Epigenetic profile of elevated cell free circulating nucleosomes in non-Hodgkin lymphoma.

Abstract

e15032 Background: Non-Hodgkin lymphoma (NHL) is a common type of hematological malignancy. The non-specific symptoms of lymphoma often delay diagnosis that is mainly based on a lymph node biopsy. However, due to their invasive nature, tissue biopsies have many limitations especially for monitoring therapeutic response where multiple biopsies may be required. Conversely, liquid biopsy offers a promising diagnosis and monitoring tool for cancer detection as it is noninvasive and easily repeatable over time compared to tissue biopsy. In this study, we investigated the circulating levels of intact nucleosomes containing the histone H3.1 isoform (Nu.Q-H3.1) in NHL and healthy subjects. Then, as histone post-translational modifications (PTMs) of circulating nucleosomes are described as potential biomarkers of various solid cancers, we investigated the epigenetic profile of nucleosomes from NHL patients following nucleosome enrichment (Nu.Q Capture) combined with mass spectrometry (MS) compared to healthy donors. Methods: In plasma K2EDTA from 9 NHL and 5 healthy subjects, we measured levels of Nu.Q-H3.1 combined with the epigenetic profile of these circulating nucleosomes using our Nu.Q Capture- mass spectrometry protocol. Subsequently, the capability of the identified histone PTMs to differentiate between NHL and healthy plasma was tested in an independent cohort (n = 24 NHL patients and n = 35 healthy donors) and in two patients undergoing treatment course using available quantitative Nu.Q immunoassays. Results: We describe a high level of circulating H3.1-nucleosomes in human plasma NHL patients compared to healthy subjects. This level of H3.1-nucleosomes was correlated with an elevated concentration of cfDNA and is consistent with the DNA distribution size observed by the Bioanalyzer around 146 bp. In addition, the mass spectrometric analysis of the nucleosome enriched extracts allowed us to profile the epigenetic pattern of circulating nucleosomes in NHL patients. Our analysis demonstrated increased levels of H3.1 as well as the lysine acetylation and methylations of the histone H3 in plasma from NHL patients. Furthermore, the clinical validation of the histone PTMs pattern using immunoassays identified a significant increase in the levels of H3.1-nucleosomes as well as 6 histone PTMs (H3K9Me1, H3K27Me3, H3K36Me3, H3K9Ac, H3K14Ac, H3K18Ac) in NHL patients in comparison with healthy donors. Finally, the application of this histone PTMs pattern on NHL patients demonstrated the potential use of these new biomarkers present in liquid biopsy to evaluate the therapeutic response and monitoring of tumor progression. Conclusions: Our results indicate that levels of Nu.Q-H3.1 are particularly elevated in NHL patients and may be a useful diagnostic tool. Moreover, our work emphasizes the crucial roles of the epigenetic marks present on circulating nucleosomes to detect and monitor diseases such as lymphoma.