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Cell migration is a method that plays an important role in wound healing, cell differentiation, embryonic development, etc.

Breast cancer is a heterogeneous cancer, and it has been distinguished into four subtypes: luminal A, luminal B, HER2-positive and basal-like. Molecular mutations, epigenetic alterations, hormone exposure and immune microenvironment are related to the progression of breast cancer.

Apoptosis, also called programmed cell death, is generally characterized by distinct morphological characteristics.

TUNEL staining detects DNA strand breaks by using terminal deoxynucleotidyl transferase to add labeled nucleotides to exposed 3′-OH DNA termini, generating either microscopic staining in fixed cells or tissue sections, or fluorescence/cytometric signal in cell suspensions. TUNEL positivity reflects DNA fragmentation but should not be interpreted alone as definitive apoptosis, because TUNEL can also label necrotic, autolytic, mechanically damaged, or DNA-repair-associated DNA breaks.

Flow cytometric DNA-content cell-cycle staining measures the fluorescence intensity of DNA-bound fluorochromes in single cells or nuclei to estimate DNA content distributions, allowing assignment of populations to G0/G1, S, and G2/M phases by DNA histogram deconvolution. Propidium iodide (PI) intercalates into DNA, and PI fluorescence is proportional to cellular DNA content when staining is performed under conditions that make DNA accessible and minimize non-DNA signal. Cells with G2/M DNA content are expected to show approximately twice the fluorescence intensity of G0/G1 cells, while S-phase cells occupy intermediate fluorescence values. PI-based DNA-content analysis can also detect cells with fractional DNA content, often reported as sub-G1, when DNA fragmentation and extraction during staining reduce retained DNA signal in apoptotic cells. DAPI is an alternative DNA fluorochrome for univariate DNA-content analysis, while bivariate approaches combining DNA content with proliferation

The chemotaxis gradient chamber assay is based on the principle of observing directional cell migration in response to a stable, linear or quasi-linear concentration gradient of a chemoattractant formed between two fluid reservoirs separated by a narrow observation chamber. Cells placed within the chamber respond to the gradient by polarized movement toward higher chemoattractant concentrations, allowing quantification of chemotactic behavior in real time under microscopy. The classic Zigmond chamber design enables simultaneous visualization of gradient formation and individual cell trajectories, making it suitable for studying leukocyte chemotaxis and other motile cell types in vitro.

The under-agarose cell migration assay is a classical in vitro chemotaxis method designed to evaluate directed cell movement through a semi-solid agarose matrix toward soluble chemoattractant gradients, enabling visualization and quantification of leukocyte or motile cell migration in a confined 2D-like environment. In this system, cells and chemoattractants are placed in separate wells cut into an agarose gel, allowing diffusion-driven gradient formation that guides directional migration, which is typically assessed by measuring migration distance, cell morphology changes, and accumulation toward the chemoattractant source. This assay has been widely used to study neutrophil and leukocyte chemotaxis as a simple alternative to filter-based migration systems and allows direct microscopic observation of migrating cells under near-physiological confinement conditions.

The Transwell/Boyden chamber migration assay measures cell movement through a porous membrane separating an upper and lower chamber, usually after a chemoattractant gradient is established by placing cells in the upper chamber and chemoattractant-containing medium in the lower chamber. The readout is generated by quantifying cells that traverse the membrane and appear on the lower membrane surface or in the lower chamber, depending on whether the cell type is adherent or non-adherent. This assay reflects chemotactic or haptotactic migration rather than matrix invasion unless an extracellular-matrix barrier is added to the membrane.

Apoptosis is a regulated, generally non-lytic cell-death pathway that removes unwanted, damaged, infected, or abnormal cells through coordinated morphological changes, caspase activation, DNA fragmentation, and membrane remodeling. The intrinsic apoptosis pathway is controlled mainly by mitochondrial outer membrane permeabilization, BCL-2 family proteins, cytochrome c release, apoptosome formation, caspase-9 activation, and downstream executioner caspase-3/7 activation. The extrinsic apoptosis pathway is initiated by death receptors such as Fas, TNFR, and TRAIL receptors, which recruit adaptor proteins and activate caspase-8 before engaging executioner caspases or mitochondrial amplification through BID cleavage. Apoptosis is linked to many phenotypes, including cancer cell killing, tissue homeostasis, immune regulation, neurodegeneration, infection response, and treatment-induced cytotoxicity; unresolved questions include how apoptosis interacts with necroptosis, pyroptosis, ferroptos

