Three-Dimensional, Scaffolded Tumor Model to Study Cell-Driven Microenvironment Effects and Therapeutic Responses

Bioengineered Silk Protein-Based 3D In Vitro Models for Tissue Engineering and Drug Development: From Silk Matrix Properties to Biomedical Applications

3D in vitro model has emerged as a valuable tool for studying tissue development, drug screening, and disease modeling. 3D systems can accurately replicate tissue microstructures and physiological features, mirroring the in vivo microenvironment departing from conventional 2D cell cultures. Various 3D in vitro models utilizing biomacromolecules like collagen and synthetic polymers have been developed to meet diverse research needs and address the complex challenges of contemporary research. Silk proteins, bearing structural and functional similarities to collagen, have been increasingly employed to construct advanced 3D in vitro systems, surpassing the limitations of 2D cultures. This review examines silk proteins' composition, structure, properties, and functions, elucidating their role in 3D in vitro models. Furthermore, recent advances in biomedical applications involving silk-based organoid models are discussed. In particular, the unique physiological attributes of silk matrix constituents in in vitro tissue constructs are highlighted, providing a meticulous evaluation of their importance. Additionally, it outlines the current research hurdles and complexities while contemplating future avenues, thereby paving the way for developing complex and biomimetic silk protein-based microtissues.

Transcriptional Landscape of 3D vs. 2D Ovarian Cancer Cell Models

Three-dimensional (3D) cancer models are revolutionising research, allowing for the recapitulation of an in vivo-like response through the use of an in vitro system, which is more complex and physiologically relevant than traditional monolayer cultures. Cancers such as ovarian (OvCa) are prone to developing resistance, are often lethal, and stand to benefit greatly from the enhanced modelling emulated by 3D cultures. However, the current models often fall short of the predicted response, where reproducibility is limited owing to the lack of standardised methodology and established protocols. This meta-analysis aims to assess the current scope of 3D OvCa models and the differences in the genetic profiles presented by a vast array of 3D cultures. An analysis of the literature (Pubmed.gov) spanning 2012-2022 was used to identify studies with paired data of 3D and 2D monolayer counterparts in addition to RNA sequencing and microarray data. From the data, 19 cell lines were found to show differential regulation in their gene expression profiles depending on the bio-scaffold (i.e., agarose, collagen, or Matrigel) compared to 2D cell cultures. The top genes differentially expressed in 2D vs. 3D included C3, CXCL1, 2, and 8, IL1B, SLP1, FN1, IL6, DDIT4, PI3, LAMC2, CCL20, MMP1, IFI27, CFB, and ANGPTL4. The top enriched gene sets for 2D vs. 3D included IFN-α and IFN-γ response, TNF-α signalling, IL-6-JAK-STAT3 signalling, angiogenesis, hedgehog signalling, apoptosis, epithelial-mesenchymal transition, hypoxia, and inflammatory response. Our transversal comparison of numerous scaffolds allowed us to highlight the variability that can be induced by these scaffolds in the transcriptional landscape and identify key genes and biological processes that are hallmarks of cancer cells grown in 3D cultures. Future studies are needed to identify which is the most appropriate in vitro/preclinical model to study tumour microenvironments.

Influence of lyophilization primary drying time and temperature on porous silk scaffold fabrication for biomedical applications

