The lymphatic system contains intraluminal leaflet valves that function to bias lymph flow back towards the heart. These valves are present in the collecting lymphatic vessels, which generally have ...lymphatic muscle cells and can spontaneously pump fluid. Recent studies have shown that the valves are open at rest, can allow some backflow, and are a source of nitric oxide (NO). To investigate how these valves function as a mechanical valve and source of vasoactive species to optimize throughput, we developed a mathematical model that explicitly includes Ca
-modulated contractions, NO production and valve structures. The 2D lattice Boltzmann model includes an initial lymphatic vessel and a collecting lymphangion embedded in a porous tissue. The lymphangion segment has mechanically-active vessel walls and is flanked by deformable valves. Vessel wall motion is passively affected by fluid pressure, while active contractions are driven by intracellular Ca
fluxes. The model reproduces NO and Ca
dynamics, valve motion and fluid drainage from tissue. We find that valve structural properties have dramatic effects on performance, and that valves with a stiffer base and flexible tips produce more stable cycling. In agreement with experimental observations, the valves are a major source of NO. Once initiated, the contractions are spontaneous and self-sustained, and the system exhibits interesting non-linear dynamics. For example, increased fluid pressure in the tissue or decreased lymph pressure at the outlet of the system produces high shear stress and high levels of NO, which inhibits contractions. On the other hand, a high outlet pressure opposes the flow, increasing the luminal pressure and the radius of the vessel, which results in strong contractions in response to mechanical stretch of the wall. We also find that the location of contraction initiation is affected by the extent of backflow through the valves.
Tumor-draining lymph nodes (TDLNs) are important for tumor antigen-specific T cell generation and effective anticancer immune responses. However, TDLNs are often the primary site of metastasis, ...causing immune suppression and worse outcomes. Through cross-species single-cell RNA-Seq analysis, we identified features defining cancer cell heterogeneity, plasticity, and immune evasion during breast cancer progression and lymph node metastasis (LNM). A subset of cancer cells in the lymph nodes exhibited elevated MHC class II (MHC-II) gene expression in both mice and humans. MHC-II+ cancer cells lacked costimulatory molecule expression, leading to regulatory T cell (Treg) expansion and fewer CD4+ effector T cells in TDLNs. Genetic knockout of MHC-II reduced LNM and Treg expansion, while overexpression of the MHC-II transactivator, Ciita, worsened LNM and caused excessive Treg expansion. These findings demonstrate that cancer cell MHC-II expression promotes metastasis and immune evasion in TDLNs.
Here we integrated multiphoton laser scanning microscopy and the registration of second harmonic generation images of collagen fibers to overcome difficulties in tracking stromal cell-matrix ...interactions for several days in live mice. We show that the matrix-modifying hormone relaxin increased tumor-associated fibroblast (TAF) interaction with collagen fibers by stimulating β1-integrin activity, which is necessary for fiber remodeling by matrix metalloproteinases.
Owing to their electromagnetic properties, tunability and biocompatibility, gold nanorods (GNRs) are being investigated as multifunctional probes for a range of biomedical applications. However, ...detection beyond the reach of traditional fluorescence and two-photon approaches and quantitation of their concentration in biological tissue remain challenging tasks in microscopy. Here we show how the size and aspect ratio that impart GNRs with their plasmonic properties also make them a source of entropy. We report on how depolarization can be exploited as a strategy to visualize GNR diffusion and distribution in biologically relevant scenarios
,
and
. We identify a deterministic relation between depolarization and nanoparticle concentration. As a result, some of the most stringent experimental conditions can be relaxed, and susceptibility to artefacts is reduced, enabling microscopic and macroscopic applications.
Preclinical and clinical studies positively correlate the expression of vascular endothelial growth factor (VEGF)-C in tumors and the incidence of lymph node metastases. However, how VEGF-C regulates ...individual steps in the transport of tumor cells from the primary tumor to the draining lymph nodes is poorly understood. Here, we image and quantify these steps in tumors growing in the tip of the mouse ear using intravital microscopy of the draining lymphatic vessels and lymph node, which receives spontaneously shed tumor cells. We show that VEGF-C overexpression in cancer cells induces hyperplasia in peritumor lymphatic vessels and increases the volumetric flow rate in lymphatics at the base of the ear by 40%. The increases in lymph flow rate and peritumor lymphatic surface area enhance the rate of tumor cell delivery to lymph nodes, leading to a 200-fold increase in cancer cell accumulation in the lymph node and a 4-fold increase in lymph node metastasis. In our model, VEGF-C overexpression does not confer any survival or growth advantage on cancer cells. We also show that an anti-VEGF receptor (VEGFR)-3 antibody reduces both lymphatic hyperplasia and the delivery of tumor cells to the draining lymph node, leading to a reduction in lymph node metastasis. However, this treatment is unable to prevent the growth of tumor cells already seeded in lymph nodes. Collectively, our results indicate that VEGF-C facilitates lymphatic metastasis by increasing the delivery of cancer cells to lymph nodes and therapies directed against VEGF-C/VEGFR-3 signaling target the initial steps of lymphatic metastasis.