The 3D collagen/hydrogel matrix migration assay is based on embedding cells within or on top of a fibrillar collagen type I-rich three-dimensional matrix to model in vivo-like extracellular matrix (ECM) architecture, enabling analysis of cell migration through a physically and biochemically relevant scaffold. In contrast to 2D migration systems, cells in 3D matrices interact with fibrillar collagen networks, requiring coordinated adhesion remodeling and proteolytic or non-proteolytic deformation mechanisms to move through confined spaces, thereby providing a more physiologically relevant readout of invasive and migratory behavior in tissue-like environments. Cell movement in 3D collagen matrices is typically quantified by tracking single-cell trajectories, invasion depth, or matrix penetration over time, reflecting combined effects of cytoskeletal dynamics, cell-ECM adhesion turnover, and ECM remodeling. These systems are widely used to study tumor cell invasion and stromal cell motili

Cell invasion is the ability of cells to migrate from one area to another via the extracellular matrix. Cell invasion is the response of normal and cancer cells to chemical and mechanical stimuli. Before migrating to a new region, the extracellular matrix is degraded by proteases within the cell. Cell invasion often occurs during wound repair, vascularization and inflammation, abnormal tissue invasion, and tumor cell metastasis.

The Cell-Exclusion Zone (CEZ) migration assay is an in vitro 2D cell migration method in which a defined cell-free area is created using removable physical barriers such as silicone stoppers, allowing cells to be seeded around the barrier and subsequently migrate into the cleared zone after barrier removal. This approach enables quantification of collective cell migration by monitoring repopulation of the initially cell-free region over time using microscopy-based imaging. Compared with scratch-based wound healing assays, barrier-based exclusion methods are designed to avoid mechanical damage to the extracellular matrix and reduce injury-induced effects on boundary cells, thereby improving interpretability of migration behavior in vitro. The assay readout is typically the progressive reduction in the cell-free area or the number of cells invading the exclusion zone, reflecting coordinated cell motility relevant to physiological processes such as wound healing, epithelial repair, and ca

Chemotaxis gradient chamber assays measure directional cell migration in response to a soluble chemical gradient by imaging cells as they move across a defined observation region; the readout is generated from time-lapse cell trajectories, displacement toward the gradient, forward migration index, trajectory plots, rose/polar plots, and statistical tests of non-random directionality. The Dunn chamber is a direct-viewing glass chamber in which cells migrate across a bridge between control and chemoattractant wells, allowing observation of cells in a linear concentration gradient; related direct-viewing formats include the Insall chamber, which supports defined unidirectional gradients and high numerical-aperture microscopy, and the μ-Slide Chemotaxis chamber, which supports long-term live-cell imaging and gradient characterization with fluorescent dye.

The scratch/wound-healing migration assay measures collective migration of adherent cells into an experimentally created cell-free gap in a confluent monolayer. The readout is generated by imaging the gap immediately after scratching and at later time points, then quantifying reduction in wound area, wound width, or percentage closure as cells move into the denuded region. Gap closure reflects cell migration but may also include cell proliferation, so interpretation should distinguish migration-focused conditions from proliferation-driven closure when possible, such as by using short assay windows, serum-controlled conditions, cell counting, or proliferation controls reported in published protocols.

Annexin V-based apoptosis assays rely on the detection of phosphatidylserine (PS) externalization from the inner leaflet of the plasma membrane to the outer leaflet, an early biochemical hallmark of apoptosis. Fluorescently labeled Annexin V binds PS in a calcium-dependent manner, enabling identification of early apoptotic cells by flow cytometry or fluorescence microscopy. When combined with a membrane-impermeant DNA-binding dye (e. g. , propidium iodide), this approach allows discrimination between viable (Annexin V−/dye−), early apoptotic (Annexin V+/dye−), and late apoptotic or necrotic (Annexin V+/dye+) cell populations by assessing membrane integrity and PS exposure.

Bromodeoxyuridine (BrdU) incorporation assay is based on the principle that BrdU, a thymidine analog, is incorporated into newly synthesized DNA during the S phase of the cell cycle, thereby serving as a marker of DNA replication and cellular proliferation. Incorporated BrdU can be detected using anti-BrdU antibodies following DNA denaturation, enabling visualization or quantification of proliferating cells through immunochemical detection methods such as immunofluorescence or immunohistochemistry.

Neural crest (NC) and neuronal cell migration explant assays are in vitro systems in which neural tube-derived tissues are cultured to allow premigratory or newly emigrated neural crest cells to undergo epithelial-to-mesenchymal transition (EMT), migrate away from the explant, and form a measurable radial outgrowth that reflects migratory capacity and environmental responsiveness. These assays typically quantify migration by measuring the expansion of cell outgrowth from neural tube or neural plate border explants over time, often comparing early and later timepoints to derive a migration index such as a radius ratio, which reflects net cell dispersal from the explant core. Neural tube explant cultures preserve key aspects of neural crest behavior, including EMT, migration, and early differentiation, making them suitable for assessing intrinsic migratory ability and extrinsic cue dependence. However, studies emphasize that migratory outgrowth from neural tube explants may include non-n

Patient-derived orthotopic xenograft (PDOX) modeling implants fresh patient tumor tissue or patient-derived tumor cells into the anatomically corresponding organ or tissue site of immunodeficient mice, usually by surgical orthotopic implantation, to preserve patient tumor histology, local microenvironmental context, invasion, metastatic behavior, and treatment-response features better than subcutaneous implantation. PDOX readouts include tumor engraftment, orthotopic tumor growth, local invasion, metastasis, recurrence after resection, histologic similarity to the donor tumor, biomarker retention, molecular concordance, survival, and response or resistance to therapy. PDOX models are used for preclinical drug testing and individualized therapy evaluation, but engraftment success varies by tumor type and specimen quality.

