P-101: Detection of m-protein in acetonitrile precipitates of serum by MALDI-TOF mass spectrometry: a novel methodology

Abstract

<h3>Background</h3> MALDI-TOF-mass spectrometry (MS) has demonstrated superior analytical sensitivity for the detection of M-protein. We present the results of an alternative methodology by MALDI-TOF mass spectrometry (MS) for M-protein analysis. <h3>Methods</h3> Serum samples from patients with newly diagnosed plasma cell dyscrasias (MGUS, multiple myeloma, plasmacytoma and AL amyloidosis) with evidence of monoclonal gammopathy underwent a direct reagent-based extraction process using acetonitrile (ACN) precipitation. Serum κ and λ were validated using immuno-enrichment by anti-κ and anti-λ biotin-labelled antibodies immobilised on streptavidin magnetic beads. MALDI-TOF MS measurements were obtained using alpha-cyano-4-hydroxycinnamic acid as a matrix. The images obtained were overlaid on apparently healthy donor serum samples to confirm the presence of an M-protein peak. <h3>Results</h3> Characteristic M-protein peaks were observed in the ACN precipitates of serum within the predicted κ and λ mass/charge (m/z) range. The κ and λ peaks were confirmed by immuno-enrichment analysis. Sixty-seven patient samples with monoclonal gammopathy were chosen for ACN precipitation and analysed by MALDI-TOF MS. There was a demonstrable peak suggestive of M-protein in all the samples. The characteristic "polytypic-like" M-protein was additionally observed in patient samples with AL amyloidosis. The Daratumumab peak was additionally identified in one patient on D-VRd induction therapy. The concordance rate with serum immunofixation electrophoresis and serum free light chain analysis was 95%. <h3>Conclusions</h3> We report the results of a low-cost process using ACN precipitation to enrich κ and λ light chains for MALDI-TOF MS analysis. <h3>Disclosure of Conflicts of Interest</h3> Gopal Gopisetty, Nikita Mehra, Subramani Jayavelu, Indian provisional patent application no: 202041009443 filed in March 2020