Most colorectal cancers (CRC) are initiated by mutations of APC, leading to increased b-catenin-mediated signaling. However, continued requirement of Wnt/b-catenin signaling for tumor progression in the context of acquired KRAS and other mutations is less well-established. To attenuate Wnt/b-catenin signaling in tumors, we have developed potent and specific small-molecule tankyrase inhibitors, G007-LK and G244-LM, that reduce Wnt/b-catenin signaling by preventing poly(ADP-ribosyl)ation-dependent AXIN degradation, thereby promoting b-catenin destabilization. We show that novel tankyrase inhibitors completely block ligand-driven Wnt/b-catenin signaling in cell culture and display approximately 50% inhibition of APC mutation-driven signaling in most CRC cell lines. It was previously unknown whether the level of AXIN protein stabilization by tankyrase inhibition is sufficient to impact tumor growth in the absence of normal APC activity. Compound G007-LK displays favorable pharmacokinetic properties and inhibits in vivo tumor growth in a subset of APC-mutant CRC xenograft models. In the xenograft model most sensitive to tankyrase inhibitor, COLO-320DM, G007-LK inhibits cell-cycle progression, reduces colony formation, and induces differentiation, suggesting that b-catenin-dependent maintenance of an undifferentiated state may be blocked by tankyrase inhibition. The full potential of the antitumor activity of G007-LK may be limited by intestinal toxicity associated with inhibition of Wnt/b-catenin signaling and cell proliferation in intestinal crypts. These results establish proof-of-concept antitumor efficacy for tankyrase inhibitors in APC-mutant CRC models and uncover potential diagnostic and safety concerns to be overcome as tankyrase inhibitors are advanced into the clinic. Cancer Res; 73(10); 3132-44. Ó2013 AACR.

Increased nuclear accumulation of b-catenin, a mediator of canonical Wnt signaling, is found in numerous tumors and is frequently associated with tumor progression and metastasis. Inhibition of Wnt/b-catenin signaling therefore is an attractive strategy for anticancer drugs. In this study, we have identified a novel small molecule inhibitor of the b-catenin signaling pathway, JW55, that functions via inhibition of the PARP domain of tankyrase 1 and tankyrase 2 (TNKS1/2), regulators of the b-catenin destruction complex. Inhibition of TNKS1/2 poly(ADP-ribosyl)ation activity by JW55 led to stabilization of AXIN2, a member of the b-catenin destruction complex, followed by increased degradation of b-catenin. In a dose-dependent manner, JW55 inhibited canonical Wnt signaling in colon carcinoma cells that contained mutations in either the APC (adenomatous polyposis coli) locus or in an allele of b-catenin. In addition, JW55 reduced XWnt8-induced axis duplication in Xenopus embryos and tamoxifen-induced polyposis formation in conditional APC mutant mice. Together, our findings provide a novel chemotype for targeting canonical Wnt/b-catenin signaling through inhibiting the PARP domain of TNKS1/2. Cancer Res; 72(11); 2822-32. Ó2012 AACR.

The cerebral cortex is a complex laminated structure generated by the sequential migration of developing neurons from the ventricular zone. One of the molecules that may play a role in cortical morphogenesis is N-cadherin since its blocking causes disruption of the ordered arrangement of cells in other neural tissues, such as the neural retina. Here, we show that when the N-cadherin gene had been conditionally deleted in the mouse cerebral cortex, the intra-cortical structures were nearly completely randomized; e.g., mitotic cells and postmitotic cells were scattered throughout the cortex without any order. These defects seemed to mainly originate from the disruption of the adherens junctions (AJs) localized in the apical end of neuroepithelial cells, where N-cadherin is normally most highly concentrated. In the absence of N-cadherin, neuroepithelial or radial glial cells could not expand their bodies or processes to span the distance between the ventricular and pial surfaces and therefore terminated them in the middle zone of the cortex. These results demonstrate that N-cadherin is essential for maintaining the normal architecture of neuroepithelial or radial glial cells and that their disruption randomizes the internal structures of the cortex.

