Properties of Monocyte-Derived Dendritic Cells Loaded With Lysates of Cancer Cells Exposed to Cytotoxic Peptides.

Background: This study is based on the idea of using tumor cell membrane lysis induced by diarylethene-containing analog of cytotoxic peptides (CPs) - gramicidin S to create a new approach for obtaining dendritic cells (DCs)-based anticancer vaccine. It is supposed that cancer cells undergoing immunogenic cell death release the damage-associated molecular patterns (DAMPs), and thus enhance immunogenic maturation and activation of DCs. The aim of this study is to analyze the phenotypic and functional characteristics of the generated monocyte-derived DCs loaded with CPs-treated lysates of tumor cells.

Materials and methods: The triple-negative human breast cancer cell line MDA-MB-231 was used in the study. DCs were generated from peripheral blood monocytes using a recombinant human granulocytemacrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). Tumor cells were treated with LMB033 CPs containing a diarylethene fragment (photoswitch) in two ring forms - "closed" with low activity and toxicity and "open" with high activity. The obtained lysates of tumor cells were co-incubated with human monocyte-derived DCs. The analysis of the phenotypic characteristics of DCs was performed by a flow cytometry using monoclonal antibodies to CD83, CD86, CD11c, HLA-DR, and HLA-ABC. The expression level of mRNA of cytokine genes and indoleamine 2,3-dioxygenase (IDO) gene was determined using the quantitative real-time PCR.

Results: The highest cytotoxic effect on MDA-MB-231 cells was detected after 6-h incubation with the open form of LMB033 at concentrations of 16 and 32 μM. The studied CPs even at the lower of the tested concentrations caused externalization of phosphatidylserine in almost 100% of apoptotic cells of MB-MDA-231 cells following 6-h incubation. Loading monocyte-derived DCs with lysate of MDA-MB-231 cells treated with LMB033 peptide in open or closed forms caused a different effect on the antigen-presenting properties of cells depending on the form of the peptide. Compared to DCs loaded with untreated lysate, a significant increase in the number of mature activated CD83+ DCs was found after loading with lysates of cells treated with open (16 μM) or closed (32 μM) forms of LMB033. CPs-induced lysates of MDA-MB-231 cells did not cause significant changes in the expression of mRNA of Th1 polarizing cytokines TNF-α, IL-12, neither did these lysates activate the transcription of the genes of immunosuppressive cytokines and IL-10, TGF-β, and the IDO gene. This indicates the absence of the activation of the immunosuppressive properties of the generated DCs.

Conclusion: The presented data open the prospects for developing an effective antitumor immunotherapeutic vaccine based on DCs using CPs LMB033.