CHEK1 and small cell lung carcinoma: To determine whether Wee1 plays a causal role in the resistance to Chk1 inhibitors, we examined the cytotoxic effect of prexasertib in combination with the Wee1 inhibitor MK1775 in acquired‐resistant cell lines (H792LYR and GLC4LYR) and four additional parental SCLC cells (H82, H128, H209 and DMS114).