In summary, these findings highlight a key role for PI3K/mTOR signalling in GLI1 regulation in HH-driven cancers and suggest that combined PI3Kα/mTOR inhibition may be particularly interesting for the development of effective treatment strategies in high-risk medulloblastomas.
We demonstrate that this multitarget agent suppresses medulloblastoma growth in vitro and in vivo through antagonism of Smo and Gli1, which is a novel mechanism of action in Hh inhibition.
We found that FGFR signaling represses GLI1 expression downstream of activated SMO in the SHH MB line DAOY and induces <i>MKI67</i>, <i>HES1</i>, and <i>BMI1</i> in DAOY and in the group 3 MB line HD-MBO3.
In the present study, we show that concomitant inhibition of Hedgehog (HH) signaling by the glioma-associated oncogene homolog1 (GLI1)-targeting agent GANT61 and the antiapoptotic BCL-2 protein family member MCL-1 by A-1210477 synergistically induces cell death in HH-driven cancers, i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB) cells.
Numb is considered as a tumor suppressor playing critical roles in determining cell fate and has been shown to target the oncogenic transcription factor Gli1 for Itch-dependent ubiquitination, resulting in suppression of the oncogenic sonic hedgehog signaling in medulloblastoma.
Together, these findings reveal a novel noncanonical GLI1 regulation and provide a potential therapeutic target for the treatment of cancers with aberrant Hh pathway activation, such as medulloblastoma.
Moreover, FOXS1 is both highly expressed and positively correlated with GLI1 in medulloblastoma samples of the Sonic HH subgroup, further arguing for the existence of FOXS1/GLI1 interplay in human tumors.
These data demonstrated that Gli1 is an important mediator of the SHH pathway activity in MB, and may be a novel agent for use in combined chemotherapeutic regimens.
Collectively, this data unveil a novel mechanism of inhibition of Gli1 function, which is exclusive for human cells and may be exploited for the treatment of Medulloblastoma or other Gli1 driven tumors.
Five differentially expressed genes in medulloblastoma (GLI1, SPHK1, SHROOM2, PDLIM3, and OTX2) were found to associate with Hh pathway activation status.
When compared with MB as a reference, the median GLI1 mRNA expression in GBM appeared 14.8 fold lower than that of the "high-Hh" cluster of MB but 5.6 fold higher than that of the "low-Hh" cluster of MB.
Synergism between Hedgehog-GLI and EGFR signaling in Hedgehog-responsive human medulloblastoma cells induces downregulation of canonical Hedgehog-target genes and stabilized expression of GLI1.
The GLI1 mRNA is highly edited at nucleotide 2179 by adenosine deamination in normal cerebellum, but the extent of this modification is reduced in cell lines from the cerebellar tumor medulloblastoma.
Compound 11d suppressed transcription factor Gli1 mRNA expression in tumor-associated stromal tissue and inhibited tumor growth (treatment/control ratio, 3%) in a mouse medulloblastoma allograft model owing to the improved PK profile based on increased solubility.
Compound 12b suppressed stromal Gli1 mRNA expression in a murine model and demonstrated antitumor activity in a murine medulloblastoma allograft model.
Mathematical analysis of the relationship between the drug's pharmacokinetics and Gli1 pharmacodynamics in patched(+/-) medulloblastoma tumor models yielded similar tumor and skin Gli1 IC(50) values, suggesting that skin can be used as a surrogate tissue for the measurement of tumor Gli1 levels.
Analysis of Hh pathway activity and PK/PD modeling reveals that vismodegib inhibits Gli1 with a similar IC(50) in both the medulloblastoma and D5123 models (0.165 μmol/L ±11.5% and 0.267 μmol/L ±4.83%, respectively).
Therefore, by targeting multiple genes regulating the differentiation state of GNPs, Atoh1 collaborates with the pro-proliferative Gli1-dependent transcriptional program to influence medulloblastoma development.
In addition, the targets suggest a pathway through which GLI1 may ultimately affect medulloblastoma cell proliferation, survival and genomic stability by converging on p53, SGK1, MGMT and NTRK2.