Three-Dimensional Patient-Derived In Vitro Sarcoma Models: Promising Tools for Improving Clinical Tumor Management

Abstract

Over the past decade, the development of new targeted therapeutics directed against specific molecular pathways involved in tumor cell proliferation and survival has allowed an essential improvement in carcinoma treatment. Unfortunately, the scenario is different for sarcomas, a group of malignant neoplasms originating from mesenchymal cells, for which the main therapeutic approach still consists in the combination of surgery, chemotherapy, and radiation therapy. The lack of innovative approaches in sarcoma treatment stems from the high degree of heterogeneity of this tumor type, with more that 70 different histopathological subtypes, and the limited knowledge of the molecular drivers of tumor development and progression. Currently, molecular therapies are available mainly for the treatment of gastrointestinal stromal tumor, a soft-tissue malignancy characterized by an activating mutation of the tyrosine kinase KIT. Since the first application of this approach, a strong effort has been made to understand sarcoma molecular alterations that can be potential targets for therapy. The low incidence combined with the high level of histopathological heterogeneity makes the development of clinical trials for sarcomas very challenging. For this reason, preclinical studies are needed to better understand tumor biology with the aim to develop new targeted therapeutics. Currently, these studies are mainly based on in vitro testing, since cell lines, and in particular patient-derived models, represent a reliable and easy to handle tool for investigation. In the present review, we summarize the most important models currently available in the field, focusing in particular on the three-dimensional spheroid/organoid model. This innovative approach for studying tumor biology better represents tissue architecture and cell-cell as well as cell-microenvironment crosstalk, which are fundamental steps for tumor cell proliferation and survival.

Keywords: drug screening; in vitro organoid culture; patient-derived in vitro model; personalized medicine; preclinical model; sarcoma; sarcoma treatment.

Figure 1

Differentiation of normal mesenchymal stem cells (A) and altered differentiation (B). (B) The difference between the two hypotheses, whereby the initiating aberration occurs either at a later stage of differentiation (hypothesis 1) or hits the stem cell (hypothesis 2). Modified from the study by Teicher (24).

Figure 2

Different approaches for 3D cell culture model development. (A) Cellular spheroids: single cells from primary or stable cell lines aggregate together forming 3D structures. (B) Organotypic coculture: epithelial cells are cocultured with stroma cells embedded in a supporting matrix. (C) Organotypic slice culture: tissue slices obtained from the whole organ or from fragments of it are directly cultivated ex vivo. (D) Tissue organoids (PD3D™): primary cells isolated from fresh tissue without prior cell enrichment are grown as 3D multicellular structures [Modified from Silvestri et al. (64)].

Figure 3

Different methods for 3D spheroids development and growth. (A) Non-adhesive surfaces: culture plates with modified surfaces to reduce cell adhesion stimulate cell aggregation and formation of 3D structures. (B) Spinner flasks: stirred or rotating vessels are used to prevent cell adhesion to the surface of the plate allowing 3D spheroids formation. (C) Hanging drop: cells seeded in small drops of medium form cellular aggregates at the tip of the drop due to gravity forces. (D) Microcarrier beads: cells adhere to and proliferate on the surface of natural or synthetic solid beads forming 3D structures. (E) Hydrogel matrices: cells are seeded into matrices of natural or synthetic origin forming 3D structures by single cells aggregation or by monoclonal cell growth. [Modified from Silvestri et al. (64)].

Figure 4

Sarcoma spheroids growing in Matrigel-based three-dimensional cell culture.