Production of Uniform 3D Microtumors in Hydrogel Microwell Arrays for Measurement of Viability, Morphology, and Signaling Pathway Activation

[Characterization of a 3-dimensional tuberculosis spheroid model constructed using human monocytic THP-1 cells and Bacillus Calmette-Guerin]

OBJECTIVE

To establish a 3-dimensional tuberculosis spheroid model for studying the formation and characteristics of tuberculous granuloma in vivo.

METHODS

Human myeloid leukemia mononuclear THP-1 cells and Bacillus Calmette-Guerin (BCG) were mixed in a 3D cell culture plate and co-cultured in the presence of PMA for 3 days. The growth of the spheroid was examined every 24 h, and the distribution of bacteria, cell survival rate, transformation of the monocytes into macrophages, and penetration of fluorescently labeled nanoparticles into the cell spheroids and tuberculosis spheroids were observed using confocal laser scanning microscopy. The BCG and cell architecture within the 3D tuberculosis spheroid was observed using transmission electron microscopy. Image-iTTM red hypoxia probe, H2O2 test kit, and a waterproof pen PH meter were used to detect the differences in the microenvironment between BCG-infected and non-infected 3D tuberculous spheroids. The utility of this 3D tuberculous spheroids for assessing antibiotic effects of rifampicin and levofloxacin was evaluated by plate colony counting.

RESULTS

In the cell-bacterial suspensions, stable 3-D tuberculous spheroids (50-200 μm) occurred slowly, in which the cells adhered tightly with numerous bacteria in the center, and necrotic cells and monocytederived macrophages were seen within the spheroids. Drug penetration was difficult in the 3D tuberculous spheroids as compared with the non-infected cell spheroids. Transmission electron microscopy revealed the presence of cell necrosis and a large number of BCG in the macrophages in the tuberculous spheroids. The tuberculosis spheroid had a more hypoxic microenvironment than the non-infected cell spheroids with higher H2O2 content and nearly a neutral PH. The tuberculous spheroid model was capable of evaluating the efficacy of anti-tuberculosis drugs, and among them rifampicin showed a stronger antibacterial effect.

CONCLUSION

The 3-D tuberculous spheroid model established in this study provides a useful platform for studies of tuberculous granuloma.

Live Imaging of 3D Hanging Drop Arrays through Manipulation of Light-Responsive Pyroelectric Slippery Surface and Chip Adhesion

Three-dimensional (3D) hanging drop cell culture is widely used in organoid culture because of its lack of selection pressure and rapid cell aggregation. However, current hanging drop technology has limitations, such as a dependence on complex microfluidic transport channels or specific capillary force templates for drop formation, which leads to unchangeable drop features. These methods also hinder live imaging because of space and complexity constraints. Here, we have developed a hanging drop construction method and created a flexible 3D hanging drop construction platform composed of a manipulation module and an adhesion module. Their harmonious operation allows for the easy construction of hanging drops of varying sizes, types, and patterns. Our platform produces a cell hanging drop chip with small sizes and clear fields of view, thereby making it compatible with live imaging. This platform has great potential for personalized medicine, cancer and drug discovery, tissue engineering, and stem cell research.

Bioinspired mineralization of engineered living materials to promote osteogenic differentiation

In this work, Engineered Living Materials (ELMs), based on the combination of genetically-modified bacteria and mineral-reinforced organic matrices, and endowed with self-healing or regenerative properties and adaptation to specific biological environments were developed. Concretely, we produced ELMs combining human mesenchymal stem cells (hMSCs) and Lactococcus lactis (L. lactis), which was specifically programmed to deliver bone morphogenetic protein (BMP-2) upon external stimulation using nisin, into mineralized alginate matrices. The hybrid organic/inorganic matrix was built through a protocol, inspired by bone mineralization, in which alginate (Alg) assembly and apatite (HA) mineralization occurred simultaneously driven by calcium ions. Chemical composition, structure and reologhical properties of the hybrid 3D matrices were dedicately optimized prior the incorportation of the living entities. Then, the same protocol was reproduced in the presence of hMSC and engineered L. lactis that secrete BMP-2 resulting in 3D hybrid living hydrogels. hMSC viability and osteogenic differentiation in the absence and presence of the bacteria were evaluated by live/dead and quantitative real-time polymerase chain reaction (qPCR) and immunofluorescence assays, respectively. Results demonstrate that these 3D engineered living material support osteogenic differentiation of hMSCs due to the synergistic effect between HA and the growth factors BMP-2 delivered by L. lactis.

Harnessing graphene oxide nanocarriers for siRNA delivery in a 3D spheroid model of lung cancer

Gene therapy has been recently proposed as an effective strategy for cancer treatment. A significant body of literature proved the effectiveness of nanocarriers to deliver therapeutic agents to 2D tumour models, which are simple but not always representative of the in vivo reality. In this study, we analyze the efficiency of 3D spheroids combined with a minimally modified graphene oxide (GO)-based nanocarrier for siRNA delivery as a new system for cell transfection. Small interfering RNA (siRNA) targeting cluster of differentiation 47 (CD47; CD47_siRNA) was used as an anti-tumour therapeutic agent to silence the genes expressing CD47. This is a surface marker able to send a "don't eat me" signal to macrophages to prevent their phagocytosis. Also, we report the analysis of different GO formulations, in terms of size (small: about 100 nm; large: >650 nm) and functionalization (unmodified or modified with polyethylene glycol (PEG) and the dendrimer PAMAM), aiming to establish the efficiency of unmodified GO as a nanocarrier for the transfection of A549 lung cancer spheroids. Small modified GO (smGO) showed the highest transfection efficiency values (>90%) in 3D models. Interestingly, small unmodified GO (sGO) was found to be promising for transfection, with efficiency values >80% using a higher siRNA ratio (i.e., 3 : 1). These results demonstrated the higher efficiency of spheroids compared to 2D models for transfection, and the high potential of unmodified GO to carry siRNA, providing a promising new in vitro model system for the analysis of anticancer gene therapies.

Intracellular mechanics and TBX3 expression jointly dictate the spreading mode of melanoma cells in 3D environments

Cell stiffness and T-box transcription factor 3 (TBX3) expression have been identified as biomarkers of melanoma metastasis in 2D environments. This study aimed to determine how mechanical and biochemical properties of melanoma cells change during cluster formation in 3D environments. Vertical growth phase (VGP) and metastatic (MET) melanoma cells were embedded in 3D collagen matrices of 2 and 4 mg/ml collagen concentrations, representing low and high matrix stiffness. Mitochondrial fluctuation, intracellular stiffness, and TBX3 expression were quantified before and during cluster formation. In isolated cells, mitochondrial fluctuation decreased and intracellular stiffness increased with increase in disease stage from VGP to MET and increased matrix stiffness. TBX3 was highly expressed in soft matrices but diminished in stiff matrices for VGP and MET cells. Cluster formation of VGP cells was excessive in soft matrices but limited in stiff matrices, whereas for MET cells it was limited in soft and stiff matrices. In soft matrices, VGP cells did not change the intracellular properties, whereas MET cells exhibited increased mitochondrial fluctuation and decreased TBX3 expression. In stiff matrices, mitochondrial fluctuation and TBX3 expression increased in VGP and MET, and intracellular stiffness increased in VGP but decreased in MET cells. The findings suggest that soft extracellular environments are more favourable for tumour growth, and high TBX3 levels mediate collective cell migration and tumour growth in the earlier VGP disease stage but play a lesser role in the later metastatic stage of melanoma.

