On-chip recapitulation of the tumor microenvironment: A decade of progress

One of the hurdles to the development of new anticancer therapies is the lack of in vitro models which faithfully reproduce the in vivo tumor microenvironment (TME). Understanding the dynamic relationships between the components of the TME in a controllable, scalable, and reliable setting would indeed support the discovery of biological targets impacting cancer diagnosis and therapy. Cancer research is increasingly shifting from traditional two-dimensional (2D) cell culture toward three-dimensional (3D) culture models, which have been demonstrated to increase the significance and predictive value of in vitro data. In this scenario, microphysiological systems (also known as organs-on-chip) have emerged as a relevant technological platform enabling more predictive investigation of cell-cell and cell-ECM interplay in cancer, attracting a significant research effort in the last years. This review illustrates one decade of progress in the field of tumor-microenvironment-on-chip (TMOC) approaches, exploiting either cell-laden microfluidic chambers or microfluidic confined tumor spheroids to model the TME. TMOCs have been designed to recapitulate several aspects of the TME, including tumor cells, the tumor-associated stroma, the immune system, and the vascular component. Significantly, the last aspect has emerged for its pivotal role in orchestrating cellular interactions and modulating drug pharmacokinetics on-chip. A further advancement has been represented by integration of TMOCs into multi-organ microphysiological systems, with the final aim to follow the metastatic cascade to target organs and to study the effects of chemotherapies at a systemic level. We highlight that the increased degree of complexity achieved by the most advanced TMOC models has enabled scientists to shed new light on the role of microenvironmental factors in tumor progression, metastatic cascade, and response to drugs.

Engineered 3D ex vivo models to recapitulate the complex stromal and immune interactions within the tumor microenvironment

Cancer thrives in a complex environment where interactions between cellular and acellular components, surrounding the tumor, play a crucial role in disease development and progression. Despite significant progress in cancer research, the mechanism driving tumor growth and therapeutic outcomes remains elusive. Two-dimensional (2D) cell culture assays and in vivo animal models are commonly used in cancer research and therapeutic testing. However, these models suffer from numerous shortcomings including lack of key features of the tumor microenvironment (TME) & cellular composition, cost, and ethical clearance. To that end, there is an increased interest in incorporating and elucidating the influence of TME on cancer progression. Advancements in 3D-engineered ex vivo models, leveraging biomaterials and microengineering technologies, have provided an unprecedented ability to reconstruct native-like bioengineered cancer models to study the heterotypic interactions of TME with a spatiotemporal organization. These bioengineered cancer models have shown excellent capabilities to bridge the gap between oversimplified 2D systems and animal models. In this review article, we primarily provide an overview of the immune and stromal cellular components of the TME and then discuss the latest state-of-the-art 3D-engineered ex vivo platforms aiming to recapitulate the complex TME features. The engineered TME model, discussed herein, are categorized into three main sections according to the cellular interactions within TME: (i) Tumor-Stromal interactions, (ii) Tumor-Immune interactions, and (iii) Complex TME interactions. Finally, we will conclude the article with a perspective on how these models can be instrumental for cancer translational studies and therapeutic testing.

Engineered Tumor-Immune Microenvironment On A Chip to Study T Cell-Macrophage Interaction in Breast Cancer Progression

Evolving knowledge about the tumor-immune microenvironment (TIME) is driving innovation in designing novel therapies against hard-to-treat breast cancer. Targeting the immune components of TIME has emerged as a promising approach for cancer therapy. While recent immunotherapies aim at restoring antitumor immunity, counteracting tumor escape remains challenging. Hence there is a pressing need to better understand the complex tumor-immune crosstalk within TIME. Considering this imperative, this study aims at investigating the crosstalk between the two abundant immune cell populations within the breast TIME-macrophages and T cells, in driving tumor progression using an organotypic 3D in vitro tumor-on-a-chip (TOC) model. The TOC features distinct yet interconnected organotypic tumor and stromal entities. This triculture platform mimics the complex TIME, embedding the two immune populations in a suitable 3D matrix. Analysis of invasion, morphometric measurements, and flow cytometry results underscores the substantial contribution of macrophages to tumor progression, while the presence of T cells is associated with a deceleration in the migratory behavior of both cancer cells and macrophages. Furthermore, cytokine analyses reveal significant upregulation of leptin and RANTES (regulated on activation, normal T Cell expressed and secreted) in triculture. Overall, this study highlights the complexity of TIME and the critical role of immune cells in cancer progression.

