Self-Assembling Peptide Gels for 3D Prostate Cancer Spheroid Culture

TempEasy 3D Hydrogel Coculture System Provides Mechanistic Insights into Prostate Cancer Bone Metastasis

Patients diagnosed with advanced prostate cancer (PCa) often experience incurable bone metastases; however, a lack of relevant experimental models has hampered the study of disease mechanisms and the development of therapeutic strategies. In this study, we employed the recently established Temperature-based Easy-separable (TempEasy) 3D cell coculture system to investigate PCa bone metastasis. Through coculturing PCa and bone cells for 7 days, our results showed a reduction in PCa cell proliferation, an increase in neovascularization, and an enhanced metastasis potential when cocultured with bone cells. Additionally, we observed increased cell proliferation, higher stemness, and decreased bone matrix protein expression in bone cells when cocultured with PCa cells. Furthermore, we demonstrated that the stiffness of the extracellular matrix had a negligible impact on molecular responses in both primary (PCa cells) and distant malignant (bone cells) sites. The TempEasy 3D hydrogel coculture system is an easy-to-use and versatile coculture system that provides valuable insights into the mechanisms of cell-cell communication and interaction in cancer metastasis.

Supramolecular gels - a panorama of low-molecular-weight gelators from ancient origins to next-generation technologies

Supramolecular gels, self-assembled from low-molecular-weight gelators (LMWGs), have a long history and a bright future. This review provides an overview of these materials, from their use in lubrication and personal care in the ancient world, through to next-generation technologies. In academic terms, colloid scientists in the 19th and early 20th centuries first understood such gels as being physically assembled as a result of weak interactions, combining a solid-like network having a degree of crystalline order with a highly mobile liquid-like phase. During the 20th century, industrial scientists began using these materials in new applications in the polymer, oil and food industries. The advent of supramolecular chemistry in the late 20th century, with its focus on non-covalent interactions and controlled self-assembly, saw the horizons for these materials shifted significantly beyond their historic rheological applications, expanding their potential. The ability to tune the LMWG chemical structure, manipulate hierarchical assembly, develop multi-component systems, and introduce new types of responsive and interactive behaviour, has been transformative. Furthermore, the dynamics of these materials are increasingly understood, creating metastable gels and transiently-fueled systems. New approaches to shaping and patterning gels are providing a unique opportunity for more sophisticated uses. These supramolecular advances are increasingly underpinning and informing next-generation applications - from drug delivery and regenerative medicine to environmental remediation and sustainable energy. In summary, this article presents a panorama over the field of supramolecular gels, emphasising how both academic and industrial scientists are building on the past, and engaging new fundamental insights and innovative concepts to open up exciting horizons for their future use.

Substance P-Derived Extracellular-Matrix-Mimicking Peptide Hydrogel as a Cytocompatible Biomaterial Platform

Self-assembled short peptide-based hydrogel platforms have become widely applicable biomedical therapeutic maneuvers for their soft, tunable architecture, which can influence cellular behavior and morphology to an inordinate extent. In this work, a short supramolecular hydrogelator peptide, substance P, has been designed and synthesized from the C terminus conserved "FFGLM" section of a biologically abundant neuropeptide by using a fusion approach. In addition, to incorporate a good hydrophobic-hydrophilic balance, the truncated pentapeptide segment was further C-terminally modified by the incorporation of an integrin-binding "RGD" motif. Thanks to its N-terminal Fmoc group, this octapeptide ensemble "FFGLMRGD" undergoes rapid self-assembly to give rise to an injectable, pH-responsive, hydrogel-based self-supporting platform that exhibited good cytocompatibility with the cultured mammalian cells under both 2D and 3D culture conditions without exerting any potent cytotoxic effect in a Live/Dead experiment. A rheological experiment demonstrated its hydrogel-like mechanical properties, including thixotropicity. The atomic force microscopy and field emission scanning electron microscopy images of the fabricated hydrogel show a tangled fibrous surface topography owing to the presence of the N-terminal Fmoc-FF residue. Furthermore, an in-vitro scratch assay performed on fibroblast cell lines confirmed the wound-ameliorating potency of this designed hydrogel; this substantiates its future therapeutic prospects.

Prostate cancer and bone: clinical presentation and molecular mechanisms

Prostate cancer (PCa) is an increasingly prevalent health problem in the developed world. Effective treatment options exist for localized PCa, but metastatic PCa has fewer treatment options and shorter patient survival. PCa and bone health are strongly entwined, as PCa commonly metastasizes to the skeleton. Since androgen receptor signaling drives PCa growth, androgen-deprivation therapy whose sequelae reduce bone strength constitutes the foundation of advanced PCa treatment. The homeostatic process of bone remodeling - produced by concerted actions of bone-building osteoblasts, bone-resorbing osteoclasts, and regulatory osteocytes - may also be subverted by PCa to promote metastatic growth. Mechanisms driving skeletal development and homeostasis, such as regional hypoxia or matrix-embedded growth factors, may be subjugated by bone metastatic PCa. In this way, the biology that sustains bone is integrated into adaptive mechanisms for the growth and survival of PCa in bone. Skeletally metastatic PCa is difficult to investigate due to the entwined nature of bone biology and cancer biology. Herein, we survey PCa from origin, presentation, and clinical treatment to bone composition and structure and molecular mediators of PCa metastasis to bone. Our intent is to quickly yet effectively reduce barriers to team science across multiple disciplines that focuses on PCa and metastatic bone disease. We also introduce concepts of tissue engineering as a novel perspective to model, capture, and study complex cancer-microenvironment interactions.