Towards a New 3Rs Era in the construction of 3D cell culture models simulating tumor microenvironment

Three-dimensional cell culture technology (3DCC) sits between two-dimensional cell culture (2DCC) and animal models and is widely used in oncology research. Compared to 2DCC, 3DCC allows cells to grow in a three-dimensional space, better simulating the in vivo growth environment of tumors, including hypoxia, nutrient concentration gradients, micro angiogenesis mimicism, and the interaction between tumor cells and the tumor microenvironment matrix. 3DCC has unparalleled advantages when compared to animal models, being more controllable, operable, and convenient. This review summarizes the comparison between 2DCC and 3DCC, as well as recent advances in different methods to obtain 3D models and their respective advantages and disadvantages.

Microstructured soft devices for the growth and analysis of populations of homogenous multicellular tumor spheroids

Multicellular tumor spheroids are rapidly emerging as an improved in vitro model with respect to more traditional 2D culturing. Microwell culturing is a simple and accessible method for generating a large number of uniformly sized spheroids, but commercially available systems often do not enable researchers to perform complete culturing and analysis pipelines and the mechanical properties of their culture environment are not commonly matching those of the target tissue. We herein report a simple method to obtain custom-designed self-built microwell arrays made of polydimethylsiloxane or agarose for uniform 3D cell structure generation. Such materials can provide an environment of tunable mechanical flexibility. We developed protocols to culture a variety of cancer and non-cancer cell lines in such devices and to perform molecular and imaging characterizations of the spheroid growth, viability, and response to pharmacological treatments. Hundreds of tumor spheroids grow (in scaffolded or scaffold-free conditions) at homogeneous rates and can be harvested at will. Microscopy imaging can be performed in situ during or at the end of the culture. Fluorescence (confocal) microscopy can be performed after in situ staining while retaining the geographic arrangement of spheroids in the plate wells. This platform can enable statistically robust investigations on cancer biology and screening of drug treatments.

Three-Dimensional Human Brain Organoids to Model HIV-1 Neuropathogenesis

Studying neurological diseases have long been hampered by the lack of physiologically relevant models to resemble the complex human brain and the associated pathologies. Three-dimensional brain organoids have emerged as cutting-edge technology providing an alternative in vitro model to study healthy neural development and function as well as pathogenesis of neurological disorders and neuropathologies induced by pathogens. Nonetheless,  the absence of immune cells in current models poses a barrier to fully recapitulate brain microenvironment during the onset of HIV-1-associated neuropathogenesis. To address this and to further the brain organoid technology, we have incorporated HIV-target microglia into brain organoids, generating a complex multicellular interaction, which mimics the HIV-1-infected brain environment. Here we describe the method to generate a brain organoid consisting on neurons, astrocytes, and microglia (with and without HIV infection) that recapitulate the HIV-associated neuropathology. This model has tremendous potential to expand our knowledge on neuronal dysfunction associated with HIV-1 infection of glia.

P4HA2: A link between tumor-intrinsic hypoxia, partial EMT and collective migration

Epithelial-to-mesenchymal transition (EMT), a well-established phenomenon studied across pan-cancer types, has long been known to be a major player in driving tumor invasion and metastasis. Recent studies have highlighted the importance of partial EMT phenotypes in metastasis. Initially thought as a transitional state between epithelial and mesenchymal phenotypic states, partial EMT state is now widely recognized as a key driver of intra-tumoral heterogeneity and phenotypic plasticity, further accelerating tumor metastasis and therapeutic resistance. However, how tumor microenvironment regulates partial EMT phenotypes remains unclear. We have developed unique size-controlled three-dimensional microtumor models that recapitulate tumor-intrinsic hypoxia and the emergence of collectively migrating cells. In this study, we further interrogate these microtumor models to understand how tumor-intrinsic hypoxia regulates partial EMT and collective migration in hypoxic large microtumors fabricated from T47D breast cancer cells. We compared global gene expression profiles of hypoxic, migratory microtumors to that of non-hypoxic, non-migratory microtumors at early and late time-points. Using our microtumor models, we identified unique gene signatures for tumor-intrinsic hypoxia (early versus late), partial EMT and migration (pre-migratory versus migratory phenotype). Through differential gene expression analysis between the microtumor models with an overlap of hypoxia, partial EMT and migration signatures, we identified prolyl 4-hydroxylase subunit 2 (P4HA2), a hypoxia responsive gene, as a central regulator common to hypoxia, partial EMT and collective migration. Further, the inhibition of P4HA2 significantly blocked collective migration in hypoxic microtumors. Thus, using the integrated computational-experimental analysis, we identify the key role of P4HA2 in tumor-intrinsic hypoxia-driven partial EMT and collective migration.

Scalable Formation of Highly Viable and Functional Hepatocellular Carcinoma Spheroids in an Oxygen-Permeable Microwell Device for Anti-Tumor Drug Evaluation

For high-throughput anti-cancer drug screening, microwell arrays may serve as an effective tool to generate uniform and scalable tumor spheroids. However, microwell arrays are commonly anchored in non-oxygen-permeable culture plates, leading to limited oxygen supply for avascular spheroids. Herein, a polydimethylsiloxane (PDMS)-based oxygen-permeable microwell device is introduced for generating highly viable and functional hepatocellular carcinoma (HCC) spheroids. The PDMS sheets at the bottom of the microwell device provide a high flux of oxygen like in vivo neighboring hepatic sinusoids. Owing to the better oxygen supply, the generated HepG2 spheroids are larger in size and exhibit higher viability and proliferation with less cell apoptosis and necrosis. These spheroids also exhibit lower levels of anaerobic cellular respiration and express higher levels of liver-related functions. In anti-cancer drug testing, spheroids cultured in PDMS plates show a significantly stronger resistance against doxorubicin because of the stronger stem-cell and multidrug resistance phenotype. Moreover, higher expression of vascular endothelial growth factor-A produces a stronger angiogenesis capability of the spheroids. Overall, compared to the spheroids cultured in conventional non-oxygen-permeable plates, these spheroids can be used as a more favorable model for early-stage HCCs and be applied in high-throughput anti-cancer drug screening.

Biomimetic Hydrogels in the Study of Cancer Mechanobiology: Overview, Biomedical Applications, and Future Perspectives

Hydrogels are biocompatible polymers that are tunable to the system under study, allowing them to be widely used in medicine, bioprinting, tissue engineering, and biomechanics. Hydrogels are used to mimic the three-dimensional microenvironment of tissues, which is essential to understanding cell–cell interactions and intracellular signaling pathways (e.g., proliferation, apoptosis, growth, and survival). Emerging evidence suggests that the malignant properties of cancer cells depend on mechanical cues that arise from changes in their microenvironment. These mechanobiological cues include stiffness, shear stress, and pressure, and have an impact on cancer proliferation and invasion. The hydrogels can be tuned to simulate these mechanobiological tissue properties. Although interest in and research on the biomedical applications of hydrogels has increased in the past 25 years, there is still much to learn about the development of biomimetic hydrogels and their potential applications in biomedical and clinical settings. This review highlights the application of hydrogels in developing pre-clinical cancer models and their potential for translation to human disease with a focus on reviewing the utility of such models in studying glioblastoma progression.

