Small Extracellular Vesicles Promote Stiffness-mediated Metastasis

Tissue stiffness is a critical prognostic factor in breast cancer and is associated with metastatic progression. Here we show an alternative and complementary hypothesis of tumor progression whereby physiologic matrix stiffness affects the quantity and protein cargo of small extracellular vesicles (EV) produced by cancer cells, which in turn aid cancer cell dissemination. Primary patient breast tissue released by cancer cells on matrices that model human breast tumors (25 kPa; stiff EVs) feature increased adhesion molecule presentation (ITGα2β1, ITGα6β4, ITGα6β1, CD44) compared with EVs from softer normal tissue (0.5 kPa; soft EVs), which facilitates their binding to extracellular matrix proteins including collagen IV, and a 3-fold increase in homing ability to distant organs in mice. In a zebrafish xenograft model, stiff EVs aid cancer cell dissemination. Moreover, normal, resident lung fibroblasts treated with stiff and soft EVs change their gene expression profiles to adopt a cancer-associated fibroblast phenotype. These findings show that EV quantity, cargo, and function depend heavily on the mechanical properties of the extracellular microenvironment.

SIGNIFICANCE

Here we show that the quantity, cargo, and function of breast cancer-derived EVs vary with mechanical properties of the extracellular microenvironment.

Small extracellular vesicles promote stiffness-mediated metastasis

Tissue stiffness is a critical prognostic factor in breast cancer and is associated with metastatic progression. Here we show an alternative and complementary hypothesis of tumor progression whereby physiological matrix stiffness affects the quantity and protein cargo of small EVs produced by cancer cells, which in turn drive their metastasis. Primary patient breast tissue produces significantly more EVs from stiff tumor tissue than soft tumor adjacent tissue. EVs released by cancer cells on matrices that model human breast tumors (25 kPa; stiff EVs) feature increased adhesion molecule presentation (ITGα 2 β 1 , ITGα 6 β 4 , ITGα 6 β 1 , CD44) compared to EVs from softer normal tissue (0.5 kPa; soft EVs), which facilitates their binding to extracellular matrix (ECM) protein collagen IV, and a 3-fold increase in homing ability to distant organs in mice. In a zebrafish xenograft model, stiff EVs aid cancer cell dissemination through enhanced chemotaxis. Moreover, normal, resident lung fibroblasts treated with stiff and soft EVs change their gene expression profiles to adopt a cancer associated fibroblast (CAF) phenotype. These findings show that EV quantity, cargo, and function depend heavily on the mechanical properties of the extracellular microenvironment.

Deep learning identification of stiffness markers in breast cancer

While essential to our understanding of solid tumor progression, the study of cell and tissue mechanics has yet to find traction in the clinic. Determining tissue stiffness, a mechanical property known to promote a malignant phenotype in vitro and in vivo, is not part of the standard algorithm for the diagnosis and treatment of breast cancer. Instead, clinicians routinely use mammograms to identify malignant lesions and radiographically dense breast tissue is associated with an increased risk of developing cancer. Whether breast density is related to tumor tissue stiffness, and what cellular and non-cellular components of the tumor contribute the most to its stiffness are not well understood. Through training of a deep learning network and mechanical measurements of fresh patient tissue, we create a bridge in understanding between clinical and mechanical markers. The automatic identification of cellular and extracellular features from hematoxylin and eosin (H&E)-stained slides reveals that global and local breast tissue stiffness best correlate with the percentage of straight collagen. Importantly, the percentage of dense breast tissue does not directly correlate with tissue stiffness or straight collagen content.

Recapitulation of molecular regulators of nuclear motion during cell migration

Cell migration is a highly orchestrated cellular event that involves physical interactions of diverse subcellular components. The nucleus as the largest and stiffest organelle in the cell not only maintains genetic functionality, but also actively changes its morphology and translocates through dynamic formation of nucleus-bound contractile stress fibers. Nuclear motion is an active and essential process for successful cell migration and nucleus self-repairs in response to compression and extension forces in complex cell microenvironment. This review recapitulates molecular regulators that are crucial for nuclear motility during cell migration and highlights recent advances in nuclear deformation-mediated rupture and repair processes in a migrating cell.

Biological membranes in EV biogenesis, stability, uptake, and cargo transfer: an ISEV position paper arising from the ISEV membranes and EVs workshop

Paracrine and endocrine roles have increasingly been ascribed to extracellular vesicles (EVs) generated by multicellular organisms. Central to the biogenesis, content, and function of EVs are their delimiting lipid bilayer membranes. To evaluate research progress on membranes and EVs, the International Society for Extracellular Vesicles (ISEV) conducted a workshop in March 2018 in Baltimore, Maryland, USA, bringing together key opinion leaders and hands-on researchers who were selected on the basis of submitted applications. The workshop was accompanied by two scientific surveys and covered four broad topics: EV biogenesis and release; EV uptake and fusion; technologies and strategies used to study EV membranes; and EV transfer and functional assays. In this ISEV position paper, we synthesize the results of the workshop and the related surveys to outline important outstanding questions about EV membranes and describe areas of consensus. The workshop discussions and survey responses reveal that while much progress has been made in the field, there are still several concepts that divide opinion. Good consensus exists in some areas, including particular aspects of EV biogenesis, uptake and downstream signalling. Areas with little to no consensus include EV storage and stability, as well as whether and how EVs fuse with target cells. Further research is needed in these key areas, as a better understanding of membrane biology will contribute substantially towards advancing the field of extracellular vesicles.

