A 40-year-old man with relapsing-remitting multiple sclerosis (MS) developed primary central nervous system lymphoma (PCNSL) after having received 21 doses of natalizumab monotherapy. PCNSL is a disease of the elderly, with the majority of patients being diagnosed in the 7th to 8th decade of life. Immunodeficiency, iatrogenic immunosuppression, and some autoimmune diseases are known as predisposing conditions, and in these patients PCNSL peaks in the 4th decade. Because there is no increased prevalence of PCNSL in MS, and the patient was otherwise not immunocompromised, an association between natalizumab therapy and PCNSL cannot be ruled out.

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In this work, a novel standardization strategy for quantitative elemental bioimaging is evaluated. More specifically, multi-element quantification by laser ablation-inductively coupled plasma-time-of-flight mass spectrometry (LA-ICP-TOFMS) is performed by multi-point calibration using gelatin-based micro-droplet standards and validated using in-house produced reference materials. Fully automated deposition of micro-droplets by micro-spotting ensured precise standard volumes of 400 ± 5 pL resulting in droplet sizes of around 200 μm in diameter. The small dimensions of the micro-droplet standards and the use of a low-dispersion laser ablation setup reduced the analysis time required for calibration by LA-ICPMS significantly. Therefore, as a key advance, high-throughput analysis (pixel acquisition rates of more than 200 Hz) enabled to establish imaging measurement sequences with quality control- and standardization samples comparable to solution-based quantification exercises by ICP-MS. Analytical figures of merit such as limit of detection, precision, and accuracy of the calibration approach were assessed for platinum and for elements with biological key functions from the lower mass range (phosphorus, copper, and zinc). As a proof-of-concept application, the tool-set was employed to investigate the accumulation of metal-based anticancer drugs in multicellular tumor spheroid models at clinically relevant concentrations.

Treatment with plecstatin-1 resulted in disruption of the cytoskeleton and phosphorylation of the stress marker eIF2α, and induction of an immunogenic cell death signature, including calreticulin, high mobility group protein B and extracellular ATP.