Advances in the study of spheroids as versatile models to evaluate biological interactions of inorganic nanoparticles

Spheroids are in vitro three-dimensional multicellular microstructures able to mimic the biological microenvironment, including the complexity of tumor architecture. Therefore, results closer to those expected for in vivo organisms can be reached using spheroids compared to the cell culture monolayer model. Inorganic nanoparticles (NPs) have also been playing relevant roles in the comprehension of biological processes. Moreover, they have been probed as novel diagnostic and therapeutical nanosystems. In this context, in this review, we present applications, published in the last five years, which show that spheroids can be versatile models to study and evaluate biological interactions involving inorganic NPs. Applications of spheroids associated with (i) basic studies to assess the penetration profile of nanostructures, (ii) the evaluation of NP toxicity, and (iii) NP-based therapeutical approaches are described. Fundamentals of spheroids and their formation methods are also included. We hope that this review can be a reference and guide future investigations related to this interesting three-dimensional biological model, favoring advances to Nanobiotechnology.

Poly-guanidine shows high cytotoxicity in glioma cell cultures and glioma stem cells

Glioblastoma multiforme (GBM) is a malignant CNS tumor with a poor prognosis. GBM shows aberrant glycosylation with hypersialylation. This property is a potential target for therapy. This study investigates the growth inhibitory efficacy of poly-guanidine (GuaDex), with an affinity for sialic acid (Sia). Glioma cell cultures and patient-derived glioma cell lines (PDGCLs) expressing Prominin-1 (CD133) were used. Human fibroblasts and astrocyte-derived cells were used as controls. Temozolomide (standard GBM drug, TMZ) and DMSO were used as a comparison. GuaDex at 1–10 µM concentrations, were incubated for 3.5–72 h and with PDGCLs cells for 6–24 h. The cytotoxicity was estimated with a fluorometric cytotoxicity assay (FMCA). Fluorescence-labelled GuaDex was used to study the cell interactions. Sia expression was confirmed with a fluorescence labelled Sia binding lectin. Expression of glial fibrillary acidic protein was determined. GuaDex induction of growth inhibition was fast, showing after less than 5 min incubation while the control cells were not affected even after 50 min incubation. The growth inhibitory effect on PDGCLs spheroids was persistent still showing after 4 weeks post-treatment. The growth inhibition of GuaDex was induced at low µM concentrations while TMZ induced only a slight inhibition at mM concentrations. GuaDex efficacy appears significant and warrants further studies.

Detection and impact of hypoxic regions in multicellular tumor spheroid cultures formed by head and neck squamous cell carcinoma cells lines

In solid tumors like head and neck cancer (HNC), chronic and acute hypoxia have serious adverse clinical consequences including poorer overall patient prognosis, enhanced metastasis, increased genomic instability, and resistance to radiation-, chemo-, or immuno-therapies. However, cells in the two-dimensional monolayer cultures typically used for cancer drug discovery experience 20%-21% O₂ levels (normoxic) which are 4-fold higher than O₂ levels in normal tissues and ≥10-fold higher than in the hypoxic regions of solid tumors. The oxygen electrodes, exogenous bio-reductive markers, and increased expression of endogenous hypoxia-regulated proteins like HIF-1α generally used to mark hypoxic regions in solid tumors are impractical in large sample numbers and longitudinal studies. We used a novel homogeneous live-cell permeant HypoxiTRAK™ (HPTK) molecular probe compatible with high content imaging detection, analysis, and throughput to identify and quantify hypoxia levels in live HNC multicellular tumor spheroid (MCTS) cultures over time. Accumulation of fluorescence HPTK metabolite in live normoxic HNC MCTS cultures correlated with hypoxia detection by both pimonidazole and HIF-1α staining. In HNC MCTSs, hypoxic cytotoxicity ratios for the hypoxia activated prodrugs (HAP) evofosfamide and tirapazamine were much smaller than have been reported for uniformly hypoxic 2D monolayers in gas chambers, and many viable cells remained after HAP exposure. Cells in solid tumors and MCTSs experience three distinct O₂ microenvironments dictated by their distances from blood vessels or MCTS surfaces, respectively; oxic, hypoxic, or intermediate levels of hypoxia. These studies support the application of more physiologically relevant in vitro 3D models that recapitulate the heterogeneous microenvironments of solid tumors for preclinical cancer drug discovery.

Automated Assessment of Cancer Drug Efficacy On Breast Tumor Spheroids in Aggrewell™400 Plates Using Image Cytometry

Tumor spheroid models have proven useful in the study of cancer cell responses to chemotherapeutic compounds by more closely mimicking the 3-dimensional nature of tumors in situ. Their advantages are often offset, however, by protocols that are long, complicated, and expensive. Efforts continue for the development of high-throughput assays that combine the advantages of 3D models with the convenience and simplicity of traditional 2D monolayer methods. Herein, we describe the development of a breast cancer spheroid image cytometry assay using T47D cells in Aggrewell™400 spheroid plates. Using the Celigo^® automated imaging system, we developed a method to image and individually track thousands of spheroids within the Aggrewell™400 microwell plate over time. We demonstrate the use of calcein AM and propidium iodide staining to study the effects of known anti-cancer drugs Doxorubicin, Everolimus, Gemcitabine, Metformin, Paclitaxel and Tamoxifen. We use the image cytometry results to quantify the fluorescence of calcein AM and PI as well as spheroid size in a dose dependent manner for each of the drugs. We observe a dose-dependent reduction in spheroid size and find that it correlates well with the viability obtained from the CellTiter96^® endpoint assay. The image cytometry method we demonstrate is a convenient and high-throughput drug-response assay for breast cancer spheroids under 400 μm in diameter, and may lay a foundation for investigating other three-dimensional spheroids, organoids, and tissue samples.

Reproduction of the Antitumor Effect of Cisplatin and Cetuximab Using a Three-dimensional Spheroid Model in Oral Cancer

Background/Aim: Cancer research has been conducted using cultured cells as part of drug discovery testing, but conventional two-dimensional culture methods are unable to reflect the complex tumor microenvironment. On the other hand, three-dimensional cultures have recently been attracting attention as in vitro models that more closely resemble the in vivo physiological environment. The purpose of this study was to establish a 3D culture method for oral cancer and to verify its practicality. Materials and Methods: Three-dimensional cultures were performed using several oral cancer cell lines. Western blotting was used for protein expression analysis of the collected cell masses (spheroids), and H-E staining was used for structural observation. The cultures were exposed to cisplatin and cetuximab and the morphological changes of spheroids over time and the expression changes of target proteins were compared. Results: Each cell line formed spheroidal cell aggregates and showed enhancement of cell adhesion molecules over time. H-E staining showed tumor tissue-like structures specific to each cell line. Cisplatin showed concentration-dependent antitumor effects due to loss of cell adhesion and spheroid disruption in each cell line, while cetuximab exhibited antitumor effects that correlated with EGFR expression in each cell line. Conclusion: Spheroids made from oral cancer cell lines appeared to have tumor-like characteristics that may reflect their clinical significance. In the future, it may become possible to produce tumor spheroids from tissue samples of oral cancer patients, and then apply them to drug screening and to develop individualized diagnostic and treatment methods.