Advances in Microfluidic Technologies in Organoid Research

Organoids have emerged as major technological breakthroughs and novel organ models that have revolutionized biomedical research by recapitulating the key structural and functional complexities of their in vivo counterparts. The combination of organoid systems and microfluidic technologies has opened new frontiers in organoid engineering and offers great opportunities to address the current challenges of existing organoid systems and broaden their biomedical applications. In this review, the key features of the existing organoids, including their origins, development, design principles, and limitations, are described. Then the recent progress in integrating organoids into microfluidic systems is highlighted, involving microarrays for high-throughput organoid manipulation, microreactors for organoid hydrogel scaffold fabrication, and microfluidic chips for functional organoid culture. The opportunities in the nascent combination of organoids and microfluidics that lie ahead to accelerate research in organ development, disease studies, drug screening, and regenerative medicine are also discussed. Finally, the challenges and future perspectives in the development of advanced microfluidic platforms and modified technologies for building organoids with higher fidelity and standardization are envisioned.

3D Biomimetic Models to Reconstitute Tumor Microenvironment In Vitro: Spheroids, Organoids, and Tumor-on-a-Chip

Decades of efforts in engineering in vitro cancer models have advanced drug discovery and the insight into cancer biology. However, the establishment of preclinical models that enable fully recapitulating the tumor microenvironment remains challenging owing to its intrinsic complexity. Recent progress in engineering techniques has allowed the development of a new generation of in vitro preclinical models that can recreate complex in vivo tumor microenvironments and accurately predict drug responses, including spheroids, organoids, and tumor-on-a-chip. These biomimetic 3D tumor models are of particular interest as they pave the way for better understanding of cancer biology and accelerating the development of new anticancer therapeutics with reducing animal use. Here, the recent advances in developing these in vitro platforms for cancer modeling and preclinical drug screening, focusing on incorporating hydrogels are reviewed to reconstitute physiologically relevant microenvironments. The combination of spheroids/organoids with microfluidic technologies is also highlighted to better mimic in vivo tumors and discuss the challenges and future directions in the clinical translation of such models for drug screening and personalized medicine.

Vorinostat targets UBE2C to reverse epithelial-mesenchymal transition and control cervical cancer growth through the ubiquitination pathway

Vorinostat is a histone deacetylase inhibitor (HDACi) that was demonstrated in our previous study to inhibit the proliferation, migration, and invasion of cervical cancer cells by regulating the PI3K/Akt signaling pathway. However, the molecular mechanism of vorinostat in cervical cancer treatment remains to be further elucidated. A nude mouse xenograft model was established to analyze the antitumor effect of vorinostat in vivo. The combination of iTRAQ-based proteomics and parallel reaction monitoring (PRM) technology has proven to be an efficient and reliable method to identify potential targets for cancer chemotherapy. In this study, 254 differentially expressed proteins in vorinostat-treated cervical cancer cells, among which 180 were upregulated and 74 were downregulated, were identified by using an iTRAQ-based proteomic strategy. Subsequent bioinformatic and PRM analysis of these differentially expressed proteins indicated that UBE2C is a promising target of vorinostat in the inhibition of cervical cancer cell proliferation. We confirmed that the expression of endogenous UBE2C in cervical cancer cell lines was significantly higher than that in normal cervical epithelial cell lines. Additionally, we found that vorinostat downregulated the expression of UBE2C, SQSTM1/p62, N-cadherin, vimentin and upregulated E-cadherin in SiHa and HeLa cells. Our results also showed that vorinostat can downregulate the expression of SQSTM1/p62, N-cadherin, and vimentin during the treatment of cervical cancer cells by regulating UBE2C, while upregulating the expression of E-cadherin. In conclusion, vorinostat reverses epithelial-mesenchymal transition by targeting UBE2C and controls the proliferation of cervical cancer cells through the ubiquitination pathway. UBE2C can be used as a promising target for the development of vorinostat treatment strategies.

