Overcoming resistance to Sonic Hedgehog inhibition by targeting p90 ribosomal S6 kinase in pediatric medulloblastoma.
BACKGROUND
Molecular subtyping has allowed for the beginning of personalized treatment in children suffering from medulloblastoma (MB). However, resistance inevitably emerges against these therapies, particularly in the Sonic Hedgehog (SHH) subtype. We found that children with SHH subtype have the worst outcome underscoring the need to identify new therapeutic targets.


METHODS
High content screening of a 129 compound library identified agents that inhibited SHH MB growth. Lead molecular target levels, p90 ribosomal S6 kinase (RSK) were characterized by immunoblotting and qRT-PCR. Comparisons were made to human neural stem cells (hNSC). Impact of inhibiting RSK with the small molecule BI-D1870 or siRNA was assessed in growth assays (monolayer, neurosphere, and soft agar). NanoString was used to detect RSK in a cohort of 66 patients with MB. To determine BI-D1870 pharmacokinetics/pharmacodynamics, 100 mg/kg was I.P. injected into mice and tissues were collected at various time points.


RESULTS
Daoy, ONS76, UW228, and UW426 MB cells were exquisitely sensitive to BI-D1870 but unresponsive to SHH inhibitors. Anti-tumor growth corresponded with inactivation of RSK in MB cells. BI-D1870 had no effect on hNSCs. Inhibiting RSK with siRNA or BI-D1870 suppressed growth, induced apoptosis, and sensitized cells to SHH agents. Notably, RSK expression is correlated with SHH patients. In mice, BI-D1870 was well-tolerated and crossed the blood-brain barrier (BBB).


CONCLUSIONS
RSK inhibitors are promising because they target RSK which is correlated with SHH patients as well as cause high levels of apoptosis to only MB cells. Importantly, BI-D1870 crosses the BBB, acting as a scaffold for development of more long-lived RSK inhibitors.
Department of Pediatrics, British Columbia Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada.
Mary Rose
MR
Pambid
Rachel
R
Berns
Hans H
HH
Adomat
Kaiji
K
Hu
Joanna
J
Triscott
Norbert
N
Maurer
Natalia
N
Zisman
Vijay
V
Ramaswamy
Cynthia E
CE
Hawkins
Michael D
MD
Taylor
Christopher
C
Dunham
Emma
E
Guns
Sandra E
SE
Dunn
D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002528:Cerebellar Neoplasms / Q000201:enzymology / Q000235:genetics*; D002648:Child; D002853:Chromatography, Liquid; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004354:Drug Screening Assays, Antitumor; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D005434:Flow Cytometry; D053823:Hedgehog Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D015151:Immunoblotting; D008297:Male; D013058:Mass Spectrometry; D008527:Medulloblastoma / Q000201:enzymology / Q000235:genetics*; D051379:Mice; D011621:Pteridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D034741:RNA, Small Interfering; D060888:Real-Time Polymerase Chain Reaction; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors*; D014018:Tissue Distribution; D059467:Transcriptome; D014162:Transfection
D000970:Antineoplastic Agents; C516541:BI D1870; D004791:Enzyme Inhibitors; D053823:Hedgehog Proteins; D011621:Pteridines; D034741:RNA, Small Interfering; D038744:Ribosomal Protein S6 Kinases, 90-kDa
Sonic Hedgehog medulloblastoma; p90 ribosomal S6 kinase; resistance