Synergistic inhibition of metastatic breast cancer by dual-chemotherapy with excipient-free rhein/DOX nanodispersions

Abstract Background: The treatment of metastatic cancer continues to be very challenging worldwide. Notably, excipient-free nanodispersions that are entirely composed of pharmaceutically active molecules are regarded as promising candidates for the next generation of drug formulations. These molecules are mainly formulated from the self-assembly of drug molecules that enable the safe and effective delivery of therapeutic drugs to local diseased lesions. Herein, we developed a novel and green approach for preparing nanoparticles via the self-assembly of rhein (RHE) and doxorubicin (DOX) molecules, named RHE/DOX nanoparticles (RD NPs); this assembly was associated with π−π stacking interactions and did not involve any organic solvents. Results：Molecular dynamics (MD) simulations showed that DOX molecules tend to assemble around RHE molecules through intermolecular forces. With the advantage of nanosizing, RD NPs improved the intracellular drug retention of DOX. As a dual-drug-loaded nanoformulation, the toxicity of RD NPs to tumor cells in vitro was synergistically enhanced. The combination of DOX and RHE in nanoparticles exhibited a synergistic effect with a combination index (CI) value of 0.51 and showed a stronger ability to induce cell apoptosis compared to that of free DOX. Furthermore, RD NPs treatment not only effectively suppressed primary tumor growth but also successfully inhibited tumor metastasis both in vitro and in vivo, with a good safety profile. Conclusion: The generation of pure nanodrugs via a self-assembly approach might be an option and may provide inspiration for the fabrication of new excipient-free nanodispersions, especially for two small molecular antitumor drugs that could potentially have synergistic antiproliferation effects against metastatic breast cancer.