Microengineered 3D Tumor Models for Anti-Cancer Drug Discovery in Female-Related Cancers

The burden of cancer continues to increase in society and negatively impacts the lives of numerous patients. Due to the high cost of current treatment strategies, there is a crucial unmet need to develop inexpensive preclinical platforms to accelerate the process of anti-cancer drug discovery to improve outcomes in cancer patients, most especially in female patients. Many current methods employ expensive animal models which not only present ethical concerns but also do not often accurately predict human physiology and the outcomes of anti-cancer drug responsiveness. Conventional treatment approaches for cancer generally include systemic therapy after a surgical procedure. Although this treatment technique is effective, the outcome is not always positive due to various complex factors such as intratumor heterogeneity and confounding factors within the tumor microenvironment (TME). Patients who develop metastatic disease still have poor prognosis. To that end, recent efforts have attempted to use 3D microengineered platforms to enhance the predictive power and efficacy of anti-cancer drug screening, ultimately to develop personalized therapies. Fascinating features of microengineered assays, such as microfluidics, have led to the advancement in the development of the tumor-on-chip technology platforms, which have shown tremendous potential for meaningful and physiologically relevant anti-cancer drug discovery and screening. Three dimensional microscale models provide unprecedented ability to unveil the biological complexities of cancer and shed light into the mechanism of anti-cancer drug resistance in a timely and resource efficient manner. In this review, we discuss recent advances in the development of microengineered tumor models for anti-cancer drug discovery and screening in female-related cancers. We specifically focus on female-related cancers to draw attention to the various approaches being taken to improve the survival rate of women diagnosed with cancers caused by sex disparities. We also briefly discuss other cancer types like colon adenocarcinomas and glioblastoma due to their high rate of occurrence in females, as well as the high likelihood of sex-biased mutations which complicate current treatment strategies for women. We highlight recent advances in the development of 3D microscale platforms including 3D tumor spheroids, microfluidic platforms as well as bioprinted models, and discuss how they have been utilized to address major challenges in the process of drug discovery, such as chemoresistance, intratumor heterogeneity, drug toxicity, etc. We also present the potential of these platform technologies for use in high-throughput drug screening approaches as a replacements of conventional assays. Within each section, we will provide our perspectives on advantages of the discussed platform technologies.

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.

The role of tumor-stroma interactions on desmoplasia and tumorigenicity within a microengineered 3D platform

The tumor microenvironment has been demonstrated to play a crucial role in modulating cancer progression. Amongst various cell types within the tumor microenvironment, cancer associated fibroblasts (CAFs) are in abundance, serving to modulate the biophysical properties of the stromal matrix, through excessive deposition of extracellular matrix (ECM) proteins that leads to enhanced tumor progression. There is still a critical need to develop a fundamental framework on the role of tumor-stromal cell interactions on desmoplasia and tumorigenicity. Herein, we developed a 3D microengineered organotypic tumor-stroma model incorporated with breast cancer cells surrounded by CAF-embedded collagen matrix. We further integrated our platform with atomic force microscopy (AFM) to study the dynamic changes in stromal stiffness during active tumor invasion. Our findings primarily demonstrated enhanced tumor progression in the presence of CAFs. Furthermore, we highlighted the crucial role of crosstalk between tumor cells and CAFs on stromal desmoplasia, where we identified the role of tumor-secreted PDGF-AA/-BB on elevated matrix stiffness. Inhibition of the activity of PDGFRs in CAFs led to attenuation of stromal stiffness. Overall, our work presents a well-controlled tumor microenvironment model capable of dissecting specific biophysical and biochemical signaling cues which lead to stromal desmoplasia and tumor progression.

Application of microfluidic technology in cancer research and therapy

Cancer is a heterogeneous disease that requires a multimodal approach to diagnose, manage and treat. A better understanding of the disease biology can lead to identification of novel diagnostic/prognostic biomarkers and the discovery of the novel therapeutics with the goal of improving patient outcomes. Employing advanced technologies can facilitate this, enabling better diagnostic and treatment for cancer patients. In this regard, microfluidic technology has emerged as a promising tool in the studies of cancer, including single cancer cell analysis, modeling angiogenesis and metastasis, drug screening and liquid biopsy. Microfluidic technologies have opened new ways to study tumors in the preclinical and clinical settings. In this chapter, we highlight novel application of this technology in area of fundamental, translational and clinical cancer research.

SAHA and EGCG Promote Apoptosis in Triple-negative Breast Cancer Cells, Possibly Through the Modulation of cIAP2

BACKGROUND/AIM

Inhibition of apoptosis is one of the hallmarks of cancer, and anti-apoptotic genes are often targets of genetic and epigenetic alterations. Cellular inhibitor of apoptosis 2 (cIAP2) has a role in degrading caspases by linking them to ubiquitin molecules, and is upregulated in triple-negative breast cancer (TNBC). Previous studies have demonstrated that cIAP2 may play a role in the epithelial-to-mesenchymal transition (EMT).

