Abstract 1013: Circulating H3K27 methylated nucleosome concentration in lung cancer improves the contributive value of ctDNA molecular profiling result at diagnosis
Authors: Gauthier Arnaud , Candiracci Julie , Grolleau Emmanuel , Lescuyer Gaelle , Barthelemy David , Haon Christine , Geiduer Florence , Raffin Margaux , Hardat Nathalie , Balandier Julie , Rabeuf Rémi , Wozny Anne-Sophie , Rodriguez-Lafrasse Claire , Rommelaere Guillaume , Subtil Fabien , Couraud Sébastien , Herzog Marielle , Payen-Gay Lea 
Published: June 2023

Abstract
Background: In patients with advanced lung adenocarcinoma cancers, a subset can be cured by radiotherapy, and/or combined regimens, including chemotherapy, immunotherapy, or targeted therapies based on somatic molecular profiling. Nucleosomes are basic elements of chromatin, composed of 147bp DNA wrapped around an octamer of histones. Cell-free DNA (cfDNA) and nucleosomes are released into the bloodstream upon cell death. In addition to genetic somatic alterations, epigenetic modifications are found to play a key role in tumorigenesis of different cancers. The trimethylated histone H3 at lysine 27 (H3K27Me3) is well known as a transcription-repressive mark and proven to be involved in tumorigenesis, cell cycle progression and proliferation dysregulation. However, the concentration of circulating nucleosomes, as a biomarker of the contributive value of circulating tumor DNA (ctDNA) molecular profiling in patient management at diagnosis has not previously been investigated.
Patients and Methods: Plasmas were retrospectively collected from patients with NSCLC at initial diagnosis before treatment (CIRCAN’s cohort, N= 198) and from healthy donors (N=100). We carried out targeted next-generation sequencing (NGS) on paired plasmas. Samples were divided in two sub-groups based on the genetic results: ctDNA negative or positive for presence of somatic alterations. The concentration of global circulating nucleosomes as well as specific methylated marks: H3K4Me2-, H3K9Me3-, H3K27Me3- or H3K36Me3-nucleosomes were measured using chemiluminescent Nu.Q® immunoassays (Belgian Volition SRL, Belgium).
Results: Among all the different nucleosome forms evaluated, the highest coefficient correlations with cfDNA concentration were observed for H3K27Me3-nucleosomes (r=0.72, p&lt;0.0001). At a cut-off of 14 ng/ml of H3K27Me3-nucleosomes Nu.Q® assay showed a sensitivity of 69.2% (n=137) at 95% specificity for lung cancers vs healthy donors (AUC= 0.92). Interestingly, by combining H3K37Me3 level and ctDNA molecular profile, we found a contributive diagnostic value of molecular profiling results in 77% of the plasmas versus only 40% using NGS alone as per current practice. 32% of plasmas were positive for both H3K27Me3 and ctDNA; 37% are H3K27Me3-positive but ctDNA-negative; 8% of the samples were ctDNA-positive/H3K27Me3-negative and 23% are negative for both H3K27Me3 and ctDNA.
Conclusions: High levels of Nu.Q® H3K27Me3 and the absence of detecting somatic alterations strongly support the presence of non-mutated ctDNA in the corresponding plasma. This greatly improves the confidence in the negative molecular results in cfDNA in LC. This may allow the indication of individualized therapeutic regimens with a short-time medical decision and may reduce invasive tissue re-biopsies.
Citation Format: Arnaud Gauthier, Julie Candiracci, Emmanuel Grolleau, Gaelle Lescuyer, David Barthelemy, Christine Haon, Florence Geiduer, Margaux Raffin, Nathalie Hardat, Julie Balandier, Rémi Rabeuf, Anne-Sophie Wozny, Claire Rodriguez-Lafrasse, Guillaume Rommelaere, Fabien Subtil, Sébastien Couraud, Marielle Herzog, Lea Payen-Gay. Circulating H3K27 methylated nucleosome concentration in lung cancer improves the contributive value of ctDNA molecular profiling result at diagnosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1013.