solutions with proof-of-premise for all these problems. I have demonstrated that tabletop magnetic resonance elastography of punch biopsies can bridge the gap between in vivo elastography based MRI and atomic force microscopy based tissue rheology. I have set up a new atomic force microscope with a special hybrid stage to scan large tissue areas and an upright fluorescence macroscope for simultaneous long distance imaging of the cells scanned. The co-alignment of mechanical data and image permit to determine uniquely whether the mechanical data stem from connective or cellular tissue, which has hampered the interpretation of previously obtained data. The most important technological breakthrough is achieved when combining the technologies mentioned above with fluorescence microscopy since it permits the continuous imaging of the same position in question from the scale of a whole patient down to the subcellular scale. Moreover, my group has pushed spinning disk confocal microscopy to a new limit. We have achieved that the motion of all cells in a cell spheroid can be tracked reliably. Consequent fixation and clearance staining permits us to precisely determine cell shape and cellular organization within the spheroids.
In mature humans, tissues are solid-like, which allows the organism to exert shear stresses and move. As a prerequisite for metastasis, tumor tissues need to behave like a fluid, facilitating that cells can move. New properties emerge in a cell collective that are not simply the sum or average of the single cell properties. Nature does not use cells as simple building blocks like Lego stones. Only in cell monolayers, cell jamming and unjamming has been previously found. As cells have more degrees of freedom in 3D, it is not clear if these 2D results hold up in 3D. Thus as a first step to research the role of unjamming in tumor progression I had to show that cell jamming exists in 3D. Close to volume fraction one above sphere packing I have proven that 3D cellular tissues can modulate their mechanical behavior between solid and fluid by jamming and unjamming. From a physics perspective it seems to be highly unlikely that cells can squeeze

Work performed

01/08/2017 > 31/01/2019

HUMAN RESOURCES, EQUIPMENT, AND PATIENT SAMPLES Most of the personnel required to conduct the research for the project has already been working and was trained in my lab. Consequentially, my graduate students have started work directly with the commencement of the project without delays due to training. Graduate students assigned to the project who have previously been on the payroll of Leipzig University and have not been paid by other funding agencies were not immediately transferred to ERC funding. I have been waiting until their contracts expire to ensure a cost effective transition. It needed over a year to find a suitable medical technician to help with the clinical samples. Nevertheless, this did not hinder the work flow in characterizing patient samples. As one of the two postdocs for the projects I was able to hire Dr Thomas Fuhs, a leading expert in scanning probe techniques, perfectly suited for the project. Since the essential expertise for the project has been specifically developed in my lab I decided to hold off in hiring a second postdoc. My students Steffen Grosser and JÃ¼rgen Lippoldt, who are currently paid by the university, will graduate by the end of the year. They have developed the absolutely indispensable cell tracking methods for the project. Thus, I will use the currently unused funds in human resources to keep them in my lab as postdocs to assure that the project will not experience slowdown. I would like to explicitly state that I have consciously not spend all available funding for human resources. This has created no delays in the project and all money will be spent. Moreover, I have received a 50% teaching relief to focus on the project. The Magnetic Resonance Elastography (MRE) tabletop device has been bought and installed. Using the stateâ€™s infrastructure funds for biotechnology, I have upgraded our labâ€™s Atomic Force Microscopy (AFM) facility with an AFM especially designed to investigate tissue samples and I have doubled our cell culture facilities. All this happened no later than fall 2017. Together with the new head of the Department of Gynecology, Prof Bahriye Aktas, I optimized the flow of patient samples (cervix, breast).
TECHNOLOGICAL ACHIEVEMENTS In collaboration with Prof Ingolf Sack from the CharitÃ© my graduate student Frank Sauer with his undergraduate student Nazar Shrivastava have assembled a tabletop MRE and optimized it to investigate punch biopsies (see Fig.1). It currently characterizes cross-sections of the sample and full imaging capabilities are currently implemented. In partnership with Prof Rustem Valiullin from our department we started to combine MRE with magnetic resonance based water diffusion measurements (DWI). Frank Sauer validated the device with collagen gels of different densities and stiffness and simultaneously measured water diffusion. These assessments turned out to be more far reaching than simple control measurements. We learned that collagen networks gain their viscous behavior, i.e, relax, through intrafibrillar friction and that hydrodynamic drag plays a minor role in these polymer networks (see Fig 2). The intrafibrillar friction is multirelaxational and leads to a power law behavior, which my graduate students Tina, HÃ¤ndler and Carsten Schuldt as well as my undergraduate student Cary Tutmarc have further successfully investigated [2, 5]. Frank has authored a publication about our collagen results with the new MRE device, which has just been published for publication in Soft Matter [7]. Beyond my plans to use the tabletop MRE device for punch biopsies it has demonstrated to be a valuable alternative to standard rheometers. Moreover, my results point out the possibility that a combination of MRE and DWI can distinguish between connective and cellular tissue since water diffuses freely in collagen networks and behaves subdiffusive in cells due to molecular crowding.
In addition, I bought a new AFM especially tailored t

Final results

01/08/2017 > 31/01/2019

â€¢ My lab has proven that in 3D cell-based tissues solid behavior can be achieved by cell jamming, while the fluid state is associated with cell unjamming. In the jammed state cells cannot move. In the fluid state cells can move freely despite being above the volume fraction for sphere packing. Cell motility is essential for embryonic development and metastasis. Unjamming is a novel fundamental mechanism how tissue behavior is controlled.
â€¢ My labâ€™s results strongly support the presence of a new type of jamming transition previously unknown in physics. Conventional density driven jamming occurs at packing densities of a much lower volume fraction. The new transition correlates with cell shape. Collectives of elongated cells behave fluid and round cells behave solid.
â€¢ My current results point towards the picture that healthy epithelial tissues are jammed, while pathological mesenchymal tissue is at least partially unjammed. I intend to find the intracellular changes that trigger unjamming.
â€¢ My students have established quantitative 3D cell tracking in dense tissue models such as organoids and cell spheroids. Having already provided proof of premise we will perform long term cell tracking in vital tumor samples as a more realistic replacement for vital imaging in mice.
â€¢ With this technique my lab will validate that solid tumors (mama and cervix carcinoma) consist of fluid areas with motile cells embedded in a solid backbone of jammed cells.
â€¢ Using AFM-based rheology my postdoc Dr Fuhs will measure the complex shear modulus in cell spheroids and punch biopsies of patient tumors to determine how tissue fluidity relates to unjamming as well as cell shape.
â€¢ For multiscale characterization of tissues my group will use a unique combination of techniques, which we have developed, to continuously image the same piece of tissue from in vivo and organ-level scale down to the molecular scale.
â€¢ Since elongated shape correlates with cell motility I will evaluate to what extent it can serve as a predictive metastatic marker. In the same spirit I will assess whether MRE measurements can determine unjammed, fluid areas in the tumor mass as parts of the tumor that contain potential metastatic cancer cells.