PD-L1 Blockade by Atezolizumab Downregulates Signaling Pathways Associated with Tumor Growth, Metastasis, and Hypoxia in Human Triple Negative Breast Cancer.

Reem Saleh,Rowaida Z Taha,Eyad Elkord,Varun Sasidharan Nair,Nehad M Alajez

doi:10.3390/cancers11081050

Reem Saleh, Rowaida Z Taha + Show 3 more

Open Access

https://doi.org/10.3390/cancers11081050

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Journal: Cancers	Publication Date: Jul 25, 2019
Citations: 50	License type: CC BY 4.0

Affiliation: Hamad bin Khalifa University, Qatar Foundation

Abstract

Triple negative breast cancer (TNBC) is the most aggressive type of breast cancer, which shows resistance to common breast cancer therapies, as it lacks the expression of the most common breast cancer targets. Therefore, TNBC treatment remains a challenge. Targeting programmed cell death-ligand 1 (PD-L1) by monoclonal antibodies (mAbs), for example, atezolizumab, has revolutionized the treatment for various cancer types. However, the therapeutic efficacy of targeting PD-L1 in TNBC is currently under investigation. In this study, we investigated the molecular mechanisms by which the human TNBC cell line MDA-MB-231, expressing PD-L1, responds to atezolizumab, using RNA-Seq. Transcriptome analysis revealed 388 upregulated and 362 downregulated genes in response to atezolizumab treatment. The expression of selected genes, from RNA-Seq data, was subsequently validated using RT-qPCR in the MDA-MB-231 and MDA-MB-468 TNBC cells following atezolizumab treatment. Bioinformatics analysis revealed that atezolizumab downregulates genes promoting cell migration/invasion and metastasis, epithelial-mesenchymal transition (EMT), cell growth/proliferation/survival, and hypoxia. On the contrary, genes associated with apoptosis and DNA repair were upregulated in response to atezolizumab treatment. Gene set enrichment analyses revealed that a significant number of these genes are related to the NF-kB, PI3K/Akt/mTOR, MAPK, and CD40 signaling pathways. Using functional assays, we confirmed that atezolizumab increases MDA-MB-231 cell apoptosis/necrosis, and reduces their proliferation and viability. Collectively, our findings provide novel insights into the molecular mechanisms/signaling pathways by which atezolizumab exerts inhibitory effects on TNBC, thereby inhibiting EMT/metastasis, tumor growth/survival, and the induction of hypoxia.

Highlights

Breast cancer is one of the most common causes of cancer-related deaths among females around the world [1]
Almost all MDA-MB-231 cells were positive for programmed cell death-ligand 1 (PD-L1), the detection of the Cancers 2019, 11, x atezolizumab treatment, compared to non-treated cells and cells treated with isotype control
Data from western blots showed no difference in PD-L1 protein treated cells11,(Figure expression following atezolizumab treatment at 24 h (Figure 1C)

Summary

Introduction

Breast cancer is one of the most common causes of cancer-related deaths among females around the world [1]. Triple negative breast cancer (TNBC) is the most aggressive type of breast cancer, characterized by high grades, and high rates of distant metastasis and poor survival [2]. Immunotherapy in the form of monoclonal antibodies (mAbs) targeting the programmed cell death 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) axis have revolutionized the treatment for various cancer types [4,5,6,7,8]. Unlike these cancer types, most breast tumors are less immunogenic and exhibit low T cell infiltrate [9]. TNBC exhibits a high number of intratumoral and stromal tumor-infiltrating lymphocytes (TILs), suggesting that immunotherapy could be beneficial [9]

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Conclusion