Reshaping in vitro Models of Breast Tissue: Integration of Stromal and Parenchymal Compartments in 3D Printed Hydrogels

An integrative alginate-based 3D in vitro model to explore epithelial-stromal cell dynamics in the breast tumor microenvironment

The tumor microenvironment (TME) orchestrates cellular and extracellular matrix (ECM) interactions, playing a key role in tumorigenesis, tumor growth, and metastization. Investigating the interplay between stromal-epithelial cells within the TME is paramount for understanding cancer mechanisms but demands reliable biological models. 3D-models have emerged as powerful in vitro tools, but many fall short in replicating cell-cell/cell-matrix interactions. This study introduces a novel hybrid 3D-model of the breast TME, combining epithelial cells, cancer-associated fibroblasts (CAFs), and their ECM. To build the stromal compartment, porous 3D-printed alginate scaffolds were seeded with CAFs, which proliferated and produced ECM. The pores were infused with oxidized peptide-modified alginate hydrogel laden with MCF10A cells, forming the parenchymal compartment. The hybrid system supported epithelial morphogenesis into acini surrounded by fibroblasts and ECM, and could be readily solubilized to recover cells, their matrix, and sequestered soluble factors. Proteome profiling of the retrieved ECM showed upregulation of proteins associated with matrix assembly/remodeling, epithelial-to-mesenchymal transition (EMT), and cancer. The TME-like microenvironment induced a partial EMT in MCF10A cells, generating a hybrid population with epithelial and mesenchymal features, characteristic of aggressive phenotypes. Our model provided new insights into epithelial-stromal interactions within the TME, offering a valuable tool for cancer research in a physiologically-relevant 3D setting.

Visible light photo-crosslinking of biomimetic gelatin-hyaluronic acid hydrogels for adipose tissue engineering

Tissue engineering (TE) of adipose tissue (AT) is a promising strategy that can provide 3D constructs to be used for in vitro modelling, overcoming the limitations of 2D cell cultures by closely replicating the complex breast tissue extracellular matrix (ECM), cell-cell, and cell-ECM interactions. However, the challenge in developing 3D constructs of AT resides in designing artificial matrices that can mimic the structural properties of native AT and support adipocytes biological functions. Herein, we developed photocrosslinkable hydrogels by employing gelatin methacrylate (GelMA) and hyaluronic acid methacrylate (HAMA) to mimic the collagenous and glycosaminoglycan components of AT microenvironment, respectively. The physico-mechanical properties of the hydrogels were tuned to target AT biomimetic properties by varying the hydrogel formulation (with or without hyaluronic acid), and the amount of photoinitiator (ruthenium/sodium persulfate) used to crosslink the hydrogels via visible light. The physical and mechanical properties of the developed hydrogels were tuned by varying the material formulation and the photoinitiator concentration. Preadipocytes were encapsulated inside the hydrogels and differentiated into mature adipocytes. Findings enlightened that HAMA addition in hybrid hydrogels boosted an increased lipid accumulation. The engineered biomimetic adipocyte-based constructs resulted promising as scaffolds or 3D in vitro models of AT.

Tunable Hybrid Hydrogels of Alginate and Cell-Derived dECM to Study the Impact of Matrix Alterations on Epithelial-to-Mesenchymal Transition

Epithelial-to-mesenchymal transition (EMT) is crucial for tumor progression, being linked to alterations in the extracellular matrix (ECM). Understanding the ECM's role in EMT can uncover new therapeutic targets, yet replicating these interactions in vitro remains challenging. It is shown that hybrid hydrogels of alginate (ALG) and cell-derived decellularized ECM (dECM), with independently tunable composition and stiffness, are useful 3D-models to explore the impact of the breast tumor matrix on EMT. Soft RGD-ALG hydrogels (200 Pa), used as neutral bulk material, supported mammary epithelial cells morphogenesis without spontaneous EMT, allowing to define the gene, protein, and biochemical profiles of cells at different TGFβ1-induced EMT states. To mimic the breast tumor composition, dECM from TGFβ1-activated fibroblasts (adECM) are generated, which shows upregulation of tumor-associated proteins compared to ndECM from normal fibroblasts. Using hybrid adECM-ALG hydrogels, it is shown that the presence of adECM induces partial EMT in normal epithelial cells, and amplifes TGF-β1 effects compared to ALG and ndECM-ALG. Increasing the hydrogel stiffness to tumor-like levels (2.5 kPa) have a synergistic effect, promoting a more evident EMT. These findings shed light on the complex interplay between matrix composition and stiffness in EMT, underscoring the utility of dECM-ALG hydrogels as a valuable in vitro platform for cancer research.

