Quantification of Citrullinated Histone H3 Bound DNA for Detection of Neutrophil Extracellular Traps.

Formation of neutrophil extracellular traps (NETs) has been associated with multiple pathologies including cancer. While the visualization of NETs by microscopy is a routine technique, their quantification presents a number of challenges. Commonly, as citrullination of histone H3 is required for NET formation, the presence of this modified histone along with DNA is considered to be a hallmark of NETs. Here, we describe and validate a novel assay for the quantification of NETs based on the detection of citrullinated histone H3 bound to DNA (CitH3DNA binding assay). Using this assay, we investigated the effect of phorbol 12-myristate 13-acetate (PMA) on NET formation by neutrophils isolated from the bone marrow of control and myeloma-bearing mice. We found that PMA induced citrullination of histone H3, an increase in the level of CitH3DNA, and NET formation in neutrophils from both tumor-free and myeloma-bearing mice. The levels of CitH3DNA in the NET fractions, as measured by our assay, directly correlated with the citrullination of histone H3 in neutrophils, as detected by Western blotting, and were significantly higher in PMA-stimulated compared to unstimulated neutrophils. Neutrophils from tumor-bearing mice produced more NETs than those from tumor-free counterparts following stimulation with PMA. The increase in NET production correlated with significantly higher histone H3 citrullination levels and increased measurements of CitH3DNA. Thus, our data indicate that bone marrow neutrophils from myeloma-bearing hosts are prone to NET formation.

A Novel Peptidylarginine Deiminase 4 (PAD4) Inhibitor BMS-P5 Blocks Formation of Neutrophil Extracellular Traps and Delays Progression of Multiple Myeloma.

Multiple myeloma is a plasma cell malignancy, which grows in the bone marrow (BM). The major population of cells in the BM is represented by neutrophils and they can form neutrophil extracellular traps (NET). Here, we investigated whether multiple myeloma cells induce NET formation and whether targeting this process would delay multiple myeloma progression. We demonstrated that murine and human multiple myeloma cells stimulate citrullination of histone H3 and NET formation by neutrophils and that this process is abrogated by pharmacological targeting of peptidylarginine deiminase 4 (PAD4) with a novel-specific small molecule inhibitor BMS-P5. Administration of BMS-P5 to multiple myeloma-bearing mice delays appearance of symptoms and disease progression. Taken together, our data demonstrate that targeting PAD4 may be beneficial for treatment of multiple myeloma.