# Inhibitory Effect of Interleukin-24 on Programmed Death Ligand 1 Expression via a Eukaryotic Translation Initiation Factor 2 Alpha Kinase 2-Dependent Pathway in Human Triple-Negative Breast Cancer

## TL;DR

This study shows that interleukin-24 reduces PD-L1 levels in aggressive breast cancer cells and enhances chemotherapy effectiveness.

## Contribution

The novel finding is that IL-24 suppresses PD-L1 via PKR activation, improving doxorubicin's anti-cancer effects in TNBC.

## Key findings

- IL-24 treatment reduces PD-L1 protein levels in MDA-MB-231 cells.
- PKR is identified as a key mediator of IL-24–induced PD-L1 suppression.
- Combining IL-24 with doxorubicin increases chemotherapy sensitivity and lowers PD-L1.

## Abstract

Background/Objectives: Programmed death ligand 1 (PD-L1) is often overexpressed in triple-negative breast cancer (TNBC), where it helps the tumor evade the immune system and promotes tumor growth. Interleukin-24 (IL-24) is recognized for its anti-tumor activity, although its role in immune regulation remains unclear. In this study, we examined the role of IL-24 in regulating PD-L1 and its anti-cancer activity in TNBC cells. Methods: The study used TNBC cell lines treated with IL-24, delivered via a non-replicating adenovirus vector expressing the IL-24 gene. Assays included MTT for cell viability, Annexin V for apoptosis, Western blot for protein analysis, and qRT-PCR for mRNA analysis. Results: We found that the highly aggressive MDA-MB-231 cells had significantly higher PD-L1 levels. We discovered that treatment with IL-24 reduced cell growth, induced apoptosis, and significantly decreased PD-L1 protein levels in MDA-MB-231 cells. Mechanistically, we identified PKR, also known as eukaryotic translation initiation factor 2 alpha kinase 2, as a key mediator of IL-24–induced PD-L1 suppression. Additionally, doxorubicin, a primary chemotherapy drug used to treat triple-negative breast cancer, decreases PD-L1 expression and increases the sensitivity when combined with IL-24. Conclusions: In this study, we show that IL-24 decreases PD-L1 expression in MDA-MB-231 cells through PKR activation, enhances the anti-tumor effects of Doxorubicin, and may enable lower doses that reduce toxicity and further decrease PD-L1 levels. These findings suggest that IL-24 could serve as a valuable target for therapeutic intervention and suggest that it can improve doxorubicin’s effectiveness against aggressive breast cancer.