Arsenic trioxide inhibits human cancer cell growth and tumor development in mice by blocking Hedgehog/GLI pathway

Ewing sarcoma: biology-based therapeutic perspectives

Ewing sarcoma, a rare malignancy of childhood and adolescence, has attracted wide research interest. Tumor-specific chromosomal translocations generate aberrant EWS-ETS transcription factors, which alter intracellular signaling networks through gene and protein expression and are considered to be the primary tumor-initiating event. Ewing sarcoma therefore offers insights into principle molecular mechanisms of cancer development and maintenance. Still, despite long-standing research, biology-based targeted treatment strategies for Ewing sarcoma are only beginning to emerge. This article provides an overview of the biological basis and putative targeted treatment options.

Basal cell carcinoma - molecular biology and potential new therapies

Basal cell carcinoma (BCC) of the skin, the most common malignancy in individuals of mixed European descent, is increasing in incidence due to an aging population and sun exposure habits. The realization that aberrant activation of Hedgehog signaling is a pathognomonic feature of BCC development has opened the way for exciting progress toward understanding BCC biology and translation of this knowledge to the clinic. Genetic mouse models closely mimicking human BCCs have provided answers about the tumor cell of origin, and inhibition of Hedgehog signaling is emerging as a potentially useful targeted therapy for patients with advanced or multiple BCCs that have hitherto lacked effective treatment.

A new era for an ancient drug: arsenic trioxide and Hedgehog signaling

Arsenic has been used for ages as a therapeutic agent. Currently, it is an FDA approved drug to treat acute promyelocytic leukemia where it leads to degradation of the PML-RAR fusion protein. It has been shown to have various other targets in cells such as JNK, NFκB, thioredoxin reductase, and MAPK pathways. Most of its effects in cells have been through arsenic's ability to bind to thiol groups in cysteine residues. Recent evidence has shown that arsenic can inhibit the Hedgehog pathway by inhibiting GLI proteins. The proposed mechanism of action is through direct binding. Potential binding sites include the critical cysteine residues in GLI zinc finger domains. The role of the Hedgehog pathway has been implicated in many cancers such as basal cell carcinoma, medulloblastoma, Ewing sarcoma, and rhabdoid tumors. Current Hedgehog pathway inhibitors have been fraught with resistance issues and so arsenic trioxide may provide an alternative therapy when combined with these other inhibitors or after acquired resistance.

Hedgehog inhibition as an anti-cancer strategy

Dysregulated Hedgehog (Hh) signaling has been implicated in a growing number of human cancers. Although first identified as an important developmental signaling pathway crucial for cellular proliferation, differentiation, and migration during organogenesis in invertebrates, these fundamental processes have been co-opted in human cancers. Initial evidence for the Hh pathway in tumor biology comes from mutations of signaling pathway components in a hereditary cancer syndrome that typically results in basal-cell carcinoma and medulloblastoma. Subsequent analysis revealed that Hh pathway mutations are found in sporadic tumors as well as activated Hh signaling in several epithelial cancers independent of Hh pathway mutation status. Further, recent evidence has demonstrated paracrine Hh signaling within stromal cells of the tumor microenvironment with implications for drug delivery. Several Hh antagonists targeting the Hh receptor, Smoothened (SMO), have been developed and show efficacy in preclinical studies and early-stage clinical trials in humans. However, major issues with these small molecule compounds include rapid acquired resistance, potential developmental toxicities secondary to use in children, and limited efficacy in cancers driven by Hh signaling downstream of the SMO receptor.

Canonical and noncanonical Hedgehog/GLI signaling in hematological malignancies

The highly conserved Hedgehog/GLI signaling pathway regulates multiple aspects of embryonic development and plays a decisive role in tissue homeostasis and the hematopoietic system by controlling cell fate decisions, stem cell self-renewal, and activation. Loss of negative control of Hedgehog signaling contributes to tumor pathogenesis and progression. In the classical view of canonical Hedgehog signaling, Hedgehog ligand binding to its receptor Patched culminates in the activation of the key pathway activator Smoothened, followed by activation of the GLI transcription factors. Its essential function and druggability render Smoothened well suited to therapeutic intervention. However, recent evidence suggests a critical role of Smoothened-independent regulation of GLI activity by several other signaling pathways including the PI3K/AKT and RAS/RAF/MEK/ERK axes. In addition, the contribution of canonical Hedgehog signaling via Patched and Smoothened to normal and malignant hematopoiesis has been the subject of recent controversies. In this review, we discuss the current understanding and controversial findings of canonical and noncanonical GLI activation in hematological malignancies in light of the current therapeutic strategies targeting the Hedgehog pathway.

