SKLB-D18 is a potent and selective inhibitor of ERK1/2 and ERK5, with IC50 values of 38.69, 40.12, and 59.72 nM, respectively. It also serves as an autophagy agonist, influencing mTOR/p70S6K and NCOA4-mediated ferroptosis, potentially mitigating multidrug resistance. SKLB-D18 demonstrates significantly superior efficacy against triple-negative breast cancer (TNBC) in both in vitro and in vivo studies.