Echappement à la chimiothérapie et émergence de cellules plus agressives : Importance de l’hétérogénéité tumorale

Activated by chemotherapy, senescence is a suppressive response which prevents cell cycle progress through activation of the p53-p21 and p16-Rb signaling pathways. However, despite the efficiency of this suppression, cancer cells can emerge to induce clinical relapse. In this study, we analyzed senescence escape in response to irinotecan, one of the first line treatment used in colorectal cancer. After treatment, senescence is induced in LS174T cell but a subpopulation of cells finally resume proliferation. Persistent cells (PLCs) are composed of an heterogenous mixture of senescent (PLS) and dividing cells (PLD). In spite of PLS, PLCs are able to grow in vivo as efficiently as parental LS174T cells. Importantly, persistence induced the emergence of more transformed cells characterized by the ability to grow in low adhesion conditions. PLD emergence and anoikis resistance depend on Mcl-1, Bcl-xL and p21. PLD and PLS enrichment, by flow cytometry, allowed us to identify PLS as essential for anoikis resistance. Our results suggest that PLS establish a favorable environment for the transformation of unaffected cells. Mcl-1 and Bcl-xL role in each population remains to be determined, but inhibitors of these protein used in combination with irinotecan should restrict the heterogeneity of the response and tumoral aggressiveness.Les dommages de l’ADN, induits par les traitements de chimiothérapie, sont responsables de l’induction de la sénescence, un arrêt définitif du cycle cellulaire dépendant des voies p53-p21 et p16-Rb. L'efficacité de cette suppression n’est pas optimale en raison d’une hétérogénéité de réponse à la chimiothérapie. Dans cette étude, nous avons analysé l’échappement à la sénescence en réponse à l’irinotécan, un traitement des cancers colorectaux. Dans les cellules LS174T, le processus de sénescence est induit mais des cellules conservent leurs capacités prolifératives et l’exercent après l’élimination du traitement. Les cellules proliférantes (PLD) et sénescentes (PLS) forment un mélange hétérogène appelé cellules persistantes (PLCs). Alors qu’elles sont constituées d’une part importante de cellules sénescentes, les PLCs sont capables de former des tumeurs in vivo, de manière comparable aux cellules parentales. De façon intéressante, le traitement est également associé à l’augmentation de l’agressivité caractérisée par la croissance en faible adhérence. L’émergence des PLD et la résistance à l’anoikis sont dépendantes de l’expression des protéines Mcl-1, Bcl-xL et p21. L’enrichissement des PLD et PLS, réalisé par cytométrie en flux, a permis d’identifier les PLS comme nécessaires à la résistance à l’anoikis. Les PLS pourraient donc créer un environnement favorable à la transformation de cellules non touchées par le traitement. Alors que le rôle de Mcl-1 et Bcl-xL dans chaque population reste à déterminer, l’utilisation d’inhibiteurs de ces protéines combinés à l’irinotécan pourrait limiter l’hétérogénéité de réponse à la chimiothérapie et l’agressivité tumorale

Distinct Merkel Cell Polyomavirus Molecular Features in Tumour and Non Tumour Specimens from Patients with Merkel Cell Carcinoma

Merkel Cell Polyomavirus (MCPyV) is associated with Merkel Cell carcinoma (MCC), a rare, aggressive skin cancer with neuroendocrine features. The causal role of MCPyV is highly suggested by monoclonal integration of its genome and expression of the viral large T (LT) antigen in MCC cells. We investigated and characterized MCPyV molecular features in MCC, respiratory, urine and blood samples from 33 patients by quantitative PCR, sequencing and detection of integrated viral DNA. We examined associations between either MCPyV viral load in primary MCC or MCPyV DNAemia and survival. Results were interpreted with respect to the viral molecular signature in each compartment. Patients with MCC containing more than 1 viral genome copy per cell had a longer period in complete remission than patients with less than 1 copy per cell (34 vs 10 months, P = 0.037). Peripheral blood mononuclear cells (PBMC) contained MCPyV more frequently in patients sampled with disease than in patients in complete remission (60% vs 11%, P = 0.00083). Moreover, the detection of MCPyV in at least one PBMC sample during follow-up was associated with a shorter overall survival (P = 0.003). Sequencing of viral DNA from MCC and non MCC samples characterized common single nucleotide polymorphisms defining 8 patient specific strains. However, specific molecular signatures truncating MCPyV LT were observed in 8/12 MCC cases but not in respiratory and urinary samples from 15 patients. New integration sites were identified in 4 MCC cases. Finally, mutated-integrated forms of MCPyV were detected in PBMC of two patients with disseminated MCC disease, indicating circulation of metastatic cells. We conclude that MCPyV molecular features in primary MCC tumour and PBMC may help to predict the course of the disease

