Different Response of Ptch Mutant and Ptch Wildtype Rhabdomyosarcoma Toward SMO and PI3K Inhibitors

Albert Rosenberger,Julia Bauer,Christian Dullin,Rosalie Ridzewski,Heidi Hahn,Anja Uhmann,Kai Dittmann,Simone Fulda,Maria Kuzyakova,Natalie Geyer,Hans-Ulrich Schildhaus

doi:10.3389/fonc.2018.00396

Albert Rosenberger, Julia Bauer + Show 9 more

Open Access

https://doi.org/10.3389/fonc.2018.00396

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Abstract

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma with poor prognosis. RMS frequently show Hedgehog (HH) pathway activity, which is predominantly seen in the embryonal subtype (ERMS). They also show activation of Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) signaling. Here we compared the therapeutic effectiveness and the impact on HH target gene expression of Smoothened (SMO) antagonists with those of the PI3K inhibitor pictilisib in ERMS with and without mutations in the HH receptor Patched1 (PTCH). Our data demonstrate that growth of ERMS showing canonical Hh signaling activity due to Ptch germline mutations is efficiently reduced by SMO antagonists. This goes along with strong downregulation of the Hh target Gli1. Likewise Ptch mutant tumors are highly responsive toward the PI3K inhibitor pictilisib, which involves modulation of AKT and caspase activity. Pictilisib also modulates Hh target gene expression, which, however, is rather not correlated with its antitumoral effects. In contrast, sporadic ERMS, which usually express HH target genes without having PTCH mutation, apparently lack canonical HH signaling activity. Thus, stimulation by Sonic HE (SHH) or SAG (Smoothened agonist) or inhibition by SMO antagonists do not modulate HH target gene expression. In addition, SMO antagonists do not provoke efficient anticancer effects and rather exert off-target effects. In contrast, pictilisib and other PI3K/AKT/mTOR inhibitors potently inhibit cellular growth. They also efficiently inhibit HH target gene expression. However, of whether this is correlated with their antitumoral effects it is not clear. Together, these data suggest that PI3K inhibitors are a good and reliable therapeutic option for all ERMS, whereas SMO inhibitors might only be beneficial for ERMS driven by PTCH mutations.

Highlights

Hedgehog (HH) signaling plays a major role in a variety of human cancers
Since a siRNAmediated knock-down of PTCH in a cell line derived from a sporadic ERMS would probably not adequately reflect this situation, we tested the drugs in primary tumor cell cultures from Ptch mutant mice (Ptch+/−)
The incubation of the primary murine tumor cells with vismodegib, sonidegib, or HhAntag significantly reduced the expression of the Hh target Gli1, but not of Hhip (Figure 1)

Summary

Introduction

Hedgehog (HH) signaling plays a major role in a variety of human cancers. The main components of the canonical HH signaling pathway are HH ligands, the transmembrane proteinsPatched (PTCH) and Smoothened (SMO) and GLI transcription factors. Upon binding of HH to PTCH this repression is released This leads to accumulation of SMO in the primary cilium where it triggers the modulation of a variety of proteins, which results in translocation of the GLI2 and GLI3 transcription factors into the nucleus. This activates the expression of HH target genes, which include GLI1 that can amplify the response on transcriptional level. In contrast to GLI1, the prediction of pathway activity from HHIP and PTCH levels is more difficult, because the respective proteins mediate a negative feedback by sequestering HH [for review see [1]]

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