An innovative methodology proposed by researchers with the Colorectal Cancer Laboratory at IRB Barcelona opens up the possibility to study human tumours by means of tracing genetic modifications. Such an approach had previously been feasible only in animal models and it may have broad applicability for the analysis of cancer cell diversity during human tumour development in vitro or after transplantation of tumours to a recipient animal.

“There is a large interest to study how distinct tumour cell population contribute to the evolution of the disease. Until know, these studies have necessary involved experiments of tumour dissociation and cell isolation, which have raised many conceptual and technical caveats. In essence, this new approach brings the power of mouse genetic tools to study human cancer and overcomes the limitations of identifying and tracking tumour cell populations in an intact environment,” explains ICREA Research Professor Eduard Batlle, who led the study published in the journal EMBO Molecular Medicine.

The researchers combine two novel methodologies, namely patient–derived tumour organoids (an organoid is a miniaturized and simplified version of an organ that is produced in vitro in three dimensions and that shows realistic micro–anatomy), and CRISPR/Cas9 genome–editing techniques (which allow the introduction of markers into genes of interest). The scientists consider that the combined method proved “particularly well suited” for analysing the diversity of cell populations within cancers as it allows the labelling and tracing of distinct tumour cells through desired marker genes.

“For the first time we can analyse cell lineage relationships in growing tumours, and this technique will help us to address how distinct cell populations contribute to growth, dissemination, and resistance to therapy,” wrote the IRB Barcelona authors in reference to the impact expected.

To illustrate the usefulness of this approach, postdoctoral fellow Carme Cortina and PhD student Gemma Turon, who contributed equally as first authors of the study, engineered human colorectal cancer cell organoids to carry a fluorescent marker inserted at LGR5 genes locus, which encodes a stem cell–specific gene. Until now, analysis of cells that express this gene in human tumours had been hampered by the lack of good commercial reagents to recognise this protein. “We have been able to follow LGR5+ cancer stem cell gene for the first time and reveal novel information about their behaviour in human cancers,” says Carme Cortina.

The analysis demonstrated that LGR5+ cells express a gene programme similar to that of normal intestinal stem cells and that they are capable of propagating the disease to recipient hosts very efficiently. The experiments also confirmed that human colorectal cancer cells adopt a hierarchical organisation reminiscent of that of the normal colonic epithelium.

Furthermore, Batlle and colleagues implemented this technology to map the fate of these cells within human CRC and discovered that LGR5+ tumour cells show long–term renewal and multilineage differentiation capacity – both hallmarks of stemness. Finally, the scientists also demonstrated that a subset of LGR5+ cells are dormant and do not divide or proliferate. It might be of interest to study the involvement of this dormant population in resistance to chemotherapy treatments.