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Theard PL, Linke AJ, Sealover NE, Daley BR, Yang J, Cox K, Kortum RL. SOS2 modulates the threshold of EGFR signaling to regulate osimertinib efficacy and resistance in lung adenocarcinoma. Mol Oncol 2024; 18:641-661. [PMID: 38073064 PMCID: PMC10920089 DOI: 10.1002/1878-0261.13564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 10/23/2023] [Accepted: 12/08/2023] [Indexed: 01/02/2024] Open
Abstract
Son of sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic receptor tyrosine kinase (RTK)-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR tyrosine kinase inhibitor (EGFR-TKI) osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion (SOS2KO ) sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation, oncogenic transformation, and survival. Bypassing RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2KO inhibited hepatocyte growth factor (HGF)-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long-term in situ resistance assay, most osimertinib-resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2KO cultures that became osimertinib resistant primarily underwent non-RTK-dependent epithelial-mesenchymal transition (EMT). Since bypassing RTK reactivation and/or tertiary EGFR mutations represent most osimertinib-resistant cancers, these data suggest that targeting proximal RTK signaling, here exemplified by SOS2 deletion, has the potential to delay the development osimertinib resistance and enhance overall clinical responses for patients with EGFR-mutated LUAD.
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Affiliation(s)
- Patricia L. Theard
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Amanda J. Linke
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Nancy E. Sealover
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Brianna R. Daley
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Johnny Yang
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Katherine Cox
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
| | - Robert L. Kortum
- Department of Pharmacology and Molecular TherapeuticsUniformed Services University of the Health SciencesBethesdaMDUSA
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Sealover NE, Theard PT, Hughes JM, Linke AJ, Daley BR, Kortum RL. In situ modeling of acquired resistance to RTK/RAS-pathway-targeted therapies. iScience 2024; 27:108711. [PMID: 38226159 PMCID: PMC10788224 DOI: 10.1016/j.isci.2023.108711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 10/31/2023] [Accepted: 12/08/2023] [Indexed: 01/17/2024] Open
Abstract
Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Here, we describe an in situ resistance assay (ISRA) that reliably models acquired resistance to RTK/RAS-pathway-targeted therapies across cell lines. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show that acquired osimertinib resistance can be significantly delayed by inhibition of proximal RTK signaling using SHP2 inhibitors. Isolated osimertinib-resistant populations required SHP2 inhibition to resensitize cells to osimertinib and reduce MAPK signaling to block the effects of enhanced activation of multiple parallel RTKs. We additionally modeled resistance to targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.
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Affiliation(s)
- Nancy E. Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Patricia T. Theard
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Jacob M. Hughes
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Amanda J. Linke
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Brianna R. Daley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - Robert L. Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
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Daley BR, Sealover NE, Sheffels E, Hughes JM, Gerlach D, Hofmann MH, Kostyrko K, Mair B, Linke A, Beckley Z, Frank A, Dalgard C, Kortum RL. SOS1 inhibition enhances the efficacy of and delays resistance to G12C inhibitors in lung adenocarcinoma. bioRxiv 2023:2023.12.07.570642. [PMID: 38106234 PMCID: PMC10723384 DOI: 10.1101/2023.12.07.570642] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Clinical effectiveness of KRAS G12C inhibitors (G12Cis) is limited both by intrinsic and acquired resistance, necessitating the development of combination approaches. We found that targeting proximal receptor tyrosine kinase (RTK) signaling using the SOS1 inhibitor (SOS1i) BI-3406 both enhanced the potency of and delayed resistance to G12Ci treatment, but the extent of SOS1i effectiveness was modulated by both SOS2 expression and the specific mutational landscape. SOS1i enhanced the efficacy of G12Ci and limited rebound RTK/ERK signaling to overcome intrinsic/adaptive resistance, but this effect was modulated by SOS2 protein levels. Survival of drug-tolerant persister (DTP) cells within the heterogeneous tumor population and/or acquired mutations that reactivate RTK/RAS signaling can lead to outgrowth of tumor initiating cells (TICs) that drive therapeutic resistance. G12Ci drug tolerant persister cells showed a 2-3-fold enrichment of TICs, suggesting that these could be a sanctuary population of G12Ci resistant cells. SOS1i re-sensitized DTPs to G12Ci and inhibited G12C-induced TIC enrichment. Co-mutation of the tumor suppressor KEAP1 limits the clinical effectiveness of G12Cis, and KEAP1 and STK11 deletion increased TIC frequency and accelerated the development of acquired resistance to G12Ci in situ. SOS1i both delayed acquired G12Ci resistance and limited the total number of resistant colonies regardless of KEAP1 and STK11 mutational status. These data suggest that SOS1i could be an effective strategy to both enhance G12Ci efficacy and prevent G12Ci resistance regardless of co-mutations.