In Vitro Miniaturized Tuberculosis Spheroid Model

Tuberculosis (TB) is a public health concern that impacts 10 million people around the world. Current in vitro models are low throughput and/or lack caseation, which impairs drug effectiveness in humans. Here, we report the generation of THP-1 human monocyte/macrophage spheroids housing mycobacteria (TB spheroids). These TB spheroids have a central core of dead cells co-localized with mycobacteria and are hypoxic. TB spheroids exhibit higher levels of pro-inflammatory factor TNFα and growth factors G-CSF and VEGF when compared to non-infected control. TB spheroids show high levels of lipid deposition, characterized by MALDI mass spectrometry imaging. TB spheroids infected with strains of differential virulence, Mycobacterium tuberculosis (Mtb) HN878 and CDC1551 vary in response to Isoniazid and Rifampicin. Finally, we adapt the spheroid model to form peripheral blood mononuclear cells (PBMCs) and lung fibroblasts (NHLF) 3D co-cultures. These results pave the way for the development of new strategies for disease modeling and therapeutic discovery.

Quantifying nanotherapeutic penetration using a hydrogel-based microsystem as a new 3D in vitro platform

The huge gap between 2D in vitro assays used for drug screening and the in vivo 3D physiological environment hampered reliable predictions for the route and accumulation of nanotherapeutics in vivo. For such nanotherapeutics, multi-cellular tumour spheroids (MCTS) are emerging as a good alternative in vitro model. However, the classical approaches to produce MCTS suffer from low yield, slow process, difficulties in MCTS manipulation and compatibility with high-magnification fluorescence optical microscopy. On the other hand, spheroid-on-chip set-ups developed so far require a practical knowledge of microfluidics difficult to transfer to a cell biology laboratory. We present here a simple yet highly flexible 3D model microsystem consisting of agarose-based microwells. Fully compatible with the multi-well plate format conventionally used in cell biology, our simple process enables the formation of hundreds of reproducible spheroids in a single pipetting. Immunostaining and fluorescence imaging including live high-resolution optical microscopy can be performed in situ, with no manipulation of spheroids. As a proof of principle of the relevance of such an in vitro platform for nanotherapeutic evaluation, this study investigates the kinetics and localisation of nanoparticles within colorectal cancer MCTS cells (HCT-116). The nanoparticles chosen are sub-5 nm ultrasmall nanoparticles made of polysiloxane and gadolinium chelates that can be visualized in MRI (AGuIX®, currently implicated in clinical trials as effective radiosensitizers for radiotherapy) and confocal microscopy after addition of Cy5.5. We show that the amount of AGuIX® nanoparticles within cells is largely different in 2D and 3D. Using our flexible agarose-based microsystems, we are able to resolve spatially and temporally the penetration and distribution of AGuIX® nanoparticles within MCTS. The nanoparticles are first found in both extracellular and intracellular space of MCTS. While the extracellular part is washed away after a few days, we evidenced intracellular localisation of AGuIX®, mainly within the lysosomal compartment, but also occasionally within mitochondria. Hence, our agarose-based microsystem appears as a promising 3D in vitro user-friendly platform for investigation of nanotherapeutic transport, ahead of in vivo studies.

A Novel SimpleDrop Chip for 3D Spheroid Formation and Anti-Cancer Drug Assay

Cell culture is important for the rapid screening of anti-cancer drug candidates, attracting intense interest. Traditional 2D cell culture has been widely utilized in cancer biological research. However, 3D cellular spheroids are able to recapitulate the in vivo microenvironment of tissues or tumors. Thus far, several 3D cell culture methods have been developed, for instance, the hanging drop method, spinner flasks and micropatterned plates. Nevertheless, these methods have been reported to have some disadvantages, for example, medium replacement is inconvenient or causes cellular damage. Here, we report on an easy-to-operate and useful micro-hole culture chip (SimpleDrop) for 3D cellular spheroid formation and culture and drug analysis, which has advantages over the traditional method in terms of its ease of operation, lack of shear force and environmentally friendliness. On this chip, we observed the formation of a 3D spheroid clearly. Three drugs (paclitaxel, cisplatin and methotrexate) were tested by both cell viability assay and drug-induced apoptotic assay. The results show that the three drugs present a similar conclusion: cell viability decreased over time and concentration. Moreover, the apoptotic experiment showed a similar trend to the live/dead cell assay, in that the fraction of the apoptotic and necrotic cells correlated with the concentration and time. All these results prove that our SimpleDrop method is a useful and easy method for the formation of 3D cellular spheroids, which shows its potential for both cell-cell interaction research, tissue engineering and anticancer drug screening.

Identifying Molecular Signatures of Distinct Modes of Collective Migration in Response to the Microenvironment Using Three-Dimensional Breast Cancer Models

Simple Summary

The objective of this study was to investigate the role of two microenvironmental factors, namely, tumor-intrinsic hypoxia and secretome in inducing collective migration. We utilized three-dimensional (3D) discrete-sized microtumor models, which recapitulate hallmarks of transition of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC). Tumor-intrinsic hypoxia induced directional migration in large hypoxic microtumors while secretome from large microtumors induced radial migration in non-hypoxic microtumors. This highlights the emergence phenotypic heterogeneity and plasticity in cancer cells in response to different microenvironmental stimuli. To unravel mechanisms underlying these two distinct modes of migration, we performed differential gene expression analysis of hypoxia- and secretome-induced migratory phenotypes using non-migratory, non-hypoxic microtumors as controls. We proposed unique gene signature sets related to tumor-intrinsic hypoxia, hypoxia-induced epithelial-mesenchymal transition (EMT), as well as hypoxia-induced directional migration and secretome-induced radial migration.

Abstract

Collective cell migration is a key feature of transition of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) among many other cancers, yet the microenvironmental factors and underlying mechanisms that trigger collective migration remain poorly understood. Here, we investigated two microenvironmental factors, tumor-intrinsic hypoxia and tumor-secreted factors (secretome), as triggers of collective migration using three-dimensional (3D) discrete-sized microtumor models that recapitulate hallmarks of DCIS-IDC transition. Interestingly, the two factors induced two distinct modes of collective migration: directional and radial migration in the 3D microtumors generated from the same breast cancer cell line model, T47D. Without external stimulus, large (600 µm) T47D microtumors exhibited tumor-intrinsic hypoxia and directional migration, while small (150 µm), non-hypoxic microtumors exhibited radial migration only when exposed to the secretome of large microtumors. To investigate the mechanisms underlying hypoxia- and secretome-induced directional vs. radial migration modes, we performed differential gene expression analysis of hypoxia- and secretome-induced migratory microtumors compared with non-hypoxic, non-migratory small microtumors as controls. We propose unique gene signature sets related to tumor-intrinsic hypoxia, hypoxia-induced epithelial-mesenchymal transition (EMT), as well as hypoxia-induced directional migration and secretome-induced radial migration. Gene Set Enrichment Analysis (GSEA) and protein-protein interaction (PPI) network analysis revealed enrichment and potential interaction between hypoxia, EMT, and migration gene signatures for the hypoxia-induced directional migration. In contrast, hypoxia and EMT were not enriched in the secretome-induced radial migration, suggesting that complete EMT may not be required for radial migration. Survival analysis identified unique genes associated with low survival rate and poor prognosis in TCGA-breast invasive carcinoma dataset from our tumor-intrinsic hypoxia gene signature (CXCR4, FOXO3, LDH, NDRG1), hypoxia-induced EMT gene signature (EFEMP2, MGP), and directional migration gene signature (MAP3K3, PI3K3R3). NOS3 was common between hypoxia and migration gene signature. Survival analysis from secretome-induced radial migration identified ATM, KCNMA1 (hypoxia gene signature), and KLF4, IFITM1, EFNA1, TGFBR1 (migration gene signature) to be associated with poor survival rate. In conclusion, our unique 3D cultures with controlled microenvironments respond to different microenvironmental factors, tumor-intrinsic hypoxia, and secretome by adopting distinct collective migration modes and their gene expression analysis highlights the phenotypic heterogeneity and plasticity of epithelial cancer cells.

