Bimodal ntrk expression and correlation with activation of PI3K/AKT pathway in lung cancer.

Abstract

e21535 Background: N TRK (NTRK1, NTRK2 or NTRK3) fusions are oncogenic drivers of various types of cancer and lead to activation of the PI3K/AKT pathway. Treatment of patients with NTRK fusion using TRK inhibitors, such as larotrectinib or entrectinib, is associated with high response rates ( > 75%). However these fusions are very rare in most common cancers, such as lung and colorectal cancers. We examined the expression levels of NTRK1, NTRK2, and NTRk3 in non-small cell lung cancer using targeted RNA sequencing. We also examined the effects of NTRK overexpression on PI3K/AKT pathway in non-small cell lung cancer. Methods: RNA was extracted from 160 FFPE samples of non-small cell lung cancers and sequenced using targeted next generation sequencing (NGS). The RNA sequencing was based on hybrid capture using a targeted panel of 1408 genes. The number of reads ranged from 5 to 10 million. The RNA levels were measured using Cufflinks as FPKM. Results: NTRK2 fusion was detected in one sample (0.04%). However, overexpression of NTRK1-3 mRNA was more common and showed bimodal expression pattern. Most of the samples (75%) had low levels (median 0.6, 6,79, and 3.17 FPKM for NTR2, NTRK2, and NTRK3, respectively) while the upper 25% of samples had significantly (P < 0.0001) higher levels (Median 2.7, 280, and 17.7 KPFM for NTRK1, NTRK2, and NTRK3, respectively). There was significant difference in expression between the three genes (P < 0.0001). The highest levels were detected in NTRK2 and lowest in NTRK1. In addition, significant variation in alternative splicing was noted in NTRK2. All cases with high expression levels (above the upper quartile) showed significant variation in alternative splicing involving almost all exons. To explore, if high expression correlates with activation of the PI3K/AKT1 pathway, we examined the correlation between high levels (above upper quartile) of NTRK2 with various genes in PI3K/AKT pathway. High levels of NTRK2 mRNA (above the upper quartile) correlated with significantly higher levels of PIK3CA (P < 0.0001) and MDM2 (P = 0.0001). There was no correlation between high expression of NTRK1 or NTRK3 and PIK3CA or MDM2 mRNA. Conclusions: Although fusions involving NTRK1-3 genes in lung cancer are rare, significantly high expression levels can be seen almost 25% of lung cancers. Furthermore, high expression in NTRK2 correlates with activation in the PI3K/AKT pathway. This data suggests that therapy targeting NTRK2 overexpression and/or activation of PI3K/AKT pathway in patients with high NTRK2 mRNA should be explored.