2 Reliance upon ancestral mutations is maintained in colorectal cancers that heterogeneously evolve during targeted therapies

Abstract

IntroductionClinical effectiveness of targeted therapies is often transitory and virtually all patients develop secondary resistance. The heterogeneous mechanisms of resistance and the sub-clonal evolution pattern of cell populations that emerge upon pharmacological selection limit disease control with subsequent lines of therapy. We used colorectal cancer (CRC) to test the hypothesis that ancestral oncogenic event (such as WNT pathway alterations) shared by every cell sub-clone might be better suited as therapeutic targets than heterogeneous events in the branches, as the former remain present in each drug-resistant cell independently from its genetic drift.Material and methodsExome analysis was performed on a panel of CRC cells that became resistant to commonly used targeted agents to uncover genetic alterations acquired under drug selective pressure. Tumour evolution of resistant cell population was then inferred through EXPANDs software. β-catenin activity, cell growth and death were measured upon functional and pharmacological modulation of WNT pathway in resistant cells and preclinical models established from tissues biopsy obtained from CRC patients who relapsed during treatment with targeted therapies.Results and discussionsExome sequencing and phylogenetic tracking unveiled a complex sub-clonal architecture in CRC resistance cell populations, indicating parallel evolution of multiple independent cellular lineages, each associated with distinct genomic landscapes. Functional and pharmacological inhibition of WNT signalling induces cell death in CRC preclinical models, regardless of drug type or resistance mechanisms. Pharmacological blockade of WNT pathway resulted in translocation of β-catenin to the plasma membrane, decreased of β-catenin dependent Tcf/LEF transcriptional activity, and cell growth impairment despite massive molecular drift of resistant derivatives. Concomitant blockade of WNT and MAPK signalling restrained evolution of drug-resistant clones and prevent onset of secondary resistance.ConclusionIn summary, reliance of CRC on the WNT pathway is preserved in later phases of colorectal carcinogenesis when tumours face genomic bottlenecks and sub-clonal evolution driven by administration of target therapies; thus offering the possibility of a common therapeutic strategy to overcome secondary resistance to treatments.