Designing ECM-inspired supramolecular scaffolds by utilizing the interactions between a minimalistic neuroactive peptide and heparin

Short bioactive peptide-based supramolecular hydrogels are emerging as interesting candidates for developing scaffolds for tissue engineering applications. However, proteins and peptides represent only a single class of molecules present in the native ECM, thus, recapitulating the complete ECM microenvironment via only peptide-based biomaterials is extremely challenging. In this direction, complex multicomponent-based biomaterials have started gaining importance for achieving the biofunctional complexity and structural hierarchy of the native ECM. Sugar-peptide complexes can be explored in this direction as they provide essential biological signaling required for cellular growth and survival in vivo. In this direction, we explored the fabrication of an advanced scaffold by employing heparin and short bioactive peptide interactions at the molecular level. Interestingly, the addition of heparin into the peptide has significantly modulated the supramolecular organization, nanofibrous morphology and the mechanical properties of the scaffold. Additionally, the combined hydrogels demonstrated superior biocompatibility as compared to the peptide counterpart at certain ratios. These newly developed scaffolds were also observed to be stable under 3-D cell culture conditions and supported cellular adhesion and proliferation. Most importantly, the inflammatory response was also minimized in the case of combined hydrogels as compared to heparin. We expect that this approach of using simple non-covalent interactions between the ECM-inspired small molecules to fabricate biomaterials with improved mechanical and biological properties could advance the current knowledge on designing ECM mimetic biomaterials. Such an attempt would create a novel, adaptable and simplistic bottom-up strategy for the invention of new and more complex biomaterials of ECM origin with advanced functions.

Animal-derived products in science and current alternatives

More than fifty years after the 3Rs definition and despite the continuous implementation of regulatory measures, animals continue to be widely used in basic research. Their use comprises not only in vivo experiments with animal models, but also the production of a variety of supplements and products of animal origin for cell and tissue culture, cell-based assays, and therapeutics. The animal-derived products most used in basic research are fetal bovine serum (FBS), extracellular matrix proteins such as Matrigel™, and antibodies. However, their production raises several ethical issues regarding animal welfare. Additionally, their biological origin is associated with a high risk of contamination, resulting, frequently, in poor scientific data for clinical translation. These issues support the search for new animal-free products able to replace FBS, Matrigel™, and antibodies in basic research. In addition, in silico methodologies play an important role in the reduction of animal use in research by refining the data previously to in vitro and in vivo experiments. In this review, we depicted the current available animal-free alternatives in in vitro research.

Let’s Go 3D! New Generation of Models for Evaluating Drug Response and Resistance in Prostate Cancer

Prostate cancer (PC) is the third most frequently diagnosed cancer worldwide and the second most frequent in men. Several risk factors can contribute to the development of PC, and those include age, family history, and specific genetic mutations. So far, drug testing in PC, as well as in cancer research in general, has been performed on 2D cell cultures. This is mainly because of the vast benefits these models provide, including simplicity and cost effectiveness. However, it is now known that these models are exposed to much higher stiffness; lose physiological extracellular matrix on artificial plastic surfaces; and show changes in differentiation, polarization, and cell–cell communication. This leads to the loss of crucial cellular signaling pathways and changes in cell responses to stimuli when compared to in vivo conditions. Here, we emphasize the importance of a diverse collection of 3D PC models and their benefits over 2D models in drug discovery and screening from the studies done so far, outlining their benefits and limitations. We highlight the differences between the diverse types of 3D models, with the focus on tumor–stroma interactions, cell populations, and extracellular matrix composition, and we summarize various standard and novel therapies tested on 3D models of PC for the purpose of raising awareness of the possibilities for a personalized approach in PC therapy.

Click chemistry functionalization of self-assembling peptide hydrogels

Self-assembling peptide (SAP) hydrogels provide a fibrous microenvironment to cells while also giving users control of biochemical and mechanical cues. Previously, biochemical cues were introduced by physically mixing them with SAPs prior to hydrogel assembly, or by incorporating them into the SAP sequence during peptide synthesis, which limited flexibility and increased costs. To circumvent these limitations, we developed "Click SAPs," a novel formulation that can be easily functionalized via click chemistry thiol-ene reaction. Due to its high cytocompatibility, the thiol-ene click reaction is currently used to crosslink and functionalize other types of polymeric hydrogels. In this study, we developed a click chemistry compatible SAP platform by addition of a modified lysine (lysine-alloc) to the SAP sequence, enabling effective coupling of thiol-containing molecules to the SAP hydrogel network. We demonstrate the flexibility of this approach by incorporating a fluorescent dye, a cellular adhesion peptide, and a matrix metalloproteinase-sensitive biosensor using the thiol-ene reaction in 3D Click SAPs. Using atomic force microscopy, we demonstrate that Click SAPs retain the ability to self-assemble into fibers, similar to previous systems. Additionally, a range of physiologically relevant stiffnesses can be achieved by adjusting SAP concentration. Encapsulated cells maintain high viability in Click SAPs and can interact with adhesion peptides and a matrix metalloproteinase biosensor, demonstrating that incorporated molecules retain their biological activity. The Click SAP platform supports easier functionalization with a wider array of bioactive molecules and enables new investigations with temporal and spatial control of the cellular microenvironment.

