Gradient-sized control of tumor spheroids on a single chip

Size and shape control of microgel-encapsulating tumor spheroid via a user-friendly solenoid valve-based sorter and its application on precise drug testing

The precision of previous cancer research based on tumor spheroids, especially the microgel-encapsulating tumor spheroids, was limited by the high heterogeneity in the tumor spheroid size and shape. Here, we reported a user-friendly solenoid valve-based sorter to reduce this heterogeneity. The artificial intelligence algorithm was employed to detect and segmentate the tumor spheroids in real-time for the size and shape calculation. A simple off-chip solenoid valve-based sorting actuation module was proposed to sort out target tumor spheroids with the desired size and shape. Utilizing the developed sorter, we successfully uncovered the drug response variations on cisplatin of lung tumor spheroids in the same population but with different sizes and shapes. Moreover, with this sorter, the precision of drug testing on the spheroid population level was improved to a level comparable to the precise but complex single spheroid analysis. The developed sorter also exhibits significant potential for organoid morphology and sorting for precision medicine research.

Reconfigurable Hanging Drop Microarray Platform for On-Demand Preparation and Analysis of Spheroid Array

In response to the increasing demand for spheroid-based cancer research, the importance of developing integrated platforms that can simultaneously facilitate high-throughput spheroid production and multiplexed analysis is emphasized. In addition, the understanding of how the size and cellular composition of tumors directly influence their internal structures and functionalities underlines the critical need to produce spheroids of diverse sizes and compositions on a large scale. To address this rising demand, this work presents a configurable and linkable in vitro three-dimensional (3D) cell culture kit (CLiCK) for spheroids, termed CLiCK-Spheroid. This platform consists of three primary components: a hanging drop microarray (HDMA), a concave pillar microarray (CPMA), and gradient blocks. The HDMA alone produces a homogeneous spheroid array, while its combination with the gradient block enables one-step generation of a size-gradient spheroid array. Using the size-gradient spheroid arrays, the occurrence of necrotic cores based on spheroid size is demonstrated. Additionally, spheroids in a single batch can be conveniently compartmentalized and regrouped using a CPMA, enhancing the versatility of spheroid arrays and enabling multiplexed drug treatments. By combining the different assembly methods, this work has achieved high-throughput production of cell composition-gradient spheroid arrays, with noticeable variations in morphology and vascularization based on cell compositions.

Compressible Hollow Microlasers in Organoids for High-Throughput and Real-Time Mechanical Screening

Mechanical stress within organoids is a pivotal indicator in disease modeling and pharmacokinetics, yet current tools lack the ability to rapidly and dynamically screen these mechanics. Here, we introduce biocompatible and compressible hollow microlasers that realize all-optical assessment of cellular stress within organoids. The laser spectroscopy yields identification of cellular deformation at the nanometer scale, corresponding to tens of pascals stress sensitivity. The compressibility enables the investigation of the isotropic component, which is the fundamental mechanics of multicellular models. By integrating with a microwell array, we demonstrate the high-throughput screening of mechanical cues in tumoroids, establishing a platform for mechano-responsive drug screening. Furthermore, we showcase the monitoring and mapping of dynamic contractile stress within human embryonic stem cell-derived cardiac organoids, revealing the internal mechanical inhomogeneity within a single organoid. This method eliminates time-consuming scanning and sample damage, providing insights into organoid mechanobiology.

3D stem-like spheroids-on-a-chip for personalized combinatorial drug testing in oral cancer

BACKGROUND

Functional drug testing (FDT) with patient-derived tumor cells in microfluidic devices is gaining popularity. However, the majority of previously reported microfluidic devices for FDT were limited by at least one of these factors: lengthy fabrication procedures, absence of tumor progenitor cells, lack of clinical correlation, and mono-drug therapy testing. Furthermore, personalized microfluidic models based on spheroids derived from oral cancer patients remain to be thoroughly validated. Overcoming the limitations, we develop 3D printed mold-based, dynamic, and personalized oral stem-like spheroids-on-a-chip, featuring unique serpentine loops and flat-bottom microwells arrangement.

RESULTS

This unique arrangement enables the screening of seven combinations of three drugs on chemoresistive cancer stem-like cells. Oral cancer patients-derived stem-like spheroids (CD 44+) remains highly viable (> 90%) for 5 days. Treatment with a well-known oral cancer chemotherapy regimen (paclitaxel, 5 fluorouracil, and cisplatin) at clinically relevant dosages results in heterogeneous drug responses in spheroids. These spheroids are derived from three oral cancer patients, each diagnosed with either well-differentiated or moderately-differentiated squamous cell carcinoma. Oral spheroids exhibit dissimilar morphology, size, and oral tumor-relevant oxygen levels (< 5% O2). These features correlate with the drug responses and clinical diagnosis from each patient's histopathological report.

