Panoply™ Human IGF1R Over-expressing Stable Cell Line

The phosphatidylinositol 3-kinase δ (PI3K-δ) inhibitor idelalisib is approved for the treatment of chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma, but the mechanism by which some patients develop resistance remains unclear. Here, researchers modeled resistance to PI3K-δ inhibitor in vivo using a serial tumor transfer and treatment scheme in mice. Whole-exome sequencing did not reveal any relapsed mutations that could explain PI3K-δ inhibitor resistance. In the mouse model, PI3K-δ inhibitor resistance was due to a signaling pathway shift mediated by persistent and functionally relevant activation of the insulin-like growth factor 1 receptor (IGF1R), leading to enhanced MAPK signaling in resistant tumors. In vitro overexpression of IGF1R confirmed its important role in PI3K-δ inhibitor resistance. In PI3K-δ inhibitor-resistant tumors, the upregulation of IGF1R was mediated by the functional activation and enhanced nuclear localization of the forkhead box protein O1 transcription factor and glycogen synthase kinase 3β. In human chronic lymphocytic leukemia (CLL), high expression of IGF1R is associated with trisomy 12. CLL cells from patients treated with idelalisib showed reduced sensitivity to idelalisib in vitro, accompanied by enhanced MAPK signaling and significant upregulation of IGF1R. Therefore, these findings highlight that other signaling pathways play a dominant role in drug resistance and survival of cancer cells under PI3K-δ inhibition.

To verify whether IGF1R upregulation functionally promotes iPI3K-δ resistance, researchers constructed IGF1R-overexpressing mouse A20 cells. A20 cells were chosen because they do not express endogenous IGF1R and exhibited higher sensitivity to GS-649443 in vitro compared to Ba/F3 and 300-19 mouse cell lines. In IGF1R-overexpressing A20 cells, p-ERK levels were significantly elevated (Figure 1A), and the response to GS-649443 treatment was significantly reduced compared to control cells (Figure 1B). Since IGF1R upregulation has been confirmed to be associated with iPI3K-δ resistance in mouse tumors, the researchers evaluated the relevance of IGF1R and other RTKs in human CLL. This study analyzed the expression levels of key receptor tyrosine kinases (RTKs) expressed in hematopoietic cells from 337 previously untreated patient samples. These RTKs included IGF1R, IGF2R, INSR, FGFR1, FGFR2, FGFR3, FGFR4, ROR1, ROR2, DDR1, DDR2, LTK, AXL, PDGFRA, PDGFRB, ERBB2, ERBB3, ALK, TIE1, and RET. Unsupervised cluster analysis identified two main clusters, the primary difference being the expression level of IGF1R (Figure 1C). Although the expression levels of other RTKs were low, FGFR1 expression was elevated in some cases with low IGF1R expression (Figure 1C).

Figure 1. Upregulation of IGF1R is associated with iPI3K-δ resistance in mouse tumors. (Scheffold A, et al., 2019)