Enhanced motility and interaction of nasopharyngeal carcinoma with epithelial cells in confined microwells

The three-dimensional (3D) structure of the extracellular matrix and cell-cell contacts are two important cues to altering cell migration behavior and the tumor formation process. In this work, we designed and fabricated microwell arrays with a grating-patterned bottom in polydimethylsiloxane platforms to systematically study the effects of confinement, changes in topography, and cell-cell contacts on the migration behavior of nasopharyngeal carcinoma (NPC43) and immortalized nasopharyngeal epithelial (NP460) cells by time-lapse imaging. When two types of cells were co-cultured in microwells, the migration speed and spreading area of NPC43 cells were significantly increased, which might be attributed to the heterotypic cell-cell contacts with NP460 cells. On a flat surface, NPC43 cells could not form clusters due to the frequent interruptions by the active movements of NP460 cells. However, in 3D microwell arrays, clusters of NPC43 cells formed on the bottom surface while the majority of NP460 cells migrated onto the sidewalls. These cell clusters could be further processed to form spheroids for drug screening. These results also revealed that the 3D microenvironments and cell-cell contacts could have significant implications for NPC cell migration and initiation of tumor formation, which will provide insight for NPC progression and dissemination.

Modification Strategies for Ionic Complementary Self-Assembling Peptides: Taking RADA16-I as an Example

Ion-complementary self-assembling peptides have been studied in many fields for their distinct advantages, mainly due to their self-assembly properties. However, their shortcomings, such as insufficient specific activity and poor mechanical properties, also limited their application. For the better and wider application of these promising biomaterials, ion-complementary self-assembling peptides can be modified with their self-assembly properties not being destroyed to the greatest extent. The modification strategies were reviewed by taking RADA16-I as an example. For insufficient specific activity, RADA16-I can be structurally modified with active motifs derived from the active domain of the extracellular matrix or other related active factors. For weak mechanical properties, materials with strong mechanical properties or that can undergo chemical crosslinking were used to mix with RADA16-I to enhance the mechanical properties of RADA16-I. To improve the performance of RADA16-I as drug carriers, appropriate adjustment of the RADA16-I sequence and/or modification of the RADA16-I-related delivery system with polymer materials or specific molecules can be considered to achieve sustained and controlled release of specific drugs or active factors. The modification strategies reviewed in this paper may provide some references for further basic research and clinical application of ion-complementary self-assembling peptides and their derivatives.

Biofunctional peptide-click PEG-based hydrogels as 3D cell scaffolds for corneal epithelial regeneration

Poly(ethylene glycol) (PEG)-based hydrogels as highly promising 3D cell scaffolds have been widely implemented in the field of tissue regrowth and regeneration, yet the functionalized PEG hydrogel providing dynamic, cell-instructive microenvironments is inherently difficult to obtain. Here, we have exploited the specificity of click reaction to develop a set of hydrogels based on 4-arm PEG tetraazide (4-arm-PEG-N₃) and di-propargylated peptides (GRGDG and GRDGG) with tunable physicochemical properties applicable for 3D cell scaffolds. The azide groups of PEG were reacted with the alkynyl groups of peptides, catalyzed by copper to form triazole rings, thus generating a cross-linked hydrogel. The gelation time and mechanical strength of the hydrogels varied according to the PEG/peptide feed ratio. The resulting hydrogel exhibited a typical porous microstructure and suitable swelling behavior. The in vitro cytotoxicity test indicated that the resulting hydrogels did not cause apparent cytotoxicity against human corneal epithelial cells (HCECs). After co-incubation with HCECs, the density of RGD as well as peptide sequence in the hydrogels remarkably affected the cell attachment, spreadability, and proliferation. Additionally, the proposed hydrogel showed high ocular biocompatibility after being embedded subconjunctivally into rabbit eyes. Overall, these findings highlighted that the biofunctional hydrogels formed by PEG and RGD motifs via a controllable click reaction might be promising 3D cell scaffolds for corneal epithelial regeneration.

Advancements in Three Dimensional In-Vitro Cell Culture Models

The scientific field is observing a gradual shift from monolayer cultures to three-dimensional (3D) models, as they give a more relevant data in pre-clinical stages. This review summarizes the major techniques and materials used to develop 3D platforms, especially for cancer. It also discusses the challenges and some unresolved issues of the field and highlights some techniques that have made it to the market.