CONCLUSIONS

Overall, we demonstrate the influence of tumor differentiation status on treatment responses, which has been rarely carried out in the previous reports. To the best of our knowledge, this is the first report demonstrating extensive work on development of microfluidic based oral cancer spheroid model for personalized combinatorial drug screening. Furthermore, the obtained clinical correlation of drug screening data represents a significant advancement over previously reported personalized spheroid-based microfluidic devices. Finally, the maintenance of patient-derived spheroids with high viability under oral cancer relevant oxygen levels of less than 5% O2 is a more realistic representation of solid tumor microenvironment in our developed device.

Microarray Platforms Based on 3D Printing

This paper introduces an innovative method for the fabrication and infusion of microwell arrays based on digital light processing (DLP) 3D printing. A low-cost DLP 3D printer is employed to fabricate microstructures rapidly with a broad dynamic range while maintaining high precision and fidelity. We constructed microwell arrays with varying diameters, from 200 to 2000 μm and multiple aspect ratios, in addition to microchannels with widths ranging from 45 to 1000 μm, proving the potential and flexibility of this fabrication method. The superimposition of parallel microchannels onto the microwell array, facilitated by positive or negative pressure, enabled the transfer of liquid to the microwells. Upon removal of the microchannel chip, a dispensed microdroplet array was obtained. This array can be modulated by adjusting the volume of the microwells and the inflow fluid. The filled microwell array allows chip-to-chip dispensing to the microreactor array through binding and centrifugation, facilitating multistep and multireagent assays. The 3D printing approach also enables the fabrication of intricate cavity designs, such as micropyramid arrays, which can be integrated with parallel microchannels to generate spheroid flowcells. This device demonstrated the ability to generate spheroids and manipulate their environment. We have successfully utilized precise modulation of spheroids size and performed parallel drug dose-response assays to evaluate its effectiveness. Furthermore, we managed to execute dynamic drug combinations based on a compact spheroids array, utilizing two orthogonal parallel microchannels. Our findings suggest that both the combination and temporal sequence of drug administration have a significant impact on therapeutic outcomes.

Formation and Growth of Co-Culture Tumour Spheroids: New Compartment-Based Mathematical Models and Experiments

Co-culture tumour spheroid experiments are routinely performed to investigate cancer progression and test anti-cancer therapies. Therefore, methods to quantitatively characterise and interpret co-culture spheroid growth are of great interest. However, co-culture spheroid growth is complex. Multiple biological processes occur on overlapping timescales and different cell types within the spheroid may have different characteristics, such as differing proliferation rates or responses to nutrient availability. At present there is no standard, widely-accepted mathematical model of such complex spatio-temporal growth processes. Typical approaches to analyse these experiments focus on the late-time temporal evolution of spheroid size and overlook early-time spheroid formation, spheroid structure and geometry. Here, using a range of ordinary differential equation-based mathematical models and parameter estimation, we interpret new co-culture experimental data. We provide new biological insights about spheroid formation, growth, and structure. As part of this analysis we connect Greenspan's seminal mathematical model to co-culture data for the first time. Furthermore, we generalise a class of compartment-based spheroid mathematical models that have previously been restricted to one population so they can be applied to multiple populations. As special cases of the general model, we explore multiple natural two population extensions to Greenspan's seminal model and reveal biological mechanisms that can describe the internal dynamics of growing co-culture spheroids and those that cannot. This mathematical and statistical modelling-based framework is well-suited to analyse spheroids grown with multiple different cell types and the new class of mathematical models provide opportunities for further mathematical and biological insights.

Simple droplet microfluidics platform for drug screening on cancer spheroids

3D in vitro biological systems are progressively replacing 2D systems to increase the physiological relevance of cellular studies. Microfluidics-based approaches can be powerful tools towards such biomimetic systems, but often require high-end complicated and expensive processes and equipment for microfabrication. Herein, a drug screening platform is proposed, minimizing technicality and manufacturing steps. It provides an alternate way of spheroid generation in droplets in tubes. Droplet microfluidics then elicit multiple droplets merging events at programmable times, to submit sequentially the spheroids to chemotherapy and to reagents for cytotoxicity screening. After a comprehensive study of tumorogenesis within the droplets, the system is validated for drug screening (IC50) with chemotherapies in cancer cell lines as well as cells from a patient-derived-xenografts (PDX). As compared to microtiter plates methods, our system reduces the initial number of cells up to 10 times and opens new avenues towards primary tumors drug screening approaches.