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Affiliation(s)
- Brianna R Daley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Nancy E Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Erin Sheffels
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Jacob M. Hughes
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | | | | | - Kaja Kostyrko
- Boehringer Ingelheim RCV GmbH & Co KG, Vienna, Austria
| | - Barbara Mair
- Boehringer Ingelheim RCV GmbH & Co KG, Vienna, Austria
| | - Amanda Linke
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Zaria Beckley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Andrew Frank
- Henry M. Jackson Foundation for the Advancement of Military Medicine; Bethesda, MD, USA
- Student Bioinformatics Initiative, Center for Military Precision Health, Uniformed Services University of the Health Sciences; Bethesda, MD, USA
| | - Clifton Dalgard
- The American Genome Center, Department of Anatomy, Cell Biology, and Genetics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
| | - Robert L Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814
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Daley BR, Vieira HM, Rao C, Hughes JM, Beckley ZM, Huisman DH, Chatterjee D, Sealover NE, Cox K, Askew JW, Svoboda RA, Fisher KW, Lewis RE, Kortum RL. SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status. Proc Natl Acad Sci U S A 2023; 120:e2313137120. [PMID: 37972068 PMCID: PMC10666034 DOI: 10.1073/pnas.2313137120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 09/20/2023] [Indexed: 11/19/2023] Open
Abstract
KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.
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Affiliation(s)
- Brianna R. Daley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
| | - Heidi M. Vieira
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE68198
| | - Chaitra Rao
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE68198
| | - Jacob M. Hughes
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
| | - Zaria M. Beckley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
| | - Dianna H. Huisman
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE68198
| | - Deepan Chatterjee
- Department of Integrative Physiology and Molecular Medicine, University of Nebraska Medical Center, Omaha, NE68198
| | - Nancy E. Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
| | - Katherine Cox
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
| | - James W. Askew
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE68198
| | - Robert A. Svoboda
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE68198
| | - Kurt W. Fisher
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE68198
| | - Robert E. Lewis
- Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE68198
| | - Robert L. Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD20814
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Theard PL, Linke AJ, Sealover NE, Daley BR, Yang J, Cox K, Kortum RL. SOS2 regulates the threshold of mutant EGFR-dependent oncogenesis. bioRxiv 2023:2023.01.20.524989. [PMID: 37425733 PMCID: PMC10327037 DOI: 10.1101/2023.01.20.524989] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2023]
Abstract
Son of Sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic RTK-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR-TKI osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit PI3K/AKT pathway activation, oncogenic transformation, and survival. Bypass RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2 KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2 KO inhibited HGF-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long term in situ resistance assay, a majority of osimertinib resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2 KO cultures that became osimertinib resistant primarily underwent non-RTK dependent EMT. Since bypass RTK reactivation and/or tertiary EGFR mutations represent the majority of osimertinib-resistant cancers, these data suggest that targeting SOS2 has the potential to eliminate the majority of osimertinib resistance.
