Carvacrol Selectively Induces Mitochondria-Related Apoptotic Signaling in Primary Breast Cancer-Associated Fibroblasts

<b>Background/Objectives</b>: Cancer-associated fibroblasts (CAFs) are key stromal mediators of breast tumor progression and therapy resistance. Carvacrol, a dietary monoterpenic phenol, exhibits antiproliferative activity in cancer cells, but its effects on primary human breast CAFs remain unclear. This study aimed to determine whether carvacrol selectively induces mitochondria-related apoptotic signaling in breast CAFs while sparing normal fibroblasts (NFs). <b>Methods</b>: Primary fibroblast cultures were established from invasive ductal carcinoma tissues (CAFs, <i>n</i> = 9) and nonmalignant breast tissues (NFs, <i>n</i> = 5) and validated by α-SMA and FAP immunofluorescence. Cells were exposed to 400 μM carvacrol. Apoptosis was assessed by TUNEL assay and BAX/BCL-XL Western blotting. Changes in signaling pathways were evaluated by analyzing PPARα/NF-κB, sirtuin (SIRT1, SIRT3), autophagy-related markers (LAMP2A, p62), and matrix metalloproteinases (MMP-2, MMP-3). In silico molecular docking and 100-ns molecular dynamics simulations were performed to examine interactions between carvacrol and caspase-3 and caspase-9. <b>Results</b>: Carvacrol induced a pronounced, time-dependent apoptotic response in CAFs, with TUNEL-based viability declining to approximately 10% of control levels by 12 h and a marked increase in the BAX/BCL-XL ratio. In contrast, NFs exhibited minimal TUNEL positivity and no significant change in BAX/BCL-XL. In CAFs, but not NFs, carvacrol reduced PPARα expression and NF-κB nuclear localization, increased SIRT1 and SIRT3 levels, selectively suppressed MMP-3 while partially normalizing MMP-2, and altered autophagy-related markers (decreased LAMP2A and accumulation of p62), consistent with autophagic stress and possible impairment of autophagic flux. Computational analyses revealed stable carvacrol binding to caspase-3 and caspase-9 with modest stabilization of active-site loops, supporting caspase-dependent, mitochondria-related apoptosis. <b>Conclusions</b>: Carvacrol selectively targets breast cancer-associated fibroblasts by inducing mitochondria-related apoptotic signaling while largely sparing normal fibroblasts. This effect is accompanied by coordinated modulation of PPARα/NF-κB, sirtuin, autophagy, and MMP pathways. These findings support further evaluation of carvacrol as a microenvironment-directed adjunct in breast cancer therapy.