Epidermal growth factor receptor (EGFR) gene mutations activate the KRAS-RAF-MEK-ERK pathway in
lung cancer cells. EGFR
tyrosine kinase inhibitors (TKIs) such as
gefitinib induce apoptosis of
cancer cells, but prolonged treatment is often associated with acquired resistance. Here, we identified a novel MEK1/2 inhibitor,
CZ0775, and compared its cytotoxic effects to those of
AZD6244 (
selumetinib) in
non-small cell lung cancer (NSCLC) cell lines harboring EGFR mutations. The
lapatinib-sensitive HCC827 and PC9 and
lapatinib-resistant H1650 and H1975 cell lines showed poor responses to
CZ0775 and
AZD6244 monotherapy with an IC50 > 10 μM. By contrast, combination treatment with
lapatinib and
CZ0775 inhibited cell proliferation and produced a 2-fold higher number of
annexin V-labeled cells than
lapatinib alone in H1975 cells. Furthermore, combination treatment decreased phosphorylated extracellular signal related
kinase (p-ERK) and
survivin levels and upregulated the expression of the
pro-apoptotic protein BIM.
siRNA-mediated BIM depletion reduced
caspase-3 activity (~40%) in
lapatinib and
CZ0775 treated H1975 cells. An in vitro ERK activity assay showed that p-ERK levels were approximately a 3-fold lower in H1975 cells treated with
CZ0775 and
lapatinib combination than in cells treated with
lapatinib alone.
CZ0775 was more cytotoxic than
AZD6244 when used in combination with
lapatinib. Our results suggest that combination treatment with CZ0774 and EGFR inhibitors is a promising therapeutic approach for the treatment of EGFR-TKI-resistant
lung cancers and its effect is mediated by the inhibition of ERK and the induction of BIM.