Functional analysis of somatic mutations affecting receptor tyrosine kinase family in metastatic colorectal cancer

Besides the detection of somatic receptor tyrosine kinases (RTKs) mutations in tumor samples, the current challenge is to interpret their biological relevance in order to give patients effective targeted treatment. By high-throughput sequencing of the 58 RTK exons of healthy tissues, colorectal tumors, and hepatic metastases from 30 patients, 38 different somatic mutations in RTKs were identified. The RTK-kinase-domain mutations present in both tumors and metastases were reconstituted in order to perform an unbiased functional study. Among eight variants found in seven RTKs (EPHA4-Met726Ile, EPHB2-Val621Ile, ERBB4-Thr731Met, FGFR4-Ala585Thr, FLT4-Leu1014Phe, KIT-Pro875Leu, NTRK2-Leu584Val and NTRK2-Lys618Thr), none displayed significantly increased tyrosine kinase activity. Consistently, none of them induced transformation of NIH3T3 fibroblasts. On the contrary, two RTK variants (FGFR4-Ala585Thr and FLT4-Leu1014Phe) caused drastic inhibition of their kinase activity. These findings indicate that these RTK variants are not suitable targets and highlight the importance of functional studies to validate RTK mutations as potential therapeutic target.