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P1.05 - Poster Session 1 - Preclinical Models of Therapeutics/Imaging (ID 156)
- Event: WCLC 2013
- Type: Poster Session
- Track: Biology
- Presentations: 1
- Coordinates: 10/28/2013, 09:30 - 16:30, Exhibit Hall, Ground Level
P1.05-004 - Molecular mechanism of resistance to afatinib in EGFR-mutated non-small cell lung cancer (NSCLC) cell lines and potential therapeutic implications (ID 1230)
09:30 - 16:30 | Author(s): A. Garuti
Somatic activating mutations in the tyrosine kinase (TK) domain of EGFR are harbored by 10-20% of Caucasian NSCLC patients (pts). Reversible TK inhibitors (TKIs), including erlotinib or gefitinib, have demonstrated significantly longer progression-free survival compared to chemotherapy alone in EGFR-mutated pts. Nevertheless, the majority of these tumors develop drug resistance due to an acquired mutation (T790M) in EGFR that determines disease progression. Recent clinical trials have demonstrated interesting activity of the irreversible EGFR-TKI afatinib (BIBW-2992) in advanced NSCLC carrying EGFR mutations and in unselected pts failing previous treatments with reversible TKIs. The aim of this study was to clarify the mechanisms of acquired resistance to afatinib using in vitro models of resistant cell lines.
A dose-escalation study was performed to establish afatinib-resistant (R) clones in NSCLC cell lines harboring different EGFR mutations: H-1650 (exon 19 delE746-A750) and H-1975 (exon 21 L858R/exon 20 T790M). The entire genomes of parental (P) and R cells were screened by array comparative genomic hybridization (aCGH) using a 105 k oligonucleotide microarray. All EGFR and KRAS exons and 10 known hot spots (5 in genes involved in the EGFR signaling cascade and 5 in genes frequently altered in NSCLC) were deep sequenced using an Ion PGM™ Sequencer in P and R cells. The relative expression of 92 genes belonging to the EGF pathway was studied by quantitative polymerase chain reaction (qPCR). The expression of proteins related to the EGF pathway, including EGFR, AKT and ERK (total and activated forms), was investigated by Western blot.
Genomic analysis indicated that both R cell lines had genomic profiles similar to the P cells. However, H-1975-R showed 3p and 12p loss and gains at 4q and 10q compared to the P cell line. Sequence analyses identified a novel frame-shift mutation within exon 14 of MET and confirmed EGFR mutation status in 100% of H1975-R cells. In contrast, H-1650-R cells showed a single-base deletion 12 bp upstream of exon 8 of PIK3CA within a sequence of nine repeated Ts. Furthermore, a novel missense variant (exon 8 K368E) was found in FGFR2 in both R cell lines compared to the P cell line. Gene expression profiles identified an increase in the FGFR2 and PIK3 regulatory subunits and EGFR ligand silencing in H-1975-R. Notably, H-1975-R cells maintained in afatinib-free medium for over 6 months showed higher EGFR and AKT phosphorylation compared to the P cell lines.
The lack of novel EGFR mutations suggests the involvement of other mechanisms implicated in afatinib resistance. In particular, the identification of mutations involving MET and FGFR2 in H-1975 and PI3KCA in H-1650 suggests their contribution to resistance against irreversible TKIs, sparing EGFR activation. Furthermore, the different mutation status of the two cell lines indicates that the T790M mutation may be partially responsible for the mechanism of resistance. Validation studies are ongoing to confirm the genomic results. In conclusion, these preliminary data may help identify novel therapeutic strategies to delay or reverse resistance to irreversible TKIs in EGFR-mutated NSCLC patients.