Hedgehog signaling in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment

The Hedgehog (HH) signaling pathway plays important roles in gastrointestinal carcinogenesis and the gastrointestinal tumor microenvironment (TME). Aberrant HH signaling activation may accelerate the growth of gastrointestinal tumors and lead to tumor immune tolerance and drug resistance. The interaction between HH signaling and the TME is intimately involved in these processes, for example, tumor growth, tumor immune tolerance, inflammation, and drug resistance. Evidence indicates that inflammatory factors in the TME, such as interleukin 6 (IL-6) and interferon-γ (IFN-γ), macrophages, and T cell-dependent immune responses, play a vital role in tumor growth by affecting the HH signaling pathway. Moreover, inhibition of proliferating cancer-associated fibroblasts (CAFs) and inflammatory factors can normalize the TME by suppressing HH signaling. Furthermore, aberrant HH signaling activation is favorable to both the proliferation of cancer stem cells (CSCs) and the drug resistance of gastrointestinal tumors. This review discusses the current understanding of the role and mechanism of aberrant HH signaling activation in gastrointestinal carcinogenesis, the gastrointestinal TME, tumor immune tolerance and drug resistance and highlights the underlying therapeutic opportunities.

Secondary clonal hematologic neoplasia following successful therapy for acute promyelocytic leukemia (APL): A report of two cases and review of the literature

Although rare, secondary clonal hematologic neoplasia may occur after successful therapy for acute promyelocytic leukemia (APL). These secondary clonal events may be considered therapy-related, but may also be due to an underlying background of clonal hematopoiesis from which both malignancies may develop. In this manuscript, we describe two patients with secondary clones after APL therapy characterized in one patient by deletion of chromosome 11q23 and, in the other, by monosomy of chromosome 7, and also provide a review of all secondary clonal disorders described after APL therapy. We suggest that since most reports identify karyotypic abnormalities not typically associated with chemotherapy, there may be another mechanism underlying secondary clonal development after complete response to initial APL therapy.

Druggable glycolytic requirement for Hedgehog-dependent neuronal and medulloblastoma growth

Aberrant activation of SHH pathway is a major cause of medulloblastoma (MB), the most frequent brain malignancy of the childhood. A few Hedgehog inhibitors, all antagonizing the membrane transducer Smo, have been approved or are under clinical trials for the treatment of human MB. However, the efficacy of these drugs is limited by the occurrence of novel mutations or by activation of downstream or non-canonical Hedgehog components. Thus, the identification of novel druggable downstream pathways represents a critical step to overcome this problem. In the present work we demonstrate that aerobic glycolysis is a valuable HH-dependent downstream target, since its inhibition significantly counteracts the HH-mediated growth of normal and tumor cells. Hedgehog activation induces transcription of hexokinase 2 (HK2) and pyruvate kinase M2 (PKM2), two key gatekeepers of glycolysis. The process is mediated by the canonical activation of the Gli transcription factors and causes a robust increase of extracellular lactate concentration. We show that inhibition of glycolysis at different levels blocks the Hedgehog-induced proliferation of granule cell progenitors (GCPs), the cells from which medulloblastoma arises. Remarkably, we demonstrate that this glycolytic transcriptional program is also upregulated in SHH-dependent tumors and that pharmacological targeting with the pyruvate kinase inhibitor dichloroacetate (DCA) efficiently represses MB growth in vitro and in vivo. Together, these data illustrate a previously uncharacterized pharmacological strategy to target Hedgehog dependent growth, which can be exploited for the treatment of medulloblastoma patients.