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Tumorigenesis and tumor progression relies on the dialectics between tumor cells, the extracellular matrix and its remodelling enzymes, neighbouring cells and soluble cues. The host immune response is crucial in eliminating or promoting tumor growth and the reciprocal coevolution of tumor and immune cells, during disease progression and in response to therapy, shapes tumor fate by activating innate and adaptive mechanisms. The phenotypic plasticity is a common feature of epithelial and immune cells and epithelial-mesenchymal transition (EMT) is a dynamic process, governed by microenvironmental stimuli, critical in tumor cell shaping, increased tumor cell heterogeneity and stemness. In this review we will outline how the dysregulation of microenvironmental signaling is crucial in determining tumor plasticity and EMT, arguing how therapy resistance hinges on these dynamics.

Both embryonic and adult stem cells are endowed with a superior capacity to prevent the accumulation of genetic lesions, repair them, or avoid their propagation to daughter cells, which would be particularly detrimental to the whole organism. Inducible pluripotent stem cells also display a robust DNA damage response, but the stability of their genome is often conditioned by the mutational history of the cell population of origin, which constitutes an obstacle to clinical applications. Cancer stem cells are particularly tolerant to DNA damage and fail to undergo senescence or regulated cell death upon accumulation of genetic lesions. Such a resistance contributes to the genetic drift of evolving tumors as well as to their limited sensitivity to chemo- and radiotherapy. Here, we discuss the pathophysiological and therapeutic implications of the molecular pathways through which stem cells cope with DNA damage.

The propagation of whole-chromosome (aneuploid) or whole-genome (polyploid) defects is normally prevented by robust cell-intrinsic mechanisms. Moreover, non-diploid cells are under strict immunological surveillance. Nonetheless, tumors contain a high percentage of non-diploid genomes, indicating that malignant cells acquire the ability to bypass these control mechanisms and obtain a survival/proliferation benefit from bulky karyotypic defects. The non-diploid state imposes a significant metabolic burden on cancer cells and hence can be selectively targeted for therapeutic purposes. Here we discuss the impact of abnormal karyotypes on oncogenesis, tumor progression, and response to treatment, focusing on the biochemical and metabolic liabilities of non-diploid cells that can be harnessed for the development of novel chemo(immuno)therapeutic regimens against cancer.

Introduction Cancer stem cells (CSCs) are subsets of multipotent SCs responsible for tumour development, propagation and evolution, whose targeting is required for tumour eradication. There is (pre)clinical evidence on a role of CSCs in therapeutic resistance and intra-tumour heterogeneity, which limits the efficacy of antineoplastic regimens. In this context, CSCs reportedly share with embryonic/adult SCs a very robust DNA damage response, which favours the survival and resistance to genotoxins, and can be exploited for therapeutic purposes. Material and methods We generated a panel of ~30 CRC patient-derived tumorspheres enriched for CSCs (CRC-SCs) and characterised them at the genetic level. To discover potential monotherapeutic anti-CSC agents, we performed high-throughput screenings on multiple CRC-SCs with a library of clinically-relevant drugs. Flow cytometry, fluorescence microscopy and epistatic analyses were conducted to uncover the mechanism of action of identified compound(s), while genetic, cytogenetic and phosphoproteomic studies were carried out to identify predictive biomarkers. DNA replication stress (RS) levels were evaluated by analysing phosphorylated ATM/RPA foci and by performing COMET and DNA fibre assays, and were modulated by single administration of genome destabilising agents or by prolonged exposure to increased doses of compounds targeting the replication stress response (RSR). Results and discussions We demonstrated that the CHK1 inhibitor LY2606368 is a potent anti-CSC agent able to kill more than one third of CRC-SCs, both in vitro and in vivo. Moreover, we provided evidence of high but heterogeneous RS levels in CRC-SCs, showing that, in CRC-SCs, RS is mainly boosted endogenously by p53 deficiency, supernumerary chromosomes and DNA replication abnormalities, which results in high dependency on CHK1-mediated RSR. Accordingly, formerly LY2606368-resistant CRC-SCs were sensitised by boosting DNA replication errors or inducing whole-genome doubling, while formerly LY2606368-sensitive CRC-SCs made resistant by the continuous in vitro or in vivo administration of LY2606368 displayed diminished RS levels due to RSR rewiring, and became independent on CHK1. Conclusion Our results demonstrate that RSR is efficient and rewirable in CSCs thereby constituting a prominent therapeutic target. In particular, we designed dedicated RS-modulating or RSR-targeting strategies for long-term CSC depletion in CRC.

Introduction Immunogenic chemotherapy (IC) induces immunogenic cell death (ICD), which, similar to viral infection, leads to a cancer-cell autonomous Type-I-Interferon (IFN-I) signalling. This immunological signature is crucial for effective antitumor responses but may paradoxically promote the emergence of a rare population of cancer stem cells (CSCs) acting as a chemoresistant niche within the tumour and roots for metastasis and relapse. In this study, we have investigated the role of IFN-I during IC in inducing a cancer editing program resulting in the appearance of poor immunogenic CSCs. Material and methods Human and murine tumour cell lines were treated in vitro with ICD-inducers or IFN-I as control and the induction of CSC were analysed by cytofluorometry, quantitative real time (qRT)-PCR, 3D culture and functional assays. Free and vesicle-mediated nucleic acid transfer during ICD has been characterised by co-culture experiments. IC-induced CSC immunogenicity has been studied through cytofluorometry, microfluidic devices and in vivo experiments. All experiments have been done in triplicate and statistical significance evaluated by two-tailed Student’s t test and two-way ANOVA. Results and discussions The transient/acute induction of IFN-I during ICD is followed by the appearance of a rare population of CSCs. Both free nucleic acids and extracellular vesicles are released during tumour ICD constituting the upstream inducers of IFN-I-mediated reprogramming of neighbouring cells. IC-induced CSCs display epithelial-to-mesenchymal transition traits, multidrug resistance and regenerative properties, and a significant tumorigenic potential when inoculated in immunodeficient and immunocompetent mice. As expected, tumour growth and size are reduced in the presence of an intact immune system. Experiments on microfluidic devices reveal a poor immunogenic potential of CSCs, further confirmed by the expression of immune checkpoint blockers. Conclusion Our results pinpoint a surprising link between ICD, IFN-I and CSCs. Elucidating the mechanisms of CSC editing together with a deep characterisation of CSC (immune) properties could be crucial to prevent tumour relapse. This could undoubtedly have dramatic implications for the clinical management of cancer in an era of terrific development of precision combined chemo-immune therapy.