近藤 次郎

Gold-mediated base pairing in nucleic acids has remained poorly understood, despite structural analogies with mercury and silver ions known to coordinate selectively to mismatched base pairs. Here, the crystal structures of a CAu(I)C base pair and a CGAu(I)C base triple formed with natural nucleobases are reported. Although solution-phase thermodynamic analysis of Au(I) coordination is technically unfeasible, structural evidence supports its selective insertion into the base mismatches. In contrast, duplexes incorporating 2-thiocytosine form square-planar complexes with Au(III), and melting temperature analysis shows significant thermal stabilization. The distinct coordination geometries of Au(I) and Au(III) arise from differences in oxidation state and preferred coordination numbers, with Au(I) favoring linear two-coordinate structures and Au(III) forming square-planar complexes stabilized by thiocarbonyl donors. These findings establish a structure-guided strategy for oxidation-state-selective metal coordination in nucleic acids, paving the way for the design of metal-responsive DNA architectures with tunable properties.

Tumor stromal remodeling is an obstacle for immune checkpoint inhibitors (ICI). A stroma modifying small interfering RNA (siRNA) to carbohydrate sulfotransferase 15 (CHST15) was recently shown to enhance tumor-infiltrating T cells, yet its impact on antitumor response of ICI remains unexplored. In mouse pancreatic cancer KPC and Pan02 subcutaneous syngeneic tumor models, mice were divided into 4 groups for treatment; (1) control, (2) CHST15 siRNA monotherapy, (3) anti-programmed death receptor 1 (PD-1) monotherapy, and (4) combination therapy with CHST15 siRNA and anti-PD-1 antibody. Mice were sacrificed after 2 week-treatments and anti-tumor effects were evaluated by immunohistochemistry for KPC and flow cytometry for Pan02 model, respectively. In the KPC model, combination treatment with intratumoral CHST15 siRNA (0.9-1.0 mg/kg) and systemic anti-PD-1 antibody (5 mg/kg) synergistically and robustly suppressed tumor growth with a significant increase of tumor-infiltrating CD4+ and CD8+ T cells compared to anti-PD-1 monotherapy. In the Pan02 model, combination treatment with CHST15 siRNA and anti-PD-1 showed anti-tumor effect with significant increases in % necrosis area of the tumor, and tumor-infiltrating T cells compared to the control. Notably, the combination therapy dramatically diminishes Ly6C+Ly6G+ granulocytic myeloid-derived suppressor cells (MDSCs) compared to anti-PD-1 monotherapy. The present study demonstrated the robust synergy between systemic anti-PD-1 antibody and a single stroma modifying agent. Combination usage of intratumoral CHST15 siRNA would provide a novel therapeutic option to trigger the remarkable effect of ICI on this most hard-to-treat solid tumor.