Lyophilization of protein solutions, such as silk fibroin (silk), produces porous scaffolds useful for tissue engineering (TE). The impact of modifying lyophilization primary drying parameters on scaffold properties has not yet been explored previously. In this work, changes to primary drying duration and temperature were investigated using 3%, 6%, 9%, and 12% (w/v) silk solutions, via protocols labeled as Long Hold, Slow Ramp, and Standard. The 9% and 12% scaffolds were not successfully fabricated using the Standard protocol, while the Long Hold and Slow Ramp protocols resulted in scaffolds from all silk solution concentrations. Scaffolds fabricated using the Long Hold protocol had higher Young's moduli, smaller pore Feret diameters, and faster degradation. To investigate the utility of the different lyophilized scaffolds for in vitro cell culturing, the HepaRG liver cell line was cultured in the 3% to 12% scaffolds fabricated using the Long Hold protocol. The HepaRG cells grown in 3% scaffolds initially had greater lipid accumulation and metabolic activity than the other groups, although these differences were no longer apparent by Day 28. The deoxyribonucleic acid content of the HepaRG cells grown in 3% scaffold group was also initially significantly higher than the other groups. Significant differences in gene expression by 9% scaffolded HepaRG cells (CK19, HNFα) were seen on Day 14 while significant differences by 12% scaffolded HepaRG cells (ALB, APOA4) were seen on Day 28. Overall, modifying the primary drying parameters and silk concentration resulted in lyophilized scaffolds with tunable properties useful for TE applications.

HepaRG Maturation in Silk Fibroin Scaffolds: Toward Developing a 3D In Vitro Liver Model

In vitro liver models are necessary tools for the development of new therapeutics. HepaRG cells are a commonly used cell line to produce hepatic progenitor cells and hepatocytes. This study demonstrates for the first time the suitability of 3% silk scaffolds to support HepaRG growth and differentiation. The modulus and pore size of 3% silk scaffolds were shown to be within the desired range for liver cell growth. The optimal seeding density for HepaRG cells on silk scaffolds was determined. The growth and maturation of scaffolded HepaRG cells was evaluated for 28 days, where the first 14 days of culture were a proliferation period and the last 14 days of culture were a differentiation period using dimethyl sulfoxide (DMSO) treatment. After the first 14 days of culture, the scaffolded HepaRG cells exhibited increased metabolic activity and albumin secretion compared to monolayer cultured controls and preserved these attributes through the duration of culture. Additionally, after the first 14 days of culture, the scaffolded HepaRG cells displayed a significantly reduced expression of genes associated with hepatocyte maturation. This difference in expression was no longer apparent after 28 days of culture, suggesting that the cells underwent rapid differentiation within the scaffold. The functionalization of silk scaffolds with extracellular matrix (ECM) components (type I collagen and/or an arginylglycylaspartic acid (RGD)-containing peptide) was investigated to determine the impact on HepaRG cell attachment and maturation. The inclusion of ECM components had no noticeable impact on cell attachment but did significantly influence CYP3A4 expression and albumin secretion. Finally, the matrix support provided by the 3% silk scaffolds could prime the HepaRG cells for steatosis liver model applications, as evidenced by lipid droplet accumulation and expression of steatosis-related genes after 24 h of exposure to oleic acid. Overall, our work demonstrates the utility of silk scaffolds in providing a modifiable platform for liver cell growth.

Development of a mechanically matched silk scaffolded 3D clear cell renal cell carcinoma model

Development of a 3D, biomaterials-based model for clear cell renal cell carcinoma (ccRCC) would be advantageous for understanding disease progression in vitro. This study demonstrated the development of lyophilized silk scaffolds that mechanically match the experimentally determined Young's modulus for ex vivo ccRCC samples and normal kidney tissue. Scaffolds fabricated from silk solutions ranging from 3 to 12% (w/v) were evaluated through mechanical testing. Following mechanical characterization of ccRCC samples, it was demonstrated that 6% silk scaffolds mechanically matched ccRCC samples. No impact of pathological grade and stage on the calculated ccRCC modulus was observed and all tumors evaluated mechanically matched the 6% silk scaffold formulation. Stratifying tissue specimens based upon histological observations (e.g. evidence of high levels of collagen deposition) resulted in no significant differences between groups. To investigate the impact of a mechanically matched culturing environment on in vitro ccRCC disease characteristics a model ccRCC cell line, 786-O, was utilized. Scaffolded 786-O cells demonstrated increased lipid droplet accumulation, a hallmark of ccRCC, compared to standard two-dimensional (2D) culture conditions. Additionally, scaffolded 786-O cells demonstrated increased expression of genes associated with ccRCC aggressiveness (ex. VEGFA, TNF, and IL-6) or immune markers under investigation as therapeutic targets (ex. PDL1, CTLA4). Comparison with 786-O cells grown on non-mechanically matched scaffolds demonstrated that these improved ccRCC characteristics were driven by scaffold modulus. Overall, our findings support the use of silk scaffolds in replicating physiologic tumor behavior for clear cell renal cell carcinoma and provide a platform for investigating disease progression.