Self-Assembled Peptide Habitats to Model Tumor Metastasis

Metastatic tumours are complex ecosystems; a community of multiple cell types, including cancerous cells, fibroblasts, and immune cells that exist within a supportive and specific microenvironment. The interplay of these cells, together with tissue specific chemical, structural and temporal signals within a three-dimensional (3D) habitat, direct tumour cell behavior, a subtlety that can be easily lost in 2D tissue culture. Here, we investigate a significantly improved tool, consisting of a novel matrix of functionally programmed peptide sequences, self-assembled into a scaffold to enable the growth and the migration of multicellular lung tumour spheroids, as proof-of-concept. This 3D functional model aims to mimic the biological, chemical, and contextual cues of an in vivo tumor more closely than a typically used, unstructured hydrogel, allowing spatial and temporal activity modelling. This approach shows promise as a cancer model, enhancing current understandings of how tumours progress and spread over time within their microenvironment.

Biomaterials via peptide assembly: Design, characterization, and application in tissue engineering

A core challenge in biomaterials, with both fundamental significance and technological relevance, concerns the rational design of bioactive microenvironments. Designed properly, peptides can undergo supramolecular assembly into dynamic, physical hydrogels that mimic the mechanical, topological, and biochemical features of native tissue microenvironments. The relatively facile, inexpensive, and automatable preparation of peptides, coupled with low batch-to-batch variability, motivates the expanded use of assembling peptide hydrogels for biomedical applications. Integral to realizing dynamic peptide assemblies as functional biomaterials for tissue engineering is an understanding of the molecular and macroscopic features that govern assembly, morphology, and biological interactions. In this review, we first discuss the design of assembling peptides, including primary structure (sequence), secondary structure (e.g., α-helix and β-sheets), and molecular interactions that facilitate assembly into multiscale materials with desired properties. Next, we describe characterization tools for elucidating molecular structure and interactions, morphology, bulk properties, and biological functionality. Understanding of these characterization methods enables researchers to access a variety of approaches in this ever-expanding field. Finally, we discuss the biological properties and applications of peptide-based biomaterials for engineering several important tissues. By connecting molecular features and mechanisms of assembling peptides to the material and biological properties, we aim to guide the design and characterization of peptide-based biomaterials for tissue engineering and regenerative medicine. STATEMENT OF SIGNIFICANCE: Engineering peptide-based biomaterials that mimic the topological and mechanical properties of natural extracellular matrices provide excellent opportunities to direct cell behavior for regenerative medicine and tissue engineering. Here we review the molecular-scale features of assembling peptides that result in biomaterials that exhibit a variety of relevant extracellular matrix-mimetic properties and promote beneficial cell-biomaterial interactions. Aiming to inspire and guide researchers approaching this challenge from both the peptide biomaterial design and tissue engineering perspectives, we also present characterization tools for understanding the connection between peptide structure and properties and highlight the use of peptide-based biomaterials in neural, orthopedic, cardiac, muscular, and immune engineering applications.

Lyophilized Gelatin@non-Woven Scaffold to Promote Spheroids Formation and Enrich Cancer Stem Cell Incidence

A gelatin@non-woven fabric (gelatin@NWF) hybrid scaffold with tailored micropore structures was fabricated by lyophilizing, using gelatin to support cells and the NWF matrix as a frame to enforce the mechanical stability of gelatin. By freezing the gelatin and NWF hybrid in liquid nitrogen and subsequently lyophilizing and crosslinking the process, the gelatin@NWF scaffold was prepared to support cell growth and promote cell aggregation and spheroids’ formation. The results indicated that by tuning the lyophilizing temperature, the micropore size on the gelatin could be tailored. Consequently, tumor spheroids can be formed on gelatin@NWF scaffolds with honeycomb-like pores around 10 µm. The cell spheroids formed on the tailored gelatin@NWF scaffold were characterized in cancer stem cell (CSC)-associated gene expression, chemotherapy drug sensitivity, and motility. It was found that the expression of the CSC-associated biomarkers SOX2, OCT4, and ALDH1A1 in gene and protein levels in DU 145 cell spheres formed on gelatin@NWF scaffolds were significantly higher than in those cells grown as monolayers. Moreover, cells isolated from spheroids grown on gelatin@NWF scaffold showed higher drug resistance and motility. Tumor spheroids can be formed on a long-term storage scaffold, highlighting the potential of gelatin@NWF as a ready-to-use scaffold for tumor cell sphere generation and culturing.

Next-generation cancer organoids

Organotypic models of patient-specific tumours are revolutionizing our understanding of cancer heterogeneity and its implications for personalized medicine. These advancements are, in part, attributed to the ability of organoid models to stably preserve genetic, proteomic, morphological and pharmacotypic features of the parent tumour in vitro, while also offering unprecedented genomic and environmental manipulation. Despite recent innovations in organoid protocols, current techniques for cancer organoid culture are inherently uncontrolled and irreproducible, owing to several non-standardized facets including cancer tissue sources and subsequent processing, medium formulations, and animal-derived three-dimensional matrices. Given the potential for cancer organoids to accurately recapitulate the intra- and intertumoral biological heterogeneity associated with patient-specific cancers, eliminating the undesirable technical variability accompanying cancer organoid culture is necessary to establish reproducible platforms that accelerate translatable insights into patient care. Here we describe the current challenges and recent multidisciplinary advancements and opportunities for standardizing next-generation cancer organoid systems.

