Modèles in vivo de tumeurs gliales pédiatriques : développement et application en préclinique

Les tumeurs gliales sont les tumeurs cérébrales les plus fréquemment retrouvées chez l’enfant. Les gliomes infiltrant du tronc cérébral (DIPG) sont la forme la plus agressive des gliomes pédiatriques. Les épendymomes (EPN) restent actuellement difficilement curables et à l’origine de fréquentes rechutes. Le manque de matériel biologique et l'absence de modèles in vitro et in vivo pertinents ont longtemps entravé le développement de nouvelles thérapeutiques dans ces deux cancers. Des études récentes ont montré que le DIPG est caractérisé par une mutation unique située sur la queue régulatrice de l’histone H3 dans l’un des deux gènes HIST1H3B/C ou H3F3A. En revanche, aucune cible moléculaire n’a pu être identifiée par séquençage du génome dans les EPN. Récemment, il a été montré que le profil de méthylation des EPN permet de diviser les EPN de la fosse postérieure (EPN-PF) et les EPN supratentoriels (EPN-ST) en neuf sous-groupes différents.Dans un premier temps, nous avons développé des xénogreffes par stéréotaxie dans la souris Nude (i) de manière directe en greffant directement les cellules tumorales afin d’obtenir des modèles PDOX (Patient Derived Orthotopic Xenograft), et (ii) de manière indirecte en cultivant in vitro les cellules tumorales avant injection in vivo afin d’obtenir des modèles de CDOX (Cell Derived Orthotopic Xenograft). Ainsi, nous avons obtenu 15 PDOX et 8 CDOX bioluminescentes de DIPG différents à partir de biopsies de patient au diagnostic ; ainsi que 3 PDOX d’EPN-PF et 1 PDOX d’EPN-ST à partir de résections tumorales de patient au diagnostic ou à la rechute. Une analyse approfondie des tumeurs de DIPG obtenues montre que les xénogreffes conservent le phénotype de la tumeur du patient, en particulier les principales caractéristiques du DIPG, tout en reflétant l’hétérogénéité interindividuelle observée chez les patients. L’histologie des xénogreffes d’EPN relève leur pertinence vis-à-vis de la maladie. A partir de ces PDOX, nous avons pu générer 3 PDOX bioluminescentes sans sélection clonale in vitro au préalable. Puis, nous avons évalué le mébendazole dans deux modèles CDOX de DIPG. La toxicité du médicament utilisé à forte dose de manière chronique n’a pas permis de mettre en évidence un effet thérapeutique décisif. Enfin, nous avons adapté un système d’ouverture de la barrière hématoencéphalique (BHE) à l’aide d’ultrasons non focalisés couplés à des microbulles dans nos modèles in vivo deDIPG. Malgré l’ouverture de la BHE, il n’a pas été possible de potentialiser l’effet thérapeutique du panobinostat dans une CDOX de DIPG, le passage du médicament n’étant pas augmenté dans le tissu cérébral. Nous sommes actuellement en cours d’évaluation d’un nouveau médicament candidat, l’irinotécan

Polo-like Kinase Inhibitor Volasertib Exhibits Antitumor Activity and Synergy with Vincristine in Pediatric Malignancies

Polo-like kinase 1 (PLK1) controls the main cell-cycle checkpoints, suggesting utility of its inhibition for cancer treatment, including of highly proliferative pediatric cancer. This preclinical study explored the selective PLK1 inhibitor volasertib (BI 6727) alone and combined with chemotherapy in pediatric malignancies. Inhibition of proliferation was explored in vitro using dimethylthiazol carboxymethoxyphenyl sulfophenyl tetrazolium (MTS) assay. Mice bearing human xenografts were treated with weekly intravenous injections of volasertib. Volasertib inhibited proliferation in all 40 cell lines tested, with a mean half-maximal growth inhibitory concentration of 313 nmol/l (range: 4-5000 nmol/l). Volasertib was highly active against RMS-1 alveolar rhabdomyosarcoma xenografts, resulting in 100% tumor regression. Activity was associated with complete and prolonged G2/M arrest and subsequent apoptotic cell death. Volasertib showed synergistic activity with vincristine but antagonistic effects with etoposide. These findings support the further exploration of volasertib for pediatric malignancies, particularly alveolar rhabdomyosarcoma, and its combination with mitotic spindle poiso

Regorafenib: Antitumor Activity upon Mono and Combination Therapy in Preclinical Pediatric Malignancy Models.

