Targeting the Hedgehog Pathway in Pediatric Medulloblastoma

Medulloblastoma (MB), a primitive neuroectomal tumor of the cerebellum, is the most common malignant pediatric brain tumor. The cause of MB is largely unknown, but aberrant activation of Hedgehog (Hh) pathway is responsible for ~30% of MB. Despite aggressive treatment with surgical resection, radiation and chemotherapy, 70%-80% of pediatric medulloblastoma cases can be controlled, but most treated patients suffer devastating side effects. Therefore, developing a new effective treatment strategy is urgently needed. Hh signaling controls transcription of target genes by regulating activities of the three Glioma-associated oncogene (Gli1-3) transcription factors. In this review, we will focus on current clinical treatment options of MB and discuss mechanisms of drug resistance. In addition, we will describe current known molecular pathways which crosstalk with the Hedgehog pathway both in the context of medulloblastoma and non-medulloblastoma cancer development. Finally, we will introduce post-translational modifications that modulate Gli1 activity and summarize the positive and negative regulations of the Hh/Gli1 pathway. Towards developing novel combination therapies for medulloblastoma treatment, current information on interacting pathways and direct regulation of Hh signaling should prove critical

Hedgehog Pathway Inhibitors against Tumor Microenvironment

Targeting the hedgehog (HH) pathway to treat aggressive cancers of the brain, breast, pancreas, and prostate has been ongoing for decades. Gli gene amplifications have been long discovered within malignant glioma patients, and since then, inhibitors against HH pathway-associated molecules have successfully reached the clinical stage where several of them have been approved by the FDA. Albeit this success rate implies suitable progress, clinically used HH pathway inhibitors fail to treat patients with metastatic or recurrent disease. This is mainly due to heterogeneous tumor cells that have acquired resistance to the inhibitors along with the obstacle of effectively targeting the tumor microenvironment (TME). Severe side effects such as hyponatremia, diarrhea, fatigue, amenorrhea, nausea, hair loss, abnormal taste, and weight loss have also been reported. Furthermore, HH signaling is known to be involved in the regulation of immune cell maturation, angiogenesis, inflammation, and polarization of macrophages and myeloid-derived suppressor cells. It is critical to determine key mechanisms that can be targeted at different levels of tumor development and progression to address various clinical issues. Hence current research focus encompasses understanding how HH controls TME to develop TME altering and combinatorial targeting strategies. In this review, we aim to discuss the pros and cons of targeting HH signaling molecules, understand the mechanism involved in treatment resistance, reveal the role of the HH pathway in anti-tumor immune response, and explore the development of potential combination treatment of immune checkpoint inhibitors with HH pathway inhibitors to target HH-driven cancers

Medulloblastoma: Clinical Challenges and Emerging Molecular Discoveries

Medulloblastoma is the most common type of malignant brain tumor in children, responsible for 25% of pediatric brain cancers. Conventional treatment methods, which include surgery, radiotherapy, and chemotherapy, have improved overall survival rates for patients with medulloblastoma to over 50%. A majority of survivors, however, suffer serious long-term side effects, including developmental, neurological, and psychosocial deficits. Now entering clinical trials for sonic hedgehog-driven medulloblastomas, Smoothened inhibitors have been FDA approved for the treatment of basal cell carcinomas. However, treatment efficacy endures only for a few months before lesion relapses and drug resistance occurs. Therefore, there is an urgent need for new therapies to reduce the significant problems associated with current drug-resistant treatments. In this chapter, we will illustrate the clinical presentation and current treatment methods for medulloblastoma and detail the molecular pathways within each of the four molecular subgroups of medulloblastoma, with an eye for possible candidates for novel combination therapies

