FGF19 signaling through the FGFR4/β-klotho receptor complex has been shown to be a key driver of growth and survival in a subset of hepatocellular carcinomas, making selective FGFR4 inhibition an attractive treatment opportunity. A kinome-wide sequence alignment highlighted a poorly conserved cysteine residue within the FGFR4 ATP-binding site at position 552, two positions beyond the gate-keeper residue. Several strategies for targeting this cysteine to identify FGFR4 selective inhibitor starting points are summarized which made use of both rational and unbiased screening approaches. The optimization of a 2-formylquinoline amide hit series is described in which the aldehyde makes a hemithioacetal reversible-covalent interaction with cysteine 552. Key challenges addressed during the optimization are improving the FGFR4 potency, metabolic stability, and solubility leading ultimately to the highly selective first-in-class clinical candidate roblitinib.

The molecular events during nongenotoxic carcinogenesis and their temporal order are poorly understood but thought to include long-lasting perturbations of gene expression. Here, we have investigated the temporal sequence of molecular and pathological perturbations at early stages of phenobarbital (PB) mediated liver tumor promotion in vivo. Molecular profiling (mRNA, microRNA [miRNA], DNA methylation, and proteins) of mouse liver during 13 weeks of PB treatment revealed progressive increases in hepatic expression of long noncoding RNAs and miRNAs originating from the Dlk1-Dio3 imprinted gene cluster, a locus that has recently been associated with stem cell pluripotency in mice and various neoplasms in humans. PB induction of the Dlk1-Dio3 cluster noncoding RNA (ncRNA) Meg3 was localized to glutamine synthetase-positive hypertrophic perivenous hepatocytes, suggesting a role for β-catenin signaling in the dysregulation of Dlk1-Dio3 ncRNAs. The carcinogenic relevance of Dlk1-Dio3 locus ncRNA induction was further supported by in vivo genetic dependence on constitutive androstane receptor and β-catenin pathways. Our data identify Dlk1-Dio3 ncRNAs as novel candidate early biomarkers for mouse liver tumor promotion and provide new opportunities for assessing the carcinogenic potential of novel compounds.

Determining the human relevance of structurally and functionally distinct non-genotoxic carcinogenic compounds that induce a diverse range of tissue-, gender-, strain-and speciesspecific tumors in animals remains a major challenge for toxicologists. Nevertheless, elucidating mechanisms of xenobiotic-induced tumors in animals can provide industry, environmental and regulatory scientists with valuable tools for cancer hazard identification and risk assessment. The discovery that aberrant epigenetic events frequently accompany genetic mutations in human cancers has stimulated efforts to deploy integrated epigenomic and transcriptomic profiling of xenobiotic-induced non-genotoxic carcinogenesis (NGC) in animal models, enabling enhanced mechanistic interpretation and novel early biomarker discovery. Recent advances in the mapping and functional characterization of mammalian tissue-specific epigenomes also provides new opportunities to characterize the crossstrain/-species chromatin architecture of non-genotoxic carcinogen effector genes and to predict their potential for modulation by xenobiotics in human tissue. Since xenobioticinduced perturbations of gene regulation are intimately associated with the underlying DNA sequence, there is a need to integrate the impact of genotype on susceptibility to NGC. Furthermore, the potential association of xenobiotic target modulation with tumorigenic phenotypes can be assessed using genetic models and cancer genome resources. Finally, we discuss how epigenomic profiling may be used to critically assess the comparability and validity of cellular NGC models versus in vivo-derived tissue samples and some of key challenges associated with incorporating epigenetic mechanisms and biomarkers into cancer risk assessment.

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