Ploidy‐Dependent Response to Anticancer Drugs of Human Embryonic Stem Cells

Polyploidy is normally found in numerous tissues and cell types in the generally diploid human body and is crucial for proper development. However, polyploidy, and especially triploidy, can also be found in malignant tumours and is often associated with chemoresistance, stemness and metastatic capabilities. Here, we utilise our isogenic haploid, diploid and triploid human embryonic stem cell (hESC) lines to study the effect of ploidy on the response to four different anticancer drugs. Surprisingly, we show that triploid cells are more sensitive to chemotherapy-induced apoptosis and cell cycle arrest than diploid and haploid cells, correlated with higher levels of DNA damage. This phenotype is regulated by p53, as it was reversed in TP53-KO cells, where triploid mutant cells display higher resistance to the chemotherapies we applied compared to mutant haploid and diploid cells. The reversal from sensitivity to resistance, driven by TP53-KO of the triploid cells, was accompanied by a reversal in the enrichment of DNA repair, replication and cell division related genes, compared to their diploid counterparts. Conversely, triploidy triggered DNA damage-induced differentiation in both WT and TP53-KO treated cells, pointing to a ploidy-dependent response not mediated by p53. In addition, we show that cancer cell lines also display similar ploidy-dependent anticancer drug responses to our TP53-KO hESCs. These findings uncover the interplay between ploidy and the p53 pathway in determining the outcome of anticancer therapeutics, and display the potential use of isogenic hESCs, differing only in their ploidy level, in studying the impact of ploidy on chemotherapy response.