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Affiliation(s)
- Patricia L. Theard
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Amanda J. Linke
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Nancy E. Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Brianna R. Daley
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Johnny Yang
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Katherine Cox
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
| | - Robert L Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA 20814
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Sealover NE, Theard PL, Hughes JM, Linke AJ, Daley BR, Kortum RL. In situ modeling of acquired resistance to RTK/RAS pathway targeted therapies. bioRxiv 2023:2023.01.27.525958. [PMID: 36747633 PMCID: PMC9901014 DOI: 10.1101/2023.01.27.525958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Intrinsic and acquired resistance limit the window of effectiveness for oncogene-targeted cancer therapies. Preclinical studies that identify synergistic combinations enhance therapeutic efficacy to target intrinsic resistance, however, methods to study acquired resistance in cell culture are lacking. Here, we describe a novel in situ resistance assay (ISRA), performed in a 96-well culture format, that models acquired resistance to RTK/RAS pathway targeted therapies. Using osimertinib resistance in EGFR-mutated lung adenocarcinoma (LUAD) as a model system, we show acquired resistance can be reliably modeled across cell lines using objectively defined osimertinib doses. Similar to patient populations, isolated osimertinib-resistant populations showed resistance via enhanced activation of multiple parallel RTKs so that individual RTK inhibitors did not re-sensitize cells to osimertinib. In contrast, inhibition of proximal RTK signaling using the SHP2 inhibitor RMC-4550 both re-sensitized resistant populations to osimertinib and prevented the development of osimertinib resistance as a primary therapy. Similar, objectively defined drug doses were used to model resistance to additional RTK/RAS pathway targeted therapies including the KRASG12C inhibitors adagrasib and sotorasib, the MEK inhibitor trametinib, and the farnesyl transferase inhibitor tipifarnib. These studies highlight the tractability of in situ resistance assays to model acquired resistance to targeted therapies and provide a framework for assessing the extent to which synergistic drug combinations can target acquired drug resistance.
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Hebron KE, Wan X, Roth JS, Liewehr DJ, Sealover NE, Frye WJ, Kim A, Stauffer S, Perkins OL, Sun W, Isanogle KA, Robinson CM, James A, Awasthi P, Shankarappa P, Luo X, Lei H, Butcher D, Smith R, Edmondson EF, Chen JQ, Kedei N, Peer CJ, Shern JF, Figg WD, Chen L, Hall MD, Difilippantonio S, Barr FG, Kortum RL, Robey RW, Vaseva AV, Khan J, Yohe ME. The Combination of Trametinib and Ganitumab is Effective in RAS-Mutated PAX-Fusion Negative Rhabdomyosarcoma Models. Clin Cancer Res 2023; 29:472-487. [PMID: 36322002 PMCID: PMC9852065 DOI: 10.1158/1078-0432.ccr-22-1646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/22/2022] [Accepted: 10/31/2022] [Indexed: 11/05/2022]
Abstract
PURPOSE PAX-fusion negative rhabdomyosarcoma (FN RMS) is driven by alterations in the RAS/MAP kinase pathway and is partially responsive to MEK inhibition. Overexpression of IGF1R and its ligands is also observed in FN RMS. Preclinical and clinical studies have suggested that IGF1R is itself an important target in FN RMS. Our previous studies revealed preclinical efficacy of the MEK1/2 inhibitor, trametinib, and an IGF1R inhibitor, BMS-754807, but this combination was not pursued clinically due to intolerability in preclinical murine models. Here, we sought to identify a combination of an MEK1/2 inhibitor and IGF1R inhibitor, which would be tolerated in murine models and effective in both cell line and patient-derived xenograft models of RAS-mutant FN RMS. EXPERIMENTAL DESIGN Using proliferation and apoptosis assays, we studied the factorial effects of trametinib and ganitumab (AMG 479), a mAb with specificity for human and murine IGF1R, in a panel of RAS-mutant FN RMS cell lines. The molecular mechanism of the observed synergy was determined using conventional and capillary immunoassays. The efficacy and tolerability of trametinib/ganitumab was assessed using a panel of RAS-mutated cell-line and patient-derived RMS xenograft models. RESULTS Treatment with trametinib and ganitumab resulted in synergistic cellular growth inhibition in all cell lines tested and inhibition of tumor growth in four of six models of RAS-mutant RMS. The combination had little effect on body weight and did not produce thrombocytopenia, neutropenia, or hyperinsulinemia in tumor-bearing SCID beige mice. Mechanistically, ganitumab treatment prevented the phosphorylation of AKT induced by MEK inhibition alone. Therapeutic response to the combination was observed in models without a mutation in the PI3K/PTEN axis. CONCLUSIONS We demonstrate that combined trametinib and ganitumab is effective in a genomically diverse panel of RAS-mutated FN RMS preclinical models. Our data also show that the trametinib/ganitumab combination likely has a favorable tolerability profile. These data support testing this combination in a phase I/II clinical trial for pediatric patients with relapsed or refractory RAS-mutated FN RMS.
