Repurposed ethoxzolamide reprograms antitumor immunity through β-TrCP-dependent PD-L1 ubiquitination

Area of Science:

• Oncology
• Immunology
• Pharmacology

Background:

• Programmed cell death protein 1 (PD-1)/PD-L1 blockade shows clinical efficacy in solid tumors.
• Tumor resistance to PD-1/PD-L1 blockade can be mediated by PD-L1 protein stabilization.
• Alternative strategies are needed to overcome resistance and enhance immunotherapy efficacy.

Purpose of the Study:

• To identify novel negative regulators of PD-L1.
• To investigate the mechanism of action of ethoxzolamide (EZA) on PD-L1.
• To evaluate the therapeutic potential of EZA in preclinical cancer models and clinical data.

Main Methods:

• Identified ethoxzolamide (EZA) as a carbonic anhydrase inhibitor that negatively regulates PD-L1.
• Investigated EZA's binding to the E3 ubiquitin ligase β-TrCP and its effect on PD-L1 polyubiquitination and degradation.
• Assessed EZA's impact on tumor cell PD-L1 expression, T cell-mediated cytotoxicity in vitro, and the tumor immune microenvironment in vivo.
• Analyzed EZA's synergy with anti-CTLA-4 therapy and correlated PD-L1/β-TrCP expression with patient response in non-small cell lung cancer (NSCLC).

Main Results:

• EZA binds to β-TrCP, inducing K48-linked polyubiquitination and proteasomal degradation of PD-L1.
• EZA downregulates tumor cell PD-L1, restoring T cell-mediated cytotoxicity.
• EZA reprograms the tumor immune microenvironment, reducing myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) while enhancing cytotoxic responses in murine models.
• EZA synergizes with anti-CTLA-4 therapy to overcome treatment resistance.
• High PD-L1 and low β-TrCP expression correlate with superior response in NSCLC patients treated with neoadjuvant immunotherapy.

Conclusions:

• Ethoxzolamide (EZA) functions as a novel negative regulator of PD-L1 through the β-TrCP/proteasome pathway.
• EZA demonstrates significant antitumor activity by restoring anti-tumor immunity and overcoming immunotherapy resistance.
• The PD-L1/β-TrCP axis represents a potential therapeutic target for enhancing cancer immunotherapy, particularly in NSCLC.