Mammalian Cell Division in 3D Matrices via Quantitative Confocal Reflection Microscopy

The study of how mammalian cell division is regulated in a 3D environment remains largely unexplored despite its physiological relevance and therapeutic significance. Possible reasons for the lack of exploration are the experimental limitations and technical challenges that render the study of cell division in 3D culture inefficient. Here, we describe an imaging-based method to efficiently study mammalian cell division and cell-matrix interactions in 3D collagen matrices. Cells labeled with fluorescent H2B are synchronized using the combination of thymidine blocking and nocodazole treatment, followed by a mechanical shake-off technique. Synchronized cells are then embedded into a 3D collagen matrix. Cell division is monitored using live-cell microscopy. The deformation of collagen fibers during and after cell division, which is an indicator of cell-matrix interaction, can be monitored and quantified using quantitative confocal reflection microscopy. The method provides an efficient and general approach to study mammalian cell division and cell-matrix interactions in a physiologically relevant 3D environment. This approach not only provides novel insights into the molecular basis of the development of normal tissue and diseases, but also allows for the design of novel diagnostic and therapeutic approaches.

Engineering Remotely Triggered Liposomes to Target Triple Negative Breast Cancer

Triple Negative Breast Cancer (TNBC) continues to present a challenge in the clinic, as there is still no approved targeted therapy. TNBC is the worst sub-type of breast cancer in terms of prognosis and exhibits a deficiency in estrogen, progesterone, and human epidermal growth factor 2 (HER2) receptors. One possible option for the treatment of TNBC is chemotherapy. The issue with many chemotherapy drugs is that their effectiveness is diminished due to poor water solubility, and the method of administration directly or with a co-solvent intravenously can lead to an increase in toxicity. The issues of drug solubility can be avoided by using liposomes as a drug delivery carrier. Liposomes are engineered, biological nanoconstructs that possess the ability to encapsulate both hydrophobic and hydrophilic drugs and have been clinically approved to treat cancer. Specific targeting of cancer cell receptors through the use of ligands conjugated to the surface of drug-loaded liposomes could lessen damage to normal, healthy tissue. This study focuses on polyethylene glycol (PEG)-coated, folate conjugated, benzoporphyrin derivative (BPD)-loaded liposomes for treatment via photodynamic therapy (PDT). The folate receptor is over expressed on TNBC cells so these liposomes are targeted for greater uptake into cancer cells. PDT involves remotely irradiating light at 690 nm to trigger BPD, a hydrophobic photosensitive drug, to form reactive oxygen species that cause tumor cell death. BPD also displays a fluorescence signal when excited by light making it possible to image the fluorescence prior to PDT and for theranostics. In this study, free BPD, non-targeted and folate-targeted PEGylated BPD-loaded liposomes were introduced to a metastatic breast cancer cell line (MDA-MB-231) in vitro. The liposomes were reproducibly synthesized and characterized for size, polydispersity index (PDI), zeta potential, stability, and BPD release kinetics. Folate competition tests, fluorescence confocal imaging, and MTT assay were used to observe and quantify targeting effectiveness. The toxicity of BPD before and after PDT in monolayer and 3D in vitro cultures with TNBC cells was observed. This study may contribute to a novel nanoparticle-mediated approach to target TNBC using PDT.

Remotely Triggered Nano-Theranostics For Cancer Applications

Nanotechnology has enabled the development of smart theranostic platforms that can concurrently diagnose disease, start primary treatment, monitor response, and, if required, initiate secondary treatments. Recent in vivo experiments demonstrate the promise of using theranostics in the clinic. In this paper, we review the use of remotely triggered theranostic nanoparticles for cancer applications, focusing heavily on advances in the past five years. Remote triggering mechanisms covered include photodynamic, photothermal, phototriggered chemotherapeutic release, ultrasound, electro-thermal, magneto-thermal, X-ray, and radiofrequency therapies. Each section includes a brief overview of the triggering mechanism and summarizes the variety of nanoparticles employed in each method. Emphasis in each category is placed on nano-theranostics with in vivo success. Some of the nanotheranostic platforms highlighted include photoactivatable multi-inhibitor nanoliposomes, plasmonic nanobubbles, reduced graphene oxide-iron oxide nanoparticles, photoswitching nanoparticles, multispectral optoacoustic tomography using indocyanine green, low temperature sensitive liposomes, and receptor-targeted iron oxide nanoparticles loaded with gemcitabine. The studies reviewed here provide strong evidence that the field of nanotheranostics is rapidly evolving. Such nanoplatforms may soon enable unique advances in the clinical management of cancer. However, reproducibility in the synthesis procedures of such "smart" platforms that lend themselves to easy scale-up in their manufacturing, as well as the development of new and improved models of cancer that are more predictive of human responses, need to happen soon for this field to make a rapid clinical impact.