The Role of Biomimetic Hypoxia on Cancer Cell Behaviour in 3D Models: A Systematic Review

Simple Summary

Cancer remains one of the leading causes of death worldwide. The advancements in 3D tumour models provide in vitro test-beds to study cancer growth, metastasis and response to therapy. We conducted this systematic review on existing experimental studies in order to identify and summarize key biomimetic tumour microenvironmental features which affect aspects of cancer biology. The review noted the significance of in vitro hypoxia and 3D tumour models on epithelial to mesenchymal transition, drug resistance, invasion and migration of cancer cells. We highlight the importance of various experimental parameters used in these studies and their subsequent effects on cancer cell behaviour.

Abstract

The development of biomimetic, human tissue models is recognized as being an important step for transitioning in vitro research findings to the native in vivo response. Oftentimes, 2D models lack the necessary complexity to truly recapitulate cellular responses. The introduction of physiological features into 3D models informs us of how each component feature alters specific cellular response. We conducted a systematic review of research papers where the focus was the introduction of key biomimetic features into in vitro models of cancer, including 3D culture and hypoxia. We analysed outcomes from these and compiled our findings into distinct groupings to ascertain which biomimetic parameters correlated with specific responses. We found a number of biomimetic features which primed cancer cells to respond in a manner which matched in vivo response.

Development of a stacked, porous silk scaffold neuroblastoma model for investigating spatial differences in cell and drug responsiveness

Development of in vitro, preclinical cancer models that contain cell-driven microenvironments remains a challenge. Engineering of millimeter-scale, in vitro tumor models with spatially distinct regions that can be independently assessed to study tumor microenvironments has been limited. Here, we report the use of porous silk scaffolds to generate a high cell density neuroblastoma (NB) model that can spatially recapitulate changes resulting from cell and diffusion driven changes. Using COMSOL modeling, a scaffold holder design that facilitates stacking of thin, 200 μm silk scaffolds into a thick, bulk millimeter-scale tumor model (2, 4, 6, and 8 stacked scaffolds) and supports cell-driven oxygen gradients was developed. Cell-driven oxygen gradients were confirmed through pimonidazole staining. Post-culture, the stacked scaffolds were separated for analysis on a layer-by-layer basis. The analysis of each scaffold layer demonstrated decreasing DNA and increasing expression of hypoxia related genes (VEGF, CAIX, and GLUT1) from the exterior scaffolds to the interior scaffolds. Furthermore, the expression of hypoxia related genes at the interior of the stacks was comparable to that of a single scaffold cultured under 1% O₂ and at the exterior of the stacks was comparable to that of a single scaffold cultured under 21% O₂. The four-stack scaffold model underwent further evaluation to determine if a hypoxia activated drug, tirapazamine, induced reduced cell viability within the internal stacks (region of reduced oxygen) as compared with the external stacks. Decreased DNA content was observed in the internal stacks as compared to the external stacks when treated with tirapazamine, which suggests the internal scaffold stacks had higher levels of hypoxia than the external scaffolds. This stacked silk scaffold system presents a method for creating a single culture model capable of generating controllable cell-driven microenvironments through different stacks that can be individually assessed and used for drug screening.

Biomaterial strategies to replicate gynecological tissue

Properties of native tissue can inspire biomimetic in vitro models of gynecological disease.