Objective  To investigate the effects of hydrazinocurcumin-loaded nanoparticles (HC-NPs) on the proliferation and apoptosis of breast cancer 4T1 cells in coculture conditions through the inhibition of the signal transducer and activator of transcription 3 (STAT3) signal pathway activation.

  Methods  Mouse breast cancer 4T1 cells in coculture conditions were divided into three groups, namely, the PBS control, 10% NP control, and 10% HC-NP treatment groups. Morphological investigation was conducted via Liu staining, and the survival ratio was determined via trypan blue staining. Cell cycle and apoptosis were detected using flow cytometry. Western blot analysis was used to determine the expression of STAT3, phosphorylation STAT3 (pSTAT3), c-MYC, B-cell lymphoma 2 (Bcl-2), and Bcl-2-associated X protein (Bax).

  Results  Liu staining results show that the shape of the HC-NP-treated 4T1 cells was spherical. Moreover, trypan blue staining shows that the survival ratio of the treated cells was significantly decreased compared with that of the control. Flow cytometry results show that the apoptosis rates of the HC-NP treatment groups was 24.21% ± 2.37% (P < 0.05), whereas that of The cells in the G₂/M phase increased (63.70% ± 2.53%, P < 0.05). Western blot analysis indicates that p-STAT3, c-MYC, and the ratio of Bcl-2/Bax expression decreased. However, that of total STAT3 showed no significant difference with that of the control.

  Conclusion  HC-NPs can inhibit the proliferation and promote the apoptosis of breast cancer 4T1 cells in coculture conditions, possibly by inhibiting STAT3 activity and affecting the genes related to proliferation and apoptosis.