The Hedgehog signalling pathways in human pathology

Downregulation of Sonic hedgehog signaling induces G2-arrest in genital warts

BACKGROUND

Human papillomavirus (HPV) infected keratinocyte dysfunction results in the formation of genital warts, and the specific role of Sonic hedgehog (SHh) signaling in genital warts remains elusive. Thus, this study aimed to identify the correlation between wart formation and SHh signaling.

MATERIALS AND METHODS

In this study, nine male patients with genital warts were recruited, and the expression of SHh and its downstream signal molecules Patched-1 and GLI family zinc finger 1 (Ptch1 and Gli1) was detected. Moreover, G2-phase cells in the collected genital warts samples were assessed with normal foreskin samples as a comparison. HPV6/11 were detected via in situ hybridization (ISH), and SHh expression of the corresponding paraffin sections was determined via immunohistochemical staining (IHC). In addition, an in vitro down-regulated SHh model was constructed by siRNA transfection of the HaCaT cell line, and the cell cycle was detected at 36 h by flow cytometry with propidium iodide staining.

RESULTS

SHh, Ptch1, and Gli1 in warts were significantly downregulated in the condyloma acuminatum (CA) group compared to the normal foreskin group. G2-phase cells in the middle section of the spinous layer of CA wart tissues were significantly increased. Moreover, the expression of HPV-DNA was amplified and negatively correlated with SHh activity in CA wart tissues. Lastly, the downregulation of SHh-induced G2 arrest in vitro.

CONCLUSIONS

The downregulation of the SHh signaling promotes HPV replication and the formation of warts by inducing G2/M arrest in the keratinocytes of CA.

Exploring the recent trends in perturbing the cellular signaling pathways in cancer by natural products

Cancer is commonly thought to be the product of irregular cell division. According to the World Health Organization (WHO), cancer is the major cause of death globally. Nature offers an abundant supply of bioactive compounds with high therapeutic efficacy. Anticancer effects have been studied in a variety of phytochemicals found in nature. When Food and Drug Administration (FDA)-approved anticancer drugs are combined with natural compounds, the effectiveness improves. Several agents have already progressed to clinical trials based on these promising results of natural compounds against various cancer forms. Natural compounds prevent cancer cell proliferation, development, and metastasis by inducing cell cycle arrest, activating intrinsic and extrinsic apoptosis pathways, generating reactive oxygen species (ROS), and down-regulating activated signaling pathways. These natural chemicals are known to affect numerous important cellular signaling pathways, such as NF-B, MAPK, Wnt, Notch, Akt, p53, AR, ER, and many others, to cause cell death signals and induce apoptosis in pre-cancerous or cancer cells without harming normal cells. As a result, non-toxic “natural drugs” taken from nature’s bounty could be effective for the prevention of tumor progression and/or therapy of human malignancies, either alone or in combination with conventional treatments. Natural compounds have also been shown in preclinical studies to improve the sensitivity of resistant cancers to currently available chemotherapy agents. To summarize, preclinical and clinical findings against cancer indicate that natural-sourced compounds have promising anticancer efficacy. The vital purpose of these studies is to target cellular signaling pathways in cancer by natural compounds.

The bromodomain inhibitor IBET-151 attenuates vismodegib-resistant esophageal adenocarcinoma growth through reduction of GLI signaling

The Hedgehog/GLI (HH/GLI) signaling pathway plays a critical role in human oncogenesis. Unfortunately, the clinical use of HH inhibitor(s) has been associated with serious adverse effects and mutation-related drug resistance. Since the efficacy of SMO (Smoothened) and GLI inhibitors is limited in clinical trials, there remains a critical need for the HH/GLI pathway inhibitors with different mechanisms of action. Here, we show that esophageal adenocarcinoma (EAC) cell lines are insensitive to vismodegib (SMO inhibitor) but respond to GANT61 (GLI1 inhibitor). Furthermore, we examine the role of GLI1 in tumorigenicity of EAC and how a selective bromodomain inhibitor IBET-151 downregulates transcriptional activity of the GLI1 transcription factor in EAC. Our study demonstrates that GLI1 plays an important role in tumorigenicity of EAC and that elevated GLI1 expression in patients’ ultrasound-assisted endoscopic biopsy may predict the response to neoadjuvant chemotherapy (NAC) FOLFOX. Importantly, IBET-151 abrogates the growth of vismodegib-resistant EAC cells and downregulates HH/GLI by reducing the occupancy of BRD4 at the GLI1 locus. IBET-151 also attenuates tumor growth of EAC-PDXs and does so in an on-target manner as it reduces the expression of GLI1. We identify HH/GLI signaling as a novel druggable pathway in EAC as well as validate an ability of clinically relevant GLI inhibitor to attenuate the viability of vismodegib-resistant EAC cells. Therefore, we propose that selective bromodomain inhibitors, such as IBET-151, could be used as novel therapeutic agents for EAC patients harboring GLI-dependent tumors.

