Cocultures of Mesenchymal Stem Cells and Endothelial Cells As Organotypic Models of Prostate Cancer Metastasis

Modelling bone metastasis in spheroids to study cancer progression and screen cisplatin efficacy

Most bone metastases are caused by primary breast or prostate cancer cells settling in the bone microenvironment, affecting normal bone physiology and function and reducing 5-year survival rates to 10% and 6%, respectively. To expedite clinical availability of novel and effective bone metastases treatments, reliable and predictive in vitro models are urgently required to screen for novel therapies as current in vitro 2D planar mono-culture models do not accurately predict the clinical efficacy. We herein engineered a novel human in vitro 3D co-culture model based on spheroids to study dynamic cellular quantities of (breast or prostate) cancer cells and human bone marrow stromal cells and screen chemotherapeutic efficacy and specificity of the common anticancer drug cisplatin. Bone metastatic spheroids (BMSs) were formed rapidly within 24 h, while the morphology of breast versus prostate cancer BMS differed in terms of size and circularity upon prolonged culture periods. Prestaining cell types prior to BMS formation enabled confocal imaging and quantitative image analysis of in-spheroid cellular dynamics for up to 7 days of BMS culture. We found that cancer cells in BMS proliferated faster and were less susceptible to cisplatin treatment compared to 2D control cultures. Based on these findings and the versatility of our methodology, BMS represent a feasible 3D in vitro model for screening of new bone cancer metastases therapies.

Advancing Treatment of Bone Metastases through Novel Translational Approaches Targeting the Bone Microenvironment

Bone metastases represent a lethal condition that frequently occurs in solid tumors such as prostate, breast, lung, and renal cell carcinomas, and increase the risk of skeletal-related events (SREs) including pain, pathologic fractures, and spinal cord compression. This unique metastatic niche consists of a multicellular complex that cancer cells co-opt to engender bone remodeling, immune suppression, and stromal-mediated therapeutic resistance. This review comprehensively discusses clinical challenges of bone metastases, novel preclinical models of the bone and bone marrow microenviroment, and crucial signaling pathways active in bone homeostasis and metastatic niche. These studies establish the context to summarize the current state of investigational agents targeting BM, and approaches to improve BM-targeting therapies. Finally, we discuss opportunities to advance research in bone and bone marrow microenvironments by increasing complexity of humanized preclinical models and fostering interdisciplinary collaborations to translational research in this challenging metastatic niche.

On-demand retrieval of cells three-dimensionally seeded in injectable thioester-based hydrogels

Scaffold systems that can easily encapsulate cells and safely retrieve them at the desired time are important for the advancement of cell-based medicine. In this study, we designed and fabricated thioester-based poly(ethylene glycol) (PEG) hydrogels with injectability and on-demand degradability as new scaffold materials for cells. Hydrogels can be formed in situ within minutes via thioester cross-linking between PEG molecules and can be degraded under mild conditions in response to l-cysteine molecules through thiol exchange occurring at the thioester linkage. Various cell experiments, especially with sucrose, which enables the adjustment of the osmotic pressure around the cells, showed that the damage to the cells during encapsulation and degradation was minimal, indicating the capability of on-demand retrieval of intact cells. This hydrogel system is a versatile tool in the field of cell-based research and applications such as tissue regeneration and regenerative medicine.

Human mesenchymal stem/stromal cells can be three-dimensionally encapsulated in hydrogels cross-linked with thioester linkages. Degrading the cell-embedded hydrogels by l-cysteine molecules enables safe on-demand retrieval of the cells.

Engineered In Vitro Models of Tumor Dormancy and Reactivation

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.

Chimeric antigen receptor T cells for the treatment of cancer and the future of preclinical models for predicting their toxicities

Chimeric antigen receptor T-cell therapy has achieved highly promising results in clinical trials, particularly in B-cell malignancies. However, reports of serious adverse events including a number of patient deaths have raised concerns about safety of this treatment. Presently available preclinical models are not designed for predicting toxicities seen in human patients. Besides choosing the right animal model, careful considerations must be taken in chimeric antigen receptor T-cell design and the amount of T cells infused. The development of more sophisticated in vitro models and humanized mouse models for preclinical modeling and toxicity tests will help us to improve the design of clinical trials in cancer immunotherapy.