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Affiliation(s)
- Katie E. Hebron
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892,Laboratory of Cell and Developmental Signaling, Center for Cancer Research, 8560 Progress Drive, Frederick, MD 21701
| | - Xiaolin Wan
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Jacob S. Roth
- Early Translation Branch, Division of Preclinical Innovation, National Center for Advancing Translational Sciences, 9800 Medical Center Drive, Rockville, MD 20850
| | - David J. Liewehr
- Biostatistics and Data Management Section, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Nancy E. Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Services, Bethesda, MD 20814
| | - William J.E. Frye
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, 9000 Rockville Pike, Bethesda, MD 20892
| | - Angela Kim
- Laboratory of Cell and Developmental Signaling, Center for Cancer Research, 8560 Progress Drive, Frederick, MD 21701
| | - Stacey Stauffer
- Laboratory of Cell and Developmental Signaling, Center for Cancer Research, 8560 Progress Drive, Frederick, MD 21701
| | - Olivia L. Perkins
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Wenyue Sun
- Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, 9000 Rockville Pike, Bethesda, MD 20892
| | - Kristine A. Isanogle
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Christina M. Robinson
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Amy James
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Parirokh Awasthi
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Priya Shankarappa
- Genitourinary Malignancies Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Xiaoling Luo
- Collaborative Protein Technology Resource, National Cancer Institute, NIH, Bethesda, MD 20892
| | - Haiyan Lei
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Donna Butcher
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Roberta Smith
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Elijah F. Edmondson
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Jin-Qiu Chen
- Collaborative Protein Technology Resource, National Cancer Institute, NIH, Bethesda, MD 20892
| | - Noemi Kedei
- Collaborative Protein Technology Resource, National Cancer Institute, NIH, Bethesda, MD 20892
| | - Cody J. Peer
- Genitourinary Malignancies Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Jack F. Shern
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - W. Douglas Figg
- Genitourinary Malignancies Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892
| | - Lu Chen
- Early Translation Branch, Division of Preclinical Innovation, National Center for Advancing Translational Sciences, 9800 Medical Center Drive, Rockville, MD 20850
| | - Matthew D. Hall
- Early Translation Branch, Division of Preclinical Innovation, National Center for Advancing Translational Sciences, 9800 Medical Center Drive, Rockville, MD 20850
| | - Simone Difilippantonio
- Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21701
| | - Frederic G. Barr
- Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, 9000 Rockville Pike, Bethesda, MD 20892
| | - Robert L. Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Services, Bethesda, MD 20814
| | - Robert W. Robey
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, 9000 Rockville Pike, Bethesda, MD 20892
| | - Angelina V. Vaseva
- Greehey Children’s Cancer Research Institute, UT Health San Antonio, San Antonio, Texas, USA
| | - Javed Khan
- Genetics Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892,Co-corresponding authors Correspondence: Marielle Yohe, M.D., Ph.D., Center for Cancer Research, National Cancer Institute, 8560 Progress Drive Room D3026, Frederick, MD 27101, Phone: (240) 760-7436,
| | - Marielle E. Yohe
