Aims: It has been shown that the introduction of a second mutation into the already mutated epidermal growth factor receptor (EGFR) in non-small cell lung cancer (NSCLC) will alter the sensitivity to tyrosine kinase inhibitors (TKIs). EGFR double activating mutations involving both exons 19 and 21 were previously detected in Asian patients, but the sensitivity to TKIs had not yet been characterised. Our objective was to profile the status of EGFR double mutations in Chinese NSCLC patients and to further ascertain the biological properties.
Materials and methods: In total, 145 NSCLC tumour samples from unselected Chinese NSCLC patients were sequenced to screen mutations in exons 18, 19 and 21 of EGFR. Five patients were detected to harbour the delE746-A750+L858R double activating mutations. Subcloning experiments were carried out, expression vectors inserted with corresponding full-length EGFR were constructed, and in vitro transient transfections were performed in 293T cells. Whole cell lysates were collected to assess the sensitivity to TKIs using immunoblotting.
Results: All five patients had adenocarcinoma. The frequency of double mutations was 3.4% (5/145). Three patients received and responded to gefitinib treatment. Subcloning experiments showed that all the subclones were either wild type or double mutated. At a concentration of TKIs of 0.1 microM, the autophosphorylation of the double mutant was inhibited greater than that of either single mutated EGFR. However, the difference disappeared when the concentration increased to 1 microM.
Conclusions: delE746-A750+L858R double activating EGFR mutations exist in Chinese NSCLC patients and both locate on the same allele. These patients tend to respond well to TKIs and the sensitivity to TKIs of this double mutated EGFR is enhanced compared with either single mutant. Nonetheless, the alteration in downstream signal transduction of the double mutant remains to be determined.