Perspective Chapter: Critical Role of Hedgehog in Tumor Microenvironment

Hedgehog (Hh) signaling is a highly conserved pathway that plays a pivotal role during embryonic development. Mounting evidence has implicated Hh signaling in various types of cancer. Accordingly, inhibition of aberrant Hh signaling continues to be pursed across multiple cancer types -with some success in certain malignancies. In addition, with the renaissance of antitumor immunotherapy, an in-depth understanding of the molecular mechanisms underlying how the multifaceted functions of Hh signaling shape immunologically suppressive tumor microenvironment might be the key to unlocking a new era of oncological treatments associated with a reduced propensity for the development of drug resistance. Here, we focus on the latest advances regarding the immunological effects of misregulation of Hh signaling on tumor immunity. We also review the current status of clinically approved Hh inhibitors and dissect the mechanisms of drug resistance. Finally, we discuss the potential clinical applications that harness the immunomodulatory effects of Hh signaling not only to circumvent drug resistance, but also to achieve durable efficacy following immunotherapies, thus ultimately resulting in improved patient outcomes

Activation of AMPK sensitizes medulloblastoma to Vismodegib and overcomes Vismodegib‐resistance

Vismodegib, a Smoothened antagonist, is clinically approved for treatment of human basal cell carcinoma (BCC), in the clinical trials of medulloblastoma (MB) and other cancers. However, a significant proportion of these tumors fail to respond to Vismodegib after a period of treatment. Here, we find that AMPK agonists, A769662, and Metformin, can inhibit GLI1 activity and synergize with Vismodegib to suppress MB cell growth in vitro and in vivo. Furthermore, combination of AMPK agonists with Vismodegib is effective in overcoming Vismodegib‐resistant MB. This is the first report demonstrating that combining AMPK agonist (Metformin) and SHH pathway inhibitor (Vismodegib) confers synergy for MB treatment and provides an effective chemotherapeutic regimen that can be used to overcome resistance to Vismodegib in SHH‐driven cancers

AMP-Activated Protein Kinase Directly Phosphorylates and Destabilizes Hedgehog Pathway Transcription Factor GLI1 in Medulloblastoma

The Hedgehog (Hh) pathway regulates cell differen- tiation and proliferation during development by controlling the Gli transcription factors. Cell fate de- cisions and progression toward organ and tissue maturity must be coordinated, and how an energy sensor regulates the Hh pathway is not clear. AMP- activated protein kinase (AMPK) is an important sensor of energy stores and controls protein synthe- sis and other energy-intensive processes. AMPK is directly responsive to intracellular AMP levels, inhib- iting a wide range of cell activities if ATP is low and AMP is high. Thus, AMPK can affect development by influencing protein synthesis and other processes needed for growth and differentiation. Activation of AMPK reduces GLI1 protein levels and stability, thus blocking Sonic-hedgehog-induced transcrip- tional activity. AMPK phosphorylates GLI1 at serines 102 and 408 and threonine 1074. Mutation of these three sites into alanine prevents phosphorylation by AMPK. This leads to increased GLI1 protein stability, transcriptional activity, and oncogenic potency

IKKβ Suppression of TSC1 Links Inflammation and Tumor Angiogenesis via the mTOR Pathway

SummaryTNFα has recently emerged as a regulator linking inflammation to cancer pathogenesis, but the detailed cellular and molecular mechanisms underlying this link remain to be elucidated. The tuberous sclerosis 1 (TSC1)/TSC2 tumor suppressor complex serves as a repressor of the mTOR pathway, and disruption of TSC1/TSC2 complex function may contribute to tumorigenesis. Here we show that IKKβ, a major downstream kinase in the TNFα signaling pathway, physically interacts with and phosphorylates TSC1 at Ser487 and Ser511, resulting in suppression of TSC1. The IKKβ-mediated TSC1 suppression activates the mTOR pathway, enhances angiogenesis, and results in tumor development. We further find that expression of activated IKKβ is associated with TSC1 Ser511 phosphorylation and VEGF production in multiple tumor types and correlates with poor clinical outcome of breast cancer patients. Our findings identify a pathway that is critical for inflammation-mediated tumor angiogenesis and may provide a target for clinical intervention in human cancer

A Novel Histone Deacetylase Inhibitor Exhibits Antitumor Activity via Apoptosis Induction, F-Actin Disruption and Gene Acetylation in Lung Cancer