Darinaparsin is a multivalent chemotherapeutic which induces incomplete stress response with disruption of microtubules and Shh signaling

Chemotherapeutics and other pharmaceuticals are common sources of cellular stress. Darinaparsin (ZIO-101) is a novel organic arsenical under evaluation as a cancer chemotherapeutic, but the drug's precise mechanism of action is unclear. Stress granule formation is an important cellular stress response, but the mechanisms of formation, maintenance, and dispersal of RNA-containing granules are not fully understood. During stress, small, diffuse granules initially form throughout the cytoplasm. These granules then coalesce near the nucleus into larger granules that disperse once the cellular stress is removed. Complete stress granule formation is dependent upon microtubules. Human cervical cancer (HeLa) cells, pre-treated with nocodazole for microtubule depolymerization, formed only small, diffuse stress granules upon sodium arsenite treatment. Darinaparsin, as a single agent, also induced the formation of small, diffuse stress granules, an effect similar to that of the combination of nocodazole with sodium arsenite. Darinaparsin inhibited the polymerization of microtubules both in vivo and in vitro. Interestingly, upon removal of darinaparsin, the small, diffuse stress granules completed formation with coalescence in the perinuclear region prior to disassembly. These results indicate that RNA stress granules must complete formation prior to disassembly, and completion of stress granule formation is dependent upon microtubules. Finally, treatment of cells with darinaparsin led to a reduction in Sonic hedgehog (Shh) stimulated activation of Gli1 and a loss of primary cilia. Therefore, darinaparsin represents a unique multivalent chemotherapeutic acting on stress induction, microtubule polymerization, and Shh signaling.

VMY-1-103 is a novel CDK inhibitor that disrupts chromosome organization and delays metaphase progression in medulloblastoma cells

Medulloblastoma is the most prevalent of childhood brain malignancies, constituting 25% of childhood brain tumors. Craniospinal radiotherapy is a standard of care, followed by a 12mo regimen of multi-agent chemotherapy. For children less than 3 y of age, irradiation is avoided due to its destructive effects on the developing nervous system. Long-term prognosis is worst for these youngest children and more effective treatment strategies with a better therapeutic index are needed. VMY-1-103, a novel dansylated analog of purvalanol B, was previously shown to inhibit cell cycle progression and proliferation in prostate and breast cancer cells more effectively than purvalanol B. In the current study, we have identified new mechanisms of action by which VMY-1-103 affected cellular proliferation in medulloblastoma cells. VMY-1-103, but not purvalanol B, significantly decreased the proportion of cells in S phase and increased the proportion of cells in G(2)/M. VMY-1-103 increased the sub G(1) fraction of apoptotic cells, induced PARP and caspase-3 cleavage and increased the levels of the Death Receptors DR4 and DR5, Bax and Bad while decreasing the number of viable cells, all supporting apoptosis as a mechanism of cell death. p21(CIP1/WAF1) levels were greatly suppressed. Importantly, we found that while both VMY and flavopiridol inhibited intracellular CDK1 catalytic activity, VMY-1-103 was unique in its ability to severely disrupt the mitotic spindle apparatus significantly delaying metaphase and disrupting mitosis. Our data suggest that VMY-1-103 possesses unique antiproliferative capabilities and that this compound may form the basis of a new candidate drug to treat medulloblastoma.

Novel peptide binds EWS-FLI1 and reduces the oncogenic potential in Ewing tumors

Ewing tumor is driven by the oncogenic EWS-FLI1 fusion protein that functions as an aberrant transcription factor. The identification of EWS-FLI1 protein partners is essential to enhance its vulnerability as a therapeutic target. We utilized phage display library screening against recombinant EWS-FLI1 protein. We identified 27 unique Ewing sarcoma binding peptides. The cytotoxicity evaluation of these peptides with in EWS-FLI1 containing cell lines yielded one potent peptide called ESAP1 (TMRGKKKRTRAN). ESAP1 binds EWS-FLI1 with 0.202 micromolar affinity as measured in surface plasmon resonance. The minimal interaction region of ESAP1 is characterized and found that the lysine residues are critical for cellular cytotoxicity. ESAP1 reduces the transcriptional activity of EWS-FLI1 as well as disrupts cell cycle kinetics in Ewing Tumor cells. These findings provide both a novel experimental probe and a potential therapeutic scaffold for Ewing Tumor.

Arsenic trioxide regulates the apoptosis of glioma cell and glioma stem cell via down-regulation of stem cell marker Sox2

Knowledge of the mechanism by which arsenic trioxide exerts the anti-tumor effects may help in designing a more effective regimen for therapy. Transcription factor Sox2, a key gene implicated in maintaining the "stemness" of embryonic and adult stem cells, plays an important role in the carcinogenesis and maintenance of glioblastoma. Here, we found that the expression of Sox2 at transcriptional level was decreased during As(2)O(3)-induced glioma cell apoptosis. And, the ectopic expression of Sox2 attenuated the apoptotic effect of As(2)O(3) on glioma cell. Furthermore, As(2)O(3) inhibited the self-renewal of glioma stem cells, and efficiently induces the apoptosis of glioma stem cells, at least, partly through down-regulation of Sox2. These data identify a previously unrecognized mechanism of the anti-tumor effects of arsenic trioxide.

