Review: Challenges of In Vitro CAF Modelling in Liver Cancers

Abstract

Primary and secondary liver cancer are the third cause of death in the world, and as the incidence is increasing, liver cancer represents a global health burden. Current treatment strategies are insufficient to permanently cure patients from this devastating disease, and therefore other approaches are under investigation. The importance of cancer-associated fibroblasts (CAFs) in the tumour microenvironment is evident, and many pre-clinical studies have shown increased tumour aggressiveness in the presence of CAFs. However, it remains unclear how hepatic stellate cells are triggered by the tumour to become CAFs and how the recently described CAF subtypes originate and orchestrate pro-tumoural effects. Specialized in vitro systems will be needed to address these questions. In this review, we present the currently used in vitro models to study CAFs in primary and secondary liver cancer and highlight the trend from using oversimplified 2D culture systems to more complex 3D models. Relatively few studies report on the impact of cancer (sub)types on CAFs and the tumour microenvironment, and most studies investigated the impact of secreted factors due to the nature of the models.

Keywords: 2D; 3D; cancer-associated fibroblasts; hepatic stellate cells; in vitro models; liver cancer.

Figure 1

Cellular sources of myofibroblasts or CAFs in liver cancer. CAFs are a heterogeneous group of cells derived from several sources. In the liver, the majority of CAFs are derived from HSCs, but a minor percentage of CAFs originates from Bone Marrow Cells or Circulating Fibroblasts. The most frequently used markers to define CAFs include α-SMA, FAP-1, and PDGFR-α and are shared by the different cellular CAF sources. For in vitro studies, fibroblast or HSC cell lines of mouse or human origin are often used, but some studies use CAFs isolated from Mouse or Patient Tumour Samples or Primary Hepatic Stellate Cells. Image created by Biorender.

Figure 2

Culture setups to study the effects of tumour cells on CAFs in liver cancer.