Interplay between tumor microenvironment and partial EMT as the driver of tumor progression

Epithelial-to-mesenchymal transition (EMT), an evolutionary conserved phenomenon, has been extensively studied to address the unresolved variable treatment response across therapeutic regimes in cancer subtypes. EMT has long been envisaged to regulate tumor invasion, migration, and therapeutic resistance during tumorigenesis. However, recently it has been highlighted that EMT involves an intermediate partial EMT (pEMT) phenotype, defined by incomplete loss of epithelial markers and incomplete gain of mesenchymal markers. It has been further emphasized that pEMT transition involves a spectrum of intermediate hybrid states on either side of pEMT spectrum. Emerging evidence underlines bi-directional crosstalk between tumor cells and surrounding microenvironment in acquisition of pEMT phenotype. Although much work is still ongoing to gain mechanistic insights into regulation of pEMT phenotype, it is evident that pEMT plays a critical role in tumor aggressiveness, invasion, migration, and metastasis along with therapeutic resistance. In this review, we focus on important role of tumor-intrinsic factors and tumor microenvironment in driving pEMT and emphasize that engineered controlled microenvironments are instrumental to provide mechanistic insights into pEMT biology. We also discuss the significance of pEMT in regulating hallmarks of tumor progression i.e. cell cycle regulation, collective migration, and therapeutic resistance. Although constantly evolving, current progress and momentum in the pEMT field holds promise to unravel new therapeutic targets to halt tumor progression at early stages as well as tackle the complex therapeutic resistance observed across many cancer types.

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Partial EMT phenotype drives key hallmarks of tumor progression

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Role of tumor microenvironment in pEMT phenotype via cellular signaling pathways

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Engineering 3D in vitro models to study pEMT phenotype

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Opportunities and challenges in understanding pEMT phenotype

Fabrication Method of a High-Density Co-Culture Tumor-Stroma Platform to Study Cancer Progression

Cancer has now been established as one of the most common chronic diseases due to high mortality rate. The early stage of non-invasive tumors can now be successfully treated leading to have high survival rates; however, the late stage invasive and metastatic tumors still suffer from poor treatment outcomes. Among multiple contributing factors, the role of tumor microenvironment and its complexities has been well recognized in cancer progression. Stromal cells including cancer-associated fibroblasts (CAFs), endothelial cells, adipocytes, immune cells as well as extracellular matrix (ECM) continuously interact with malignant cells and regulate various hallmarks of cancer including tumor growth, invasion, and intravasation. To better understand the role of the interaction between tumor cells and their surrounding microenvironment, numerous model systems ranging from two-dimensional (2D) assays to 3D hydrogels and in vivo murine xenografts have been utilized. While each one of these model systems exhibit certain advantages in studying biological facets of tumor progression, they are often limited to perform well-controlled mechanistic studies due to various factors including lack of tumor-stroma organotypic organization and presence of confounding biochemical and biophysical factors within the tumor microenvironment. In this regard, in the past few years, 3D in vitro microengineered model systems are becoming instrumental to precisely mimic the complexities of the native tumor microenvironment to conduct fundamental and well-designed studies for multiple purposes ranging from biological discovery to therapeutic screening. These model systems include microfluidics, micro-patterned features, and 3D organoids. In this chapter, we will outline the fabrication strategy of our microengineered 3D co-culture tumor-stromal model which comprises high-density array of tumor seeded microwells surrounded by stromal cells, such as CAFs encapsulated within collagen-based hydrogel. The developed platform provides excellent spatial organization of tumor and stromal entities with designated initial architecture and cellular positioning, therefore enabling to study the specific role of cell-cell and cell-ECM interaction on tumor proliferation/expansion, cancer cell migration as well as stromal activation. The developed platform is compatible with standard biological assays enabling gene and protein expression analyses across different types of cancer and co-culture of tumor and stromal cells.

Non-swellable F127-DA hydrogel with concave microwells for formation of uniform-sized vascular spheroids

Hydrogels with concave microwells are one of the simplest means to obtain uniform-sized cellular spheroids. However, the inherent swelling of hydrogels leads to reduced mechanical strength and thus deforms the structure of the microwells. In this study, we developed a hydrogel with microwells for formation of vascular spheroids via non-swellable di-acrylated Pluronic F127 (F127-DA), which showed higher mechanical strength than a conventional di-acrylated polyethylene glycol (PEG-DA) hydrogel. The uniform-sized vascular spheroids were spontaneously generated by human umbilical vein endothelial cells (HUVECs) and fibroblasts in the microwells. The endothelial functions of vascular spheroids were about 1-fold higher than those in two-dimensional (2D) culture, as indicated by secretion of nitric oxide (NO), prostacyclin (PGI2) and tissue factor pathway inhibitor (TFPI). Interestingly, the vascular spheroids with large diameter showed higher sensitivity to ethanol toxicity than those with small diameter, possibly due to the higher endothelial functions of large spheroids. Hence, F127-DA hydrogel with concave microwells provides a convenient way of forming uniform-sized spheroids that are useful for high throughput screening of drug/food toxicity.

Hydrogels with concave microwells are one of the simplest means to obtain uniform-sized cellular spheroids.

Three dimensional engineered models to study hypoxia biology in breast cancer

Breast cancer is the second leading cause of mortality among women worldwide. Despite the available therapeutic regimes, variable treatment response is reported among different breast cancer subtypes. Recently, the effects of the tumor microenvironment on tumor progression as well as treatment responses have been widely recognized. Hypoxia and hypoxia inducible factors in the tumor microenvironment have long been known as major players in tumor progression and survival. However, the majority of our understanding of hypoxia biology has been derived from two dimensional (2D) models. Although many hypoxia-targeted therapies have elicited promising results in vitro and in vivo, these results have not been successfully translated into clinical trials. These limitations of 2D models underscore the need to develop and integrate three dimensional (3D) models that recapitulate the complex tumor-stroma interactions in vivo. This review summarizes role of hypoxia in various hallmarks of cancer progression. We then compare traditional 2D experimental systems with novel 3D tissue-engineered models giving accounts of different bioengineering platforms available to develop 3D models and how these 3D models are being exploited to understand the role of hypoxia in breast cancer progression.