Hedgehog signaling inhibitors in solid and hematological cancers

BACKGROUND

The hedgehog signaling pathway is normally tightly regulated. Mutations in hedgehog pathway components may lead to abnormal activation. Aberrantly activated hedgehog signaling plays a major role in the development of solid and hematological cancer. In recent years, inhibitors have been developed that attenuate hedgehog signaling; 2 have been approved for use in basal cell carcinoma (BCC), while others are under development or in clinical trials. The aim of this review is to provide an overview of known hedgehog inhibitors (HHIs) and their potential for the treatment of hematological cancers and solid tumors beyond BCC.

DESIGN

Published literature was searched to identify articles relating to HHIs in noncutaneous cancer. Both preclinical and clinical research articles were included. In addition, relevant clinical trial results were identified from www.clinicaltrials.gov. Information on the pharmacology of HHIs is also included.

RESULTS

HHIs show activity in a variety of solid and hematological cancers. In preclinical studies, HHIs demonstrated efficacy in pancreatic cancer, rhabdomyosarcoma, breast cancer, and acute myeloid leukemia (AML). In clinical studies, HHIs showed activity in medulloblastoma, as well as prostate, pancreatic, and hematological cancers. Current clinical trials testing the efficacy of HHIs are underway for prostate, pancreatic, and breast cancers, as well as multiple myeloma and AML.

CONCLUSIONS

As clinical trial results become available, it will be possible to discern which additional tumor types are suited to HHI mono- or combination therapy with other anticancer agents. The latter strategy may be useful for delaying or overcoming drug resistance.

Naturally occurring small-molecule inhibitors of hedgehog/GLI-mediated transcription

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. To search for Hh/GLI inhibitors, we screened for naturally occurring inhibitors of the transcriptional activator GLI1 by using a cell-based assay. We identified zerumbone (1), zerumbone epoxide (2), staurosporinone (9), 6-hydroxystaurosporinone (10), arcyriaflavin C (11) and 5,6-dihydroxyarcyriaflavin A (12) as inhibitors of GLI-mediated transcription. In addition, we isolated physalins F (17) and B (18) from Physalis minima, which are also potent inhibitors. These compounds also inhibited GLI2-mediated transactivation. Semiquantitative RT-PCR and Western blotting analysis further revealed that 1, 9, 17, and 18 decreased Hh-related component expressions. We also show that inhibitors of GLI-mediated transactivation reduce the level of the antiapoptosis Bcl2 expression. Finally, these identified compounds were cytotoxic to PANC1 pancreatic cancer cells, which express Hh/GLI components. These results strongly suggest that the cytotoxicity of the compounds to PANC1 cells correlates with their inhibition of GLI-mediated transcription.

Basal cell nevus syndrome

PURPOSE OF REVIEW

Basal cell nevus syndrome (BCNS), is a hereditary condition transmitted as an autosomal dominant trait exhibiting high penetrance and variable expressivity. Inherited or spontaneous mutations in the human homologue of the Drosophila patched gene underlie the disorder and in addition to tumor predisposition, are associated with a range of 'patterning' defects. Recent advances, with glimpses of possible therapies are emerging, but because of the wide-ranging nature of phenotypic expression and overlap with other syndromes, there is difficulty. Finally, because of the importance of PTCH and paralogous genes in many species other than humans, reports appear in a correspondingly wide range of journals, which makes 'keeping abreast' difficult.

RECENT FINDINGS

Progress has been achieved in understanding the role of Gli-1, 2, & 3 in development of 'sporadic' BCCs and BCNS. Expression of PTCH1 is now known to be regulated by alternative promoters and a single functional Gli-binding site. Expression of FOXE1 as a new transcriptional target of Gli2 has been demonstrated in human epidermis and BCCs. Finally, the discovery of Shh pathway inhibitors such as cyclopamine, a naturally occurring alkaloid and ornithine decarboxylase inhibition suggest possible interventional therapies.

SUMMARY

In BCNS, phenotype does not correlate with position of mutations within Patched, suggesting genetic makeup and environment modulate effects of premature protein truncation induced by PTCH mutation. These developmental abnormalities occur as a result of haplo-insufficiency in heterozygotes for the mutated gene, whereas neoplastic complications arise from a classical two-hit tumor suppressor gene model. Attention is therefore turning toward TP53 and PTCH associations.