The advent of sophisticated biochemical and molecular techniques has helped advance our understanding of colorectal cancer (CRC) as a highly heterogeneous disease. However, due to the technical difficulty associated with studying intra-tumour heterogeneity, this phenomenon is not routinely evaluated in individual patients despite accumulating evidence for its influence on therapeutic response.
To assess the relationship between heterogeneity and treatment response, fluorescence microscopy was used to longitudinally monitor CRC cell populations transduced with Lentiviral Gene Ontology (LeGO) vectors expressing red, green and blue (RGB) fluorescent proteins. Individual cells and all their clonal descendants within the LeGO-transduced population express a unique fluorescent signature, allowing for assessment of drug susceptibility profiles and repopulation dynamics throughout the course of treatment at the subpopulation level.
Following exposure to an array of pharmacological compounds, clusters with heightened resistance to targeted therapies have been identified. Similarly, by monitoring LeGO subpopulations throughout treatment, it was shown that previously-dominant clusters are often outcompeted by previously-minor clusters, suggesting that the observed heterogeneity at subpopulation level is implicated in therapeutic response.
This work demonstrates how ex vivo characterisation of heterogenous treatment responses in tumour samples may aid in the identification of those at high risk of treatment resistance and recurrence, as well as in guiding these patients towards specific therapies or combination regimens from which they might benefit. Additionally, if the cellular and molecular characteristics which define the drug-resistant subpopulations can be elucidated, this may aid in the design of novel, targeted agents that will improve the clinical management of those with CRC.