Modeling HIV-1 neuropathogenesis using three-dimensional human brain organoids (hBORGs) with HIV-1 infected microglia

HIV-1 associated neurocognitive disorder (HAND) is characterized by neuroinflammation and glial activation that, together with the release of viral proteins, trigger a pathogenic cascade resulting in synaptodendritic damage and neurodegeneration that lead to cognitive impairment. However, the molecular events underlying HIV neuropathogenesis remain elusive, mainly due to lack of brain-representative experimental systems to study HIV-CNS pathology. To fill this gap, we developed a three-dimensional (3D) human brain organoid (hBORG) model containing major cell types important for HIV-1 neuropathogenesis; neurons and astrocytes along with incorporation of HIV-infected microglia. Both infected and uninfected microglia infiltrated into hBORGs resulting in a triculture system (MG-hBORG) that mirrors the multicellular network observed in HIV-infected human brain. Moreover, the MG-hBORG model supported productive viral infection and exhibited increased inflammatory response by HIV-infected MG-hBORGs, releasing tumor necrosis factor (TNF-α) and interleukin-1 (IL-1β) and thereby mimicking the chronic neuroinflammatory environment observed in HIV-infected individuals. This model offers great promise for basic understanding of how HIV-1 infection alters the CNS compartment and induces pathological changes, paving the way for discovery of biomarkers and new therapeutic targets.

Characterization of Triple-Negative Breast Cancer MDA-MB-231 Cell Spheroid Model

Background

The tumor three-dimensional (3D) spheroid model in vitro is effective on detecting malignant cells and tumorigenesis, and assessing drug resistance. Compared with two-dimensional (2D) monolayer culture, breast cancer (BC) spheroids more accurately reflect the complex microenvironment in vivo, which have been extensively reported in BC research. MDA-MB-231 cells, the triple-negative breast cancer (TNBC) cell line, display representative epithelial to mesenchymal transition (EMT) associated with BC metastasis. However, the characterization of MDA-MB-231 spheroids has been largely unknown at present, which requires further attention.

Materials and Methods

Microwell array was conducted for the formation of MDA-MB-231 spheroids. In addition, H&E staining, immunohistochemistry (IHC), CellTiter-Glo^® 3D cell viability assay, and flow cytometry were performed to investigate the structure and growth characteristics. Besides, Transwell and scratch healing assays were carried out to detect the migratory capacities compared with 2D culture. Western blotting and confocal fluorescence were selected to detect the expression of EMT-associated proteins. Additionally, the half maximal inhibitory concentration (IC₅₀) values of antitumor compounds Carboplatin and Doxorubicin were measured to assess drug resistance.

Results

The MDA-MB-231 spheroids were viable, which maintained a compact structure with zonation features for up to 9 days. Moreover, those spheroids had a slower growth rate than those cultured as a monolayer and differential zones of proliferation. The migratory capacities were significantly enhanced by transferring the spheroids to 2D adherent culture. Compared with 2D culture, the levels of EMT-associated proteins were significantly up-regulated in spheroids. Furthermore, toxicity assessment showed that spheroids exhibited an increased resistance to the antitumor compounds.

Conclusion

This study develops the simple spheroids and demonstrates their structure, growth and proliferation characteristics. According to our results, the spheroids are associated with superior EMT and high resistance to toxicological response compared with the standard 2D monocultures.

Designer Self-Assembling Peptide Hydrogels to Engineer 3D Cell Microenvironments for Cell Constructs Formation and Precise Oncology Remodeling in Ovarian Cancer

Designer self-assembling peptides form the entangled nanofiber networks in hydrogels by ionic-complementary self-assembly. This type of hydrogel has realistic biological and physiochemical properties to serve as biomimetic extracellular matrix (ECM) for biomedical applications. The advantages and benefits are distinct from natural hydrogels and other synthetic or semisynthetic hydrogels. Designer peptides provide diverse alternatives of main building blocks to form various functional nanostructures. The entangled nanofiber networks permit essential compositional complexity and heterogeneity of engineering cell microenvironments in comparison with other hydrogels, which may reconstruct the tumor microenvironments (TMEs) in 3D cell cultures and tissue-specific modeling in vitro. Either ovarian cancer progression or recurrence and relapse are involved in the multifaceted TMEs in addition to mesothelial cells, fibroblasts, endothelial cells, pericytes, immune cells, adipocytes, and the ECM. Based on the progress in common hydrogel products, this work focuses on the diverse designer self-assembling peptide hydrogels for instructive cell constructs in tissue-specific modeling and the precise oncology remodeling for ovarian cancer, which are issued by several research aspects in a 3D context. The advantages and significance of designer peptide hydrogels are discussed, and some common approaches and coming challenges are also addressed in current complex tumor diseases.

Maximizing the Value of Cancer Drug Screening in Multicellular Tumor Spheroid Cultures: A Case Study in Five Head and Neck Squamous Cell Carcinoma Cell Lines

With approval rates <5% and the probability of success in oncology clinical trials of 3.4%, more physiologically relevant in vitro three-dimensional models are being deployed during lead generation to select better drug candidates for solid tumors. Multicellular tumor spheroids (MCTSs) resemble avascular tumor nodules, micrometastases, or the intervascular regions of large solid tumors with respect to morphology, cell-cell and cell-extracellular matrix contacts, and volume growth kinetics. MCTSs develop gradients of nutrient and oxygen concentration resulting in diverse microenvironments with differential proliferation and drug distribution zones. We produced head and neck squamous cell carcinoma (HNSCC) MCTSs in 384-well U-bottom ultra-low-attachment microtiter plates and used metabolic viability and imaging methods to measure morphologies, growth phenotypes and the effects of 19 anticancer drugs. We showed that cell viability measurements underestimated the impact of drug exposure in HNSCC MCTS cultures, but that incorporating morphology and dead-cell staining analyses increased the number of drugs judged to have substantially impacted MCTS cultures. A cumulative multiparameter drug impact score enabled us to stratify MCTS drug responses into high-, intermediate-, and low-impact tiers, and maximized the value of these more physiologically relevant tumor cultures. It is conceivable that the viable cells present in MCTS cultures after drug exposure arise from drug-resistant populations that could represent a source of drug failure and recurrence. Long-term monitoring of treated MCTS cultures could provide a strategy to determine whether these drug-resistant populations represent circumstances where tumor growth is delayed and may ultimately give rise to regrowth.

New Frontiers for Biofabrication and Bioreactor Design in Microphysiological System Development

Microphysiological systems (MPSs) have been proposed as an improved tool to recreate the complex biological features of the native niche with the goal of improving in vitro-in vivo extrapolation. In just over a decade, MPS technologies have progressed from single-tissue chips to multitissue plates with integrated pumps for perfusion. Concurrently, techniques for biofabrication of complex 3D constructs for regenerative medicine and 3D in vitro models have evolved into a diverse toolbox for micrometer-scale deposition of cells and cell-laden bioinks. However, as the complexity of biological models increases, experimental throughput is often compromised. This review discusses the existing disparity between MPS complexity and throughput, then examines an MPS-terminated biofabrication line to identify the hurdles and potential approaches to overcoming this disparity.

