A pH-responsive DNA nanocarrier-mediated combined therapy for tumor hypoxia relief and enhanced photodynamic-chemotherapeutic efficacy

Improving the efficiency of drug targeted delivery and alleviating tumor cell hypoxia were crucial for photodynamic-based combination therapy to improve the anticancer effect. Herein, a novel multifunctional DNA nanocarrier (RAM) was developed for targeted delivery and pH-responsive release of toluidine blue O (TBO), doxorubicin (DOX) and anti-MCT1 siRNA (siMCT1) combined drugs. RAM was prepared by two-step self-assembly of RCA scaffold prepared by rolling circle amplification technology with multivalent AS1411 aptamer, complementary chain of i-motif sequence and siMCT1 modified by i-motif sequence. The existence of i-motif enabled RAM to respond to the micro-acid environment of tumor cells to quickly release drugs. Multispectral and molecular docking experiments showed that TBO and DOX were intercalated into RAM. Thermodynamic analysis indicated that RAM exhibited superior drug loading capacity, and the pre-loading of TBO enhancing the co-loading efficiency of combined drugs. The release of RAM-loaded drugs was expedited by an acidic environment and deoxyribonuclease I, with the release rate inversely related to the binding capacity. The multivalent AS1411 aptamer enhanced the targeting ability of RAM to MCF-7 cells. TBO could promote siMCT1 to inhibit the expression of monocarboxylate transporter 1 through PCI effect, thereby inhibiting lactic acid-driven respiration, effectively increasing local oxygen pressure, and thus significantly improving PDT efficacy. Cytotoxicity assays confirmed superior synergistic antitumor efficacy of (RAM + TBO) + DOX system. This study established a theoretical grounding for using multifunctional DNA nanocarriers in synergistic PDT-chemotherapy to co-deliver drugs and mitigate tumor hypoxia.