Figure 1. Concomitant LKB1 mutation correlates with selumetinib resistance and decreased level of p-ERK in KRAS-mutant NSCLC.

(A) Except the two cell lines (Calu-1 and H358) with controversial reported sensitivity to selumetinib, all other cell lines listed in Table 1 are included here for statistical analysis. When using IC50 > 1 μM to define resistance to selumetinib, cell lines with concomitant LKB1 mutation (excluding silent mutation) have significantly higher chance of resistance (Fisher›s exact test: p = 0.0318, two-tailed). (B) A direct comparison of IC50 between LKB1 wild type (including silent mutation) and mutant NSCLC cell lines. Whenever possible, for each cell line, the median value of reported IC50 was used for the Mann–Whitney nonparametric test. For cell lines only having a range of value, such as > x or < y μM, then x or y value was used for estimation (p = 0.042, two-tailed). The “*” stands for outliers. (C) Representative growth inhibition assay. Isogenic A549^pBabe and A549^LKB1 cells were incubated with different concentrations of selumetinib for 72 hrs. With the re-expression of LKB1, cells were more sensitive to selumetinib with lower IC50. (D) Histogram of c. Cells were tested in quadruplicates. (E) Loss of LKB1 in A549^pBabe cells was associated with low level of p-ERK, suggesting decreased dependency on MEK->ERK->MAPK signaling. (F) A similar phenomenon was observed using other isogenic cell lines. When using cells engineered with kinase dead LKB1 (K78M) as comparison, fully functional wild type LKB1 had the most definitive association with elevated level of p-ERK.