Differentiation of the chronic lymphocytic leukemia response to ibrutinib and acalabrutinib treatment by single-cell MALDI-TOF MS imaging.

Ibrutinib and acalabrutinib, Bruton's tyrosine kinase inhibitors (BTKi) used for chronic lymphocytic leukemia (CLL) treatment, aim the same target but their off-target effects are different. The aim of this study was to use single-cell MALDI TOF mass spectrometry imaging to compare the CD19+ lymphocytes' mass spectra in untreated and ibrutinib- or acalabrutinib-treated subjects in order to better understand the therapeutic effect of BTKi. 180 cells from 9 male subjects divided in 3 groups (untreated, ibrutinib-treated and acalabrutinib-treated) were analyzed using MALDI-TOF mass spectrometry analyzer. Mass spectra were acquired in the 300-600 Da mass range. Partial least squares discriminant analysis (PLS-DA) was used for evaluation of mass spectra, while Volcano plots and Venn diagram were used for a review of significantly altered m/z values. Cross-validated PLS-DA classification accuracy of cells was 85 %. Ibrutinib-treated cells overlap with the untreated cell population, while acalabrutinib-treated cells form a separate class. 13 m/z signals were specific for each BTKi group. In conclusion, single-cell MALDI-TOF mass spectrometry imaging detects differences in the mass spectra of CD19+ lymphocytes treated with two different BTKi. Drug-specific m/z signal clusters can be identified as a chemical fingerprint of the BTKi effect and represent candidates for the therapeutic response biomarkers.