Potential role of nuclear PD-L1 expression in cell-surface vimentin positive circulating tumor cells as a prognostic marker in cancer patients.

Scott Kopetz,Arun Satelli,Qing H Meng,Shulin Li,Christina Rojas,Zachary Brownlee,Izhar Singh Batth

doi:10.1038/srep28910

Scott Kopetz, Arun Satelli + Show 5 more

Open Access

https://doi.org/10.1038/srep28910

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Abstract

Although circulating tumor cells (CTCs) have potential as diagnostic biomarkers for cancer, determining their prognostic role in cancer patients undergoing treatment is a challenge. We evaluated the prognostic value of programmed death-ligand 1 (PD-L1) expression in CTCs in colorectal and prostate cancer patients undergoing treatment. Peripheral blood samples were collected from 62 metastatic colorectal cancer patients and 30 metastatic prostate cancer patients. CTCs were isolated from the samples using magnetic separation with the cell-surface vimentin(CSV)-specific 84-1 monoclonal antibody that detects epithelial-mesenchymal transitioned (EMT) CTCs. CTCs were enumerated and analyzed for PD-L1 expression using confocal microscopy. PD-L1 expression was detectable in CTCs and was localized in the membrane and/or cytoplasm and nucleus. CTC detection alone was not associated with poor progression-free or overall survival in colorectal cancer or prostate cancer patients, but nuclear PD-L1 (nPD-L1) expression in these patients was significantly associated with short survival durations. These results demonstrated that nPD-L1 has potential as a clinically relevant prognostic biomarker for colorectal and prostate cancer. Our data thus suggested that use of CTC-based models of cancer for risk assessment can improve the standard cancer staging criteria and supported the incorporation of nPD-L1 expression detection in CTCs detection in such models.

Highlights

PD-L1 is mainly a membrane protein, Ghebeh et al.[14] reported that treatment with doxorubicin downregulates cell surface PD-L1 expression and upregulates its nuclear expression in breast cancer cells, making them chemoresistant
We tested for nuclear PD-L1 (nPD-L1) expression in Circulating tumor cells (CTCs) analysis because we made an interesting observation in our initial study of HCT-116 cells in vitro
Our results indicated that the anti-PD-L1 antibody we used was very specific for PD-L1 because it was unable to detect PD-L1 expression in the HEK-293 cells (Fig. 1C), whereas we detected PD-L1 expression in PD-L1 transfected cells (Fig. 1D)

Summary

Introduction

PD-L1 is mainly a membrane protein, Ghebeh et al.[14] reported that treatment with doxorubicin downregulates cell surface PD-L1 expression and upregulates its nuclear expression in breast cancer cells, making them chemoresistant. The aberrant expression of PD-L1 in different types of cancers along with mislocalization of it in the nucleus, which promotes drug resistance, indicating poor prognosis for cancer in patients given chemotherapy, prompted us to detect nuclear PD-L1 (nPD-L1) expression in CTCs in the present study. Because CTCs are believed to withstand harsh environments in the blood apart from exposure to chemotherapy, we sought to determine whether expression of nPD-L1 in CTCs has prognostic significance for colorectal and prostate cancer

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