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, 9000 Rockville Pike, Bethesda, MD 20892,Laboratory of Cell and Developmental Signaling, Center for Cancer Research, 8560 Progress Drive, Frederick, MD 21701,Co-corresponding authors Correspondence: Marielle Yohe, M.D., Ph.D., Center for Cancer Research, National Cancer Institute, 8560 Progress Drive Room D3026, Frederick, MD 27101, Phone: (240) 760-7436,
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Yohe ME, Hebron KE, Wan X, Roth JS, Liewehr DJ, Sealover NE, Stauffer S, Feehan-Nelson O, Sun W, Isanogle KA, Robinson CM, James A, Awasthi P, Shankarappa P, Liu X, Lei H, Butcher D, Smith R, Edmonson EF, Chen JQ, Kedei N, Peer CS, Shern JF, Figg WD, Chen L, Hall MD, Difillipantonio S, Barr FG, Kortum RL, Vaseva AV, Khan J. Abstract IA023: Therapeutic efficacy of trametinib and ganitumab in RAS-mutated rhabdomyosarcoma. Clin Cancer Res 2022. [DOI: 10.1158/1557-3265.sarcomas22-ia023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Background: PAX-fusion negative rhabdomyosarcoma (FN RMS) is driven by alterations in the RAS/MAP kinase pathway and is partially responsive to MEK inhibition. Overexpression of IGF1R and its ligands is also observed in FN RMS. Preclinical and clinical studies have suggested that IGF1R is itself an important target in FN RMS. Our previous studies revealed preclinical efficacy of the MEK1/2 inhibitor, trametinib, and an IGF1R inhibitor, BMS75807, but this combination was not pursued clinically due to excessive toxicity in preclinical murine models. Here, we sought to identify a combination of an MEK1/2 inhibitor and IGF1R inhibitor that would be better tolerated in murine models and effective in both cell line and patient derived xenograft models of RAS-mutant FN RMS. Methods: Using proliferation and apoptosis assays, we studied the factorial effects of trametinib and ganitumab (AMG 479), a monoclonal antibody with specificity for human and murine IGF1R, in a panel of RAS-mutant FN RMS cell lines. The molecular mechanism of the observed synergy was determined using conventional and capillary immunoassays. The efficacy and tolerability of the combination was assessed using a panel of RAS-mutated cell-line and patient-derived RMS xenograft models. Results: Treatment with trametinib and ganitumab resulted in synergistic cellular growth inhibition in all cell lines tested and inhibition of tumor growth in five out of six models of RAS-mutant RMS. Evidence suggests that the combination had little effect on body weight loss, thrombocytopenia, neutropenia, or hyperinsulinemia in tumor-bearing SCID beige mice. Mechanistically, ganitumab treatment prevented the AKT phosphorylation that is induced by MEK inhibition alone. Therapeutic response to the combination was observed in models with an intact PI3K/PTEN axis. Conclusions: We demonstrate that combined trametinib and ganitumab is effective in a genomically diverse panel of RAS-mutated FN RMS preclinical models. The trametinib/ganitumab combination also likely has an improved tolerability profile compared to other IGF1R/MEK inhibitor combinations. These data support testing this combination in a phase I/II clinical trial for pediatric patients with relapsed or refractory RAS-mutated FN RMS.
Citation Format: Marielle E. Yohe, Katie E. Hebron, Xiaolin Wan, Jacob S. Roth, David J. Liewehr, Nancy E. Sealover, Stacey Stauffer, Olivia Feehan-Nelson, Wenyue Sun, Kristine A. Isanogle, Christina M. Robinson, Amy James, Parirokh Awasthi, Priya Shankarappa, Xiaoling Liu, Haiyan Lei, Donna Butcher, Roberta Smith, Elijah F. Edmonson, Jin-Qui Chen, Noemi Kedei, Cody S. Peer, Jack F. Shern, W. Douglas Figg, Lu Chen, Matthew D. Hall, Simone Difillipantonio, Frederic G. Barr, Robert L. Kortum, Angelina V. Vaseva, Javed Khan. Therapeutic efficacy of trametinib and ganitumab in RAS-mutated rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA023.