Facile construction of a 3D tumor model with multiple biomimetic characteristics using a micropatterned chip for large-scale chemotherapy investigation

The establishment and application of biomimetic preclinical tumor models for generalizable and high-throughput antitumor screening play a promising role in drug discovery and cancer therapeutics. Herein, a facile and robust microengineering-assisted methodology for highly biomimetic three-dimensional (3D) tumor construction for dynamic and large-scale antitumor investigation is developed using micropatterned array chips. The high fidelity, simplicity, and stability of chip fabrication are guaranteed by improved polydimethylsiloxane (PDMS) microcontact printing. The employment of a PDMS-micropatterned chip permits microscale, simple, biocompatible, and reproducible cell localization with quantity uniformity and 3D tumor array formation with geometric homogeneity. Array-like 3D tumor models possessing complex multilayer cell arrangements, diverse phenotypic gradients, and biochemical gradients were prepared based on the use of easy-to-operate chips. The applicability of the established biomimetic models in temporal and massive investigations of tumor responses to antitumor chemotherapy is also verified experimentally. The results support the importance of the dimensional geometry and biomimetic degree of 3D tumors when conducting antitumor screening to explore drug susceptibility and resistance. This work provides a facile and reliable strategy to perform highly biomimetic tumor manipulation and analysis, which holds great potential for applications in oncology, pharmacology, precision medicine, and tissue microengineering.

Autonomous Microlasers for Profiling Extracellular Vesicles from Cancer Spheroids

Self-propelled micro/nanomotors are emergent intelligent sensors for analyzing extracellular biomarkers in circulating biological fluids. Conventional luminescent motors are often masked by a highly dynamic and scattered environment, creating challenges to characterize biomarkers or subtle binding dynamics. Here we introduce a strategy to amplify subtle signals by coupling strong light-matter interactions on micromotors. A smart whispering-gallery-mode microlaser that can self-propel and analyze extracellular biomarkers is demonstrated through a liquid crystal microdroplet. Lasing spectral responses induced by cavity energy transfer were employed to reflect the abundance of protein biomarkers, generating exclusive molecular labels for cellular profiling of exosomes derived from 3D multicellular cancer spheroids. Finally, a microfluidic biosystem with different tumor-derived exosomes was employed to elaborate its sensing capability in complex environments. The proposed autonomous microlaser exhibits a promising method for both fundamental biological science and applications in drug screening, phenotyping, and organ-on-chip applications.

Large-scale high-throughput 3D culture, imaging, and analysis of cell spheroids using microchip-enhanced light-sheet microscopy

Light sheet microscopy combined with a microchip is an emerging tool in biomedical research that notably improves efficiency. However, microchip-enhanced light-sheet microscopy is limited by noticeable aberrations induced by the complex refractive indices in the chip. Herein, we report a droplet microchip that is specifically engineered to be capable of large-scale culture of 3D spheroids (over 600 samples per chip) and has a polymer index matched to water (difference <1%). When combined with a lab-built open-top light-sheet microscope, this microchip-enhanced microscopy technique allows 3D time-lapse imaging of the cultivated spheroids with ∼2.5-µm single-cell resolution and a high throughput of ∼120 spheroids per minute. This technique was validated by a comparative study on the proliferation and apoptosis rates of hundreds of spheroids with or without treatment with the apoptosis-inducing drug Staurosporine.

Microwell-based flow culture increases viability and restores drug response in prostate cancer spheroids

3D cancer spheroids represent a highly promising model for study of cancer progression and therapeutic development. Wide-scale adoption of cancer spheroids, however, remains a challenge due to the lack of control over hypoxic gradients that may cloud the assessment of cell morphology and drug response. Here, we present a Microwell Flow Device (MFD) that generates in-well laminar flow around 3D tissues via repetitive tissue sedimentation. Using a prostate cancer cell line, we demonstrate the spheroids in the MFD exhibit improved cell growth, reduced necrotic core formation, enhanced structural integrity, and downregulated expression of cell stress genes. The flow-cultured spheroids also exhibit an improved sensitivity to chemotherapy with greater transcriptional response. These results demonstrate how fluidic stimuli reveal the cellular phenotype previously masked by severe necrosis. Our platform advances 3D cellular models and enables study into hypoxia modulation, cancer metabolism, and drug screening within pathophysiological conditions.

Combinatorial Drug Screening Based on Massive 3D Tumor Cultures Using Micropatterned Array Chips

The establishment and application of a generalizable three-dimensional (3D) tumor device for high-throughput screening plays an important role in drug discovery and cancer therapeutics. In this study, we introduce a facile microplatform for considerable 3D tumor generation and combinatorial drug screening evaluation. High fidelity of chip fabrication was achieved depending on the simple and well-improved microcontact printing. We demonstrated the high stability and repeatability of the established tumor-on-a-chip system for controllable and massive production of 3D tumors with high size uniformity. Importantly, we accomplished the screening-like chemotherapy investigation involving individual and combinatorial drugs and validated the high accessibility and applicability of the system in 3D tumor-based manipulation and analysis on a large scale. This achievement in tumor-on-a-chip has potential applications in plenty of biomedical fields such as tumor biology, pharmacology, and tissue microengineering. It offers an insight into the development of the popularized microplatform with easy-to-fabricate and easy-to-operate properties for cancer exploration and therapy.

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.