Fabrication of Antheraea pernyi Silk Fibroin-Based Thermoresponsive Hydrogel Nanofibers for Colon Cancer Cell Culture

Antheraea pernyi silk fibroin (ASF)-based nanofibers have wide potential for biomaterial applications due to superior biocompatibility. It is not clear whether the ASF-based nanofibers scaffold can be used as an in vitro cancer cell culture platform. In the current study, we fabricated novel ASF-based thermoresponsive hydrogel nanofibers by aqueous electrospinning for colon cancer (LoVo) cells culture. ASF was reacted with allyl glycidyl ether (AGE) for the preparation of allyl silk fibroin (ASF-AGE), which provided the possibility of copolymerization with allyl monomer. The investigation of ASF-AGE structure by 1H NMR revealed that reactive allyl groups were successfully linked with ASF. ASF-based thermoresponsive hydrogel nanofibers (p (ASF-AGE-NIPAAm)) were successfully manufactured by aqueous electrospinning with the polymerization of ASF and N-isopropylacrylamide (NIPAAm). The p (ASF-AGE-NIPAAm) spinning solution showed good spinnability with the increase of polymerization time, and uniform nanofibers were formed at the polymerization time of 360 min. The obtained hydrogel nanofibers exhibited good thermoresponsive that the LCST was similar with PNIPAAm at about 32 °C, and good degradability in protease XIV PBS solution. In addition, the cytocompatibility of colon cancer (LoVo) cells cultured in hydrogel nanofibers was assessed. It was demonstrated that LoVo cells grown on hydrogel nanofibers showed improved cell adhesion, proliferation, and viability than those on hydrogel. The results suggest that the p (ASF-AGE-NIPAAm) hydrogel nanofibers have potential application in LoVo cells culture in vitro. This study demonstrates the feasibility of fabricating ASF-based nanofibers to culture LoVo cancer cells that can potentially be used as an in vitro cancer cell culture platform.

Recent Advances in Multicellular Tumor Spheroid Generation for Drug Screening

Multicellular tumor spheroids (MCTs) have been employed in biomedical fields owing to their advantage in designing a three-dimensional (3D) solid tumor model. For controlling multicellular cancer spheroids, mimicking the tumor extracellular matrix (ECM) microenvironment is important to understand cell-cell and cell-matrix interactions. In drug cytotoxicity assessments, MCTs provide better mimicry of conventional solid tumors that can precisely represent anticancer drug candidates' effects. To generate incubate multicellular spheroids, researchers have developed several 3D multicellular spheroid culture technologies to establish a research background and a platform using tumor modelingvia advanced materials science, and biosensing techniques for drug-screening. In application, drug screening was performed in both invasive and non-invasive manners, according to their impact on the spheroids. Here, we review the trend of 3D spheroid culture technology and culture platforms, and their combination with various biosensing techniques for drug screening in the biomedical field.

Influences of the 3D microenvironment on cancer cell behaviour and treatment responsiveness: A recent update on lung, breast and prostate cancer models

The majority of in vitro studies assessing cancer treatments are performed in two-dimensional (2D) monolayers and are subsequently validated in in vivo animal models. However, 2D models fail to accurately model the tumour microenvironment. Furthermore, animal models are not directly applicable to mimic the human scenario. Three-dimensional (3D) culture models may help to address the discrepancies of 2D and animal models. When cancer cells escape the primary tumour, they can invade at distant organs building secondary tumours, called metastasis. The development of metastasis leads to a dramatic decrease in the life expectancy of patients. Therefore, 3D systems to model the microenvironment of metastasis have also been developed. Several studies have demonstrated changes in cell behaviour and gene expression when cells are cultured in 3D compared to 2D and concluded a better comparability to cells in vivo. Of special importance is the effect seen in response to anti-cancer treatments as models are built primarily to serve as drug-testing platforms. This review highlights these changes between cancer cells grown in 2D and 3D models for some of the most common cancers including lung, breast and prostate tumours. In addition to models aiming to mimic the primary tumour site, the effects of 3D cell culturing in bone metastasis models are also described. STATEMENT OF SIGNIFICANCE: Most in vitro studies in cancer research are performed in 2D and are subsequently validated in in vivo animal models. However, both models possess numerous limitations: 2D models fail to accurately model the tumour microenvironment while animal models are expensive, time-consuming and can differ considerably from humans. It is accepted that the cancer microenvironment plays a critical role in the disease, thus, 3D models have been proposed as a potential solution to address the discrepancies of 2D and animal models. This review highlights changes in cell behaviour, including proliferation, gene expression and chemosensitivity, between cancer cells grown in 2D and 3D models for some of the most common cancers including lung, breast and prostate cancer as well as bone metastasis.