MATERIALS AND METHODS

Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was administered to triple-negative breast cancer (TNBC) cells alone or in combination with epigallocatechin-3-gallate (EGCG), a DNA methyltransferase (DNMT) inhibitor isolated from green tea.

RESULTS

The compounds were able to decrease the expression of cIAP2 while increasing the expression of pro-apoptotic caspase 7. There were also changes in histone modifications, suggesting a role of epigenetic mechanisms in these changes in expression of cIAP2. These changes resulted in an increase in apoptosis. SAHA and EGCG were also capable of limiting TNBC cell migration across a fibronectin (FN) matrix.

CONCLUSION

SAHA and EGCG reduce the metastatic potential of TNBC by inducing the apoptotic pathway.

Antioxidant and anticancer activity of synthesized 4-amino-5-((aryl substituted)-4H-1,2,4-triazole-3-yl)thio-linked hydroxamic acid derivatives

OBJECTIVES

The antioxidant and anticancer activity of twelve 5-substituted-4-amino-1,2,4-triazole-linked hydroxamic acid derivatives were evaluated.

METHODS

Previously synthesized 2-((4-amino-5-substituted-4H-1,2,4-triazol-3-yl)thio)-N-hydroxyacetamide and 3-((4-amino-5-substituted-4H-1,2,4-triazol-3-yl)thio)-N-hydroxypropanamide (6a-6l) were evaluated for in vitro antioxidant and in vivo anticancer activity. MDA-MB-231, MCF-7 and HCT 116 cell lines were used to evaluate IC₅₀ values, in vitro. Ehrlich ascites carcinoma (EAC)-induced mice model was used to evaluate in vivo anticancer potential. Different biological markers were examined for drug-related toxicities.

KEY FINDINGS

Compound 6b revealed more potent antioxidant property among all tested compounds, even than the ascorbic acid. The IC₅₀ values of compound 6b were found to be 5.71 ± 2.29 μg/ml (DPPH assay) and 4.12 ± 0.5 μg/ml (ABTS assay). Histopathology of liver sections of drug-treated mice was evaluated. Survival analysis showed that compound 6b could increase the life span as of the standard drug.

CONCLUSIONS

After the assessment of all in vivo anticancer study related data, it was found that compound 6b possess superior anticancer potency in terms of efficacy and toxicity. From this experimental design, it could be concluded that further modification of this prototypical structure will lead to develop more potent antioxidant as well as an anticancer agent in the future.

A Human Organotypic Microfluidic Tumor Model Permits Investigation of the Interplay between Patient-Derived Fibroblasts and Breast Cancer Cells

Tumor-stroma interactions significantly influence cancer cell metastasis and disease progression. These interactions are partly comprised of the cross-talk between tumor and stromal fibroblasts, but the key molecular mechanisms within the cross-talk that govern cancer invasion are still unclear. Here, we adapted our previously developed microfluidic device as a 3D in vitro organotypic model to mechanistically study tumor-stroma interactions by mimicking the spatial organization of the tumor microenvironment on a chip. We cocultured breast cancer and patient-derived fibroblast cells in 3D tumor and stroma regions, respectively, and combined functional assessments, including cancer cell migration, with transcriptome profiling to unveil the molecular influence of tumor-stroma cross-talk on invasion. This led to the observation that cancer-associated fibroblasts (CAF) enhanced invasion in 3D by inducing expression of a novel gene of interest, glycoprotein nonmetastatic B (GPNMB), in breast cancer cells, resulting in increased migration speed. Importantly, knockdown of GPNMB blunted the influence of CAF on enhanced cancer invasion. Overall, these results demonstrate the ability of our model to recapitulate patient-specific tumor microenvironments to investigate the cellular and molecular consequences of tumor-stroma interactions. SIGNIFICANCE: An organotypic model of tumor-stroma interactions on a microfluidic chip reveals that CAFs promote invasion by enhancing expression of GPNMB in breast cancer cells.