Adult medulloblastoma comprises three major molecular variants

PURPOSE

Medulloblastoma is a rare primary brain tumor in adults, whereas it constitutes the most common malignant brain tumor in children. Integrated genomics approaches revealed at least four distinct disease variants in children. The aim of this study was to investigate molecular subtypes and their prognostic implication in a large cohort of adult medulloblastomas as the biology in this age group remains poorly understood.

PATIENTS AND METHODS

We combined transcriptome and DNA copy number analyses for 28 adult medulloblastomas. Statistical and bioinformatic tools were applied to discover distinct molecular variants. Clinical and molecular characteristics of each biologic subtype were validated using immunohistochemistry on a tissue microarray derived from an independent patient cohort of adult medulloblastomas (n = 103).

RESULTS

Gene expression profiles revealed three distinct molecular variants with stable subtype separation using the 300 most varying transcripts. Distinct demographics, genetics, transcriptome, and prognosis were noted for each subtype of adult medulloblastoma. Immunohistochemistry revealed aberrant activation of the sonic hedgehog (SHH) pathway in over half of adult medulloblastomas constituting a promising molecular therapeutic target. In contrast, subtype C tumors, which comprise a robust subtype in childhood medulloblastoma are only exceptionally seen in adult cohorts. Notably, adult subtype D and Wnt/wingless tumors were associated with worse prognosis than pediatric cohorts, whereas survival for SHH tumors was similar for both age groups.

CONCLUSION

The transcriptome of adult medulloblastomas differs considerably from pediatric counterparts, both in terms of tumor biology and prognostic impact. Therefore, age-specific classification is required and must be adapted for use in clinical trials of adult medulloblastoma.

The Hedgehog's tale: developing strategies for targeting cancer

Research into basic developmental biology has frequently yielded insights into cancer biology. This is particularly true for the Hedgehog (HH) pathway. Activating mutations in the HH pathway cause a subset of sporadic and familial, skin (basal cell carcinoma) and brain (medulloblastoma) tumours. Furthermore, the growth of many human tumours is supported by HH pathway activity in stromal cells. Naturally occurring and synthetic inhibitors of HH signalling show great promise in animal models and in early clinical studies. However, it remains unclear how many cancers will ultimately benefit from these new, molecularly targeted therapies.

[Indications and current development of new targeted therapies in pediatric oncology]

Progresses performed in pediatric oncology during the last 30 years allowed to obtain about 70 to 80% healing rates. These progresses are the result of the optimization of the cytotoxic chemotherapies protocols used at standard and high doses, as well as the improvement of the local treatment. Most of the new anticancer treatments currently in developmental stage are based on targeted therapies, acting against numerous tumor cell abnormalities, like growth factors et their receptors, cell proliferation-inducing factors, molecules involved in DNA repair, cell death inducers, tumor invasion and angiogenesis. They are widely used in adult patients since 10 years and they are being more and more employed in children with cancer. The aim of this article is to review the main indications of these new targeted drugs in pediatric oncology and the new developments of these drugs.

The hedgehog/Gli signaling paradigm in prostate cancer

Hedgehog is a ligand-activated signaling pathway that regulates Gli-mediated transcription. Although most noted for its role as an embryonic morphogen, hyperactive hedgehog also causes human skin and brain malignancies. The hedgehog-related gene anomalies found in these tumors are rarely found in prostate cancer. Yet surveys of human prostate tumors show concordance of high expression of hedgehog ligands and Gli2 that correlate with the potential for metastasis and therapy-resistant behavior. Likewise, prostate cancer cell lines express hedgehog target genes, and their growth and survival is affected by hedgehog/Gli inhibitors. To date, the preponderance of data supports the idea that prostate tumors benefit from a paracrine hedgehog microenvironment similar to the developing prostate. Uncertainty remains as to whether hedgehog's influence in prostate cancer also includes aspects of tumor cell autocrine-like signaling. The recent findings that Gli proteins interact with the androgen receptor and affect its transcriptional output have helped to identify a novel pathway through which hedgehog/Gli might affect prostate tumor behavior and raises questions as to whether hedgehog signaling in prostate cancer cells is suitably measured by the expression of Gli target genes alone.

Arsenic: a potentially useful poison for Hedgehog-driven cancers

Dysregulated Hedgehog (Hh) signaling has been implicated in a growing number of human cancers. To date, most antagonists of this signaling pathway that have been developed target the Hh receptor Smoothened. However, these are predicted to have minimal effect when the pathway is activated as a result of dysregulation downstream of this receptor. In this issue of the JCI, Beauchamp and colleagues provide preclinical evidence that arsenic trioxide, a drug FDA approved for the treatment of acute promyelocytic leukemia, inhibits the growth of Ewing sarcoma and medulloblastoma cells by targeting GLI family zinc finger (GLI) proteins, which are Hh signaling pathway components downstream of Smoothened.