We then examined the response of both A375 and A375-PLX-R melanoma cells to a potent Chk1 inhibitor (PF477736) which has higher specificity over Chk2 (IC50 = 0.49 nM for Chk1 and IC50 = 47 nM for Chk2) [28, 30] and has been in phase 1 clinical trials with gemcitabine [23, 24]. The gene discussed is CHEK2; the disease is melanoma.