In situ crosslinkable multi-functional and cell-responsive alginate 3D matrix via thiol-maleimide click chemistry

In vivo, cells interact with the extracellular matrix (ECM), which provides a multitude of biophysical and biochemical signals that modulate cellular behavior. Inspired by this, we explored a new methodology to develop a more physiomimetic polysaccharide-based matrix for 3D cell culture. Maleimide-modified alginate (AlgM) derivatives were successfully synthesized using DMTMM to activate carboxylic groups. Thiol-terminated cell-adhesion peptides were tethered to the hydrogel network to promote integrin binding. Rapid and efficient in situ hydrogel formation was promoted by thiol-Michael addition "click" chemistry via maleimide reaction with thiol-flanked protease-sensitive peptides. Alginate derivatives were further ionically crosslinked by divalent ions present in the medium, which led to greater stability and allowed longer cell culture periods. By tailoring alginate's biofunctionality we improved cell-cell and cell-matrix interactions, providing an ECM-like 3D microenvironment. We were able to systematically and independently vary biochemical and biophysical parameters to elicit specific cell responses, creating custom-made 3D matrices. DMTMM-mediated maleimide incorporation is a promising approach to synthesizing AlgM derivatives that can be leveraged to produce ECM-like matrices for a broad range of applications, from in vitro tissue modeling to tissue regeneration.

Optimising a self-assembling peptide hydrogel as a Matrigel alternative for 3-dimensional mammary epithelial cell culture

Three-dimensional (3D) organoid models have been instrumental in understanding molecular mechanisms responsible for many cellular processes and diseases. However, established organic biomaterial scaffolds used for 3D hydrogel cultures, such as Matrigel, are biochemically complex and display significant batch variability, limiting reproducibility in experiments. Recently, there has been significant progress in the development of synthetic hydrogels for in vitro cell culture that are reproducible, mechanically tuneable, and biocompatible. Self-assembling peptide hydrogels (SAPHs) are synthetic biomaterials that can be engineered to be compatible with 3D cell culture. Here we investigate the ability of PeptiGel® SAPHs to model the mammary epithelial cell (MEC) microenvironment in vitro. The positively charged PeptiGel®Alpha4 supported MEC viability, but did not promote formation of polarised acini. Modifying the stiffness of PeptiGel® Alpha4 stimulated changes in MEC viability and changes in protein expression associated with altered MEC function, but did not fully recapitulate the morphologies of MECs grown in Matrigel. To supply the appropriate biochemical signals for MEC organoids, we supplemented PeptiGels® with laminin. Laminin was found to require negatively charged PeptiGel® Alpha7 for functionality, but was then able to provide appropriate signals for correct MEC polarisation and expression of characteristic proteins. Thus, optimisation of SAPH composition and mechanics allows tuning to support tissue-specific organoids.

Recent progress of mechanosensitive mechanism on breast cancer

The mechanical environment is important for tumorigenesis and progression. Tumor cells can sense mechanical signals by mechanosensitive receptors, and these mechanical signals can be converted to biochemical signals to regulate cell behaviors, such as cell differentiation, proliferation, migration, apoptosis, and drug resistance. Here, we summarized the effects of the mechanical microenvironment on breast cancer cell activity, and mechanotransduction mechanism from cellular microenvironment to cell membrane, and finally to the nucleus, and also relative mechanosensitive proteins, ion channels, and signaling pathways were elaborated, therefore the mechanical signal could be transduced to biochemical or molecular signal. Meanwhile, the mechanical models commonly used for biomechanics study in vitro and some quantitative descriptions were listed. It provided an essential theoretical basis for the occurrence and development of mechanosensitive breast cancer, and also some potential drug targets were proposed to treat such disease.

Mimicking the Natural Basement Membrane for Advanced Tissue Engineering

Advancements in the field of tissue engineering have led to the elucidation of physical and chemical characteristics of physiological basement membranes (BM) as specialized forms of the extracellular matrix. Efforts to recapitulate the intricate structure and biological composition of the BM have encountered various advancements due to its impact on cell fate, function, and regulation. More attention has been paid to synthesizing biocompatible and biofunctional fibrillar scaffolds that closely mimic the natural BM. Specific modifications in biomimetic BM have paved the way for the development of in vitro models like alveolar-capillary barrier, airway models, skin, blood-brain barrier, kidney barrier, and metastatic models, which can be used for personalized drug screening, understanding physiological and pathological pathways, and tissue implants. In this Review, we focus on the structure, composition, and functions of in vivo BM and the ongoing efforts to mimic it synthetically. Light has been shed on the advantages and limitations of various forms of biomimetic BM scaffolds including porous polymeric membranes, hydrogels, and electrospun membranes This Review further elaborates and justifies the significance of BM mimics in tissue engineering, in particular in the development of in vitro organ model systems.

Photothermal hydrogel platform for prevention of post-surgical tumor recurrence and improving breast reconstruction

Background

As one of the leading threats for health among women worldwide, breast cancer has high morbidity and mortality. Surgical resection is the major clinical intervention for primary breast tumor, nevertheless high local recurrence risk and breast tissue defect remain two main clinical dilemmas, seriously affecting survival and quality of life of patients.