Targeting the Temporal Dynamics of Hypoxia-Induced Tumor-Secreted Factors Halts Tumor Migration

Targeting microenvironmental factors that foster migratory cell phenotypes is a promising strategy for halting tumor migration. However, lack of mechanistic understanding of the emergence of migratory phenotypes impedes pharmaceutical drug development. Using our three-dimensional microtumor model with tight control over tumor size, we recapitulated the tumor size-induced hypoxic microenvironment and emergence of migratory phenotypes in microtumors from epithelial breast cells and patient-derived primary metastatic breast cancer cells, mesothelioma cells, and lung cancer xenograft cells. The microtumor models from various patient-derived tumor cells and patient-derived xenograft cells revealed upregulation of tumor-secreted factors, including matrix metalloproteinase-9 (MMP9), fibronectin (FN), and soluble E-cadherin, consistent with clinically reported elevated levels of FN and MMP9 in patient breast tumors compared with healthy mammary glands. Secreted factors in the conditioned media of large microtumors induced a migratory phenotype in nonhypoxic, nonmigratory small microtumors. Subsequent mathematical analyses identified a two-stage microtumor progression and migration mechanism whereby hypoxia induces a migratory phenotype in the initialization stage, which then becomes self-sustained through a positive feedback loop established among the tumor-secreted factors. Computational and experimental studies showed that inhibition of tumor-secreted factors effectively halts microtumor migration despite tumor-to-tumor variation in migration kinetics, while inhibition of hypoxia is effective only within a time window and is compromised by tumor-to-tumor variation, supporting our notion that hypoxia initiates migratory phenotypes but does not sustain it. In summary, we show that targeting temporal dynamics of evolving microenvironments, especially tumor-secreted factors during tumor progression, can halt tumor migration. SIGNIFICANCE: This study uses state-of-the-art three-dimensional microtumor models and computational approaches to highlight the temporal dynamics of tumor-secreted microenvironmental factors in inducing tumor migration.

Preclinical Organotypic Models for the Assessment of Novel Cancer Therapeutics and Treatment

The immense costs in both financial terms and preclinical research effort that occur in the development of anticancer drugs are unfortunately not matched by a substantial increase in improved clinical therapies due to the high rate of failure during clinical trials. This may be due to issues with toxicity or lack of clinical effectiveness when the drug is evaluated in patients. Currently, much cancer research is driven by the need to develop therapies that can exploit cancer cell adaptations to conditions in the tumor microenvironment such as acidosis and hypoxia, the requirement for more-specific, targeted treatments, or the exploitation of 'precision medicine' that can target known genomic changes in patient DNA. The high attrition rate for novel anticancer therapies suggests that the preclinical methods used in screening anticancer drugs need improvement. This chapter considers the advantages and disadvantages of 3D organotypic models in both cancer research and cancer drug screening, particularly in the areas of targeted drugs and the exploitation of genomic changes that can be used for therapeutic advantage in precision medicine.

Study of diffusive- and convective-transport mediated microtumor growth in a controlled microchamber

In this paper, we report on using mass transport to control nutrition supply of colorectal cancer cells for developing a microtumor in a confined microchamber. To mimic the spatial heterogeneity of a tumor, two microfluidic configurations based on resistive circuits are designed. One has a convection-dominated microchamber to simulate the tumor region proximal to leaky blood vessels. The other has a diffusion-dominated microchamber to mimic the tumor core that lacks blood vessels and nutrient supply. Thus, the time for nutrition to fill the microchamber can vary from tens of minutes to several hours. Results show that cells cultured under a diffusive supply of nutrition have a high glycolytic rate and a nearly constant oxygen consumption rate. In contrast, cells cultured under convective supply of nutrition have a gradual increase of oxygen consumption rate with a low glycolytic rate. This suggests that cancer cells have distinct reactions under different mass transport and nutrition supply. Using these two microfluidic platforms to create different rate of nutrition supply, it is found that a continuous microtumor that almost fills the mm-size microchamber can be developed under a low-nutrient supply environment, but not for the convective condition. It also is demonstrated that microchannels can simulate the delivery of anti-cancer drugs to the microtumor under controlled mass-transport. This method provides a means to develop a larger scale microtumor in a lab-on-a-Chip system for post development and stimulations, and microchannels can be applied to control the physical and chemical environment for anti-cancer drug screening.

High Content Screening Characterization of Head and Neck Squamous Cell Carcinoma Multicellular Tumor Spheroid Cultures Generated in 384-Well Ultra-Low Attachment Plates to Screen for Better Cancer Drug Leads

Multicellular tumor spheroid (MCTS) cultures represent more physiologically relevant in vitro cell tumor models that recapitulate the microenvironments and cell-cell or cell-extracellular matrix interactions which occur in solid tumors. We characterized the morphologies, viability, and growth behaviors of MCTSs produced by 11 different head and neck squamous cell carcinoma (HNSCC) cell lines seeded into and cultured in ultra-low attachment microtiter plates (ULA-plates) over extended periods of time. HNSCC MCTS cultures developed microenvironments, which resulted in differences in proliferation rates, metabolic activity, and mitochondrial functional activity between cells located in the outer layers of the MCTS and cells in the interior. HNSCC MCTS cultures exhibited drug penetration and distribution gradients and some developed necrotic cores. Perhaps the most profound effect of culturing HNSCC cell lines in MCTS cultures was their dramatically altered and varied growth phenotypes. Instead of the exponential growth that are characteristic of two-dimensional HNSCC growth inhibition assays, some MCTS cultures displayed linear growth rates, categorized as rapid, moderate, or slow, dormant MCTSs remained viable but did not grow, and some MCTSs exhibited death phenotypes that were either progressive and slow or rapid. The ability of MCTS cultures to develop microenvironments and to display a variety of different growth phenotypes provides in vitro models that are more closely aligned with solid tumors in vivo. We anticipate that the implementation MCTS models to screen for new cancer drugs for solid tumors like HNSCC will produce leads that will translate better in in vivo animal models and patients.

Shift from stochastic to spatially-ordered expression of serine-glycine synthesis enzymes in 3D microtumors

Cell-to-cell differences in protein expression in normal tissues and tumors are a common phenomenon, but the underlying principles that govern this heterogeneity are largely unknown. Here, we show that in monolayer cancer cell-line cultures, the expression of the five metabolic enzymes of serine-glycine synthesis (SGS), including its rate-limiting enzyme, phosphoglycerate dehydrogenase (PHGDH), displays stochastic cell-to-cell variation. By contrast, in cancer cell line-derived three-dimensional (3D) microtumors PHGDH expression is restricted to the outermost part of the microtumors' outer proliferative cell layer, while the four other SGS enzymes display near uniform expression throughout the microtumor. A mathematical model suggests that metabolic stress in the microtumor core activates factors that restrict PHGDH expression. Thus, intracellular enzyme expression in growing cell ecosystems can shift to spatially ordered patterns in 3D structured environments due to emergent cell-cell communication, with potential implications for the design of effective anti-metabolic cancer therapies.

Through the Looking Glass: In Vitro Models for Inhalation Toxicology and Interindividual Variability in the Airway

With 7 million deaths reported annually from air pollution alone, it is evident that adverse effects of inhaled toxicant exposures remain a major public health concern in the 21st century. Assessment and characterization of the impacts of air pollutants on human health stems from epidemiological and clinical studies, which have linked both outdoor and indoor air contaminant exposure to adverse pulmonary and cardiovascular health outcomes. Studies in animal models support epidemiological findings and have been critical in identifying systemic effects of environmental chemicals on cognitive abilities, liver disease, and metabolic dysfunction following inhalation exposure. Likewise, traditional monoculture systems have aided in identifying biomarkers of susceptibility to inhaled toxicants and served as a screening platform for safety assessment of pulmonary toxicants. Despite their contributions, in vivo and classic in vitro models have not been able to accurately represent the heterogeneity of the human population and account for interindividual variability in response to inhaled toxicants and susceptibility to the adverse health effects. Development of new technologies that can investigate genetic predisposition, are cost and time efficient, and are ethically sound, will enhance elucidation of mechanisms of inhalation toxicity, and aid in the development of novel pharmaceuticals and/or safety evaluation. This review will describe the classic and novel cell-based inhalation toxicity models and how these emerging technologies can be incorporated into regulatory or nonregulatory testing to address interindividual variability and improve overall human health.

