Overcoming therapeutic efficiency limitations against TRAIL-resistant tumors using re-sensitizing agent-loaded trimeric TRAIL-presenting nanocages.

Tumor-specific apoptosis-inducing ligands have attracted considerable attention in cancer therapy. But, the evasion of apoptosis by tumors can cause acquired resistance to the therapy. TNF-related apoptosis-inducing ligand (TRAIL) has been investigated as an ideal antitumor agent owing to its inherent tumor cell-specific apoptotic activity. However, there are several barriers to its wider application, including the inability for stable formation of the trimeric structure, poor stability and pharmacokinetics, and differences in the sensitivity of different tumor types. Especially, almost 70% of tumor cells have acquired resistance to TRAIL, leading to failure of TRAIL-based therapeutics in clinical trials. To overcome therapeutic efficiency limitations against TRAIL-resistant tumors, we exploited the characteristic of a naturally derived nanocage that not only delivers TRAIL in its native-like trimeric structure, but also delivers a drug (doxorubicin [DOX]) that re-sensitizes TRAIL-resistant tumor cells. These TRAIL-presenting nanocages (TTPNs) showed high loading efficiency, pH-dependent release profiles, and effective intracellular delivery of the re-sensitizing agent DOX. As a result, DOX-TTPNs efficiently re-sensitized TRAIL-resistant tumor cells to TRAIL-mediated apoptosis in vitro by regulating levels of the TRAIL receptor, DR5, and anti- and pro-apoptotic proteins involved in extrinsic and intrinsic apoptosis pathways. We further demonstrated the antitumor efficacy of DOX-TTPNs in vivo, showing that even at a very low dose, the incorporated DOX successfully re-sensitized tumors to the apoptotic effects of TRAIL, underscoring the potential of this platform as an antitumor agent. Given that other homotrimeric TNF superfamily ligands and immunotherapeutic agents can be substituted for TRAIL ligand and re-sensitizing drugs on the surface and in the inner cavity of the nanocage, respectively, this platform is potentially suitable for development of a broad range of anticancer or immunotherapeutic combinations.