Blood vessels are required for a tumor to grow and functional lymphatic vessels are required for it to disseminate to lymph
nodes. In an attempt to eradicate both the primary tumor and its lymphatic ...metastasis, we targeted both blood and lymphatic
vessels using two different tyrosine kinase inhibitors (TKIs): cediranib and vandetanib, which block vascular endothelial
growth factor receptor (VEGFR)-2 and -3 in enzymatic assays. We found that although both cediranib and vandetanib slowed the
growth rate of primary tumors and reduced blood vessel density, neither agent was able to prevent lymphatic metastasis when
given after tumor cells had seeded the lymph node. However, when given during tumor growth, cediranib reduced the diameters
of the draining lymphatic vessels, the number of tumor cells arriving in the draining lymph node, and the incidence of lymphatic
metastasis. On the other hand, vandetanib had minimal effect on any of these variables, suggesting that vandetanib did not
effectively block VEGFR-3 on lymphatic endothelial cells in our animal model. Collectively, these data indicate that the response
of lymphatic vessels to a TKI can determine the incidence of lymphatic metastasis, independent of the effect of the TKI on
blood vessels. Mol Cancer Ther 2008;7(8):2272–9
Solid stress and tissue stiffness affect tumour growth, invasion, metastasis and treatment. Unlike stiffness, which can be precisely mapped in tumours, the measurement of solid stresses is ...challenging. Here, we show that 2D spatial maps of the solid stress and the resulting elastic energy in excised or in situ tumours with arbitrary shapes and a wide range of sizes can be obtained via three distinct and quantitative techniques that rely on the measurement of tissue displacement after disruption of the confining structures. Application of these methods in models of primary tumours and metastasis revealed that (i) solid stress depends on both cancer cells and their microenvironments, (ii) solid stress increases with tumour size and (iii) mechanical confinement by the surrounding tissue substantially contributes to intratumoral solid stress. Further study of the genesis and consequences of solid stress, facilitated by the engineering principles presented here, may lead to new discoveries and therapies.Three methods for releasing solid stress in tumours provide two–dimensional mappings, sensitive estimates and in situ quantification of stress-induced tumour deformations — and thus stored elastic energy — via ultrasonography or optical microscopy.
The abnormal function of tumor blood vessels causes tissue hypoxia, promoting disease progression and treatment resistance. Although tumor microenvironment normalization strategies can alleviate ...hypoxia globally, how local oxygen levels change is not known because of the inability to longitudinally assess vascular and interstitial oxygen in tumors with sufficient resolution. Understanding the spatial and temporal heterogeneity should help improve the outcome of various normalization strategies.
We developed a multiphoton phosphorescence quenching microscopy system using a low-molecular-weight palladium porphyrin probe to measure perfused vessels, oxygen tension, and their spatial correlations in vivo in mouse skin, bone marrow, and four different tumor models. Further, we measured the temporal and spatial changes in oxygen and vessel perfusion in tumors in response to an anti-VEGFR2 antibody (DC101) and an angiotensin-receptor blocker (losartan).
We found that vessel function was highly dependent on tumor type. Although some tumors had vessels with greater oxygen-carrying ability than those of normal skin, most tumors had inefficient vessels. Further, intervessel heterogeneity in tumors is associated with heterogeneous response to DC101 and losartan. Using both vascular and stromal normalizing agents, we show that spatial heterogeneity in oxygen levels persists, even with reductions in mean extravascular hypoxia.
High-resolution spatial and temporal responses of tumor vessels to two agents known to improve vascular perfusion globally reveal spatially heterogeneous changes in vessel structure and function. These dynamic vascular changes should be considered in optimizing the dose and schedule of vascular and stromal normalizing strategies to improve the therapeutic outcome.
Breast cancer metastasizes through the lymphovascular system to the regional lymph nodes in the axilla and to both visceral and non-visceral sites. Renewed interest in the route by which tumor cells ...gain access to blood and lymphatic capillaries are the subject of research at mechanical, anatomic, pathologic, genetic, epidemiologic and molecular levels. Two papers presented at the 7th International Symposium on Cancer Metastasis in San Francisco showed tumor cells entering the systemic circulation through the sentinel lymph node. This information challenges the current paradigm where clinicians believe that access is gained through intra- and peri-tumoral blood vessels and that metastasis to axillary lymph nodes is an interesting epi-phenomenon. The sentinel lymph node era has changed the modern surgical approach to the axilla and the basis of this change is summarized in this paper. A new approach to the management of axillary metastases after systemic therapy relies on determining whether there is a complete pathologic response; if no tumor is found in the previously biopsied node, a complete axillary lymph node dissection may be avoided. African American women seem to inherit a trait from West African ancestors and tend to develop more lethal types of breast cancer. These tumors may have a molecular machinery that enhances their ability to metastasize to visceral sites and future research may unearth the mechanisms for this phenomenon.
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