1. EGFR exon 20 insertion mutations
in non-small-cell lung cancer:
preclinical data and clinical implications
종양혈액내과 R4 고원진/pf. 정재헌

2. I. Introduction II. Structure of EGFR and implications for exon 20 insertions III. Frequency of EGFR exon 20 insertions IV. Preclinical studies of EGFR exon 20 insertion mutations V. Clinical studies with EGFR exon 20 insertion mutations VI. Implications for drug development and patient care

3. I. Introductions
In 2004, the identification of somatic mutations in the epidermal growth factor receptor (EGFR) provided a new molecularly classified subgroup of NSCLC.
The multitude of mutations in the EGFR gene
1) Classic EGFR mutations; Exon 19 deletions & Exon 21 point mutation
In women, Asians, Never smokers, adenocarcimona histology
Reversible EGFR-TKIs gefitinib (I) & erlotinib (T)
2) Additional EGFR mutation; Exon 18 & Exon 21 recurrent Leu861 mutation
Some sensitivity to EGFR-TKIs
3) Some EGFR mutation; most Exon 20 insertions mutations
Not responses c reversible EGFR-TKIs

4. Epidermal growth factor receptor (EGFR) mutations

5. Structure of the tyrosine kinase domain
II. Structure of EGFR
EGFR is part of the ErbB family of
cell surface receptor tyrosine kinases;
Control signal transduction pathways
For wild-type EGFR; Dimerization of EGFR allows intracellular kinase domains to be brought into a tail-to head interaction.
Recurrent EGFR mutations are localized within or are related to the ATP-binding site of the kinase.
The enhanced Km[ATP], increased binding to EGFR TKIs, and dependency on EGFR highlights the wide therapeutic window of gefitinib and erlotinib.
Structure of the tyrosine kinase domain
of the EGFR

6. II. Implications for exon 20 insertions
The crystal structures of EGFR exon 19 deletions and exon 20 insertions mutations have not been reported.
Exon 20 of EGFR encompasses nucleotides that translate into aminoacid positions 762 to 823.
The restricted spectrum of residues that contain insertion mutations within exon 20, aminoacids Ala767 to Cys775,
; the importance of this region in orienting the kinase into a state that
controls ATP and EGFR TKI binding.

7. Exon 20 of EGFR

8. III. Frequency of EGFR exon 20 insertions
More than 90% of all reported exon 20 insertions cluster between aminoacid positions Ser768 and Val774.
Spatially located after the C-helix of the EGFR kinase domain.
Only 4·1% mutations occur within aminoacids that span the C-helix (Glu762 to Met766).
The pattern of insertion mutations affecting aminoacid positions Ser768 to Val774 after the C-helix.
This area might be important for the conformational changes.
Insertions in this region can be oncogenic by preferentially promoting the active state of EGFR’s kinase domain, and can affect Km[ATP] as well as the affinity of these receptors to gefitinib and erlotinib.

9. Relative frequency of EGFR exon 20 insertions

10. IV. Preclinical studies of EGFR exon 20 insertion mutations
The few mutations that have been studied in vitro have been
shown to be resistant to gefitinib and erlotinib.
The insertions had 50% inhibitory concentrations (IC50) to gefitinib or erlotinib, of higher than 3 μmol/L.
EGFR exon 20 mutant proteins have also been studied in the context of
irreversible EGFR TKIs.
However, patient-derived cell lines and GEMM (genetically engineered mouse) models of common EGFR exon 20 insertion mutations;
Needed to enhance preclinical understanding of the intrinsic behaviour of
these tumours.

11. In-vitro response to EGFR TKIs of EGFR exon 20 insertions, EGFR-Thr790Met, and classic EGFR mutations

12. V. Clinical studies of EGFR exon 20 insertion mutations
NSCLCs with EGFR exon 20 insertions were not as responsive to gefitinib or erlotinib.
The radiographic RR was low at 5% and it seems only 15% had prolonged periods of disease control.
Two patients with tumours harbouring Tyr764_Val765insHisHis or Met766_Ala767insAIa had prolonged periods of disease control.
Responses of NSCLCs with EGFR exon 20 insertion mutations to irreversible EGFR inhibitors are similar.
Nevertheless, a patient with delAsp770insGlyTyr had a response of 13·5 months to PF
The activity of available reversible and irreversible EGFR TKIs is limited for most EGFR exon 20 mutation-positive NSCLCs, and alternative treatment strategies may be needed for these specific tumours.

13. Clinical response to reversible EGFR TKIs of patients with EGFR exon 20 insertions

14. Clinical response to irreversible EGFR TKIs of patients with EGFR exon 20 insertions

15. VI. Implications for drug development and patient care
Classic EGFR mutations have become the most robust predictive marker for clinical benefit with EGFR TKIs.
EGFR exon 20 insertions, lead to a pattern of in-vitro resistance to
reversible (gefi tinib, erlotinib) and irreversible (neratinib, afatinib, PF ) EGFR TKIs.
Selectively screening a kinase inhibitor library for novel EGFR TKIs that are specific for the most clinically relevant EGFR insertion 20 mutations might yield a compound for preclinical and clinical studies.
Other approaches include combinations of EGFR TKIs and downstream inhibitors, with afatinib and the mTOR inhibitor rapamycin.
The combination of an EGFR monoclonal antibody (eg, cetuximab) and an irreversible EGFR TKI (eg, afatinib) has shown promise in preclinical models of EGFR Tyr790Met-driven tumours.

16. Summary
EGFR exon 20 insertion mutations are resistant to clinically achievable doses of EGFR inhibitors.
Patients with advanced NSCLC and tumours harbouring the most common EGFR exon 20 insertions should be treated with conventional systemic therapies.
Future research into the structure of EGFR exon 20 insertions and the availability of preclinical models could help identify therapeutics for this significant cohort of patients with NSCLCs.