Imatinib sensitivity as a consequence of a CSF1R-Y571D mutation and CSF1/CSF1R signaling abnormalities in the cell line GDM1

Abstract

Imatinib is usually a highly effective treatment for myeloproliferative neoplasms (MPNs) associated with ABL, PDGFRA or PDGFRB gene fusions; however, occasional imatinibresponsive patients have been reported without abnormalities of these genes. To identify novel imatinib-sensitive lesions, we screened 11 BCR-ABL-negative cell lines and identified GDM1, derived from a patient with an atypical MPN (aMPN), as being responsive to imatinib. Screening of genes encoding known imatinib targets revealed an exon 12 mutation in the colonystimulating factor 1 receptor (CSF1R; c-FMS) with a predicted Y571D amino-acid substitution. CSF1R in GDM1 was constitutively phosphorylated, but rapidly dephosphorylated on exposure to imatinib. Y571D did not transform FDCP1 cells to growth factor independence, but resulted in a significantly increased colony growth compared with controls, constitutive CSF1R phosphorylation and elevated CSF1R signaling. We found that GDM1 expresses CSF1, and CSF1 neutralization partially inhibited proliferation, suggesting the importance of both autocrine and intrinsic mechanisms of CSF1R activation. An extensive screen of CSF1R in aMPNs and acute myeloid leukemia identified three additional novel missense variants. None of these variants were active in transformation assays and are therefore likely to be previously unreported rare polymorphisms or non-pathogenic passenger mutations.

CBL mutation-related patterns of phosphorylation and sensitivity to tyrosine kinase inhibitors

“…23 Of note is that in a recent report, a mutation of CSF1R was described in GDM-1. 24 In this study, GDM-1 showed sensitivity to imatinib but in our report dasatinib showed more suppressive effect than imatinib. In fact, dasatinib showed the most effective inhibition of this CBL mutant cell line among all drugs we screened, and reduced the phosphorylation of specific RTK and non RTK proteins, which may result in an increased proliferative potential in myeloid malignancies with CBL homozygous mutations.…”

“…24 Chase et al 24 showed that CSF1R in GDM-1 is very strongly phosphorylated and that CSF1 neutralization only partially inhibited its proliferation. This result suggests that not only the effect of the driver CSF1R mutation, but also other mechanisms of proliferation, for example, through activation of various TK might be involved as demonstrated by our results.…”

New insights into the mechanisms of hematopoietic cell transformation by activated receptor tyrosine kinases

“…Several other mutations that have been described in human myeloid malignancies seem to represent rare polymorphisms or nonpathogenic mutations. 57 To our knowledge, the existence of acquired transforming mutations of c-FMS has not been confirmed in human neoplasms.…”

“…In these studies, several additional mutations have been described in the PDGFR family. 57,75,76 Some mutations were located in mutation hotspots and are likely or proven transforming mutations. However, other somatic mutations were silent at the protein level, raising the possibility that even well-characterized proto-oncogenes such as RTK can contain somatic passenger mutations.…”

Decoding directional genetic dependencies through orthogonal CRISPR/Cas screens

“…These analyses showed an approximately five orders of magnitude span in FPKM levels for the top 332 hit genes. These include non-expressed genes (21%, FPKM<10 0 ) like ABCB1, ABCG2, or CSF1R which are frequently found activated in drug resistant cancer cells from leukaemia patients 28,29 . Candidate genes also include expressed genes (79% with FPKM>10 0 ) with well-studied roles in leukaemia, like MYC, BCR-ABL1 or CDK6 30 .…”