A phenothiazine analog, PTF, suppresses breast cancer growth by inhibiting YAP signaling

• A synthetic phenothiazine analog (PTF) selectively suppresses breast cancer cells. • PTF triggers apoptosis and autophagy in breast cancer cells. • PTF modulates Akt/mTOR and MAPK signaling and alters ERβ/ERα expression profiles. • YAP suppression is required for the antitumor activity of PTF. Phenothiazines, a class of compounds originally developed for the treatment of psychotic disorders, exert antitumor activity by targeting multiple signaling pathways. In this study, we evaluated the anticancer potential of a modified phenothiazine analogue (PTF) in breast carcinoma models. Compared with its precursor trifluoperazine, PTF exhibited markedly improved efficacy in inhibiting the proliferation of MCF-7 and MDA-MB-231 breast cancer cells, while sparing non-tumorigenic mammary epithelial cells (H184B5F/M10), which showed minimal sensitivity to the compound. PTF triggered programmed cell death, accompanied by caspase activation and reduced levels of the anti-apoptotic protein Mcl-1. Immunoblot analyses demonstrated that PTF altered the activity of the Akt/mTOR/NF-κB axis and MAPK cascades, provoked endoplasmic reticulum stress, and elevated the ERβ-to-ERα expression ratio. In addition, transmission electron microscopy, confocal imaging, and immunoblotting analyses collectively demonstrated that PTF induces autophagy in OSCC cells. Importantly, enforced expression of YAP attenuated PTF-induced cytotoxic effects, whereas blocking proteasomal function prevented PTF-driven degradation of YAP, implying that YAP destabilization contributes to the cytotoxic mechanism. Collectively, these results identify PTF as a potential therapeutic lead for breast cancer, acting through coordinated induction of apoptosis and autophagy, disruption of oncogenic signaling networks, and modulation of YAP protein stability.