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Affiliation(s)
| | | | | | - Jacob S. Roth
- 3National Center for Advancing Translational Sciences, Rockville, MD,
| | | | | | | | | | - Wenyue Sun
- 2National Cancer Institute, Bethesda, MD,
| | | | | | - Amy James
- 1National Cancer Institute, Frederick, MD,
| | | | | | | | - Haiyan Lei
- 2National Cancer Institute, Bethesda, MD,
| | | | | | | | | | | | | | | | | | - Lu Chen
- 3National Center for Advancing Translational Sciences, Rockville, MD,
| | - Matthew D. Hall
- 3National Center for Advancing Translational Sciences, Rockville, MD,
| | | | | | | | - Angelina V. Vaseva
- 5University of Texas Health Science Center at San Antonio, San Antonio, TX
| | - Javed Khan
- 2National Cancer Institute, Bethesda, MD,
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Abstract
Although oncogenic driver mutations in RAS occur in 20% of cancers, heterogeneity in the biologic outputs of different RAS mutants has hampered efforts to develop effective treatments for RAS-mutated cancers. In this issue of Science Signaling, Huynh et al. show that even among KRASQ61 mutants, the specific amino acid that is substituted substantially affects mutant KRAS biologic activity and oncogenicity.
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Sealover NE, Kortum RL. Abstract 413: WT RAS signaling is an essential therapeutic target in RAS mutated cancers. Cancer Res 2022. [DOI: 10.1158/1538-7445.am2022-413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Single-agent targeting of RAS-mutated cancers using RAF/MEK/ERK or PI3K/AKT pathway inhibitors is ineffective; blocking one pathway relieves negative feedback control of RTK signaling and hyperactivates parallel effector pathways. While combined MEK and PI3K inhibition is effective in preclinical models, toxicity of this combination prevents its clinical use. Alternative strategies for treating RAS-mutated cancers are essential. Therapeutics directly targeting mutated RAS proteins have the potential to spare normal cellular function thereby lessening overall toxicity. Unfortunately, direct RAS inhibition as a monotherapy does not fully block RAS effector signaling. RAS proteins show differential activation of RAF and PI3K pathways: KRAS potently activates RAF but poorly activates PI3K, whereas HRAS potently activates PI3K but poorly activates RAF. Further, mutant RAS inhibition relieves negative feedback controls leading to rapid hyperactivation of RTK−WT RAS signaling. A more comprehensive understanding of the interplay between mutant RAS and RTK−WT RAS signaling is essential to developing rational therapeutic approaches to treat RAS-mutated cancers. We found that WT RAS enhanced mutant RAS-driven transformation by activating RAS effectors poorly engaged by mutated RAS. Further, inhibition of RAS effectors activated poorly by mutant RAS synergized with and limited resistance to mutant HRAS and KRAS inhibitors. The mutant HRAS inhibitor tipifarnib blocked PI3K signaling and synergized with MEK inhibitors in HRAS-mutated cancer cell lines; covalent KRASG12C inhibitors blocked MEK signaling and synergized with PI3K inhibitors in KRASG12C-mutated cell lines. Synergy between inhibitors of mutant RAS and RAS effectors was dependent on intact RTK/WT RAS signaling and was lost in both RASless or SOSless MEFs. Upstream of RAS, the RASGEFs SOS1 and SOS2 showed unique and overlapping functions to promote mutant RAS-driven transformation. SOS1 was critical for mutant RAS (G12V) activation and SOS1 inhibition augmented the efficacy of mutant RAS inhibitors. RTK−SOS2−PI3K signaling protected cells from anoikis and mediated mutant KRAS-driven transformation. These results should inform the design of clinical trials for patients with RAS-mutated cancers.
Citation Format: Nancy E. Sealover, Robert L. Kortum. WT RAS signaling is an essential therapeutic target in RAS mutated cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 413.
