BACKGROUND: Cancer-associated fibroblasts (CAFs) have been identified to drive chemotherapy resistance in triple-negative breast cancer (TNBC). This study evaluated the functions of CAFs-mediated suppressive ferroptosis in doxorubicin (DOX) resistance in TNBC and its detailed molecular mechanisms. METHODS: TNBC cell lines were co-cultured with CAFs isolated from DOX-sensitive (CAF/S) or DOX-resistant (CAF/R) breast cancer tissues. Cell viability and death were assessed by cell counting Kit-8 (CCK-8) and propidium iodide (PI) staining. Ferroptosis was evaluated by detection of Fe RESULTS: CAFs-derived lactate repressed ferroptosis to confer resistance of TNBC cells to DOX. Moreover, zinc finger protein 64 (ZFP64) expression was elevated in DOX-resistant TNBC and was associated with high histone lactylation level. CAFs facilitated histone lactylation to enhance ZFP64 expression, which triggered ferroptosis inhibition and DOX resistance. In addition, ZFP64 bound to the promoters of GTP cyclohydrolase-1 (GCH1) and ferritin heavy chain 1 (FTH1), thereby promoting their expression. Rescue experiments indicated that ZFP64 silencing-induced ferroptosis and high sensitivity of TNBC cells to DOX could be counteracted by GCH1 or FTH1 overexpression. CONCLUSION: CAFs acted as a ferroptosis inhibitor to cause DOX resistance of TNBC via histone lactylation-mediated ZFP64 up-regulation and subsequent promotion of GCH1-induced lipid peroxidation inhibition and FTH1-induced intracellular Fe