A pinboard by Cathy Cochrane
PhD Student at the Hudson Institute of Medical Research, Australia
Developmental Biology + Cancer Biology = Paediatric Cancer
The Hedgehog (Hh) signalling pathway, plays a critical role in biological processes that occurs in fetal development, such as stem cell maintenance, cell to cell interactions and tissue development. Secreted Hh proteins, termed Hh ligands, activate the pathway in a concentration and time dependent manner, by initiating a series of cellular responses that promotes organ development. The processes of brain, bone, heart, testis and limb development all require Hh pathway activity for successful growth and function. In addition to Hh’s multifaceted roles during normal development, aberrant Hh signalling is responsible for the initiation of progression of various cancers. Overactive Hh signalling has been established in basal cell carcinoma, medulloblastoma, lung, prostate, ovarian and breast cancer, to name a few, making the Hh pathway an area of intense study in both developmental and cancer biology. Because tumour growth and malignancy depend on Hh signalling in various cancers, drugs that block the Hh pathway have been developed to treat Hh cancers. However, recent entry of Hh-inhibitors into clinical trials have revealed mixed patient responses and prompts further exploration of Hh pathway activation, inhibition and resistance to treatment.
Abstract: Novel treatment options, including targeted therapies, are needed for patients with medulloblastoma (MB), especially for those with high-risk or recurrent/relapsed disease. Four major molecular subgroups of MB have been identified, one of which is characterized by activation of the sonic hedgehog (SHH) pathway. Preclinical data suggest that inhibitors of the hedgehog (Hh) pathway could become valuable treatment options for patients with this subgroup of MB. Indeed, agents targeting the positive regulator of the pathway, smoothened (SMO), have demonstrated efficacy in a subset of patients with SHH MB. However, because of resistance and the presence of mutations downstream of SMO, not all patients with SHH MB respond to SMO inhibitors. The development of agents that target these resistance mechanisms and the potential for their combination with traditional chemotherapy and SHH inhibitors will be discussed. Due to its extensive molecular heterogeneity, the future of MB treatment is in personalized therapy, which may lead to improved efficacy and reduced toxicity. This will include the development of clinically available tests that can efficiently discern the SHH subgroup. The preliminary use of these tests in clinical trials is also discussed herein.
Pub.: 22 Jun '14, Pinned: 22 Sep '17
Abstract: Hedgehog (Hh) signaling regulates cell fate and self-renewal in development and cancer. Canonical Hh signaling is mediated by Hh ligand binding to the receptor Patched (Ptch), which in turn activates Gli-mediated transcription through Smoothened (Smo), the molecular target of the Hh pathway inhibitors used as cancer therapeutics. Small cell lung cancer (SCLC) is a common, aggressive malignancy with universally poor prognosis. Although preclinical studies have shown that Hh inhibitors block the self-renewal capacity of SCLC cells, the lack of activating pathway mutations have cast doubt over the significance of these observations. In particular, the existence of autocrine, ligand-dependent Hh signaling in SCLC has been disputed. In a conditional Tp53;Rb1 mutant mouse model of SCLC, we now demonstrate a requirement for the Hh ligand Sonic Hedgehog (Shh) for the progression of SCLC. Conversely, we show that conditional Shh overexpression activates canonical Hh signaling in SCLC cells, and markedly accelerates tumor progression. When compared to mouse SCLC tumors expressing an activating, ligand-independent Smo mutant, tumors overexpressing Shh exhibited marked chromosomal instability and Smoothened-independent upregulation of Cyclin B1, a putative non-canonical arm of the Hh pathway. In turn, we show that overexpression of Cyclin B1 induces chromosomal instability in mouse embryonic fibroblasts lacking both Tp53 and Rb1. These results provide strong support for an autocrine, ligand-dependent model of Hh signaling in SCLC pathogenesis, and reveal a novel role for non-canonical Hh signaling through the induction of chromosomal instability.Oncogene advance online publication, 5 June 2017; doi:10.1038/onc.2017.173.
Pub.: 06 Jun '17, Pinned: 22 Sep '17
Abstract: Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.
Pub.: 14 Aug '15, Pinned: 22 Sep '17
Abstract: Aberrant Hedgehog/GLI signaling has been implicated in a diverse spectrum of human cancers, but its role in lung adenocarcinoma (LAC) is still under debate. We show that the downstream effector of the Hedgehog pathway, GLI1, is expressed in 76% of LACs, but in roughly half of these tumors, the canonical pathway activator, Smoothened, is expressed at low levels, possibly owing to epigenetic silencing. In LAC cells including the cancer stem cell compartment, we show that GLI1 is activated noncanonically by MAPK/ERK signaling. Different mechanisms can trigger the MAPK/ERK/GLI1 cascade including KRAS mutation and stimulation of NRP2 by VEGF produced by the cancer cells themselves in an autocrine loop or by stromal cells as paracrine cross talk. Suppression of GLI1, by silencing or drug-mediated, inhibits LAC cells proliferation, attenuates their stemness and increases their susceptibility to apoptosis in vitro and in vivo. These findings provide insight into the growth of LACs and point to GLI1 as a downstream effector for oncogenic pathways. Thus, strategies involving direct inhibition of GLI1 may be useful in the treatment of LACs.Oncogene advance online publication, 3 April 2017; doi:10.1038/onc.2017.91.