Chemotherapy escape and emergence of more aggressive cells : A critical role for tumoral heterogeneity

Les dommages de l’ADN, induits par les traitements de chimiothérapie, sont responsables de l’induction de la sénescence, un arrêt définitif du cycle cellulaire dépendant des voies p53-p21 et p16-Rb. L'efficacité de cette suppression n’est pas optimale en raison d’une hétérogénéité de réponse à la chimiothérapie. Dans cette étude, nous avons analysé l’échappement à la sénescence en réponse à l’irinotécan, un traitement des cancers colorectaux. Dans les cellules LS174T, le processus de sénescence est induit mais des cellules conservent leurs capacités prolifératives et l’exercent après l’élimination du traitement. Les cellules proliférantes (PLD) et sénescentes (PLS) forment un mélange hétérogène appelé cellules persistantes (PLCs). Alors qu’elles sont constituées d’une part importante de cellules sénescentes, les PLCs sont capables de former des tumeurs in vivo, de manière comparable aux cellules parentales. De façon intéressante, le traitement est également associé à l’augmentation de l’agressivité caractérisée par la croissance en faible adhérence. L’émergence des PLD et la résistance à l’anoikis sont dépendantes de l’expression des protéines Mcl-1, Bcl-xL et p21. L’enrichissement des PLD et PLS, réalisé par cytométrie en flux, a permis d’identifier les PLS comme nécessaires à la résistance à l’anoikis. Les PLS pourraient donc créer un environnement favorable à la transformation de cellules non touchées par le traitement. Alors que le rôle de Mcl-1 et Bcl-xL dans chaque population reste à déterminer, l’utilisation d’inhibiteurs de ces protéines combinés à l’irinotécan pourrait limiter l’hétérogénéité de réponse à la chimiothérapie et l’agressivité tumorale.Activated by chemotherapy, senescence is a suppressive response which prevents cell cycle progress through activation of the p53-p21 and p16-Rb signaling pathways. However, despite the efficiency of this suppression, cancer cells can emerge to induce clinical relapse. In this study, we analyzed senescence escape in response to irinotecan, one of the first line treatment used in colorectal cancer. After treatment, senescence is induced in LS174T cell but a subpopulation of cells finally resume proliferation. Persistent cells (PLCs) are composed of an heterogenous mixture of senescent (PLS) and dividing cells (PLD). In spite of PLS, PLCs are able to grow in vivo as efficiently as parental LS174T cells. Importantly, persistence induced the emergence of more transformed cells characterized by the ability to grow in low adhesion conditions. PLD emergence and anoikis resistance depend on Mcl-1, Bcl-xL and p21. PLD and PLS enrichment, by flow cytometry, allowed us to identify PLS as essential for anoikis resistance. Our results suggest that PLS establish a favorable environment for the transformation of unaffected cells. Mcl-1 and Bcl-xL role in each population remains to be determined, but inhibitors of these protein used in combination with irinotecan should restrict the heterogeneity of the response and tumoral aggressiveness

STAT3 as a new autophagy regulator

International audienceSignal transducers and activators of transcription 3 (STAT3) proteins are cytoplasmic transcription factors that translocate into the nucleus to induce transcription following growth factor or cytokine stimulation. Besides their normal functions, these proteins play an important role in cancer cells through the abnormal activation of cell cycle progression and the deregulation of survival and senescence pathways. New data obtained from the laboratory of Guido Kroemer identifies STAT3 as a new autophagy regulator. In the cytoplasm, in the absence of conventional phosphorylation on the tyrosine 705 residue, STAT3 interacts with the PKR kinase to inhibit eIF2A phosphorylation and so reduce autophagic pathways. This new and nonconventional function of STAT3 has an important role in normal cells but we suggest that it might also affect cancer cells and the response to chemotherapy treatment.</p

Echappement tumoral lors de la chimiothérapie : un choix entre sénescence et apoptose dans des tumeurs hétérogènes

