Proteolysis-targeting chimera against BCL-XL destroys tumor-infiltrating regulatory T cells

Regulatory T cells (Tregs) play an important role in maintaining immune homeostasis and, within tumors, their upregulation is common and promotes an immunosuppressive microenvironment. Therapeutic strategies that can eliminate Tregs in the tumor (i.e., therapies that do not run the risk of affecting normal tissues), are urgently needed for the development of cancer immunotherapies. Here we report our discovery of B-cell lymphoma extra-large (BCL-X-L) as a potential molecular target of tumor-infiltrating (TI) Tregs. We show that pharmacological degradation of BCL-X-L using a newly developed platelet-sparing BCL-X-L Proteolysis-targeting chimera (PROTAC) induces the apoptosis of TI-Tregs and the activation of TI-CD8(+) T cells. Moreover, these activities result in an effective suppression of syngeneic tumor growth in immunocompetent, but not in immunodeficient or CD8(+) T cell-depleted mice. Notably, treatment with BCL-X-L PROTAC does not cause detectable damage within several normal tissues or thrombocytopenia. These findings identify BCL-X-L as a target in the elimination of TI-Tregs as a component of cancer immunotherapies, and that the BCL-X-L-specific PROTAC has the potential to be developed as a therapeutic for cancer immunotherapy. Targeting regulatory T cells (Treg) represents a therapeutic option to abrogate tumor-associated immune suppression. Here the authors show that pharmacological degradation of BCL-X-L preferentially induces apoptosis of tumor-infiltrating Treg, promoting CD8 T cell activation and anti-tumor immune responses in preclinical cancer models.

Automated summary

The pharmacological degradation of BCL-X-L preferentially induces apoptosis of tumor-infiltrating Tregs, promoting CD8 T cell activation and effective suppression of tumor growth without causing damage to normal tissues or thrombocytopenia. This finding suggests that targeting BCL-X-L could be a potential therapeutic strategy for cancer immunotherapy.