Identification of theranostic biomarkers to improve the stratification of patients with pediatric liver cancer: Opportunities and challenges
Authors: Carolina Armengol, Stefano Cairo
Journal: Hepatology (2018)

Potential conflict of interest: Nothing to report. SEE ARTICLE ON PAGE 89 In the era of next‐generation sequencing and tailored treatments, the scientific community is being supplied with unprecedented tools to develop translational research. The comprehensive molecular profiling of tumors from thousands of patients is providing growing evidence that cancer is a general term to indicate different pathologies associated with different outcomes, even when occurring from the very same tissue or organ. A growing number of molecular biomarkers are being identified to support clinicians in their decisions in addition to clinical and histological parameters, with the aim to improve patient diagnosis and inform on the related risk. The molecular‐based identification of altered genes and pathways in cancer has pushed the development of drugs that target specific biological functions acquired by cancer cells to block their growth and induce their death. A theranostic biomarker allows the identification of a tumor subtype and concomitantly indicates a biological activity that can be targeted by a selective inhibitor, thus contributing to the diagnosis of the disease and indicating the therapy at the same time. Identification of theranostic biomarkers in cancer is a major goal in the era of precision medicine. The article by Hooks and collaborators describes the identification of the Fanconi anemia (FA) pathway as a theranostic marker for hepatoblastoma (HB), the most frequent malignant embryonal tumor of the liver in childhood. Despite being the predominant type of pediatric liver malignancies, HB, with a world‐wide incidence of 1.5 case/million children per year, is a very rare tumor. At diagnosis, risk assessment and treatment decisions are based on clinical parameters.1 Current cisplatin‐ and doxorubicin‐based chemotherapy protocols are very effective against primary HB. Nevertheless, around 25% of HB patients develop metastatic disease associated with poor prognosis. Due to HB rarity, the constitution of patient cohorts for clinical trials at relapse is a real challenge; therefore, the identification of new drugs for high‐risk/relapsed HB is a problematic issue. In 2008, a 16‐gene prognostic signature to discriminate distinct molecular subgroups of HB associated with different outcome was identified.2 Recent studies have adopted this signature as a reference and suggested the presence of a third molecular tumor subclass.3 Herein, Hooks et al. profiled 25 tumors and matched normal samples by RNA sequencing (RNAseq), and firm‐up this trend.4 As already shown in other studies, they observed a high frequency (80% of cases) of activating mutation of β‐catenin, a key driver of HB pathogenesis. They also observed overexpression of several markers such as DLK1 and LIN28B previously identified in independent studies, confirming that the molecular characteristics of HB are shared by different patient populations.2 Interestingly, they described a new 4‐gene signature not overlapping with the 16‐gene signature that separated the aggressive C2 subtype into two molecular classes, namely C2A, associated with high proliferation, and C2B, associated with epithelial‐mesenchymal transition (EMT) features (Fig. 1). Among the genes overexpressed in C2A, the overexpression of TOP2A, one of the four genes of the signature, accounts for the hyperproliferative trait of this tumor subtype. EMT features in C2B tumors are witnessed by the overexpression of genes such as TGFB1 and its targets, CTGF and JAG1, in addition to SNAI2 and VIM. EMT is a well‐established cellular process often associated with tumor resistance to genotoxic treatments and indicated as a cancer stem cell hallmark.6 At present, no actionable target is available to counteract EMT, whereas highly proliferative tumors often present alterations of genes involved in cell‐cycle checkpoints, chromatin remodeling, and DNA repair, against which several targeted approaches have been developed in the last 20 years.7Figure 1: Molecular classification of HB according to the 16‐gene signature (up) and identification of the druggable C2A subtype as proposed by Hook et al. (down).A main novelty in the article by Hooks et al. is the identification of bortezomib as a putative new drug for HB therapy. The researchers focused their attention on the C2A HB type and found an FA‐related signature consisting of overexpression of FANCD2, FANCI, and BRCA1 genes. FA is a recessively inherited disease associated with developmental abnormalities and increased risk of malignancies. Defective DNA repair caused by mutant FANC proteins induces chromosomal instability in hematopoietic stem cells and is considered as the primary causal factor in FA. At the genetic level, mutations in the FANCA, FANCC, and FANCG genes are the most common alterations observed and account for ∼85% of this disease.8 Conversely, no mutation of FANC genes has been reported by the researchers in their HB series. Because RNAseq data show that HuH6 and HepG2 cell lines have a transcriptional phenotype very similar to C2A, the researchers used these cells to investigate sensitivity to treatments currently used or under investigation to treat FA or to target the FA/BRCA complex. The researchers decided to test drugs that interfered with formation of the FA/BRCA complex, and they observed sensitivity of both HepG2 and HuH6 cells to bortezomib. Treatment of HB cells with bortezomib prevented FANCD2 and FANCI monoubiquitination and FANCD2/BRCA1 foci formation following cell irradiation, thus providing evidence for the mechanism of action underlying cell sensitivity. Treatment of HuH6‐derived xenografts with cisplatin and bortezomib as single agents or in combination induced attenuated tumour growth. In recent years, several targetable pathways have been shown to be aberrantly activated in HB, including the Sonic Hedgehog, PI3K/AKT/mTOR, and, more recently, the FGFR4/FGF19 pathways,9 and the drugs developed to inhibit these pathways are currently used to treat other forms of cancer. So far, very few clinical trials have been run to identify new drugs for HB patients, the most recent on the evaluation of irinotecan,11 and none to study the efficacy of a targeted treatment. This may be attributed, on one hand, to the rarity of HB and, on the other hand, to the lack of preclinical robustness and of companion biomarkers to identify patients that will benefit from the treatment. Bortezomib is a proteasome inhibitor already approved for treatment of pediatric leukemia; therefore, its use in another pediatric setting would be strongly facilitated. If confirmed, the identification of bortezomib as a new drug for HB and of a 4‐gene signature that allows the identification of patients that will benefit from this treatment would be an important step forward in the development of personalized treatment for HB patients. Recently, advances have been made in the development of preclinical tools to study HB, including new cell lines and large collections of patient‐derived xenografts.12 The availability of these models will allow the validation of new drugs and related predictive molecular markers, in order to provide convincing evidence of the pertinence of translating these discoveries into clinical acts. The need to identify and translate predictive and prognostic biomarkers into clinical practice has been well received. In this regard, definition of a consensus molecular stratification as well as validation of diagnostic/prognostic biomarkers that is planned along the first Paediatric Hepatic International Tumour Trial (PHITT; ClinicalTrials.gov Identifier: NCT03017326) offers a unique opportunity to move forward toward significant improvement of current HB management. Author names in bold designate shared co‐first authorship.