International audienceMots clés Chimiothérapie Sénescence Apoptose Hétérogénéité Résistance Cancer colorectal Résumé Contrer la résistance tumorale est un enjeu majeur des traitements de chimiothérapie. Plusieurs mécanismes d'arrêt inhibent le cycle cellulaire mais alors que ceux-ci semblaient définitifs, des études récentes décrivent l'adaptation des cellules et soulignent l'importance des contrôles mitotiques et post-mitotiques. L'ensemble de ces évènements doit donc être pris en compte pour comprendre la réponse aux chimiothérapies et identifier des marqueurs prédictifs de résistance. Cependant, pour définir ces capacités d'adaptation, il faut également considérer les réponses suppressives induites par ces points de contrôle, l'apoptose et la sénescence. L'apoptose semble un mécanisme suppresseur plus efficace, si l'on considère qu'obtenir une cellule morte est un objectif plus pertinent que de conserver une cellule tumorale arrêtée mais toujours vivante et influençant son environnement. Cependant, comparer ces mécanismes pourrait supposer que toutes les cellules au sein d'une tumeur choisissent exclusivement l'une ou l'autre des réponses. Illustrée dans le cancer colorectal, l'hétérogénéité intra-tumorale, définie comme la présence de clones et altérations différents, est certainement responsable d'une hétérogénéité de réponse au sein d'une même tumeur. De plus, les notions de cellules souches, de plasticité et de micro-environnement complexifient la théorie des stratégies thérapeutiques. La coexistence de cellules proliférantes ou dédifférenciées, de cellules tumorales ou stromales ainsi que leurs relations assurent en effet des capacités d'adaptation efficaces. Au-delà de la compréhension des méca-nismes de réponse et du choix entre apoptose et sénescence, l'hétérogénéité des cellules à cibler, leur plasticité et leur interdépendance restent donc des défis majeurs pour les futures thérapies anticancéreuses. Reçu le 16 octobre 2015 Accepté le 29 octobre 2015 Disponible sur internet le : 4 janvier 2016 tome 103 > n81 > janvier 2016 http://dx

Akt inhibition improves irinotecan treatment and prevents cell emergence by switching the senescence response to apoptosis

International audienceActivated in response to chemotherapy, senescence is a tumor suppressive mechanism that induces a permanent loss of proliferation. However, in response to treatment, it is not really known how cells can escape senescence and how irreversible or incomplete this pathway is. We have recently described that cells that escape senescence are more transformed than non-treated parental cells, they resist anoikis and rely on Mcl-1. In this study, we further characterize this emergence in response to irinotecan, a first line treatment used in colorectal cancer. Our results indicate that Akt was activated as a feedback pathway during the early step of senescence. The inhibition of the kinase prevented cell emergence and improved treatment efficacy, both in vitro and in vivo. This improvement was correlated with senescence inhibition, p21waf1 downregulation and a concomitant activation of apoptosis due to Noxa upregulation and Mcl-1 inactivation. The inactivation of Noxa prevented apoptosis and increased the number of emergent cells. Using either RNA interference or p21waf1-deficient cells, we further confirmed that an intact p53-p21-senescence pathway favored cell emergence and that its downregulation improved treatment efficacy through apoptosis induction. Therefore, although senescence is an efficient suppressive mechanism, it also generates more aggressive cells as a consequence of apoptosis inhibition. We therefore propose that senescence-inducing therapies should be used sequentially with drugs favoring cell death such as Akt inhibitors. This should reduce cell emergence and tumor relapse through a combined induction of senescence and apoptosis

Regulation of senescence escape by the cdk4–EZH2–AP2M1 pathway in response to chemotherapy

Abstract Senescence is a tumor suppressive mechanism that induces a permanent proliferative arrest in response to an oncogenic insult or to the genotoxic stress induced by chemotherapy. We have recently described that some cells can escape this arrest, either because senescence was incomplete or as a consequence of a phenotypic adaptation. Malignant cells which resisted senescence emerged as more transformed cells that resist anoikis and rely on survival pathways activated by Akt and Mcl-1. In this study, we further characterize senescence escape, investigating how emergent cells could reproliferate. During the initial step of chemotherapy-induced senescence (CIS), we found that cyclin D1 was upregulated and that cell emergence was prevented when its main partner cdk4 was inactivated. Results indicate that this kinase induced the upregulation of the EZH2 methylase, a component of the polycomb PRC2 complex. Downregulated during the early step of treatment, the methylase was reactivated in clones that escaped senescence. The inactivation of EZH2, either by siRNA or by specific inhibitors, led to a specific inhibition of cell emergence. We used quantitative proteomic analysis to identify new targets of the methylase involved in senescence escape. We identified proteins involved in receptor endocytosis and described new functions for the AP2M1 protein in the control of chemotherapy-mediated senescence. Our results indicate that AP2M1 is involved in the transmission of secreted signals produced by senescent cells, suggesting that this pathway might regulate specific receptors involved in the control of CIS escape. In light of these results, we therefore propose that the cdk4–EZH2–AP2M1 pathway plays an important role during chemotherapy resistance and senescence escape. Since targeted therapies are available against these proteins, we propose that they should be tested in the treatment of colorectal or breast cancers that become resistant to first-line genotoxic therapies