Background:
The diagnosis of lung cancer is based on invasive methods and often occurs in a late stage of the disease, which explains its poor prognosis. Nucleosomes are fragments of DNA wrapped around histones. They can be an early and non-invasive diagnostic method for lung cancer. We investigated the clinical and statistical performance of the assay levels of nucleosomes alone and in combination with cytokines in plasma from untreated lung cancer (LC) patients and what was their discriminating power towards chronic obstructive pulmonary disease (COPD) and healthy subjects. (H).
Methods:
142 plasma samples were prospectively collected: H, n = 45; LC, n = 44 and COPD, n = 53. The circulating level of intact nucleosomes containing the histone isoform H3.1 (Nu.Qª-H3.1) was tested individually and in combination with cytokines to determine their performance in the discrimination of subjects based on their underlying condition. Then, the statistical performance of each model was tested with binary logistic regression models for the best combination of biomarkers for the following groups: cancer vs control (group A), cancer vs COPD + control (group B) and cancer vs COPD (group C)). The best model for each group was then applied to two independent biobank cohorts for validation.
Results:
The results for Nu.Q-H3.1 were an area under the curve (AUC) of 0.79, for groups A, B and C; sensitivity of 68%, 66% and 66% for groups A, B and C, respectively, for a specificity of 80%. For group A, the H3.1 + IL-10 model achieved a sensitivity of 77% for a specificity of 80% with an AUC of 0.88 (R² = 55.8%). For group B, the model H3.1 + IL-6 + IL-10 reached a sensitivity of 70% with an AUC of 0.85 (R² = 40.6%). For group C, the model H3.1 + IL-6 + IL-10 reached a sensitivity of 79% with an AUC of 0.85 (R² = 46.1%). The validation cohort had a similar performance. The results for the 3 cohorts taken together were: AUC of 0.83, 0.87, and 0.90 for groups A, B, and C, respectively; sensitivity of 75%, 76% and 84% for groups A, B and C, respectively, for a specificity of 80%.
Conclusions:
Nucleosomes were detected in the plasma of patients with H, LC and COPD. The combination with cytokines as described in these models allows a good discriminating power between the three groups. Based on these encouraging results, we believe that more studies with larger numbers of patients should be conducted to confirm and validate the usefulness of these biomarkers and models.
Nucleosomes: The Next Generation of Cancer Biomarkers
A nucleosome, made up of histone proteins and the DNA wrapped around them, is the central unit of chromatin. The effect that nucleosomes have on chromatin structure and gene regulation depend on the identity of the histones that make up the nucleosome, as well as any modification of these histone proteins.
With a plethora of histone protein variants and post-translational modifications that can occur in their “histone tails,” there is a myriad of possibilities when it comes to the exact identity of a nucleosome and its function. Recently, some of these variants and modifications have been found to be associated with cancers. Furthermore, only the total number of nucleosomes detected can also indicate a disease state or correlate with the efficacy of therapy.
Recently, “liquid biopsies”, or blood draws from which biomarkers can be examined, have become an easy and less invasive method of monitoring disease status and efficacy of treatment. Nucleosomes, histones, and DNA can leak into the blood during cancer due to high cell turnover or in response to chemotherapy. Floating DNA (cfDNA and ctDNA) is an attractive biomarker, but it has been shown to be less stable than nucleosomes.
Additionally, next-generation DNA sequencing is cumbersome and expensive compared to a high-throughput ELISA assay to detect intact nucleosomes. Nucleosome-specific detection assays represent a new generation of biomarker tests: easy, fast, cost-effective, and compatible with stable proteins in liquid biopsy samples.
Histone H3.1
The Active Motif Nu.Q® H3.1 Assay Kit is designed for the detection of levels of circulating cell-free nucleosomes (cf nucleosomes) containing histone H3.1 in human serum in a high-throughput format. Histone H3.1, or the canonical form of histone H3, is deposited during DNA replication and possibly also during the repair. The H3.1 study has identified cancer-associated mutations and different affinities for histone acetyltransferase HAT1. To examine the nucleosome containing H3 for all variants, use our Nu.Q® H3 Assay. For convenience and a more quantitative interpretation of results, the Nu.Q® H3.1 Assay Kit also includes a recombinant nucleosomal protein for use as a reference standard curve. For complete details, click on the Nu. Q ™ Method tab below.
Why use Nu.Q® H3.1?
- Sensitivity: detects circulating nucleosomes in as little as 10 µl of serum or 20 µl of plasma
- Specificity: nucleosome epitope-specific antibody allows detection of intact nucleosomes only
- Quantification: Recombinant nucleosomes allow relative quantification of circulating H3.1 nucleosome levels
- Convenience: colourimetric assay in a simple 96-well strip format for high and low throughput
- Fast: results can be obtained in 5 hours