Generation of 3D Spheroids Using a Thiol-Acrylate Hydrogel Scaffold to Study Endocrine Response in ER+ Breast Cancer

Culturing cancer cells in a three-dimensional (3D) environment better recapitulates in vivo conditions by mimicking cell-to-cell interactions and mass transfer limitations of metabolites, oxygen, and drugs. Recent drug studies have suggested that a high rate of preclinical and clinical failures results from mass transfer limitations associated with drug entry into solid tumors that 2D model systems cannot predict. Droplet microfluidic devices offer a promising alternative to grow 3D spheroids from a small number of cells to reduce intratumor heterogeneity, which is lacking in other approaches. Spheroids were generated by encapsulating cells in novel thiol–acrylate (TA) hydrogel scaffold droplets followed by on-chip isolation of single droplets in a 990- or 450-member trapping array. The TA hydrogel rapidly (∼35 min) polymerized on-chip to provide an initial scaffold to support spheroid development followed by a time-dependent degradation. Two trapping arrays were fabricated with 150 or 300 μm diameter traps to investigate the effect of droplet size and cell seeding density on spheroid formation and growth. Both trapping arrays were capable of ∼99% droplet trapping efficiency with ∼90% and 55% cellular encapsulation in trapping arrays containing 300 and 150 μm traps, respectively. The oil phase was replaced with media ∼1 h after droplet trapping to initiate long-term spheroid culturing. The growth and viability of MCF-7 3D spheroids were confirmed for 7 days under continuous media flow using a customized gravity-driven system to eliminate the need for syringe pumps. It was found that a minimum of 10 or more encapsulated cells are needed to generate a growing spheroid while fewer than 10 parent cells produced stagnant 3D spheroids. As a proof of concept, a drug susceptibility study was performed treating the spheroids with fulvestrant followed by interrogating the spheroids for proliferation in the presence of estrogen. Following fulvestrant exposure, the spheroids showed significantly less proliferation in the presence of estrogen, confirming drug efficacy.

Advanced Cellular Models for Preclinical Drug Testing: From 2D Cultures to Organ-On-A-Chip Technology

Simple Summary

Novel strategies that aim at personalizing cancer therapy are in rapid evolution. In the past decade, new methods to test for the efficacy of either standard-of-care medicines or novel targeted compounds have been implemented. In this review, we introduce the reader to experimental studies that employ patient-derived material to produce spheroids, organoids, or organs-on-a-chip as platforms that allow a more accurate representation of cancer complexity compared to bidimensional cell cultures. We discuss on the versatility and reliability of these model systems, provide evidence of their usage in drug screenings, and describe potential downfalls. The open question is whether or not tumor mimicry in vitro will be, in the near future, advanced enough to prospectively inform about treatment outcome on a certain patient.

Abstract

Cancer is a complex disease arising from a homeostatic imbalance of cell-intrinsic and microenvironment-related mechanisms. A multimodal approach to treat cancer that includes surgery, chemotherapy, and radiation therapy often fails in achieving tumor remission and produces unbearable side effects including secondary malignancies. Novel strategies have been implemented in the past decades in order to replace conventional chemotherapeutics with targeted, less toxic drugs. Up to now, scientists have relied on results achieved in animal research before proceeding to clinical trials. However, the high failure rate of targeted drugs in early phase trials leaves no doubt about the inadequacy of those models. In compliance with the need of reducing, and possibly replacing, animal research, studies have been conducted in vitro with advanced cellular models that more and more mimic the tumor in vivo. We will here review those methods that allow for the 3D reconstitution of the tumor and its microenvironment and the implementation of the organ-on-a-chip technology to study minimal organ units in disease progression. We will make specific reference to the usability of these systems as predictive cancer models and report on recent applications in high-throughput screenings of innovative and targeted drug compounds.

Miniaturized and multiplexed high-content screening of drug and immune sensitivity in a multichambered microwell chip

Here, we present a methodology based on multiplexed fluorescence screening of two- or three-dimensional cell cultures in a newly designed multichambered microwell chip, allowing direct assessment of drug or immune cell cytotoxic efficacy. We establish a framework for cell culture, formation of tumor spheroids, fluorescence labeling, and imaging of fixed or live cells at various magnifications directly in the chip together with data analysis and interpretation. The methodology is demonstrated by drug cytotoxicity screening using ovarian and non-small cell lung cancer cells and by cellular cytotoxicity screening targeting tumor spheroids of renal carcinoma and ovarian carcinoma with natural killer cells from healthy donors. The miniaturized format allowing long-term cell culture, efficient screening, and high-quality imaging of small sample volumes makes this methodology promising for individualized cytotoxicity tests for precision medicine.