Cell-cycle analysis by flow cytometry measures DNA content in single cells to estimate the fraction of cells in G0/G1, S, and G2/M phases. Propidium iodide intercalates into DNA, and after RNA removal with RNase, fluorescence intensity reflects cellular DNA content: 2N cells are assigned to G0/G1, cells between 2N and 4N to S phase, and 4N cells to G2/M. DNA-content analysis alone cannot reliably separate G0 from G1 or G2 from M. Ki-67 can distinguish quiescent G0 cells from cycling cells, EdU or BrdU incorporation marks active DNA synthesis in S phase, and phospho-histone H3 staining identifies mitotic cells within the 4N population.

The following protocol uses the MTT colorimetric assay as a classic literature-established method for assessing cell viability/metabolic activity in cultured mammalian cells. MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] is reduced by metabolically active cells to a colored formazan product; the amount of formazan is quantified spectrophotometrically and provides an indirect measure of metabolically active viable cells. Importantly, MTT reduction reflects cellular oxidoreductase/metabolic activity rather than an absolute direct count of living cells, so changes in cellular metabolism can alter the signal independently of cell number.

Patient-derived xenograft (PDX) models are generated by engrafting primary human tumor tissue directly into immunodeficient mice, allowing in vivo propagation of patient tumor biology without initial in vitro adaptation. These models are used to preserve key histopathological and molecular characteristics of the original tumor and enable assessment of tumor growth dynamics and therapeutic response in a living organism. The biological readout is tumor engraftment and subsequent growth in the murine host, which reflects the ability of human tumor cells to survive, vascularize, and expand in an immunocompromised microenvironment.

Splenic and portal-vein liver metastasis xenograft models deliver tumor cells into the portal circulation so that cells reach the liver first and form hepatic metastatic lesions; splenic injection uses the spleen as an access route to the portal system, while direct portal-vein injection introduces cells into the portal vein without requiring splenectomy. The assay detects liver colonization, intrahepatic tumor growth, tumor distribution, treatment response, survival, and liver-metastasis microenvironment changes; readouts include bioluminescence or fluorescence imaging, gross liver nodule counts, liver weight or tumor burden, histology, and survival.

Subcutaneous cell-line-derived xenograft (CDX) models are established by implanting cultured human cancer cell lines into immunodeficient mice, where the injected cells form localized tumors that can be monitored in vivo as a measure of tumorigenic potential, growth kinetics, and treatment response. These models are widely used in oncology research because they allow reproducible tumor formation and enable comparative assessment of tumor growth between different cell lines or genetic manipulations in a controlled in vivo microenvironment. Subcutaneous implantation of cancer cells in immunodeficient mice is a standard approach for evaluating tumor growth behavior and therapeutic response across multiple cancer types, including prostate, esophageal, pancreatic, and colon cancer models.

Orthotopic cell-line xenograft models involve implantation of human cancer cell lines into the anatomically corresponding organ of immunodeficient mice to reproduce tumor growth within a native microenvironment, enabling more clinically relevant tumor behavior compared with subcutaneous models. These models are widely used because orthotopic placement better recapitulates tumor progression, including invasion and metastatic spread, which are often underrepresented in heterotopic implantation systems. Compared with conventional xenografts, orthotopic implantation is described as more technically complex but provides improved simulation of tumor-microenvironment interactions and metastatic behavior, making it particularly valuable for translational oncology research. Surgical orthotopic implantation approaches have been emphasized as enabling faithful reproduction of clinical cancer features, including metastasis and disease progression patterns that align with the tumor’s organ of origi

Intraperitoneal (IP) or peritoneal dissemination xenograft models are based on the introduction of human cancer cells into the peritoneal cavity of immunodeficient mice, where they attach to peritoneal surfaces, form multicellular aggregates or spheroids, and progressively generate disseminated tumor nodules that mimic advanced peritoneal metastatic disease. These models are widely used to study ovarian cancer progression, tumor-microenvironment interactions, and intraperitoneal therapeutic responses, often incorporating bioluminescence or fluorescence imaging to longitudinally monitor tumor burden in vivo. The biological principle relies on the capacity of tumor cells such as SKOV3 or related ovarian carcinoma lines to survive in suspension, aggregate within ascites-like fluid, adhere to mesothelial surfaces, and invade peritoneal organs, thereby recapitulating human peritoneal carcinomatosis patterns observed in advanced disease.