The Generation of Three-Dimensional Head and Neck Cancer Models for Drug Discovery in 384-Well Ultra-Low Attachment Microplates

The poor success rate of cancer drug discovery has prompted efforts to develop more physiologically relevant cellular models for early preclinical cancer lead discovery assays. For solid tumors, this would dictate the implementation of three-dimensional (3D) tumor models that more accurately recapitulate human solid tumor architecture and biology. A number of anchorage-dependent and anchorage-independent in vitro 3D cancer models have been developed together with homogeneous assay methods and high content imaging approaches to assess tumor spheroid morphology, growth, and viability. However, several significant technical challenges have restricted the implementation of some 3D models in HTS. We describe a method that uses 384-well U-bottomed ultra-low attachment (ULA) microplates to produce head and neck tumor spheroids for cancer drug discovery assays. The production of multicellular head and neck cancer spheroids in 384-well ULA-plates occurs in situ, does not impose an inordinate tissue culture burden for HTS, is readily compatible with automation and homogeneous assay detection methods, and produces high-quality uniform-sized spheroids that can be utilized in cancer drug cytotoxicity assays within days rather than weeks.

The production of 3D tumor spheroids for cancer drug discovery

New cancer drug approval rates are ≤5% despite significant investments in cancer research, drug discovery and development. One strategy to improve the rate of success of new cancer drugs transitioning into the clinic would be to more closely align the cellular models used in the early lead discovery with pre-clinical animal models and patient tumors. For solid tumors, this would mandate the development and implementation of three dimensional (3D) in vitro tumor models that more accurately recapitulate human solid tumor architecture and biology. Recent advances in tissue engineering and regenerative medicine have provided new techniques for 3D spheroid generation and a variety of in vitro 3D cancer models are being explored for cancer drug discovery. Although homogeneous assay methods and high content imaging approaches to assess tumor spheroid morphology, growth and viability have been developed, the implementation of 3D models in HTS remains challenging due to reasons that we discuss in this review. Perhaps the biggest obstacle to achieve acceptable HTS assay performance metrics occurs in 3D tumor models that produce spheroids with highly variable morphologies and/or sizes. We highlight two methods that produce uniform size-controlled 3D multicellular tumor spheroids that are compatible with cancer drug research and HTS; tumor spheroids formed in ultra-low attachment microplates, or in polyethylene glycol dimethacrylate hydrogel microwell arrays.

Hypoxic tumor microenvironment: Opportunities to develop targeted therapies

In recent years, there has been great progress in the understanding of tumor biology and its surrounding microenvironment. Solid tumors create regions with low oxygen levels, generally termed as hypoxic regions. These hypoxic areas offer a tremendous opportunity to develop targeted therapies. Hypoxia is not a random by-product of the cellular milieu due to uncontrolled tumor growth; rather it is a constantly evolving participant in overall tumor growth and fate. This article reviews current trends and recent advances in drug therapies and delivery systems targeting hypoxia in the tumor microenvironment. In the first part, we give an account of important physicochemical changes and signaling pathways activated in the hypoxic microenvironment. This is then followed by various treatment strategies including hypoxia-sensitive signaling pathways and approaches to develop hypoxia-targeted drug delivery systems.

Evaluation of assays for drug efficacy in a three-dimensional model of the lung

Background

The focus of the outlined work is the establishment of a three-dimensional lung model for various drug-screening applications.

Methods

The non-small cell lung cancer (NSCLC) cell line Colo699 was cultivated as monolayer (2D) on plates for 5 days or as microtissues (3D) using a hanging-drop system for 5 and 10 days. Cells and microtissues were treated with afatinib (10–80 µM), cisplatin (100–800 µM) or vinorelbine (25–200 µM) for 24 or 48 hours (h). Cell proliferation and viability were analysed by intra-cellular adenosine triphosphate (ATP) and lactate dehydrogenase release (LDH) assays, annexin V/propidium iodide (PI) staining, and cell cycle determination. Microtissue morphology and size, as well as cell death were evaluated via phase contrast microscopy.

Results

Our results demonstrate the valid determination of viability and cell death using established assays in the 3D system for drug testing. The comparison of ATP, LDH and cytometry data showed moderate (0.40) to very strong (0.99) correlations. Thereby, we observed partially significant differences in drug efficacy between microtissues and 2D cultures dependent from the applied treatment and read-out method. Altogether, microtissues developed resistance to cisplatin and vinorelbine; but remained more vulnerable to afatinib. These findings were confirmed with microscopy.

Conclusion

In summary, we established an NSCLC 3D test system with multiple assays compatible for drug-testing applications of substances with different mechanisms of action. In addition, our data support the usage of microtissues as more accurate tools for drug-efficacy testing with the possibility of long-term cultivation and treatment.

Electronic supplementary material

The online version of this article (doi:10.1007/s00432-016-2198-0) contains supplementary material, which is available to authorized users.

Three-Dimensional Breast Cancer Models Mimic Hallmarks of Size-Induced Tumor Progression

Tumor size is strongly correlated with breast cancer metastasis and patient survival. Increased tumor size contributes to hypoxic and metabolic gradients in the solid tumor and to an aggressive tumor phenotype. Thus, it is important to develop three-dimensional (3D) breast tumor models that recapitulate size-induced microenvironmental changes and, consequently, natural tumor progression in real time without the use of artificial culture conditions or gene manipulations. Here, we developed size-controlled multicellular aggregates ("microtumors") of subtype-specific breast cancer cells by using non-adhesive polyethylene glycol dimethacrylate hydrogel microwells of defined sizes (150-600 μm). These 3D microtumor models faithfully represent size-induced microenvironmental changes, such as hypoxic gradients, cellular heterogeneity, and spatial distribution of necrotic/proliferating cells. These microtumors acquire hallmarks of tumor progression in the same cell lines within 6 days. Of note, large microtumors of hormone receptor-positive cells exhibited an aggressive phenotype characterized by collective cell migration and upregulation of mesenchymal markers at mRNA and protein level, which was not observed in small microtumors. Interestingly, triple-negative breast cancer (TNBC) cell lines did not show size-dependent upregulation of mesenchymal markers. In conclusion, size-controlled microtumor models successfully recapitulated clinically observed positive association between tumor size and aggressive phenotype in hormone receptor-positive breast cancer while maintaining clinically proven poor correlation of tumor size with aggressive phenotype in TNBC. Such clinically relevant 3D models generated under controlled experimental conditions can serve as precise preclinical models to study mechanisms involved in breast tumor progression as well as antitumor drug effects as a function of tumor progression. Cancer Res; 76(13); 3732-43. ©2016 AACR.

Three-dimensional culture systems in cancer research: Focus on tumor spheroid model

Cancer cells propagated in three-dimensional (3D) culture systems exhibit physiologically relevant cell-cell and cell-matrix interactions, gene expression and signaling pathway profiles, heterogeneity and structural complexity that reflect in vivo tumors. In recent years, development of various 3D models has improved the study of host-tumor interaction and use of high-throughput screening platforms for anti-cancer drug discovery and development. This review attempts to summarize the various 3D culture systems, with an emphasis on the most well characterized and widely applied model - multicellular tumor spheroids. This review also highlights the various techniques to generate tumor spheroids, methods to characterize them, and its applicability in cancer research.