PX478-loaded silk fibroin nanoparticles reverse multidrug resistance by inhibiting the hypoxia-inducible factor

Multidrug resistance (MDR) is the main cause of clinical chemotherapy failure, and new strategies to overcome MDR are needed. We report multi-responsive silk fibroin nanoparticles (SFNs) co-loaded with the chemotherapeutic drug doxorubicin (DOX) and PX478 (a hypoxia-inducible factor inhibitor), which was functionalized with folic acid (FA). This combination could actively target tumor cells and respond to the release of PX478, inhibit the hypoxia-inducible factor (HIF) gene and its related downstream drug-resistant target genes. The FA-PX478-DOX-SFNs (F-P-D-S) combination showed accelerated drug release profiles in the media simulating the tumor microenvironment, which had acidic pH, high levels of reactive oxygen species and high levels of glutathione. Compared with PX478-DOX-SFNs (P-D-S) without targeted modification, the cellular uptake rate of F-P-D-S increased. In addition, F-P-D-S quickly achieved lysosomal escape, enabling DOX to rapidly enter the nucleus to kill the drug-resistant cells. A cytotoxicity test indicated that the IC₅₀ of DOX against MCF-7/ADR cells was 1.0 μg/mL in F-P-D-S, which was 26 times lower than that of free DOX (25.6 μg/mL). F-P-D-S significantly down-regulated HIF-1α, MDR1, VEGF and GLUT-1 and P-gp protein to overcome multidrug resistance. This effective synergistic chemotherapy strategy for HIF inhibition has potential for use in the treatment of multidrug-resistant tumors.