The multikinase inhibitor regorafenib (BAY 73-4506) exerts both anti-angiogenic and anti-tumorigenic activity in adult solid malignancies mainly advanced colorectal cancer and gastrointestinal stromal tumors. We intended to explore preclinically the potential of regorafenib against solid pediatric malignancies alone and in combination with anticancer agents to guide the pediatric development plan. In vitro effects on cell proliferation were screened against 33 solid tumor cell lines of the Innovative Therapies for Children with Cancer (ITCC) panel covering five pediatric solid malignancies. Regorafenib inhibited cell proliferation with a mean half maximal growth inhibition of 12.5 μmol/L (range 0.7 μmol/L to 28 μmol/L). In vivo, regorafenib was evaluated alone at 10 or 30 mg/kg/d or in combination with radiation, irinotecan or the mitogen-activated protein kinase kinase (MEK) inhibitor refametinib against various tumor types, including patient-derived brain tumor models with an amplified platelet-derived growth factor receptor A (PDGFRA) gene. Regorafenib alone significantly inhibited tumor growth in all xenografts derived from nervous system and connective tissue tumors. Enhanced effects were observed when regorafenib was combined with irradiation and irinotecan against PDGFRA amplified IGRG93 glioma and IGRM57 medulloblastoma respectively, resulting in 100% tumor regressions. Antitumor activity was associated with decreased tumor vascularization, inhibition of PDGFR signaling, and induction of apoptotic cell death. Our work demonstrates that regorafenib exhibits significant antitumor activity in a wide spectrum of preclinical pediatric models through inhibition of angiogenesis and induction of apoptosis. Furthermore, radio- and chemosensitizing effects were observed with DNA damaging agents in PDGFR amplified tumors

VRK3 depletion induces cell cycle arrest and metabolic reprogramming of pontine diffuse midline glioma - H3K27 altered cells

International audienceWe previously identified VRK3 as a specific vulnerability in DMG-H3K27M cells in a synthetic lethality screen targeting the whole kinome. The aim of the present study was to elucidate the mechanisms by which VRK3 depletion impact DMG-H3K27M cell fitness. Gene expression studies after VRK3 knockdown emphasized the inhibition of genes involved in G1/S transition of the cell cycle resulting in growth arrest in G1. Additionally, a massive modulation of genes involved in chromosome segregation was observed, concomitantly with a reduction in the level of phosphorylation of serine 10 and serine 28 of histone H3 supporting the regulation of chromatin condensation during cell division. This last effect could be partly due to a concomitant decrease of the chromatin kinase VRK1 in DMG following VRK3 knockdown. Furthermore, a metabolic switch specific to VRK3 function was observed towards increased oxidative phosphorylation without change in mitochondria content, that we hypothesized would represent a cell rescue mechanism. This study further explored the vulnerability of DMG-H3K27M cells to VRK3 depletion suggesting potential therapeutic combinations, e.g. with the mitochondrial ClpP protease activator ONC201

Antitumor activity of regorafenib <i>in vivo</i> against various subcutaneous pediatric tumor xenografts.

<p>Animals bearing subcutaneous RMS-1 rhabdomyosarcoma, STA-ET-1 and EW7 Ewing sarcoma, SJ-N-B8 and SK-N-AS neuroblastoma xenografts were treated orally with regorafenib at 10 mg/kg/d (light blue; R-10) and/or 30 mg/kg/d (dark blue, R-30), or with vehicle (grey, C) for a minimum of 21 days; treatment periods are indicated by bars above the graphs. (A) Graphs show arithmetic means ± standard error of mean (SEM) of tumor volumes. (B) Times to reach 5 times the initial volume (V_i) of 3–14 tumors per group is displayed as box plot, + represents means and error bars minimum to maximum values. Statistical significance was estimated by Mann-Whitney or Kruskal-Wallis tests, ****p<0.0001 ***<0.001, **<0.01., *<0.05.</p

Regorafenib activity alone and in combination against patient-derived tumor models is mediated by anti-angiogenic effects and induction of cell death.

<p>Paraffin-embedded sections of IGRG93 (left column), IGRM57 (central column) and NEM14 (right column) tumors, harvested at Day 3 post-treatment initiation, were stained immunohistochemically with anti-CD34 and anti-cleaved caspase 3 antibodies and histologically with Hematoxylin-Eosin-Saffron (HES). (A) Microvessel area and (B) apoptosis index are presented as means ± SEM of 3 controls and regorafenib 30 mg/kg/d treated tumors each (*p<0.05; Mann-Whitney). Due to extensive necrosis only one sample could be evaluated in the combination group of the IGRG93 study. For IGRM57, the assessment of viable tumor by excluding necrotic areas was estimated on HES stained sections. (C) Total lysates from individual tumors were subjected to Western blotting for expression analyses of phosphorylated (p-) and non-phosphorylated PDGFRA, PDGFRB, AKT and ERK1/2. β-actin was used as reference. C: control, R: regorafenib; X: omitted sample due to limited availability of tumor 1; RT: irradiation, Iri: irinotecan.</p