Recombinant cell-penetrating trichosanthin synergizes anti-PD-1 therapy in colorectal tumor

Alleviating immunosuppression of the tumor microenvironment is an important strategy to improve immune checkpoint therapy. It is an urgent but unmet need to develop adjuvant therapeutics for assisting the mainstay immunotherapies. Trichosanthin is an approved gynecology drug in China and its immunomodulatory effects have drawn much attention as an old drug for new applications in cancer. In this work, a recombinant cell-penetrating trichosanthin (rTCS-LMWP) was prepared via genetic fusion of a cell-penetrating peptide sequence (LMWP) to trichosanthin aiming to overcome the intratumoral penetration and intracellular delivery challenges. The potential of trichosanthin as an adjuvant therapy was explored, including its effects on tumor cells, antigen-presenting cells, tumor immune microenvironment, and the synergistic effect in combination with anti-PD-1. The results revealed that rTCS-LMWP can stimulate the maturation of dendritic cells via activating the STING-TBK1-IRF3 pathway, repolarize the protumor M2-type macrophages, and upregulate the pro-inflammatory cytokine expression. Moreover, rTCS-LMWP can enhance anti-PD-1 therapeutic efficacy in a CT26-bearing mouse model. The synergistic effect involved the induction of immunogenic cell death in the tumors, the proliferation and functionalization of cytotoxic T cells, and the suppression of the immunosuppressive regulatory T cells. These findings indicate that trichosanthin can be developed as an immunomodulator to facilitate cancer immunotherapy.