Insights into P-Glycoprotein Inhibitors: New Inducers of Immunogenic Cell Death

Area of Science:

• Cancer therapy
• Immunology
• Pharmacology

Background:

• Doxorubicin induces immunogenic cell death (ICD) but is limited by P-glycoprotein (Pgp) expression in cancer cells.
• Pgp effluxes doxorubicin and impairs calreticulin (CRT) exposure, a key signal for ICD.
• The potential of Pgp inhibitors to restore ICD is largely unexplored.

Purpose of the Study:

• To investigate whether classical Pgp inhibitors can restore doxorubicin-induced ICD in Pgp-expressing cancer cells.
• To compare the effects of Tariquidar and a novel compound, R-3, on Pgp activity, ICD, and anti-tumor immune responses.

Main Methods:

• Treatment of Pgp-expressing/doxorubicin-resistant cancer cells with doxorubicin, Tariquidar, and R-3.
• Assessment of doxorubicin accumulation, Pgp activity, CRT translocation, ATP and HMGB1 release.
• Evaluation of phagocytosis by dendritic cells and CD8+ T-lymphocyte activation.
• Analysis of Pgp internalization, ubiquitination, and interaction with CRT.

Main Results:

• Both Tariquidar and R-3 increased doxorubicin accumulation and toxicity, reduced Pgp activity, and promoted CRT, ATP, and HMGB1 release.
• Unexpectedly, only R-3 enhanced phagocytosis by dendritic cells and activated anti-tumor CD8+ T-lymphocytes.
• R-3 promoted Pgp internalization and ubiquitination, disrupting its interaction with CRT, unlike Tariquidar.
• Pgp knockout restored doxorubicin-induced ICD, mimicking the R-3 treatment phenotype.

Conclusions:

• Plasma membrane-associated Pgp prevents complete ICD, even with CRT exposure and release of danger signals.
• R-3 demonstrates a dual action: inhibiting Pgp activity and promoting its internalization, leading to restored ICD and immune activation.
• Pharmacological agents that reduce Pgp activity and amount hold promise as chemo- and immunesensitizing agents in cancer therapy.