BACKGROUND: Lung cancer is the leading cause of cancer mortality worldwide, yet the therapeutic strategy for advanced non-small cell lung cancer (NSCLC) is limitedly effective. In addition, validated histone deacetylase (HDAC) inhibitors for the treatment of solid tumors remain to be developed. Here, we propose a novel HDAC inhibitor, OSU-HDAC-44, as a chemotherapeutic drug for NSCLC. METHODOLOGY/PRINCIPAL FINDINGS: The cytotoxicity effect of OSU-HDAC-44 was examined in three human NSCLC cell lines including A549 (p53 wild-type), H1299 (p53 null), and CL1-1 (p53 mutant). The antiproliferative mechanisms of OSU-HDAC-44 were investigated by flow cytometric cell cycle analysis, apoptosis assays and genome-wide chromatin-immunoprecipitation-on-chip (ChIP-on-chip) analysis. Mice with established A549 tumor xenograft were treated with OSU-HDAC-44 or vehicle control and were used to evaluate effects on tumor growth, cytokinesis inhibition and apoptosis. OSU-HDAC-44 was a pan-HDAC inhibitor and exhibits 3-4 times more effectiveness than suberoylanilide hydroxamic acid (SAHA) in suppressing cell viability in various NSCLC cell lines. Upon OSU-HDAC-44 treatment, cytokinesis was inhibited and subsequently led to mitochondria-mediated apoptosis. The cytokinesis inhibition resulted from OSU-HDAC-44-mediated degradation of mitosis and cytokinesis regulators Auroroa B and survivin. The deregulation of F-actin dynamics induced by OSU-HDAC-44 was associated with reduction in RhoA activity resulting from srGAP1 induction. ChIP-on-chip analysis revealed that OSU-HDAC-44 induced chromatin loosening and facilitated transcription of genes involved in crucial signaling pathways such as apoptosis, axon guidance and protein ubiquitination. Finally, OSU-HDAC-44 efficiently inhibited A549 xenograft tumor growth and induced acetylation of histone and non-histone proteins and apoptosis in vivo. CONCLUSIONS/SIGNIFICANCE: OSU-HDAC-44 significantly suppresses tumor growth via induction of cytokinesis defect and intrinsic apoptosis in preclinical models of NSCLC. Our data provide compelling evidence that OSU-HDAC-44 is a potent HDAC targeted inhibitor and can be tested for NSCLC chemotherapy

Elevated expression of TDP-43 in the forebrain of mice is sufficient to cause neurological and pathological phenotypes mimicking FTLD-U

TDP-43 is a multifunctional DNA/RNA-binding factor that has been implicated in the regulation of neuronal plasticity. TDP-43 has also been identified as the major constituent of the neuronal cytoplasmic inclusions (NCIs) that are characteristic of a range of neurodegenerative diseases, including the frontotemporal lobar degeneration with ubiquitin+ inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS). We have generated a FTLD-U mouse model (CaMKII-TDP-43 Tg) in which TDP-43 is transgenically overexpressed in the forebrain resulting in phenotypic characteristics mimicking those of FTLD-U. In particular, the transgenic (Tg) mice exhibit impaired learning/memory, progressive motor dysfunction, and hippocampal atrophy. The cognitive and motor impairments are accompanied by reduced levels of the neuronal regulators phospho–extracellular signal-regulated kinase and phosphorylated cAMP response element-binding protein and increased levels of gliosis in the brains of the Tg mice. Moreover, cells with TDP-43+, ubiquitin+ NCIs and TDP-43–deleted nuclei appear in the Tg mouse brains in an age-dependent manner. Our data provide direct evidence that increased levels of TDP-43 protein in the forebrain is sufficient to lead to the formation of TDP-43+, ubiquitin+ NCIs and neurodegeneration. This FTLD-U mouse model should be valuable for the mechanistic analysis of the role of TDP-43 in the pathogenesis of FTLD-U and for the design of effective therapeutic approaches of the disease