Flipped Well-Plate Hanging-Drop Technique for Growing Three-Dimensional Tumors

Three-dimensional (3D) tumor culture techniques are gaining popularity as in vitro models of tumoral tissue analogues. Despite the widespread interest, need, and present-day effort, most of the 3D tumor culturing methodologies have not gone beyond the inventors’ laboratories. This, in turn, limits their applicability and standardization. In this study, we introduce a straightforward and user-friendly approach based on standard 96-well plates with basic amenities for growing 3D tumors in a scaffold-free/scaffold-based format. Hanging drop preparation can be easily employed by flipping a universal 96-well plate. The droplets of the medium generated by the well-plate flip (WPF) method can be easily modified to address various mechanisms and processes in cell biology, including cancer. To demonstrate the applicability and practicality of the conceived approach, we utilized human colorectal carcinoma cells (HCT116) to first show the generation of large scaffold-free 3D tumor spheroids over 1.5 mm in diameter in single-well plates. As a proof-of-concept, we also demonstrate matrix-assisted tumor culture techniques in advancing the broader use of 3D culture systems. The conceptualized WPF approach can be adapted for a range of applications in both basic and applied biological/engineering research.

Biophysical properties of hydrogels for mimicking tumor extracellular matrix

The extracellular matrix (ECM) is an essential component of the tumor microenvironment. It plays a critical role in regulating cell-cell and cell-matrix interactions. However, there is lack of systematic and comparative studies on different widely-used ECM mimicking hydrogels and their properties, making the selection of suitable hydrogels for mimicking different in vivo conditions quite random. This study systematically evaluates the biophysical attributes of three widely used natural hydrogels (Matrigel, collagen gel and agarose gel) including complex modulus, loss tangent, diffusive permeability and pore size. A new and facile method was developed combining Critical Point Drying, Scanning Electron Microscopy imaging and a MATLAB image processing program (CSM method) for the characterization of hydrogel microstructures. This CSM method allows accurate measurement of the hydrogel pore size down to nanometer resolution. Furthermore, a microfluidic device was implemented to measure the hydrogel permeability (P_d) as a function of particle size and gel concentration. Among the three gels, collagen gel has the lowest complex modulus, medium pore size, and the highest loss tangent. Agarose gel exhibits the highest complex modulus, the lowest loss tangent and the smallest pore size. Collagen gel and Matrigel produced complex moduli close to that estimated for cancer ECM. The P_d of these hydrogels decreases significantly with the increase of particle size. By assessing different hydrogels' biophysical characteristics, this study provides valuable insights for tailoring their properties for various three-dimensional cancer models.

An Innovative Customized Biomimetic Hydrogel for Drug Screening Application Potential: Biocompatibility and Cell Invasion Ability

The ability of Pluronic F127 (PF127) conjugated with tetrapeptide Gly-Arg-Gly-Asp (GRGD) as a sequence of Arg-Gly-Asp (RGD) peptide to form the investigated potential hydrogel (hereafter referred to as 3DG bioformer (3BE)) to produce spheroid, biocompatibility, and cell invasion ability, was assessed in this study. The fibroblast cell line (NIH 3T3), osteoblast cell line (MG-63), and human breast cancer cell line (MCF-7) were cultured in the 3BE hydrogel and commercial product (Matrigel) for comparison. The morphology of spheroid formation was evaluated via optical microscopy. The cell viability was observed through cell counting Kit-8 assay, and cell invasion was investigated via Boyden chamber assay. Analytical results indicated that 3BE exhibited lower spheroid formation than Matrigel. However, the 3BE appeared biocompatible to NIH 3T3, MG-63, and MCF-7 cells. Moreover, cell invasion ability and cell survival rate after invasion through the 3BE was displayed to be comparable to Matrigel. Thus, these findings demonstrate that the 3BE hydrogel has a great potential as an alternative to a three-dimensional cell culture for drug screening applications.

Responsive Sensors of Upconversion Nanoparticles

Upconversion nanoparticles are a class of luminescent materials that convert longer-wavelength near-infrared photons into visible and ultraviolet emissions. They can respond to various external stimuli, which underpins many opportunities for developing the next generation of sensing technologies. In this perspective, the unique stimuli-responsive properties of upconverting nanoparticles are introduced, and their recent implementations in sensing are summarized. Promising material development strategies for enhancing the key sensing merits, including intrinsic sensitivity, biocompatibility and modality, are identified and discussed. The outlooks on future technological developments, novel sensing concepts, and applications of nanoscale upconversion sensors are provided.

Advancements in 3D Cell Culture Systems for Personalizing Anti-Cancer Therapies

Over 90% of potential anti-cancer drug candidates results in translational failures in clinical trials. The main reason for this failure can be attributed to the non-accurate pre-clinical models that are being currently used for drug development and in personalised therapies. To ensure that the assessment of drug efficacy and their mechanism of action have clinical translatability, the complexity of the tumor microenvironment needs to be properly modelled. 3D culture models are emerging as a powerful research tool that recapitulates in vivo characteristics. Technological advancements in this field show promising application in improving drug discovery, pre-clinical validation, and precision medicine. In this review, we discuss the significance of the tumor microenvironment and its impact on therapy success, the current developments of 3D culture, and the opportunities that advancements that in vitro technologies can provide to improve cancer therapeutics.