Serum Protein Adsorption Modulates the Toxicity of Highly Positively Charged Hydrogel Surfaces

Hydrogels formed from peptide self-assembly are a class of materials that are being explored for their utility in tissue engineering, drug and cell delivery, two- and three-dimensional cell culture, and as adjuvants in surgical procedures. Most self-assembled peptide gels can be syringe-injected in vivo to facilitate the local delivery of payloads, including cells, directly to the targeted tissue. Herein, we report that highly positively charged peptide gels are inherently toxic to cells, which would seem to limit their utility. However, adding media containing fetal bovine serum, a common culture supplement, directly transforms these toxic gels into cytocompatible materials capable of sustaining cell viability even in the absence of added nutrients. Multistage mass spectrometry showed that at least 40 serum proteins can absorb to a gel's surface through electrostatic attraction ameliorating its toxicity. Further, cell-based studies employing model gels having only bovine serum albumin, fetuin-A, or vitronectin absorbed to the gel surface showed that single protein additives can also be effective depending on the identity of the cell line. Separate studies employing these model gels showed that the mechanism(s) responsible for mitigating apoptosis involve both the pacification of gel surface charge and adsorbed protein-mediated cell signaling events that activate both the PI3/Akt and MAPK/ERK pathways which are known to facilitate resistance to stress-induced apoptosis and overall cell survival.

Proteinaceous Hydrogels for Bioengineering Advanced 3D Tumor Models

The establishment of tumor microenvironment using biomimetic in vitro models that recapitulate key tumor hallmarks including the tumor supporting extracellular matrix (ECM) is in high demand for accelerating the discovery and preclinical validation of more effective anticancer therapeutics. To date, ECM-mimetic hydrogels have been widely explored for 3D in vitro disease modeling owing to their bioactive properties that can be further adapted to the biochemical and biophysical properties of native tumors. Gathering on this momentum, herein the current landscape of intrinsically bioactive protein and peptide hydrogels that have been employed for 3D tumor modeling are discussed. Initially, the importance of recreating such microenvironment and the main considerations for generating ECM-mimetic 3D hydrogel in vitro tumor models are showcased. A comprehensive discussion focusing protein, peptide, or hybrid ECM-mimetic platforms employed for modeling cancer cells/stroma cross-talk and for the preclinical evaluation of candidate anticancer therapies is also provided. Further development of tumor-tunable, proteinaceous or peptide 3D microtesting platforms with microenvironment-specific biophysical and biomolecular cues will contribute to better mimic the in vivo scenario, and improve the predictability of preclinical screening of generalized or personalized therapeutics.

Rationally Designed Protein Building Blocks for Programmable Hierarchical Architectures

Diverse natural/artificial proteins have been used as building blocks to construct a variety of well-ordered nanoscale structures over the past couple of decades. Sophisticated protein self-assemblies have attracted great scientific interests due to their potential applications in disease diagnosis, illness treatment, biomechanics, bio-optics and bio-electronics, etc. This review outlines recent efforts directed to the creation of structurally defined protein assemblies including one-dimensional (1D) strings/rings/tubules, two-dimensional (2D) planar sheets and three-dimensional (3D) polyhedral scaffolds. We elucidate various innovative strategies for manipulating proteins to self-assemble into desired architectures. The emergent applications of protein assemblies as versatile platforms in medicine and material science with improved performances have also been discussed.

Natural and Synthetic Biomaterials for Engineering Multicellular Tumor Spheroids

The lack of in vitro models that represent the native tumor microenvironment is a significant challenge for cancer research. Two-dimensional (2D) monolayer culture has long been the standard for in vitro cell-based studies. However, differences between 2D culture and the in vivo environment have led to poor translation of cancer research from in vitro to in vivo models, slowing the progress of the field. Recent advances in three-dimensional (3D) culture have improved the ability of in vitro culture to replicate in vivo conditions. Although 3D cultures still cannot achieve the complexity of the in vivo environment, they can still better replicate the cell-cell and cell-matrix interactions of solid tumors. Multicellular tumor spheroids (MCTS) are three-dimensional (3D) clusters of cells with tumor-like features such as oxygen gradients and drug resistance, and represent an important translational tool for cancer research. Accordingly, natural and synthetic polymers, including collagen, hyaluronic acid, Matrigel^®, polyethylene glycol (PEG), alginate and chitosan, have been used to form and study MCTS for improved clinical translatability. This review evaluates the current state of biomaterial-based MCTS formation, including advantages and disadvantages of the different biomaterials and their recent applications to the field of cancer research, with a focus on the past five years.

