Thus, while no synergy between gemcitabine or carboplatin and ATR inhibition was observed in the lung cancer cell lines used here, synergy between gemcitabine and Chk1 inhibition was observed in 54 T, 201 T and H460, and synergy between carboplatin and Chk1 inhibition was identified in 201 T and 239 T. Here, CHEK1 is linked to lung cancer.