Rational targeting of Cdc42 to benefit immunotherapy

ABSTRACT T cells play important role in cancer cell immunosuppression. Cancer cells can interact with immune checkpoint proteins expressed on effector T cells to cause T cell exhaustion and facilitate regulatory T (Treg) cell suppression of effector T cells. Understanding T cell immunity is an important goal in cancer

immunotherapy. Although immune checkpoint inhibitors and CAR-T cell therapies have shown tremendous promise, current immunotherapies only benefit a fraction of cancer patients, and new approaches from mechanism-driven immune modulations are needed to broaden the therapeutic benefits to less responsive patients. Targeting Treg cells to activate effector T cells to combat cancer is an

emerging concept in cancer immunotherapy. While systemic depletion of Treg cells can cause excessive T cell activation leading to autoimmunity, proper induction of Treg cell instability without side effects of autoimmune responses may open a new avenue for immune modulation. In preliminary studies, we have

found that heterozygous deletion of the Rho GTPase Cdc42 in Treg cells did not affect Treg cell homeostasis nor result in autoimmune response but caused a destabilization of Treg cells that elicited an anti-tumor immunity. Pharmacological targeting of Cdc42 with a small molecule inhibitor, CASIN, mimicked Cdc42 heterozygous deletion in destabilizing Treg cells and in gaining an anti-tumor T cell

immunity. CASIN potentiated the effects of immune checkpoint inhibitors in tumor suppression without detectable autoimmunity in mice. This project hypothesizes that the rational designed small molecules targeting Cdc42 activity can destabilize Treg cells and modulate anti-cancer immunotherapy without

inflammatory side effects. In Aim 1, to determine the molecular pharmacology of CASIN action we will define the mechanism of action of CASIN and improve CASIN efficacy. We will carry out further medicinal chemistry studies, validate CASIN derivatives for proper target engagement, and examine potential

toxicity in T cells and other cell types. In Aim 2 we will demonstrate a proof of concept for CASIN or its derivatives in targeting of Cdc42 in mouse models to trigger anti-tumor T cell immunity. We will determine the toxicity, pharmacokinetics and pharmacodynamics of CASIN and its derivatives, and examine their

preclinical efficacies in destabilizing Treg cells to elicit anti-tumor T cell immunity, alone or in combination with immune checkpoint inhibitors. Overall, our work will establish a novel concept and present a useful approach for anti-cancer immunomodulation.