Enhancement of cisplatin efficacy by lipid–CaO ₂ nanocarrier-mediated comprehensive modulation of the tumor microenvironment

Hypoxia, acidosis and high level of glutathione (GSH) are characteristic abnormalities of the tumor microenvironment (TME), which promote tumor progression, metastasis, and resistance to therapies. Previous attempts to improve therapeutic efficacy were limited to modifying individual TME elements. In this study, we proposed a comprehensive TME modulation strategy that modifies multiple elements of the TME in order to enhance cisplatin anticancer efficacy. To do so, we prepared biocompatible lipid-coated CaO₂/cisplatin nanoparticles (LipoCaO₂/DDP) by the reverse microemulsion method. We imbued CaO₂ with the following reverse-TME properties: O₂ generation, increased pH value in tumor cells, and oxidation of intracellular glutathione. In vitro experiments showed that LipoCaO₂/DDP could deplete GSH for preventing the binding of GSH to cisplatin. Simultaneously, CaO₂ could significantly downregulate multidrug resistance-associated protein 2 (MRP2) by O₂-dependent hypoxia-inducible factor 1 (HIF-1) inactivation. Hence, the complete drug-efflux pathway was blocked, and the anticancer effect of cisplatin was enhanced both in vitro and in vivo. Herein, we not only demonstrated the GSH depletion capacity of CaO₂ for the first time, but also provided a new comprehensive therapeutic strategy to overcome therapeutic resistance caused by multiple factors in the TME.