Personalized Medicine Approaches in Prostate Cancer Employing Patient Derived 3D Organoids and Humanized Mice

Prostate cancer (PCa) is the most common malignancy and the second most common cause of cancer death in Western men. Despite its prevalence, PCa has proven very difficult to propagate in vitro. PCa represents a complex organ-like multicellular structure maintained by the dynamic interaction of tumoral cells with parenchymal stroma, endothelial and immune cells, and components of the extracellular matrix (ECM). The lack of PCa models that recapitulate this intricate system has hampered progress toward understanding disease progression and lackluster therapeutic responses. Tissue slices, monolayer cultures and genetically engineered mouse models (GEMM) fail to mimic the complexities of the PCa microenvironment or reproduce the diverse mechanisms of therapy resistance. Moreover, patient derived xenografts (PDXs) are expensive, time consuming, difficult to establish for prostate cancer, lack immune cell-tumor regulation, and often tumors undergo selective engraftments. Here, we describe an interdisciplinary approach using primary PCa and tumor initiating cells (TICs), three-dimensional (3D) tissue engineering, genetic and morphometric profiling, and humanized mice to generate patient-derived organoids for examining personalized therapeutic responses in vitro and in mice co-engrafted with a human immune system (HIS), employing adaptive T-cell- and chimeric antigen receptor- (CAR) immunotherapy. The development of patient specific therapies targeting the vulnerabilities of cancer, when combined with antiproliferative and immunotherapy approaches could help to achieve the full transformative power of cancer precision medicine.

Development and Characterization of Organic Electronic Scaffolds for Bone Tissue Engineering

Bones have been shown to exhibit piezoelectric properties, generating electrical potential upon mechanical deformation and responding to electrical stimulation with the generation of mechanical stress. Thus, the effects of electrical stimulation on bone tissue engineering have been extensively studied. However, in bone regeneration applications, only few studies have focused on the use of electroactive 3D biodegradable scaffolds at the interphase with stem cells. Here a method is described to combine the bone regeneration capabilities of 3D-printed macroporous medical grade polycaprolactone (PCL) scaffolds with the electrical and electrochemical capabilities of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). PCL scaffolds have been highly effective in vivo as bone regeneration grafts, and PEDOT is a leading material in the field of organic bioelectronics, due to its stability, conformability, and biocompatibility. A protocol is reported for scaffolds functionalization with PEDOT, using vapor-phase polymerization, resulting in a conformal conducting layer. Scaffolds' porosity and mechanical stability, important for in vivo bone regeneration applications, are retained. Human fetal mesenchymal stem cells proliferation is assessed on the functionalized scaffolds, showing the cytocompatibility of the polymeric coating. Altogether, these results show the feasibility of the proposed approach to obtain electroactive scaffolds for electrical stimulation of stem cells for regenerative medicine.

Targeting dormant micrometastases: rationale, evidence to date and clinical implications

In spite of decades of research, cancer survival has increased only modestly. This is because most research is based on models of primary tumors. Slow recognition has begun that disseminated, dormant cancer cells (micrometastatic cells) that are generally resistant to chemotherapy are the culprits in recurrence, and until these are targeted effectively we can expect only slow progress in increasing overall survival from cancer. This paper reviews efforts to understand the mechanisms by which cancer cells can become dormant, and thereby identify potential targets and drugs either on the market or in clinical trials that purport to prevent metastasis. This review targets the most recent literature because several excellent reviews have covered the literature from more than two years ago. The paper also describes recent work in the authors' laboratories to develop a screening-based approach that does not require understanding of mechanisms of action or the molecular target. Success of this approach shows that targeting micrometastatic cells is definitely feasible.

Experimental models of bone metastasis: Opportunities for the study of cancer dormancy

Skeletal metastasis is prevalent in many cancers, and has been the subject of intense research, yielding innovative models to study the multiple stages of metastasis. It is now evident that, in the early stages of metastatic spread, disseminated tumour cells in the bone undergo an extended period of growth arrest in response to the microenvironment, a phenomenon known as "dormancy". Dormancy has been implicated with drug resistance, while enforced dormancy has also been seen as a radical method to control cancer, and engineering of dormant states has emerged as a novel clinical strategy. Understanding of the subject, however, is limited by the availability of models to describe early stages of metastatic spread. This mini-review provides a summary of experimental models currently being used in the study of bone metastasis and the applications of these models in the study of dormancy. Current research in developing improved models is described, leading to a discussion of challenges involved in future developments.