Functional impact and targetability of PI3KCA, GNAS, and PTEN mutations in a spindle cell rhabdomyosarcoma with MYOD1 L122R mutation.

Abstract

Spindle cell/sclerosing rhabdomyosarcoma (ssRMS) is a rare subtype of rhabdomyosarcoma, commonly harboring a gain-of-function L122R mutation in the muscle-specific master transcription factor MYOD1. MYOD1-mutated ssRMS is almost invariably fatal, and development of novel therapeutic approaches based on the biology of the disease is urgently needed. MYOD1 L122R affects the DNA-binding domain and is believed to confer MYC-like properties to MYOD1, driving oncogenesis. Moreover, the majority of the MYOD1-mutated ssRMS harbor additional alterations activating the PI3K/AKT pathway. It is postulated that the PI3K/AKT pathway cooperates with MYOD1 L122R. To address this biological entity, we established and characterized a new patient-derived ssRMS cell line OHSU-SARC001, harboring MYOD1 L122R as well as alterations in PTEN, PIK3CA, and GNAS We explored the functional impact of these aberrations on oncogenic signaling with gain-of-function experiments in C2C12 murine muscle lineage cells. These data reveal that PIK3CAI459_T462del, the novel PIK3CA variant discovered in this patient specimen, is a constitutively active kinase, albeit to a lesser extent than PI3KCAE545K, a hotspot oncogenic mutation. Furthermore, we examined the effectiveness of molecularly targeted PI3K/AKT/mTOR and RAS/MAPK inhibitors to block oncogenic signaling and suppress the growth of OHSU-SARC001 cells. Dual PI3K/mTOR (LY3023414, bimiralisib) and AKT inhibitors (ipatasertib, afuresertib) induced dose-dependent reductions in cell growth. However, mTOR-selective inhibitors (everolimus, rapamycin) alone did not exert cytotoxic effects. The MEK1/2 inhibitor trametinib did not impact proliferation even at the highest doses tested. Our data suggest that molecularly targeted strategies may be effective in PI3K/AKT/mTOR-activated ssRMS. Taken together, these data highlight the importance of utilizing patient-derived models to assess molecularly targetable treatments and their potential as future treatment options.

• Authors: Florence Choo, Igor Odintsov, Kevin Nusser, Katelyn S Nicholson, Lara Davis, Christopher L Corless, Linda Stork, Romel Somwar, Marc Ladanyi, Jessica L Davis, Monika A Davare
• Journal: Cold Spring Harbor molecular case studies (Cold Spring Harb Mol Case Stud) Vol. 8 Issue 1 (01 2022) ISSN: 2373-2873 [Electronic] United States
• PMID: 35012940 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: © 2022 Choo et al.; Published by Cold Spring Harbor Laboratory Press.

Chemical References

• Chromogranins
• MyoD Protein
• MyoD1 myogenic differentiation protein
• PI3KCA protein, human
• Transcription Factors
• Proto-Oncogene Proteins c-akt
• PTEN Phosphohydrolase
• PTEN protein, human
• GNAS protein, human
• GTP-Binding Protein alpha Subunits, Gs

Topics

• Adult
• Animals
• Cell Line, Tumor
• Child
• Chromogranins
• GTP-Binding Protein alpha Subunits, Gs
• Humans
• Mice
• Mutation
• MyoD Protein (genetics)
• Oncogenes
• PTEN Phosphohydrolase (genetics)
• Phosphatidylinositol 3-Kinases (genetics)
• Proto-Oncogene Proteins c-akt (genetics)
• Rhabdomyosarcoma (genetics)
• Transcription Factors