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

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.

Current and Future Treatment Strategies for Rhabdomyosarcoma

“…Several studies have demonstrated that targeting the Hh pathway can inhibit tumor growth and impair tumor initiation in xenografted RMS models (118,(122)(123)(124). So far, preclinical evaluation of Smo inhibitors has been difficult to interpret due to the heterogeneity of response in preclinical models, depending on the RMS cell line and Smo inhibitor assessed (125,126). Recent FDA approval of the Smo inhibitors, vismodegib, and sonidegib for the treatment of advanced basal cell carcinoma (BCC) and entry of other Smo inhibitors into clinical trials for pediatric medulloblastoma raise the possibility of expanding these inhibitors into clinical trials for pediatric RMS (127).…”

Regulation and Role of GLI1 in Cutaneous Squamous Cell Carcinoma Pathogenesis

“…Antigen retrieval methods, antibodies and antibody dilutions used for immunohistochemical stainings are listed in Supplementary Table S1 . Immunofluorescent stainings of cells with acetylated α-tubulin to detect primary cilia was done as described previously (Geyer et al, 2018). For GLI1 in situ hybridization, the RNAscope ® technology was performed using the RNAscope ® Probe Hs-GLI1 (310991) and the RNAscope ® 2.5 HD Reagent Kit-RED (322350; Advanced Cell Diagnostics) according to the manufacturer’s recommendations.…”

Autophagy and Cell Death: Antitumor Drugs Targeting Autophagy

“…The Gli1 small-molecule inhibitor, GANT61, does not only inhibit the proliferation of human hepatocellular-carcinoma cells but also synergize with itraconazole to kill breast cancer cells through the ACD pathway [18]. HhAntag, a small-molecule inhibitor of downstream element of Hh pathway, inhibits embryonal rhabdomyosarcoma (ERMS) proliferation through autophagy induction [70]. SMO antagonist, Sonidegib, selectively targets cell migration and adhesion of mantle cell lymphoma (MCL) and suppresses the proliferation of MCL via autophagy inhibition [71].…”