Fluid Shear Stress Induces Drug Resistance to Doxorubicin and Paclitaxel in the Breast Cancer Cell Line MCF7

Overcoming the effects of fluid shear stress in ovarian cancer cell lines: Doxorubicin alone or photodynamic priming to target platinum resistance

Resistance to platinum-based chemotherapies remains a significant challenge in advanced-stage high-grade serous ovarian carcinoma, and patients with malignant ascites face the poorest outcomes. It is, therefore, important to understand the effects of ascites, including the associated fluid shear stress (FSS), on phenotypic changes and therapy response, specifically FSS-induced chemotherapy resistance and the underlying mechanisms in ovarian cancer. This study investigated the effects of FSS on response to cisplatin, a platinum-based chemotherapy, and doxorubicin, an anthracycline, both of which are commonly used to manage advanced-stage ovarian cancer. Consistent with prior research, OVCAR-3 and Caov-3 cells cultivated under FSS demonstrated significant resistance to cisplatin. Examination of the role of mitochondria revealed an increase in mitochondrial DNA copy number and intracellular ATP content in cultures grown under FSS, suggesting that changes in mitochondria number and metabolic activity may contribute to platinum resistance. Interestingly, no resistance to doxorubicin was observed under FSS, the first such observation of a lack of resistance under these conditions. Finally, this study demonstrated the potential of photodynamic priming using benzoporphyrin derivative, a clinically approved photosensitizer that localizes in part to mitochondria and endoplasmic reticula, to enhance the efficacy of cisplatin, but not doxorubicin, thereby overcoming FSS-induced platinum resistance.

Insights into the mechanobiology of cancer metastasis via microfluidic technologies

During cancer metastasis, cancer cells will encounter various microenvironments with diverse physical characteristics. Changes in these physical characteristics such as tension, stiffness, viscosity, compression, and fluid shear can generate biomechanical cues that affect cancer cells, dynamically influencing numerous pathophysiological mechanisms. For example, a dense extracellular matrix drives cancer cells to reorganize their cytoskeleton structures, facilitating confined migration, while this dense and restricted space also acts as a physical barrier that potentially results in nuclear rupture. Identifying these pathophysiological processes and understanding their underlying mechanobiological mechanisms can aid in the development of more effective therapeutics targeted to cancer metastasis. In this review, we outline the advances of engineering microfluidic devices in vitro and their role in replicating tumor microenvironment to mimic in vivo settings. We highlight the potential cellular mechanisms that mediate their ability to adapt to different microenvironments. Meanwhile, we also discuss some important mechanical cues that still remain challenging to replicate in current microfluidic devices in future direction. While much remains to be explored about cancer mechanobiology, we believe the developments of microfluidic devices will reveal how these physical cues impact the behaviors of cancer cells. It will be crucial in the understanding of cancer metastasis, and potentially contributing to better drug development and cancer therapy.

Fluid shear stress enhances natural killer cell's cytotoxicity toward circulating tumor cells through NKG2D-mediated mechanosensing

Tumor cells metastasize to distant organs mainly via hematogenous dissemination, in which circulating tumor cells (CTCs) are relatively vulnerable, and eliminating these cells has great potential to prevent metastasis. In vasculature, natural killer (NK) cells are the major effector lymphocytes for efficient killing of CTCs under fluid shear stress (FSS), which is an important mechanical cue in tumor metastasis. However, the influence of FSS on the cytotoxicity of NK cells against CTCs remains elusive. We report that the death rate of CTCs under both NK cells and FSS is much higher than the combined death induced by either NK cells or FSS, suggesting that FSS may enhance NK cell's cytotoxicity. This death increment is elicited by shear-induced NK activation and granzyme B entry into target cells rather than the death ligand TRAIL or secreted cytokines TNF-α and IFN-γ. When NK cells form conjugates with CTCs or adhere to MICA-coated substrates, NK cell activating receptor NKG2D can directly sense FSS to induce NK activation and degranulation. These findings reveal the promotive effect of FSS on NK cell's cytotoxicity toward CTCs, thus providing new insight into immune surveillance of CTCs within circulation.