Pub.: 04 Apr '17, Pinned: 22 Sep '17
Abstract: Master developmental pathways, such as Notch, Wnt, and Hedgehog, are signaling systems that control proliferation, cell death, motility, migration, and stemness. These systems are not only commonly activated in many solid tumors, where they drive or contribute to cancer initiation, but also in primary and metastatic tumor development. The reactivation of developmental pathways in cancer stroma favors the development of cancer stem cells and allows their maintenance, indicating these signaling pathways as particularly attractive targets for efficient anticancer therapies, especially in advanced primary tumors and metastatic cancers. Metastasis is the worst feature of cancer development. This feature results from a cascade of events emerging from the hijacking of epithelial-mesenchymal transition, angiogenesis, migration, and invasion by transforming cells and is associated with poor survival, drug resistance, and tumor relapse. In the present review, we summarize and discuss experimental data suggesting pivotal roles for developmental pathways in cancer development and metastasis, considering the therapeutic potential. Emerging targeted antimetastatic therapies based on Notch, Wnt, and Hedgehog pathways are also discussed.
Pub.: 14 Jun '17, Pinned: 22 Sep '17
Abstract: Medulloblastoma (MB) arising from the cerebellum is the most common pediatric brain malignancy, with leptomeningeal metastases often present at diagnosis and recurrence associated with poor clinical outcome. In this study, we employed mouse MB models to explore the relationship of tumor pathophysiology and dysregulated expression of the Notch pathway transcription factor ATOH1, which is present in aggressive MB subtypes driven by aberrant Sonic Hedgehog/Patched (SHH/PTCH) signaling. In experiments with conditional Atoh1 mouse mutants crossed to Ptch1(+/-) mice which develop SHH-driven MB, animals with Atoh1 transgene expression developed highly penetrant MB at a young age with extensive leptomeningeal disease and metastasis to the spinal cord and brain, resembling xenografts of human SHH MB. Metastatic tumors retained abnormal SHH signaling like tumor xenografts. Conversely, Atoh1 expression was detected consistently in recurrent and metastatic SHH MB. ChIP-seq and gene expression profiling identified candidate ATOH1 targets in tumor cells involved in development and tumorigenesis. Among these targets specific to metastatic tumors, there was an enrichment in those implicated in extracellular matrix remodeling activity, cytoskeletal network and interaction with microenvironment, indicating a shift in transcriptomic and epigenomic landscapes during metastasis. Treatment with bone morphogenetic protein (BMP) or SHH pathway inhibitors decreased tumor cell proliferation and suppressed metastatic tumor growth, respectively. Our work reveals a dynamic ATOH1-driven molecular cascade underlying MB metastasis that offers possible therapeutic opportunities.
Pub.: 12 May '17, Pinned: 22 Sep '17
Abstract: Tight control of the balance between self-expanding symmetric and self-renewing asymmetric neural progenitor divisions is crucial to regulate the number of cells in the developing central nervous system. We recently demonstrated that Sonic hedgehog (Shh) signalling is required for the expansion of motor neuron progenitors by maintaining symmetric divisions. Here we show that activation of Shh/Gli signalling in dividing neuroepithelial cells controls the symmetric recruitment of PKA to the centrosomes that nucleate the mitotic spindle, maintaining symmetric proliferative divisions. Notably, Shh signalling upregulates the expression of pericentrin, which is required to dock PKA to the centrosomes, which in turn exerts a positive feedback onto Shh signalling. Thus, by controlling centrosomal protein assembly, we propose that Shh signalling overcomes the intrinsic asymmetry at the centrosome during neuroepithelial cell division, thereby promoting self-expanding symmetric divisions and the expansion of the progenitor pool.
Pub.: 27 Apr '17, Pinned: 22 Sep '17
Abstract: Sonidegib (LDE225) is a potent, selective Hedgehog (Hh) inhibitor of SMOOTHENED. This study explored the safety and pharmacokinetics (PK) of sonidegib in children with relapsed/recurrent tumors followed by a phase II trial in pediatric and adult patients with relapsed medulloblastoma (MB) to assess tumor response.Pediatric patients aged ≥1-<18 years were included according to a Bayesian design starting at 372mg/m2 of continuous once daily oral sonidegib. Tumor samples were analyzed for Hh pathway activation using a validated 5-gene Hh signature assay. In phase II, pediatric patients were treated at the recommended phase II dose (RP2D) while adults received 800mg daily.Sixteen adult (16 MB) and 60 pediatric (39 MB, 21 other) patients with an age range of 2-17 years were enrolled. The RP2D of sonidegib in pediatric patients was established at 680mg/m2 once daily. The phase II study was closed prematurely. The 5-gene Hh signature assay showed that the 4 complete responders (2 pediatric and 2 adult) and 1 partial responder (adult), all had Hh‑activated tumors, while 5 patients with activated Hh had either stable disease (n=3) or progressive disease (n=2). No patients with Hh-negative signatures (n=50) responded. The safety profile for pediatric patients was generally consistent with the one established for adult patients; however, growth plate changes were observed in pre-pubertal pediatric patients'.Sonidegib was well tolerated and the RP2D in pediatric patients was 680mg/m2 once daily. Five of the 10 MB patients with activated Hh pathway demonstrated complete or partial responses.
Pub.: 13 Jun '17, Pinned: 22 Sep '17
Abstract: While molecular subgrouping has revolutionized medulloblastoma classification, the extent of heterogeneity within subgroups is unknown. Similarity network fusion (SNF) applied to genome-wide DNA methylation and gene expression data across 763 primary samples identifies very homogeneous clusters of patients, supporting the presence of medulloblastoma subtypes. After integration of somatic copy-number alterations, and clinical features specific to each cluster, we identify 12 different subtypes of medulloblastoma. Integrative analysis using SNF further delineates group 3 from group 4 medulloblastoma, which is not as readily apparent through analyses of individual data types. Two clear subtypes of infants with Sonic Hedgehog medulloblastoma with disparate outcomes and biology are identified. Medulloblastoma subtypes identified through integrative clustering have important implications for stratification of future clinical trials.
Pub.: 14 Jun '17, Pinned: 22 Sep '17