Nano-enabled combinatorial immunotherapy of colorectal cancer via small molecular PD-L1 blockade and photodynamic therapy

• A novel small molecular PD-L1 inhibitor C2 and photosensitizer self-assemble to nanoparticles. • Nanoparticles enable active/passive targeting, immunogenic cell death, and precise temporal and spatial control. • C2 with outstanding affinity was selected through deep study, including Docking, HTRF, SPR and MD. • C2-Ce6 NPs could gather in MC38 tumor site more effectively and persistently and TGI up to 94.7% with strong safety. • Providing a promising approach in the PD-1/PD-L1 antibody-resistant cancers. 85% of colon cancer patients don’t respond to anti-PD-L1 due to the lack of immune infiltration while the efficacy of photodynamic therapy (PDT) was limited to hypoxic environment. Thus, a PD-L1 small molecule inhibitor C2 was chose to self-assemble into nanoparticles with photosensitizer, leveraging the unique advantages and active targeting of small molecule, the passive targeting of nanoparticles, and immunogenic cell death (ICD) induced by PDT. Stable nanoparticles C2-Ce6 NPs was formed by Ce6 and C2 meticulously selected from our compound library through Docking, Homogeneous Time Resolved Fluorescence (HTRF), Surface Plasmon Resonance (SPR), and Molecular dynamics (MD). C2-Ce6 NPs demonstrated good safety while achieving a TGI of 94.7 % in the MC38 mouse model with significantly increase of T cell infiltration, reduction of the expression of Ki67 and ICD effect proved via the detection of damage-associated molecular patterns (DAMPs), which indicated combined treatment is more advantageous. Tumor cells were subjected to both internal and external pressures, which is expected to mitigate the primary resistance and strong immunogenicity of antibody-based immune checkpoint inhibitors, further activate the immune system to broad the scope of immunotherapy indications and simultaneously enhance the efficacy comparing to single PDT.