Tumor stromal topography promotes chemoresistance in migrating breast cancer cell clusters

Multicellular clustering provides cancer cells with survival advantages and facilitates metastasis. At the tumor migration front, cancer cell clusters are surrounded by an aligned stromal topography. It remains unknown whether aligned stromal topography regulates the resistance of migrating cancer cell clusters to therapeutics. Using a hybrid nanopatterned model to characterize breast cancer cell clusters at the migration front with aligned stromal topography, we demonstrate that topography-induced migrating cancer cell clusters exhibit upregulated cytochrome P450 family 1 (CYP1) drug metabolism and downregulated glycolysis gene signatures, which correlates with unfavorable prognosis. Screening on approved oncology drugs shows that cancer cell clusters on aligned stromal topography are more resistant to diverse chemotherapeutics. Full-dose drug testings further indicate that topography induces drug resistance of hormone receptor-positive breast cancer cell clusters to doxorubicin and tamoxifen and triple-negative breast cancer cell clusters to doxorubicin by activating the aryl hydrocarbon receptor (AhR)/CYP1 pathways. Inhibiting the AhR/CYP1 pathway restores reactive oxygen species-mediated drug sensitivity to migrating cancer cell clusters, suggesting a plausible therapeutic direction for preventing metastatic recurrence.

Fluid shear stress enhances proliferation of breast cancer cells via downregulation of the c-subunit of the F1FO ATP synthase

The presence of circulating cancer cells in the bloodstream is positively correlated with metastasis. We hypothesize that fluid shear stress (FSS) occurring during circulation alters mitochondrial function, enhancing metastatic behaviors of cancer cells. MCF7 and MDA-MB-231 human breast cancer cells subjected to FSS exponentially increased proliferation. Notably, FSS-treated cells consumed more oxygen but were resistant to uncoupler-mediated ATP loss. We found that exposure to FSS downregulated the F1FO ATP synthase c-subunit and overexpression of the c-subunit arrested cancer cell migration. Approaches that regulate c-subunit abundance may reduce the likelihood of breast cancer metastasis.

Fluid shear stress in a logarithmic microfluidic device enhances cancer cell stemness marker expression

Fluid shear stress (FSS) is crucial in cancer cell survival and tumor development. Noteworthily, cancer cells are exposed to several degrees of FSS in the tumor microenvironment and during metastasis. Consequently, the stemness marker expression in cancer cells changes with the FSS signal, although it is unclear how it varies with different magnitudes and during metastasis. The current work explores the stemness and drug resistance characteristics of the cervical cancer cell line HeLa in a microfluidic device with a wide range of physiological FSS. Hence, the microfluidic device was designed to achieve a logarithmic flow distribution in four culture chambers, realizing four orders of biological shear stress on a single chip. The cell cycle analysis demonstrated altered cell proliferation and mitotic arrest after FSS treatment. In addition, EdU staining revealed increased cell proliferation with medium to low FSS, whereas high shear had a suppressing effect. FSS increased competence to withstand higher intracellular ROS and mitochondrial membrane potential in HeLa. Furthermore, stemness-related gene (Sox2, N-cadherin) and cell surface marker (CD44, CD33, CD117) expressions were enhanced by FSS mechanotransduction in a magnitude-dependent manner. In summary, these stemness-like properties were concurrent with the drug resistance capability of HeLa towards doxorubicin. Overall, our microfluidic device elucidates cancer cell survival and drug resistance mechanisms during metastasis and in cancer relapse patients.

3D Breast Tumor Models for Radiobiology Applications

Breast cancer is a leading cause of cancer-associated death in women. The clinical management of breast cancers is normally carried out using a combination of chemotherapy, surgery and radiation therapy. The majority of research investigating breast cancer therapy until now has mainly utilized two-dimensional (2D) in vitro cultures or murine models of disease. However, there has been significant uptake of three-dimensional (3D) in vitro models by cancer researchers over the past decade, highlighting a complimentary model for studies of radiotherapy, especially in conjunction with chemotherapy. In this review, we underline the effects of radiation therapy on normal and malignant breast cells and tissues, and explore the emerging opportunities that pre-clinical 3D models offer in improving our understanding of this treatment modality.

Relationship between Stemness, Reactive Oxygen Species, and Epithelial-to-Mesenchymal Transition in Model Circulating Tumor Cells

Most cancer deaths are caused by secondary metastasized tumors. The cells that spread these tumors are known as circulating tumor cells (CTCs). They exist in a dynamic environment, including exposure to fluid shear stress (FSS) that makes them susceptible to reactive oxygen species (ROS) generation. There are questions about the similarities of CTCs to cancer stem cells (CSCs) and whether the stem cell-like characteristics of CTCs allow them to proliferate and spread despite the biophysical obstacles during the metastatic process. One of those qualities is the ability to undergo the epithelial-to-mesenchymal transition (EMT). Here, MDA-MB-231 and MCF7 were modeled as CTCs by prolonged exposure to FSS using a spinner flask. They were tested for ROS generation, CSC, EMT, and Hippo pathway gene and protein markers using qRT-PCR and flow cytometry. MDA-MB-231 did not show significant changes in CSC markers, but did show significant changes in ROS, EMT, and Hippo markers (p < 0.05). Similarly, MCF7 showed significant changes in ROS and EMT markers (p < 0.05). Furthermore, both cell lines demonstrated the reverse mesenchymal-to-epithelial transition signature when allowed to recover after FSS. These results suggest that the degree of their stemness or aggressiveness affects their responses to externally applied biophysical forces and demonstrates a potential link between mechanotransduction, the Hippo pathway, and the induction of EMT in breast cancer cells.

