Bioengineered in vitro three-dimensional tumor models in endocrine cancers

Abstract

Abstract: Endocrine tumors are a heterogeneous cluster of malignancies that originate from cells that can secrete hormones. Examples include, but are not limited to, thyroid cancer, adrenocortical carcinoma, and neuroendocrine tumors. Many endocrine tumors are relatively slow to proliferate, and as such, they often do not respond well to common antiproliferative chemotherapies. Therefore, increasing attention has been given to targeted therapies and immunotherapies in these diseases. However, in contrast to other cancers, many endocrine tumors are relatively rare, and as a result, less is understood about their biology, including specific targets for intervention. Our limited understanding of such tumors is in part due to a limitation in model systems that accurately recapitulate and enable mechanistic exploration of these tumors. While mouse models and 2D cell cultures exist for some endocrine tumors, these models often may not accurately model nuances of human endocrine tumors. Mice differ from human endocrine physiology and 2D cell cultures fail to recapitulate the heterogeneity and 3D architectures of in vivo tumors. To complement these traditional cancer models, bioengineered 3D tumor models, such as organoids and tumor-on-a-chip systems, have advanced rapidly in the past decade. However, these technologies have only recently been applied to most endocrine tumors. In this review we provide descriptions of these platforms, focusing on thyroid, adrenal, and neuroendocrine tumors and how they have been and are being applied in the context of endocrine tumors.

Keywords: bioengineered; in vitro; models; organoids; three-dimensional.

Figure 1.. Depictions of various 3D tumor model form factors.

a) Homogeneous and heterogeneous tumor spheroids are generally formed by hanging drop or round bottom well cultures. No extracellular matrix component is present. b) Traditional organoids form through self-organization driven by signals from basement membrane extract hydrogels such as Matrigel. c) Other 3D tumor constructs, sometimes also referred to as organoids or 3D tumor construct, can be formed by encapsulation of tumor cells in hydrogels of defined extracellular matrix or polymer components. d) Through integration of organoids or tumor constructs with microfluidic devices more dynamic platforms such as tumor invasion and migration models can be fabricated. By integrating a tumor organoid or construct with e) an additional tissue organoid or construct or f) multiple tissue organoids or constructs, one can model metastasis of tumor cells through microfluidic systems to downstream tissue sites.

Figure 2.. Generation of cell line and patient-derived adrenocortical carcinoma organoids.

a) H295R ACC cell line organoids were created by encapsulating H295R cells within covalently crosslinked hyaluronic acid and collagen hydrogels. b) LIVE/DEAD staining shows high viability on day 5 of culture. Green – calcein AM-stained viable cells; Red – Ethidium homodimer-1-stained dead cell nuclei. c-e) Immunofluorescent staining of common ACC biomarkers, including c) beta-catenin, d) steroidal factor 1 and alpha inhibin, and IGF2. f) ACC patient-derived tumor organoids were created by encapsulating cells from ACC tumor biospecimens in the same hydrogel system. g) LIVE/DEAD staining shows high viability of ACC PTOs. h) An example of deployment of ACC PTOs in a drug response experiment using clinically relevant drugs and drug cocktails. Statistical significance: * p < 0.05; ** p < 0.01.