A Curcumin-Derived HSP70 Inhibitor Disrupts Lysosomal Function to Suppress Triple-Negative Breast Cancer Progression

Structural modification of curcumin yielded a novel series of 1,4-pentadien-3-one oxime ether derivatives, among which compound M4 exhibited exceptional antitumor activity against triple-negative breast cancer (TNBC). M4 demonstrated selective cytotoxicity against TNBC cells, inducing apoptosis and significantly reducing tumour progression and pulmonary metastasis in a 4 T1 orthotopic mouse model at doses lower than paclitaxel. Mechanistic investigations revealed that M4 directly targets heat shock protein 70 (HSP70) by binding to its ATPase domain, triggering lysosomal dysfunction characterized by pH neutralization, reduced acid sphingomyelinase activity, lipid accumulation, and cathepsin leakage. These alterations led to disruption of lysosomal function leading to impaired autophagic degradation, as evidenced by the accumulation of autophagosomes and increased levels of LC3-II/p62. Knockdown of the HSP70 gene abolished M4-induced lysosomal damage and its anti-TNBC effects, confirming HSP70 as the functional target of M4. Furthermore, inhibition of HSP70 suppressed TNBC metastasis by regulating autophagy-mediated epithelial-mesenchymal transition and stemness. M4 demonstrated selective cytotoxicity against TNBC cells, induced apoptosis, and significantly inhibited tumour progression and pulmonary metastasis in a 4 T1 orthotopic mouse model at doses lower than those of paclitaxel. The combination of M4 and paclitaxel showed synergistic anti-TNBC efficacy both in vitro and in vivo, effectively counteracting chemotherapy-induced HSP70 upregulation and autophagic activation. The study not only identifies M4 as a promising therapeutic candidate but also validates HSP70-targeted therapy as an effective combinatorial strategy with conventional chemotherapy for the treatment of TNBC.