From cell spheroids to vascularized cancer organoids: Microfluidic tumor-on-a-chip models for preclinical drug evaluations

Chemotherapy is one of the most effective cancer treatments. Starting from the discovery of new molecular entities, it usually takes about 10 years and 2 billion U.S. dollars to bring an effective anti-cancer drug from the benchtop to patients. Due to the physiological differences between animal models and humans, more than 90% of drug candidates failed in phase I clinical trials. Thus, a more efficient drug screening system to identify feasible compounds and pre-exclude less promising drug candidates is strongly desired. For their capability to accurately construct in vitro tumor models derived from human cells to reproduce pathological and physiological processes, microfluidic tumor chips are reliable platforms for preclinical drug screening, personalized medicine, and fundamental oncology research. This review summarizes the recent progress of the microfluidic tumor chip and highlights tumor vascularization strategies. In addition, promising imaging modalities for enhancing data acquisition and machine learning-based image analysis methods to accurately quantify the dynamics of tumor spheroids are introduced. It is believed that the microfluidic tumor chip will serve as a high-throughput, biomimetic, and multi-sensor integrated system for efficient preclinical drug evaluation in the future.

Mammary Tumor Organoid Culture in Non-Adhesive Alginate for Luminal Mechanics and High-Throughput Drug Screening

Mammary tumor organoids have become a promising in vitro model for drug screening and personalized medicine. However, the dependency on the basement membrane extract (BME) as the growth matrices limits their comprehensive application. In this work, mouse mammary tumor organoids are established by encapsulating tumor pieces in non-adhesive alginate. High-throughput generation of organoids in alginate microbeads is achieved utilizing microfluidic droplet technology. Tumor pieces within the alginate microbeads developed both luminal- and solid-like structures and displayed a high similarity to the original fresh tumor in cellular phenotypes and lineages. The mechanical forces of the luminal organoids in the alginate capsules are analyzed with the theory of the thick-wall pressure vessel (TWPV) model. The luminal pressure of the organoids increase with the lumen growth and can reach 2 kPa after two weeks' culture. Finally, the mammary tumor organoids are treated with doxorubicin and latrunculin A to evaluate their application as a drug screening platform. It is found that the drug response is related to the luminal size and pressures of organoids. This high-throughput culture for mammary tumor organoids may present a promising tool for preclinical drug target validation and personalized medicine.

Technological Advances in Tumor-On-Chip Technology: From Bench to Bedside

Simple Summary

Various 3D in vitro tumor models are rapidly advancing cancer research. Unlike animal models, they can be produced quickly and are amenable to high-throughput studies. Growing tumor spheroids in microfluidic tumor-on-chip platforms has particularly elevated the capabilities of such models. Tumor-on-chip devices can mimic multiple aspects of the dynamic in vivo tumor microenvironment in a precisely controlled manner. Moreover, new technologies for the on- and off-chip analysis of these tumor mimics are continuously emerging. There is thus an urgent need to review the latest developments in this rapidly progressing field. Here, we present an overview of the technological advances in tumor-on-chip technology by reviewing state-of-the-art tools for on-chip analysis. In particular, we evaluate the potential for tumor-on-chip technology to guide personalized cancer therapies. We strive to appeal to cancer researchers and biomedical engineers alike, informing on current progress, while provoking thought on the outstanding developments needed to achieve clinical-stage research.

Abstract

Tumor-on-chip technology has cemented its importance as an in vitro tumor model for cancer research. Its ability to recapitulate different elements of the in vivo tumor microenvironment makes it promising for translational medicine, with potential application in enabling personalized anti-cancer therapies. Here, we provide an overview of the current technological advances for tumor-on-chip generation. To further elevate the functionalities of the technology, these approaches need to be coupled with effective analysis tools. This aspect of tumor-on-chip technology is often neglected in the current literature. We address this shortcoming by reviewing state-of-the-art on-chip analysis tools for microfluidic tumor models. Lastly, we focus on the current progress in tumor-on-chip devices using patient-derived samples and evaluate their potential for clinical research and personalized medicine applications.

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 deep and permeable nanofibrous oval-shaped microwell array for the stable formation of viable and functional spheroids

Despite the potential of a nanofibrous (NF) microwell array as a permeable microwell array to improve the viability and functions of spheroids, thanks to the superior permeability to both gases and solutes, there have still been difficulties regarding the stable formation of spheroids in the NF microwell array due to the low aspect ratio (AR) and the large interspacing between microwells. This study proposes a nanofibrous oval-shaped microwell array, named the NOVA microwell array, with both a high AR and a high well density, enabling us to not only collect cells in the microwell with a high cell seeding efficiency, but also to generate multiple viable and functional spheroids in a uniform and stable manner. To realize a deep NOVA microwell array with a high aspect ratio (AR = 0.9) and a high well density (494 wells cm^-2), we developed a matched-mold thermoforming process for the fabrication of both size- and AR-controllable NOVA microwell arrays with various interspacing between microwells while maintaining the porous nature of the NF membrane. The human hepatocellular carcinoma (HepG2) cell spheroids cultured on the deep NOVA microwell array not only had uniform size and shape, with a spheroid circularity of 0.80 ± 0.03 at a cell seeding efficiency of 94.29 ± 9.55%, but also exhibited enhanced viability with a small fraction of dead cells and promoted functionality with increased albumin secretion, compared with the conventional impermeable microwell array. The superior characteristics of the deep NOVA microwell array, i.e. a high AR, a high well density, and a high permeability, pave the way to the production of various viable and functional spheroids and even organoids in a scalable manner.

