Hepatoblastoma (HB) represents the most common malignant liver tumor in infancy and is assumed to arise from immature liver progenitor cells by aberrant activation of genes important in embryonic development. The only recurrent genetic alteration described up to now is activating mutation of the beta-catenin gene in approx. 80% of HB cases, the key molecule of the Wnt signaling pathway. However, modeling constitutive Wnt activation in the mouse is not sufficient to drive liver tumorigenesis. To extend the understanding of the genetic basis of HB, whole exome sequencing of 8 HB patients was performed using Illumina HiSeq 2000 technology. Besides the well-described beta-catenin mutation, no other recurrent mutations could be identified. The overall mutation rate was very low, with only 3.9 mutations per tumor. However, many mutations were found in genes encoding components of the epigenetic machinery, including histones, histone deacetylases (HDAC) and demethylases, HDAC-binding corepressors, and transcription factors. These findings suggest that epigenetic misregulation rather than genetic alterations appears to be responsible for the formation of embryonal liver tumors on a beta-catenin mutated background.

Das Hepatoblastom (HB) stellt den häufigsten Lebertumor des Kindesalters dar und tritt meist innerhalb der ersten drei Lebensjahre auf. Obgleich durch die Kombination aus neoadjuvanter Chemotherapie mit chirurgischer Tumorresektion eine Vielzahl an Kindern mit HB geheilt werden kann, sind insbesondere Patienten mit Hochrisikomerkmalen wie Gefäßinvasion und Metastasen immer noch mit einer schlechten Prognose behaftet. In dieser Studie beschreiben wir anhand eines Kollektivs von 36 HB die Etablierung zweier epigenetischer Marker, die signifikant mit gefäßinvasivem Wachstum oder Metastasierung bei HB assoziiert sind. Hierbei handelt es sich um die Promoter-Hypermethylierung des insulin-like growth factor binding protein 3 (IGFBP3) und des Ras association (RalGDS/AF–6) domain family member 1 (RASSF1) Gens. Physiologische Level an IGFBP3 spielen eine wichtige Rolle bei der Regulierung des insulin-like growth factor 2 Signalwegs, der bei HB häufig konstitutiv aktiviert vorliegt. Durch die gezielte Wiedereinbringung von IGFBP3 konnten wir eine verminderte Migrations- und Invasionsfähigkeit der Lebertumorzellen erreichen. Insgesamt zeigen unsere Daten, dass IGFBP3 neben seiner tumorbiologischen Relevanz als Tumorsuppressorgen zukünftig zusammen mit RASSF1 als Marker für Hochrisiko-HB eingesetzt werden könnte.

Background: Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood with the ability to resist apoptosis by the activation of survival promoting and anti-apoptotic proteins. Methods: Efficacy of the apoptosis-inducing agent betulinic acid (BA) was determined in RMS cell cultures and in vivo by measuring cell viability, survival, apoptosis, hedgehog signalling activity, and neovascularisation. Results: Betulinic acid had a strong cytotoxic effect on RMS cells in a dose-dependent manner. The BA treatment caused a massive induction of apoptosis mediated by the intrinsic mitochondrial pathway, which could be inhibited by the broad-range caspase inhibitor zVAD.fmk. Exposure of hedgehog-activated RMS-13 cells to BA resulted in a strong decrease in GLI1 , GLI2 , PTCH1 , and IGF2 expression as well as hedgehog-responsive luciferase activity. Intraperitoneal injection of 20 mg BA per kg per day significantly retarded growth of RMS-13 xenografts in association with markedly higher counts of apoptotic cells and down-regulation of GLI1 expression compared with control tumours, while leaving microvascular density, cell proliferation, and myogenic differentiation unaffected. Conclusion: Our data show that induction of apoptosis and inhibition of hedgehog signalling are important features of the anti-tumourigenic effect of BA in RMS and advices this compound for the use in a multimodal therapy of this highly aggressive paediatric tumour.