The Role of Microenvironmental Cues and Mechanical Loading Milieus in Breast Cancer Cell Progression and Metastasis

Cancer can disrupt the microenvironments and mechanical homeostatic actions in multiple scales from large tissue modification to altered cellular signaling pathway in mechanotransduction. In this review, we highlight recent progresses in breast cancer cell mechanobiology focusing on cell-microenvironment interaction and mechanical loading regulation of cells. First, the effects of microenvironmental cues on breast cancer cell progression and metastasis will be reviewed with respect to substrate stiffness, chemical/topographic substrate patterning, and 2D vs. 3D cultures. Then, the role of mechanical loading situations such as tensile stretch, compression, and flow-induced shear will be discussed in relation to breast cancer cell mechanobiology and metastasis prevention. Ultimately, the substrate microenvironment and mechanical signal will work together to control cancer cell progression and metastasis. The discussions on breast cancer cell responsiveness to mechanical signals, from static substrate and dynamic loading, and the mechanotransduction pathways involved will facilitate interdisciplinary knowledge transfer, enabling further insights into prognostic markers, mechanically mediated metastasis pathways for therapeutic targets, and model systems required to advance cancer mechanobiology.

Microfluidic Systems with Embedded Cell Culture Chambers for High-Throughput Biological Assays

The ability to generate chemical and mechanical gradients on chips is important for either creating biomimetic designs or enabling high-throughput assays. However, there is still a significant knowledge gap in the generation of mechanical and chemical gradients in a single device. In this study, we developed gradient-generating microfluidic circuits with integrated microchambers to allow cell culture and to introduce chemical and mechanical gradients to cultured cells. A chemical gradient is generated across the microchambers, exposing cells to a uniform concentration of drugs. The embedded microchamber also produces a mechanical gradient in the form of varied shear stresses induced upon cells among different chambers as well as within the same chamber. Cells seeded within the chambers remain viable and show a normal morphology throughout the culture time. To validate the effect of different drug concentrations and shear stresses, doxorubicin is flowed into chambers seeded with skin cancer cells at different flow rates (from 0 to 0.2 μL/min). The experimental results show that increasing doxorubicin concentration (from 0 to 30 μg/mL) within chambers not only prohibits cell growth but also induces cell death. In addition, the increased shear stress (0.005 Pa) at high flow rates poses a synergistic effect on cell viability by inducing cell damage and detachment. Moreover, the ability of the device to seed cells in a 3D microenvironment was also examined and confirmed. Collectively, the study demonstrates the potential of microchamber-embedded microfluidic gradient generators in 3D cell culture and high-throughput drug screening.

Cellular Mechanisms of Circulating Tumor Cells During Breast Cancer Metastasis

Circulating tumor cells (CTCs) are cancer cells that detach from the primary site and travel in the blood stream. A higher number of CTCs increases the risk of breast cancer metastasis, and it is inversely associated with the survival rates of patients with breast cancer. Although the numbers of CTCs are generally low and the majority of CTCs die in circulation, the survival of a few CTCs can seed the development of a tumor at a secondary location. An increasing number of studies demonstrate that CTCs undergo modification in response to the dynamic biophysical environment in the blood due in part to fluid shear stress. Fluid shear stress generates reactive oxygen species (ROS), triggers redox-sensitive cell signaling, and alters the function of intracellular organelles. In particular, the mitochondrion is an important target organelle in determining the metastatic phenotype of CTCs. In healthy cells, mitochondria produce adenosine triphosphate (ATP) via oxidative phosphorylation in the electron transport chain, and during oxidative phosphorylation, they produce physiological levels of ROS. Mitochondria also govern death mechanisms such as apoptosis and mitochondrial permeability transition pore opening to, in order eliminate unwanted or damaged cells. However, in cancer cells, mitochondria are dysregulated, causing aberrant energy metabolism, redox homeostasis, and cell death pathways that may favor cancer invasiveness. In this review, we discuss the influence of fluid shear stress on CTCs with an emphasis on breast cancer pathology, then discuss alterations of cellular mechanisms that may increase the metastatic potentials of CTCs.