Project: Contribution of CTC clusters to breast cancer metastasis.
The aim of the research focuses on understanding the mechanisms of tumour dissemination by studying the “clusters” of circulating tumour cells, small groupings of tumour cells that contribute to the process of metastasis. In order to be able to perform both functional and molecular characterisation of breast cancer CTC clusters, the stage of cell dissemination has been recreated through in vitro modelling of CTC clusters. To this end, a protocol has been established to generate cell suspensions, both individual and in small clusters, which have been used in functional in vitro studies representative of the metastasis process. Furthermore, xenotransplants of these cell suspensions have been optimised and developed in animal models, such as the mouse and especially the zebrafish embryo, for the modelling of the metastatic process. The combination of these experimental approaches has allowed us to observe that CTC clusters present certain biological advantages over individual CTCs, such as increased survival in circulation due to greater resistance to haemodynamic stress in the circulation and maintenance of cell proliferation, contributing to an increased probability of successful metastasis formation. In addition, disseminated CTC clusters have been found to have differential gene expression that supports their increased survival and proliferation. These results have highlighted the importance of zebrafish as a valuable model and tool for understanding the biology of CTCs, and in particular, CTC clusters. This work has been recently published (Int. J. Mol. Sci. 2021, 22, 9279; https://doi.org/10.3390/ijms22179279). On the other hand, work has been done on the study of CTC clusters as a prognostic tool in patients with advanced breast cancer. The work carried out has allowed us to determine that the presence of CTC clusters in the blood of these patients correlates with a shorter time to progression and a shorter overall survival, establishing it as an independent prognostic factor. In addition, patients with larger CTC clusters have a higher risk of death (Cancers 2020, 12, 1111; https://doi.org/10.3390/cancers12051111).
The experience gained in these initial projects has allowed us to establish other research projects, such as the one focused on the identification of CTC cluster markers, or the one aimed at understanding the role of cells from the tumour microenvironment in the biology of CTC clusters. In the former, we studied the genomic profile of CTC clusters in comparison to individual CTCs and observed a different mutational profile, which could be involved in the metastatic capacity of the clusters. These mutations appear to be unique to the CTC clusters and not shared with mutations observed in the primary tumour. In the second project, we have observed that cancer-associated fibroblasts (CAF), one of the main components of the tumour microenvironment, are able to modify the behaviour of tumour cells in clusters, an effect dependent on the molecular characteristics of tumour cells. In addition, we have observed effects on the nesting and proliferation of CTC clusters, without significantly affecting their ability to spread. Furthermore, the data obtained indicate that CAFs play a regulatory role in the formation of CTC clusters.