Intratumoral heterogeneity of receptor tyrosine kinases EGFR and PDGFRA amplification in glioblastoma defines subpopulations with distinct growth factor response

Abstract

Glioblastoma (GBM) is distinguished by a high degree of intratumoral heterogeneity, which extends to the pattern of expression and amplification of receptor tyrosine kinases (RTKs). Although most GBMs harbor RTK amplifications, clinical trials of small-molecule inhibitors targeting individual RTKs have been disappointing to date. Activation of multiple RTKs within individual GBMs provides a theoretical mechanism of resistance; however, the spectrum of functional RTK dependence among tumor cell subpopulations in actual tumors is unknown. We investigated the pattern of heterogeneity of RTK amplification and functional RTK dependence in GBM tumor cell subpopulations. Analysis of The Cancer Genome Atlas GBM dataset identified 34 of 463 cases showing independent focal amplification of two or more RTKs, most commonly plateletderived growth factor receptor α (PDGFRA) and epidermal growth factor receptor (EGFR). Dual-color fluorescence in situ hybridization was performed on eight samples with EGFR and PDGFRA amplification, revealing distinct tumor cell subpopulations amplified for only one RTK; in all cases these predominated over cells amplified for both. Cell lines derived from coamplified tumors exhibited genotype selection under RTK-targeted ligand stimulation or pharmacologic inhibition in vitro. Simultaneous inhibition of both EGFR and PDGFR was necessary for abrogation of PI3 kinase pathway activity in the mixed population. DNA sequencing of isolated subpopulations establishes a common clonal origin consistent with late or ongoing divergence of RTK genotype. This phenomenon is especially common among tumors with PDGFRA amplification: overall, 43% of PDGFRA-amplified GBM were found to have amplification of EGFR or the hepatocyte growth factor receptor gene (MET) as well.glioma | glioblastoma genetics | mosaicism | amplicon

A glioma classification scheme based on coexpression modules of EGFR and PDGFRA

“…S9). In agreement with previous reports on the low frequencies of mosaic coamplification of EGFR and PDGFRA in gliomas (26,27), coamplification of EGFR and PDGFRA was observed in 10 of 123 EM +++ gliomas and 2 of 36 PM ++ (Chr7 Amp) gliomas of the TCGA mRNA-seq data set, but not in the other EM/PM subgroups (SI Appendix, Fig. S2).…”

Epidermal Growth Factor Receptor Variant III (EGFRvIII) Positivity in EGFR-Amplified Glioblastomas: Prognostic Role and Comparison between Primary and Recurrent Tumors

“…We did not assess regional heterogeneity of EGFR gene amplification. However, previous studies reported that EGFR amplification may be restricted to subpopulations of tumor cells, as determined in cases of glioblastomas with amplification of EGFR and PDGFRA (52,53). With respect to EGFRvIII expression, our data demonstrate that EGFRvIII immunopositivity shows marked regional heterogeneity and is often restricted to subpopulations of tumor cells in glioblastomas, thus confirming previous findings in the GGN patient cohort (17) and in several independent studies (39,42,43,51,54).…”

MET and ERBB2 Are Coexpressed in ERBB2+ Breast Cancer and Contribute to Innate Resistance

“…These analyses show that ERBB2 þ tumors are composed of subpopulations of MET À /ERBB2 þ , MET þ /ERBB2 À , and MET þ /ERBB2 þ cells. These diverse expression patterns support the results of several studies in other cancer types that have shown intratumoral heterogeneity (3,25) and which have significant implications for the development of optimal treatment strategies.…”