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Affiliation(s)
| | - Robert L. Kortum
- 1Uniformed Services University of the Health Sciences, Bethesda, MD
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11
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Theard PL, Sheffels E, Sealover NE, Linke AJ, Pratico DJ, Kortum RL. Marked synergy by vertical inhibition of EGFR signaling in NSCLC spheroids shows SOS1 is a therapeutic target in EGFR-mutated cancer. eLife 2020; 9:58204. [PMID: 32897190 PMCID: PMC7478890 DOI: 10.7554/elife.58204] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Accepted: 08/14/2020] [Indexed: 01/13/2023] Open
Abstract
Drug treatment of 3D cancer spheroids more accurately reflects in vivo therapeutic responses compared to adherent culture studies. In EGFR-mutated lung adenocarcinoma, EGFR-TKIs show enhanced efficacy in spheroid cultures. Simultaneous inhibition of multiple parallel RTKs further enhances EGFR-TKI effectiveness. We show that the common RTK signaling intermediate SOS1 was required for 3D spheroid growth of EGFR-mutated NSCLC cells. Using two distinct measures of pharmacologic synergy, we demonstrated that SOS1 inhibition strongly synergized with EGFR-TKI treatment only in 3D spheroid cultures. Combined EGFR- and SOS1-inhibition markedly inhibited Raf/MEK/ERK and PI3K/AKT signaling. Finally, broad assessment of the pharmacologic landscape of drug-drug interactions downstream of mutated EGFR revealed synergy when combining an EGFR-TKI with inhibitors of proximal signaling intermediates SOS1 and SHP2, but not inhibitors of downstream RAS effector pathways. These data indicate that vertical inhibition of proximal EGFR signaling should be pursued as a potential therapy to treat EGFR-mutated tumors. Lung cancer is the leading cause of cancer-related deaths worldwide. In non-smokers, this disease is usually caused by a mutation in a protein found on the surface of a cell, called EGFR. In healthy lung cells, these proteins trigger a chain of chemical signals that tell the cells to multiply. However, faulty forms of EFGR make the cells grow uncontrollably, leading to the formation of tumors. Current treatments use EGFR inhibitors that block the activity of these proteins. But cancer cells often become resistant to these treatments by activating other types of growth proteins. One way to overcome this resistance has been by targeting the signaling pathways within individual tumors. But since those pathways differ between tumors, it has been challenging to find a single therapy that can treat all drug-resistant cancer cells. Now, Theard et al. assessed the therapeutic effects of blocking a specific protein inside lung cells, called SOS1, which is involved in growth signaling in all tumor cells. Six different types of human lung cancer cells were used, all of which had faulty forms of EGFR, with three of the cell types showing drug resistance to current therapies. The cancer cells were either exposed to EGFR inhibitors only or to a combination of EGFR and SOS1 inhibitors. The most effective treatment was found to be through combinational therapy, with enhanced killing of drug-resistant cells. Theard et al. further assessed the effect of combinational therapy using cells kept in two different ways. Cancer cells were either grown in a two-dimensional format, with cells forming a single cell layer, or in a three-dimensional format, where cells were multi-layered and grew on top of each other as self-aggregating spheroids. Combinational therapy treatment was only successful when the cells where grown in a three-dimensional format. These findings highlight that future drug development studies should give consideration to the way cells are grown, as it can impact the results. They also provide a steppingstone towards tackling drug resistance in lung cancers that arise from EGFR mutations.
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Affiliation(s)
- Patricia L Theard
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
| | - Erin Sheffels
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
| | - Nancy E Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
| | - Amanda J Linke
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
| | - David J Pratico
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
| | - Robert L Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, United States
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Sheffels E, Sealover NE, Theard PL, Kortum RL. Anchorage-independent growth conditions reveal a differential SOS2 dependence for transformation and survival in RAS-mutant cancer cells. Small GTPases 2019; 12:67-78. [PMID: 31062644 DOI: 10.1080/21541248.2019.1611168] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The RAS family of genes (HRAS, NRAS, and KRAS) is mutated in around 30% of human tumours. Wild-type RAS isoforms play an important role in mutant RAS-driven oncogenesis, indicating that RasGEFs may play a significant role in mutant RAS-driven transformation. We recently reported a hierarchical requirement for SOS2 in mutant RAS-driven transformation in mouse embryonic fibroblasts, with KRAS>NRAS>HRAS (Sheffels et al., 2018). However, whether SOS2 deletion differentially affects mutant RAS isoform-dependent transformation in human tumour cell lines has not been tested. After validating sgRNAs that efficiently deleted HRAS and NRAS, we showed that the differential requirement for SOS2 to support anchorage-independent (3D) growth, which we previously demonstrated in MEFs, held true in cancer cells. KRAS-mutant cells showed a high dependence on SOS2 for 3D growth, as previously shown, whereas HRAS-mutant cells did not require SOS2 for 3D growth. This differential requirement was not due to differences in RTK-stimulated WT RAS activation, as SOS2 deletion reduced RTK-stimulated WT RAS/PI3K/AKT signalling in both HRAS and KRAS mutated cell lines. Instead, this differential requirement of SOS2 to promote transformation was due to the differential sensitivity of RAS-mutated cancer cells to reductions in WT RAS/PI3K/AKT signalling. KRAS mutated cancer cells required SOS2/PI3K signaling to protect them from anoikis, whereas survival of both HRAS and NRAS mutated cancer cells was not altered by SOS2 deletion. Finally, we present an integrated working model of SOS signaling in the context of mutant KRAS based on our findings and those of others.