Neurogenesis in the developing neocortex is a strictly regulated process of cell division and differentiation. Here we report that a gradual retreat of canonical Wnt signaling in the cortex from lateral-to-medial and anterior-to-posterior is a prerequisite of neurogenesis. Ectopic expression of a beta-catenin/LEF1 fusion protein maintains active canonical Wnt signaling in the developing cortex and delays the expression onset of the neurogenic factors Pax6, Ngn2 and Tbr2 and subsequent neurogenesis. Contrary to this, conditional ablation of beta-catenin accelerates expression of the same neurogenic genes. Furthermore, we show that a sustained canonical Wnt activity in the lateral cortex gives rise to cells with hippocampal characteristics in the cortical plate at the expense of the cortical fate, and to cells with dentate gyrus characteristics in the hippocampus. This suggests that the dose of canonical Wnt signaling determines cellular fate in the developing cortex and hippocampus, and that recession of Wnt signaling acts as a morphogenetic gradient regulating neurogenesis in the cortex.

Wnt signaling is involved in numerous processes during vertebrate CNS development. In this study, we used conditional Cre/loxP system in mouse to ablate or activate beta-catenin in the telencephalon in two time windows: before and after the onset of neurogenesis. We show that beta-catenin mediated Wnt signals are required to maintain the molecular identity of the pallium. Inactivation of beta-catenin in the telencephalon before neurogenesis results in downregulated expression of dorsal markers Emx1, Emx2 and Ngn2, and in ectopic up-regulation of ventral markers Gsh2, Mash1 and Dlx2 in the pallium. In contrast, ablation of ss-catenin after the onset of cortical neurogenesis (E11.5) does not result in a dorso-ventral fate shift. In addition, activation of canonical Wnt signaling in the subpallium leads to a repression of ventral telencephalic cell identities as shown by the down-regulation of subpallial markers Dlx2, Nkx2.1, Gsh2, Olig2 and Mash1. This was accompanied with an expansion of dorsal identities ventrally as shown by the expanded expression domains of pallial markers Pax6 and Ngn2. Thus, our data suggest that canonical Wnt signals are involved in maintaining the identity of the pallium by controlling expression of dorsal markers and by suppressing ventral programs from being activated in pallial progenitor cells.

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Canonical Wnt signaling is deregulated in several types of human cancer where it plays a central role in tumor cell growth and progression. Here we report the identification of 2 new small molecules that specifically inhibit canonical Wnt pathway at the level of the destruction complex. Specificity was verified in various cellular reporter systems, a Xenopus double-axis formation assay and a gene expression profile analysis. In human colorectal cancer (CRC) cells, the new compounds JW67 and JW74 rapidly reduced active b-catenin with a subsequent downregulation of Wnt target genes, including AXIN2, SP5, and NKD1. Notably, AXIN2 protein levels were strongly increased after compound exposure. Long-term treatment with JW74 inhibited the growth of tumor cells in both a mouse xenograft model of CRC and in Apc Min mice (multiple intestinal neoplasia, Min). Our findings rationalize further preclinical and clinical evaluation of these new compounds as novel modalities for cancer treatment. Cancer Res; 71(1); 197-205. Ó2011 AACR.

BackgroundTALE-class homeodomain transcription factors Meis and Pbx play important roles in formation of the embryonic brain, eye, heart, cartilage or hematopoiesis. Loss-of-function studies of Pbx1, 2 and 3 and Meis1 documented specific functions in embryogenesis, however, functional studies of Meis2 in mouse are still missing. We have generated a conditional allele of Meis2 in mice and shown that systemic inactivation of the Meis2 gene results in lethality by the embryonic day 14 that is accompanied with hemorrhaging.ResultsWe show that neural crest cells express Meis2 and Meis2-defficient embryos display defects in tissues that are derived from the neural crest, such as an abnormal heart outflow tract with the persistent truncus arteriosus and abnormal cranial nerves. The importance of Meis2 for neural crest cells is further confirmed by means of conditional inactivation of Meis2 using crest-specific AP2α-IRES-Cre mouse. Conditional mutants display perturbed development of the craniofacial skeleton with severe anomalies in cranial bones and cartilages, heart and cranial nerve abnormalities.ConclusionsMeis2-null mice are embryonic lethal. Our results reveal a critical role of Meis2 during cranial and cardiac neural crest cells development in mouse.Electronic supplementary materialThe online version of this article (doi:10.1186/s12861-015-0093-6) contains supplementary material, which is available to authorized users.