Experimental

We developed a thermoresponsive and injectable hybrid hydrogel platform (IR820/Mgel) by integration of co-loaded porous microspheres (MPs) and IR820 for preventing postoperative recurrence of breast cancer via photothermal therapy and promoting subsequent breast reconstruction.

Results

Our results suggested that IR820/Mgel could quickly heated to more than 50.0 ℃ under NIR irradiation, enabling killing effect on 4T1 cells in vitro and prevention effect on post-surgical tumor recurrence in vivo. In addition, the hydrogel platform was promising for its minimal invasion and capability of filling irregularly shaped defects after surgery, and the encapsulated MPs could help to increase the strength of gel to realize a long-term in situ function in vivo, and promoted the attachment and anchorage property of normal breast cells and adipose stem cells.

Conclusions

This photothermal hydrogel platform provides a practice paradigm for preventing locally recurrence of breast cancer and a potential option for reconstruction of breast defects.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01041-w.

Engineering a Vascularized 3D Hybrid System to Model Tumor-Stroma Interactions in Breast Cancer

The stromal microenvironment of breast tumors, namely the vasculature, has a key role in tumor development and metastatic spread. Tumor angiogenesis is a coordinated process, requiring the cooperation of cancer cells, stromal cells, such as fibroblasts and endothelial cells, secreted factors and the extracellular matrix (ECM). In vitro models capable of capturing such complex environment are still scarce, but are pivotal to improve success rates in drug development and screening. To address this challenge, we developed a hybrid alginate-based 3D system, combining hydrogel-embedded mammary epithelial cells (parenchymal compartment) with a porous scaffold co-seeded with fibroblasts and endothelial cells (vascularized stromal compartment). For the stromal compartment, we used porous alginate scaffolds produced by freeze-drying with particle leaching, a simple, low-cost and non-toxic approach that provided storable ready-to-use scaffolds fitting the wells of standard 96-well plates. Co-seeded endothelial cells and fibroblasts were able to adhere to the surface, spread and organize into tubular-like structures. For the parenchymal compartment, a designed alginate gel precursor solution load with mammary epithelial cells was added to the pores of pre-vascularized scaffolds, forming a hydrogel in situ by ionic crosslinking. The 3D hybrid system supports epithelial morphogenesis in organoids/tumoroids and endothelial tubulogenesis, allowing heterotypic cell-cell and cell-ECM interactions, while presenting excellent experimental tractability for whole-mount confocal microscopy, histology and mild cell recovery for down-stream analysis. It thus provides a unique 3D in vitro platform to dissect epithelial-stromal interactions and tumor angiogenesis, which may assist in the development of selective and more effective anticancer therapies.

Engineering a Chemically Defined Hydrogel Bioink for Direct Bioprinting of Microvasculature

Vascularizing printed tissues is a critical challenge in bioprinting. While protein-based hydrogel bioinks have been successfully used to bioprint microvasculature, their compositions are ill-defined and subject to batch variation. Few studies have focused on engineering proangiogenic bioinks with defined properties to direct endogenous microvascular network formation after printing. Here, a peptide-functionalized alginate hydrogel bioink with defined mechanical, rheological, and biochemical properties is developed for direct bioprinting of microvascularized tissues. An integrin-binding peptide (RGD) and a vascular endothelial growth factor-mimetic peptide with a protease-sensitive linker are conjugated onto a biodegradable alginate to synergistically promote vascular morphogenesis and capillary-scale endothelial tube formation. Partial ionic crosslinking before printing converts the otherwise unprintable hydrogel into a viscoelastic bioink with excellent printability and cytocompatibility. We use the bioink to fabricate a compartmentalized vascularized tissue construct, wherein we observe pericyte-endothelial cell colocalization and angiogenic sprouting across a tissue interface, accompanied by deposition of fibronectin and collagen in vascular and tissue components, respectively. This study provides a tunable and translational "off-the-shelf" hydrogel bioink with defined composition for vascularized bioprinting.

3D Bioprinting of In Vitro Models Using Hydrogel-Based Bioinks

Coronavirus disease 2019 (COVID-19), which has recently emerged as a global pandemic, has caused a serious economic crisis due to the social disconnection and physical distancing in human society. To rapidly respond to the emergence of new diseases, a reliable in vitro model needs to be established expeditiously for the identification of appropriate therapeutic agents. Such models can be of great help in validating the pathological behavior of pathogens and therapeutic agents. Recently, in vitro models representing human organs and tissues and biological functions have been developed based on high-precision 3D bioprinting. In this paper, we delineate an in-depth assessment of the recently developed 3D bioprinting technology and bioinks. In particular, we discuss the latest achievements and future aspects of the use of 3D bioprinting for in vitro modeling.