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Affiliation(s)
- Erin Sheffels
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences , Bethesda, MD, USA
| | - Nancy E Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences , Bethesda, MD, USA
| | - Patricia L Theard
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences , Bethesda, MD, USA
| | - Robert L Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences , Bethesda, MD, USA
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13
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Sheffels E, Sealover NE, Wang C, Kim DH, Vazirani IA, Lee E, M Terrell E, Morrison DK, Luo J, Kortum RL. Oncogenic RAS isoforms show a hierarchical requirement for the guanine nucleotide exchange factor SOS2 to mediate cell transformation. Sci Signal 2018; 11:11/546/eaar8371. [PMID: 30181243 DOI: 10.1126/scisignal.aar8371] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
About a third of tumors have activating mutations in HRAS, NRAS, or KRAS, genes encoding guanosine triphosphatases (GTPases) of the RAS family. In these tumors, wild-type RAS cooperates with mutant RAS to promote downstream effector activation and cell proliferation and transformation, suggesting that upstream activators of wild-type RAS are important modulators of mutant RAS-driven oncogenesis. The guanine nucleotide exchange factor (GEF) SOS1 mediates KRAS-driven proliferation, but little is understood about the role of SOS2. We found that RAS family members have a hierarchical requirement for the expression and activity of SOS2 to drive cellular transformation. In mouse embryonic fibroblasts (MEFs), SOS2 critically mediated mutant KRAS-driven, but not HRAS-driven, transformation. Sos2 deletion reduced epidermal growth factor (EGF)-dependent activation of wild-type HRAS and phosphorylation of the kinase AKT in cells expressing mutant RAS isoforms. Assays using pharmacological inhibitors revealed a hierarchical requirement for signaling by phosphoinositide 3-kinase (PI3K) in promoting RAS-driven cellular transformation that mirrored the requirement for SOS2. KRAS-driven transformation required the GEF activity of SOS2 and was restored in Sos2-/- MEFs by expression of constitutively activated PI3K. Finally, CRISPR/Cas9-mediated deletion of SOS2 reduced EGF-stimulated AKT phosphorylation and synergized with MEK inhibition to revert the transformed phenotype of human KRAS mutant pancreatic and lung tumor cells. These results indicate that SOS2-dependent PI3K signaling mediates mutant KRAS-driven transformation, revealing therapeutic targets in KRAS-driven cancers. Our data also reveal the importance of three-dimensional culture systems in investigating the mediators of mutant KRAS.
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Affiliation(s)
- Erin Sheffels
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Nancy E Sealover
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Chenyue Wang
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Do Hyung Kim
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Isabella A Vazirani
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Elizabeth Lee
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Elizabeth M Terrell
- Laboratory of Cell and Developmental Signaling, National Cancer Institute (NCI)-Frederick, Frederick, MD 21702, USA
| | - Deborah K Morrison
- Laboratory of Cell and Developmental Signaling, National Cancer Institute (NCI)-Frederick, Frederick, MD 21702, USA
| | - Ji Luo
- Laboratory of Cancer Biology and Genetics, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, MD 20892, USA
| | - Robert L Kortum
- Department of Pharmacology and Molecular Therapeutics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
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