Three-Dimensional Cell Cultures as an In Vitro Tool for Prostate Cancer Modeling and Drug Discovery

In the last decade, three-dimensional (3D) cell culture technology has gained a lot of interest due to its ability to better recapitulate the in vivo organization and microenvironment of in vitro cultured cancer cells. In particular, 3D tumor models have demonstrated several different characteristics compared with traditional two-dimensional (2D) cultures and have provided an interesting link between the latter and animal experiments. Indeed, 3D cell cultures represent a useful platform for the identification of the biological features of cancer cells as well as for the screening of novel antitumor agents. The present review is aimed at summarizing the most common 3D cell culture methods and applications, with a focus on prostate cancer modeling and drug discovery.

pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

Peptide-based biopolymers represent highly promising biocompatible materials with multiple applications, such as tailored drug delivery, tissue engineering and regeneration, and as stimuli-responsive materials. Herein, we report the pH- and concentration-dependent self-assembly and conformational transformation of the newly synthesized octapeptide PEP-1. At pH 7.4, PEP-1 forms β-sheet-rich secondary structures into fractal-like morphologies, as verified by circular dichroism (CD), Fourier-transform infrared (FTIR) spectroscopy, thioflavin T (ThT) fluorescence spectroscopy assay, and atomic force microscopy (AFM). Upon changing the pH value (using pH 5.5 and 13.0), PEP-1 forms different types of secondary structures and resulting morphologies due to electrostatic repulsion between charged amino acids. PEP-1 can also form helical or random-coil secondary structures at a relatively low concentration. The obtained pH-sensitive self-assembly behavior of the target octapeptide is expected to contribute to the development of novel drug nanocarrier assemblies.

Three-dimensional culture and clinical drug responses of a highly metastatic human ovarian cancer HO-8910PM cells in nanofibrous microenvironments of three hydrogel biomaterials

Background

Ovarian cancer is a highly aggressive malignant disease in gynecologic cancer. It is an urgent task to develop three-dimensional (3D) cell models in vitro and dissect the cell progression-related drug resistance mechanisms in vivo. In the present study, RADA16-I peptide has the reticulated nanofiber scaffold networks in hydrogel, which is utilized to develop robust 3D cell culture of a high metastatic human ovarian cancer HO-8910PM cell line accompanied with the counterparts of Matrigel and collagen I.

Results

Consequently, HO-8910PM cells were successfully cultivated in three types of hydrogel biomaterials, such as RADA16-I hydrogel, Matrigel, and collagen I, according to 3D cell culture protocols. Designer RADA16-I peptide had well-defined nanofiber networks architecture in hydrogel, which provided nanofiber cell microenvironments analogous to Matrigel and collagen I. 3D-cultured HO-8910PM cells in RADA16-I hydrogel, Matrigel, and collagen I showed viable cell proliferation, proper cell growth, and diverse cell shapes in morphology at the desired time points. For a long 3D cell culture period, HO-8910PM cells showed distinct cell aggregate growth patterns in RADA16-I hydrogel, Matrigel, and collagen I, such as cell aggregates, cell colonies, cell clusters, cell strips, and multicellular tumor spheroids (MCTS). The cell distribution and alignment were described vigorously. Moreover, the molecular expression of integrin β1, E-cadherin and N-cadherin were quantitatively analyzed in 3D-cultured MCTS of HO-8910PM cells by immunohistochemistry and western blotting assays. The chemosensitivity assay for clinical drug responses in 3D context indicated that HO-8910PM cells in three types of hydrogels showed significantly higher chemoresistance to cisplatin and paclitaxel compared to 2D flat cell culture, including IC₅₀ values and inhibition rates.

Conclusion

Based on these results, RADA16-I hydrogel is a highly competent, high-profile, and proactive nanofiber scaffold to maintain viable cell proliferation and high cell vitality in 3D cell models, which may be particularly utilized to develop useful clinical drug screening platform in vitro.

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

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

Controlling Neuronal Cell Growth through Composite Laminin Supramolecular Hydrogels

Designing an extracellular matrix mimic by biofunctionalization of polymeric scaffolds is a popular strategy and extremely crucial for facilitating the interactions between cells and the matrix. To this direction, supramolecular gels are gaining exponential attention over the last few years, owing to their potential biocompatibility and biodegradability. In spite of diverse biological roles of native laminin, the bioactivities of self-assembling laminin-derived short peptides were less explored. In this work, we have explored the minimalist design to develop hydrogel scaffolds based on IKVAV and YIGSR peptides individually and their composite matrix, which can provide structurally and functionally relevant materials for tissue engineering. Till date, composite supramolecular gels solely made up of self-assembling IKVAV and YIGSR peptides have never been reported. Such composite gels can be a closer mimic of natural laminin protein, which could mimic the essential functions of the short peptide fragments present on different chains of the extracellular matrix protein, laminin. Interestingly, we used a unique strategy of simple mixing of the two laminin mimetic peptides, which tend to induce coassembly with a self-sorted nanofibrous network with relatively enhanced mechanical strength. The physicochemical properties of the biofunctional hydrogels were studied using different microscopic, spectroscopic, and rheology techniques. To assess the bioactivity of laminin-derived scaffolds in controlling neuronal cell growth, its biocompatibility, cellular growth, and proliferation were quantified using C6 glial cells and SHSY5Y neuroblastoma cells. The live/dead staining further confirmed the adhesion and proliferation of the cells. A significant increase in neurite length provides clear evidence on mimicking the neurite extension function of native laminin protein by its short derivatives. Interestingly, similar β-III tubulin expression and cell cycle phases were observed, in comparison to control, which indicated normal cellular functioning of the cells cultured over short laminin hydrogel scaffolds. All bioassays suggested that Fmoc YIGSR promotes growth of neural cells to a greater extent and maintains healthier morphology, in comparison to hydrophobic Fmoc IKVAV, owing to the entangled longer fibrous network formed by YIGSR peptide. It is expected that thinner long fibers provide a more uniform surface and are more supportive for cell adhesion in comparison to hydrophobic, shorter fibers IKVAV peptide. However, in composite gels, the detrimental effect of hydrophobic IKVAV peptide could be reduced and better adhesion and proliferation could be achieved along with enhanced cell survival. These observations demonstrate the high potential of the laminin-derived hydrogels in tissue engineering and neuronal stem cell differentiation in future.