The Role of Desmoplasia and Stromal Fibroblasts on Anti-cancer Drug Resistance in a Microengineered Tumor Model

Introduction

Cancer associated fibroblasts (CAFs) are known to participate in anti-cancer drug resistance by upregulating desmoplasia and pro-survival mechanisms within the tumor microenvironment. In this regard, anti-fibrotic drugs (i.e., tranilast) have been repurposed to diminish the elastic modulus of the stromal matrix and reduce tumor growth in presence of chemotherapeutics (i.e., doxorubicin). However, the quantitative assessment on impact of these stromal targeting drugs on matrix stiffness and tumor progression is still missing in the sole presence of CAFs.

Methods

We developed a high-density 3D microengineered tumor model comprised of MDA-MB-231 (highly invasive breast cancer cells) embedded microwells, surrounded by CAFs encapsulated within collagen I hydrogel. To study the influence of tranilast and doxorubicin on fibrosis, we probed the matrix using atomic force microscopy (AFM) and assessed matrix protein deposition. We further studied the combinatorial influence of the drugs on cancer cell proliferation and invasion.

Results

Our results demonstrated that the combinatorial action of tranilast and doxorubicin significantly diminished the stiffness of the stromal matrix compared to the control. The two drugs in synergy disrupted fibronectin assembly and reduced collagen fiber density. Furthermore, the combination of these drugs, condensed tumor growth and invasion.

Conclusion

In this work, we utilized a 3D microengineered model to tease apart the role of tranilast and doxorubicin in the sole presence of CAFs on desmoplasia, tumor growth and invasion. Our study lay down a ground work on better understanding of the role of biomechanical properties of the matrix on anti-cancer drug efficacy in the presence of single class of stromal cells.

A three-dimensional (3D) organotypic microfluidic model for glioma stem cells - Vascular interactions

Glioblastoma (GBM) is one of the deadliest forms of cancer. Despite many treatment options, prognosis of GBM remains dismal with a 5-year survival rate of 4.7%. Even then, tumors often recur after treatment. Tumor recurrence is hypothesized to be driven by glioma stem cell (GSC) populations which are highly tumorigenic, invasive, and resistant to several forms of therapy. GSCs are often concentrated around the tumor vasculature, referred to as the vascular niche, which are known to provide microenvironmental cues to maintain GSC stemness, promote invasion, and resistance to therapies. In this work, we developed a 3D organotypic microfluidic platform, integrated with hydrogel-based biomaterials, to mimic the GSC vascular niche and study the influence of endothelial cells (ECs) on patient-derived GSC behavior and identify signaling cues that mediate their invasion and phenotype. The established microvascular network enhanced GSC migration within a 3D hydrogel, promoted invasive morphology as well as maintained GSC proliferation rates and phenotype (Nestin, SOX2, CD44). Notably, we compared migration behavior to in vivo mice model and found similar invasive morphology suggesting that our microfluidic system could represent a physiologically relevant in vivo microenvironment. Moreover, we confirmed that CXCL12-CXCR4 signaling is involved in promoting GSC invasion in a 3D vascular microenvironment by utilizing a CXCR4 antagonist (AMD3100), while also demonstrating the effectiveness of the microfluidic as a drug screening assay. Our model presents a potential ex vivo platform for studying the interplay of GSCs with its surrounding microenvironment as well as development of future therapeutic strategies tailored toward disrupting key molecular pathways involved in GSC regulatory mechanisms.

Microfluidic Tumor-Vascular Model to Study Breast Cancer Cell Invasion and Intravasation

Cancer is a major leading cause of disease-related death in the world. The severe impact of cancer can be attributed to poor understanding of the mechanisms involved in earliest steps of the metastatic cascade, specifically invasion into the surrounding stroma and intravasation into the blood capillaries. However, conducting integrated biological studies of invasion and intravasation have been challenging, within in vivo models and traditional in vitro assay, due to difficulties in establishing a precise tumor microenvironment. To that end, in this work, a novel 3D microfluidic platform comprised of concentric three-layer cell-laden hydrogels for simultaneous investigation of breast cancer cell invasion and intravasation as well as vasculature maturation influenced by tumor-vascular crosstalk is developed. It was demonstrated that the presence of spontaneously formed vasculature enhance MDA-MB-231 invasion into the 3D stroma. Following invasion, cancer cells are visualized intravasating into the outer vasculature. Additionally, invading cancer cells significantly reduce vessel diameter while increasing permeability, consistent with previous in vivo studies. Major signaling cytokines involved in tumor-vascular crosstalk that govern cancer cell invasion and intravasation are further identified. Taken together, this platform will enable unique insights of critical biological events within the metastatic cascade, with significant potential for developing efficient cancer therapeutics.