A new method for the study of biophysical and morphological parameters in 3D cell cultures: Evaluation in LoVo spheroids treated with crizotinib

Three-dimensional (3D) culture systems like tumor spheroids represent useful in vitro models for drug screening and more broadly for cancer biology research, but the generation of uniform populations of spheroids remains challenging. The possibility to properly characterize spheroid properties would increase the reliability of these models. To address this issue different analysis were combined: i) a new device and relative analytical method for the accurate, simultaneous, and rapid measurement of mass density, weight, and size of spheroids, ii) confocal imaging, and iii) protein quantification, in a clinically relevant 3D model. The LoVo colon cancer cell line forming spheroids, treated with crizotinib (CZB) an ATP-competitive small-molecule inhibitor of the receptor tyrosine kinases, was employed to study and assess the correlation between biophysical and morphological parameters in both live and fixed cells. The new fluidic-based measurements allowed a robust phenotypical characterization of the spheroids structure, offering insights on the spheroids bulk and an accurate measurement of the tumor density. This analysis helps overcome the technical limits of the imaging that hardly penetrates the thickness of 3D structures. Accordingly, we were able to document that CZB treatment has an impact on mass density, which represents a key marker characterizing cancer cell treatment. Spheroid culture is the ultimate technology in drug discovery and the adoption of such precise measurement of the tumor characteristics can represent a key step forward for the accurate testing of treatment’s potential in 3D in vitro models.

A Microfluidic Multisize Spheroid Array for Multiparametric Screening of Anticancer Drugs and Blood-Brain Barrier Transport Properties

Physiological-relevant in vitro tissue models with their promise of better predictability have the potential to improve drug screening outcomes in preclinical studies. Despite the advances of spheroid models in pharmaceutical screening applications, variations in spheroid size and consequential altered cell responses often lead to nonreproducible and unpredictable results. Here, a microfluidic multisize spheroid array is established and characterized using liver, lung, colon, and skin cells as well as a triple-culture model of the blood-brain barrier (BBB) to assess the effects of spheroid size on (a) anticancer drug toxicity and (b) compound penetration across an advanced BBB model. The reproducible on-chip generation of 360 spheroids of five dimensions on a well-plate format using an integrated microlens technology is demonstrated. While spheroid size-related IC50 values vary up to 160% using the anticancer drugs cisplatin (CIS) or doxorubicin (DOX), reduced CIS:DOX drug dose combinations eliminate all lung microtumors independent of their sizes. A further application includes optimizing cell seeding ratios and size-dependent compound uptake studies in a perfused BBB model. Generally, smaller BBB-spheroids reveal an 80% higher compound penetration than larger spheroids while verifying the BBB opening effect of mannitol and a spheroid size-related modulation on paracellular transport properties.

Oncoimmunology Meets Organs-on-Chip

Oncoimmunology represents a biomedical research discipline coined to study the roles of immune system in cancer progression with the aim of discovering novel strategies to arm it against the malignancy. Infiltration of immune cells within the tumor microenvironment is an early event that results in the establishment of a dynamic cross-talk. Here, immune cells sense antigenic cues to mount a specific anti-tumor response while cancer cells emanate inhibitory signals to dampen it. Animals models have led to giant steps in this research context, and several tools to investigate the effect of immune infiltration in the tumor microenvironment are currently available. However, the use of animals represents a challenge due to ethical issues and long duration of experiments. Organs-on-chip are innovative tools not only to study how cells derived from different organs interact with each other, but also to investigate on the crosstalk between immune cells and different types of cancer cells. In this review, we describe the state-of-the-art of microfluidics and the impact of OOC in the field of oncoimmunology underlining the importance of this system in the advancements on the complexity of tumor microenvironment.

