SRSF2-p95 hotspot mutation is highly associated with advanced forms of mastocytosis and mutations in epigenetic regulator genes.

Mastocytosis is a rare and chronic disease with phenotypes ranging from indolent to severe. Prognosis for this disease is variable and very few biomarkers to predict disease evolution or outcome are currently known. We have performed comprehensive screening in our large cohort of mastocytosis patients for mutations previously found in other myeloid diseases and that could serve as prognostic indicators. KIT, SRSF2-P95 and TET2 mutations were by far the most frequent, detected in 81%, 24% and 21% of patients, respectively. Where TET2 and SRSF2-P95 mutation both correlated with advanced disease phenotypes, SRSF2-P95 hotspot mutation was found almost exclusively in patients diagnosed with associated clonal hematologic non-mast cell disease. Statistically, TET2 and SRSF2-P95 mutations were highly associated, suggesting a mechanistic link between these two factors. Finally, analysis of both clonal and sorted cell populations from patients confirms the presence of these mutations in the mast cell component of the disease, suggests an ontological mutation hierarchy and provides evidence for the expansion of multiple clones. This highlights the prognostic potential of such approaches, if applied systematically, for delineating the roles of specific mutations in predisposing and/or driving distinct disease phenotypes.

Liquid chromatography-tandem mass spectrometry assay for therapeutic drug monitoring of the tyrosine kinase inhibitor, midostaurin, in plasma from patients with advanced systemic mastocytosis.

We developed and validated quantitative bioanalytical liquid chromatography-tandem mass spectrometry assay for the protein kinase inhibitor, midostaurin. Plasma samples were pre-treated using a protein precipitation with methanol containing midostaurin-d5 as an internal standard. After centrifugation, 5µL of the supernatant was injected into the chromatographic system. The system consisted of a 3.5µm particle bonded octadecyl silica column, with gradient elution using a mixture of 0.1% (v/v) formic acid in acetonitrile and 10mM ammonium formate in water with 0.1% formic acid. The analyte was quantified using the selected reaction-monitoring mode of a triple quadrupole mass spectrometer equipped with a heated electrospray interface. The assay was validated in a 75-2500ng/mL calibration range. For quality control, within-day and between-day precisions were 1.2-2.8%, and 1.2-6.9%, respectively. The ß-expectation tolerance limit (accuracy) met the limits of acceptance ±15% (±20% for the LLQ). The drug was sufficiently stable under all relevant analytical conditions. The assay has successfully been used to assess drug levels for therapeutic drug monitoring in patients presenting advanced systemic mastocytosis and treated with the promising midostaurin.