Design of a Peptide-Based Electronegative Hydrogel for the Direct Encapsulation, 3D Culturing, in Vivo Syringe-Based Delivery, and Long-Term Tissue Engraftment of Cells

Soft materials that facilitate the three-dimensional (3D) encapsulation, proliferation, and facile local delivery of cells to targeted tissues will aid cell-based therapies, especially those that depend on the local engraftment of implanted cells. Herein, we develop a negatively charged fibrillar hydrogel based on the de novo-designed self-assembling peptide AcVES3-RGDV. Cells are easily encapsulated during the triggered self-assembly of the peptide leading to gel formation. Self-assembly is induced by adjusting the ionic strength and/or temperature of the solution, while avoiding large changes in pH. The AcVES3-RGDV gel allows cell-material attachment enabling both two-dimensional and 3D cell culture of adherent cells. Gel-cell constructs display shear-thin/recovery rheological properties enabling their syringe-based delivery. In vivo cellular fluorescence as well as tissue resection experiments show that the gel supports the long-term engraftment of cells delivered subcutaneously into mice.

The Tumor-on-Chip: Recent Advances in the Development of Microfluidic Systems to Recapitulate the Physiology of Solid Tumors

The ideal in vitro recreation of the micro-tumor niche-although much needed for a better understanding of cancer etiology and development of better anticancer therapies-is highly challenging. Tumors are complex three-dimensional (3D) tissues that establish a dynamic cross-talk with the surrounding tissues through complex chemical signaling. An extensive body of experimental evidence has established that 3D culture systems more closely recapitulate the architecture and the physiology of human solid tumors when compared with traditional 2D systems. Moreover, conventional 3D culture systems fail to recreate the dynamics of the tumor niche. Tumor-on-chip systems, which are microfluidic devices that aim to recreate relevant features of the tumor physiology, have recently emerged as powerful tools in cancer research. In tumor-on-chip systems, the use of microfluidics adds another dimension of physiological mimicry by allowing a continuous feed of nutrients (and pharmaceutical compounds). Here, we discuss recently published literature related to the culture of solid tumor-like tissues in microfluidic systems (tumor-on-chip devices). Our aim is to provide the readers with an overview of the state of the art on this particular theme and to illustrate the toolbox available today for engineering tumor-like structures (and their environments) in microfluidic devices. The suitability of tumor-on-chip devices is increasing in many areas of cancer research, including the study of the physiology of solid tumors, the screening of novel anticancer pharmaceutical compounds before resourcing to animal models, and the development of personalized treatments. In the years to come, additive manufacturing (3D bioprinting and 3D printing), computational fluid dynamics, and medium- to high-throughput omics will become powerful enablers of a new wave of more sophisticated and effective tumor-on-chip devices.

pH-Responsive Biocompatible Supramolecular Peptide Hydrogel

Peptide-based hydrogels are highly promising for various biomedical applications owing to their precise self-assembly, biocompatibility, and sensitivity toward biologically relevant external stimuli. Herein, we report pH-responsive self-assembly and gelation of a highly biocompatible amphiphilic peptide PEP-1. This is an octa-peptide and double mutant of a naturally occurring β-strand peptide fragment of the protein Galectin-1, available in bovine spleen. PEP-1 was synthesized by using the Rink amide resin as the solid support in a homemade apparatus. At pH 7.4, it exhibits spontaneous gelation with very high yield stress of 88.0 Pa and gel-to-sol temperature of 84 °C at C = 2.0 wt %. Microscopy studies revealed entangled fibrillar morphology whereas circular dichroism, Fourier tranform IR, and Thioflavin T assay indicated formation of β-sheet rich secondary structure. The assembled state was found to be stable in neutral pH whereas either decrease or increase in the pH resulted in disassembly owing to the presence of the pH responsive Asp and Lys residues. The gel network showed ability to entrap water-soluble guest molecules such as Calcein which could be selectively released at acidic pH whereas under neutral condition the release was negligible. MTT assay revealed remarkable biocompatibility of the PEP-1 gel as almost 100% cells were alive after 48 h incubation in the presence of PEP-1 (2.0 mg/mL).

Designing a bioactive scaffold from coassembled collagen–laminin short peptide hydrogels for controlling cell behaviour

Exploring the potential of bifunctional collagen–laminin mimetic peptide based co-assembling gels for cell culture applications.