Unidirectional intercellular communication on a microfluidic chip

Cell co-culture serves as a standard method to study intercellular communication. However, random diffusion of signal molecules during co-culture may arouse crosstalk among different types of cells and hide directive signal-target responses. Here, a microfluidic chip is proposed to study unidirectional intercellular communication by spatially controlling the flow of the signal molecules. The chip contains two separated chambers connected by two channels where the culture media flows oppositely. A zigzag signal-blocking channel is designed to study the function of a specific signal. The chip is applied to study the unidirectional communication between tumor cells and stromal cells. It shows that the expression of α-smooth muscle actin (a marker of cancer-associated fibroblast (CAF)) of both MRC-5 fibroblasts and mesenchymal stem cells can be up-regulated only by the secreta from invasive MDA-MB-231 cells, but not from non-invasive MCF-7 cells. The proliferation of the tumor cells can be improved by the stromal cells. Moreover, transforming growth factor beta 1 is found as one of the main factors for CAF transformation via the signal-blocking function. The chip achieves unidirectional cell communication along X-axis, signal concentration gradient along Y-axis and 3D cell culture along Z-axis, which provides a useful tool for cell communication studies.

Fabrication of Tunable 3D Cellular Structures in High Volume Using Magnetic Levitation Guided Assembly

Tunable and reproducible size with high circularity is an important limitation to obtain three-dimensional (3D) cellular structures and spheroids in scaffold free tissue engineering approaches. Here, we present a facile methodology based on magnetic levitation (MagLev) to fabricate 3D cellular structures rapidly and easily in high-volume and low magnetic field. In this study, 3D cellular structures were fabricated using magnetic levitation directed assembly where cells are suspended and self-assembled by contactless magnetic manipulation in the presence of a paramagnetic agent. The effect of cell seeding density, culture time, and paramagnetic agent concentration on the formation of 3D cellular structures was evaluated for NIH/3T3 mouse fibroblast cells. In addition, magnetic levitation guided cellular assembly and 3D tumor spheroid formation was examined for five different cancer cell lines: MCF7 (human epithelial breast adenocarcinoma), MDA-MB-231 (human epithelial breast adenocarcinoma), SH-SY5Y (human bone-marrow neuroblastoma), PC-12 (rat adrenal gland pheochromocytoma), and HeLa (human epithelial cervix adenocarcinoma). Moreover, formation of a 3D coculture model was successfully observed by using MDA-MB-231 dsRED and MDA-MB-231 GFP cells. Taken together, these results indicate that the developed MagLev setup provides an easy and efficient way to fabricate 3D cellular structures and may be a feasible alternative to conventional methodologies for cellular/multicellular studies.

A Highly Reproducible Micro U-Well Array Plate Facilitating High-Throughput Tumor Spheroid Culture and Drug Assessment

3D multicellular tumor spheroids (MCTSs) have recently emerged as a landmark for cancer research due to their inherent traits that are physiologically relevant to primary tumor microenvironments. A facile approach-laser-ablated micro U-wells-has been widely adopted in the past decade. However, the differentiation of microwell uniformities and the construction of arrays have all remained elusive. Herein, an improved laser-ablated microwell array technique is proposed that can not only achieve arrayed MCTSs with identical sizes but can also perform high-throughput drug assessments in situ. Three critical laser ablation parameters, including frequency, duty cycle, and pulse number, are investigated to generate microwells flexibly with a range from 170 to 400 μm. The choice of microwells is optimally arranged into an array via precise control of horizontal spacing (d x) and vertical spacing (d y) amenable of cell-loss-free culture during cell seeding. Harvested T24, A549 and Huh-7 MCTSs from the microwell array correspond to approximately 75 to 140 μm in diameter. Anticancer drug screening of cisplatin validated IC50 values in 2D and MCTS conditions are 3.5 versus 9.1 μM (T24), 11.8 versus 277.7 μM (A549) and 33.5 versus 52.8 μM (Huh-7), and the permeability is measured to range from 0.042 to 0.58 μm min-1.

Spheroid Trapping and Calcium Spike Estimation Techniques toward Automation of 3D Culture

We present a spheroid trapping device, compatible with traditional tissue culture plates, to confine microtissues in a small area and allow suspension cultures to be treated like adherent cultures with minimal loss of spheroids due to aspiration. We also illustrate an automated morphology-independent procedure for cell recognition, segmentation, and a calcium spike detection technique for high-throughput analysis in 3D cultured tissue. Our cell recognition technique uses a maximum intensity projection of spatial-temporal data to create a binary mask, which delineates individual cell boundaries and extracts mean fluorescent data for each cell through a series of intensity thresholding and cluster labeling operations. The temporal data are subject to sorting for imaging artifacts, baseline correction, smoothing, and spike detection algorithms. We validated this procedure through analysis of calcium data from 2D and 3D SHSY-5Y cell cultures. Using this approach, we rapidly created regions of interest (ROIs) and extracted fluorescent intensity data from hundreds of cells in the field of view with superior data fidelity over hand-drawn ROIs even in dense (3D tissue) cell populations. We sorted data from cells with imaging artifacts (such as photo bleaching and dye saturation), classified nonfiring and firing cells, estimated the number of spikes in each cell, and documented the results, facilitating large-scale calcium imaging analysis in both 2D and 3D cultures. Since our recognition and segmentation technique is independent of morphology, our protocol provides a versatile platform for the analysis of large confocal calcium imaging data from neuronal cells, glial cells, and other cell types.