Targeted proteomic analysis for monitoring of multiple myeloma progression

Background: Multiple myeloma (MM) is a cancer of plasma cells that produce monoclonal immunoglobulins (mAb). Despite the development of new therapeutics, MM is associated with a high probability of persistent minimal residual disease (MRD) and relapse. Relapse in MM is driven by clonal heterogeneity and evolution, which can lead to the selection of drug-resistant malignant plasma cell (PC) clones. Monitoring of these residual PC clones is currently limited due to the invasiveness of bone marrow biopsy and the low sampling frequency. The primary objective was to test sensitive method for detection of malignant clones based on mAb analysis in human serum to monitor MM progression.

Methods: Our approach utilizes human serum or selectively isolated mAb from this serum as an initial material. Subsequently, the samples are digested using proteolytic enzymes and analysed using a targeted approach focused on the variable (CDR3) region of mAb. The analysis is performed using nanoLC separation hyphenated to a high-resolution mass spectrometer (Exploris 480, Thermo Scientific). Specific sequence of CDR3 was determined using sequencing of the corresponding DNA regions from myeloma cells. Patient samples before and after treatment were included in this study. The efficacy of the method was also evaluated on mAb standards spiked into human sera.

Results: The analytical workflow demonstrated the ability to detect mAb in serum with an exceptionally low limit of detection (≤5 mg.L-1). The analysis of digested preisolated mAb using targeted nanoLC-MS/MS detection proved to be more effective than the same analysis of crude human sera. Consequently, the method is deemed suitable for the sensitive detection of HC corresponding to malignant clones. The high sensitivity of the workflow allows for the sensitive monitoring of patients after treatment when analysis of the unique CDR3 region prior to MRD is conducted.

Conclusions: These findings permit the careful monitoring of patients in short time intervals and the detection of disease progression.