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In multiple myeloma (MM) disease, malignant plasma cells produce excessive quantities of a monoclonal immunoglobulin (Ig), known as M-protein. M-protein levels are measured in the serum of patients with MM using electrophoresis techniques to determine the response to treatment. However, therapeutic monoclonal antibodies, such as isatuximab, may confound signals using electrophoresis assays. We developed a robust assay based on immunocapture and liquid chromatography coupled to high-resolution mass spectrometry (IC-HPLC-HRMS) in order to eliminate this interference. Following immunocapture of Ig and free light chains (LC) in serum, heavy chains (HC) and LC were dissociated using dithiothreitol, sorted by liquid chromatography and analyzed using HRMS (Q-Orbitrap). This method allowed the M-proteins to be characterized and the signals from isatuximab and M-proteins to be discriminated. As M-protein is specific to each patient, no standards were available for absolute quantification. We therefore used alemtuzumab (an IgG kappa mAb) as a surrogate analyte for the semiquantification of M-protein in serum. This assay was successfully validated in terms of selectivity/specificity, accuracy/precision, robustness, dilution linearity, and matrix variability from 10.0 to 200 μg/mL in human serum. This method was used for clinical assessment of samples and eliminated potential interference due to isatuximab when monitoring patients with MM.

The ICARIA-MM study was sponsored by Sanofi. The authors thank, Helgi van de Velde, Valérie Boutet, Shujia Dai, Deborah DiNoto, Graziella Engelvin, Olivier Fedeli, Sébastien Hugla, Dominique Mouret, Béatrice Pradeilles, and Alain Roccon, all employees of Sanofi, for their contribution to the study, technology, and comments on the manuscript. The authors thank the participating patients and their families, and the study centers and investigators, for their contributions to the study. The medical writing support was provided by John Clarke, PhD and Stephanie Brillhart, PhD of Elevate Medical Affairs, contracted by Sanofi Genzyme for publication support services.

8529 Background: We report updated data from a Phase Ib study of Isa, a CD38 monoclonal antibody, plus VCd or VRd in transplant ineligible patients (pts) with NDMM (NCT02513186). Methods: Isa-VCd: Isa (10 or 20 mg/kg; weekly [QW] cycle 1 [C1], then Q2W), V (1.3 mg/m2; twice weekly C1, then QW), C (300 mg/m2; QW C1, then Days [D] 1, 8, 15 to C12), d (20 mg; twice weekly C1, then D1, 2, 8, 9, 15, 16, 22, 23 to C12). Isa-VRd: Isa (10 mg/kg), V and d as described above; R (25 mg/day; D1–14 and D22–35). Efficacy and safety were evaluated. Conventional (M-protein levels) and minimal residual disease (MRD) IMWG response assessments were compared. MRD negativity was assessed at 10−5 by next-generation sequencing and flow. Mass Spectrometry (MS) negativity (no detectable serum M-protein) was assessed for 13 pts by Immuno-Capture and Liquid Chromatography coupled to High Resolution MS. Results: As of Nov 18, 2019, 17 pts were treated with Isa-VCd (10 mg/kg, n = 13; 20 mg/kg, n = 4), 27 with Isa-VRd; 53% and 63% remained on treatment, respectively. Infusion reactions were seen in 53% of Isa-VCd and 63% of Isa-VRd pts; Grade ≥3 infections in 23% and 37%; serious adverse events in 47% and 52%. See table for efficacy. 3 MRD positive pts were MS positive with persistent detectable M-protein ( > 10 µg/mL). 8/10 MRD negative pts were MS positive (4 at 5-10 µg/mL; 4 at > 10 µg/mL) and 2/10 were MS negative ( < 5 µg/mL). Stable residual M-protein was observed by MS up to 23 months post-MRD negativity. All pts tested by MS are still progression-free. Conclusions: Isa-VCd/VRd shows encouraging efficacy and tolerability in NDMM. MS seems to be more sensitive than MRD; low levels of M-protein were detectable even in MRD negative pts. Clinical trial information: NCT02513186 . [Table: see text]

SummaryPharmacokinetic analyses of clopidogrel are hampered by the existence of multiple active metabolite isomers (H1 to H4) and their instability in blood. We sought to retest the pharmacodynamic activities of the four individual active metabolite isomers in vitro, with the ultimate aim of determining the isomers responsible for clopidogrel activity in vivo. In vitro activity was evaluated by measuring binding of [33P]-2-methylthio-ADP on P2Y12-expressing Chinese hamster ovary (CHO) cells and human platelets in platelet-rich plasma (PRP). A stereoselective method that used reverse-phase ultra high-performance liquid chromatography (UHPLC) and tandem mass spectrometry (MS) was developed to measure individual concentrations of the stable 3’-methoxyacetophe-none (MP) derivatives of H1–H4. The new method was used to analyze plasma samples from clopidogrel-treated subjects enrolled in a phase I clinical trial. In vitro binding assays confirmed the previously observed biological activity of H4 (IC50: CHO-P2Y12: 0.12 μM; PRP: 0.97 μM) and inactivity of H3, and demonstrated that H1 was also inactive. Furthermore, H2 demonstrated approximately half of the biological activity in vitro compared with H4. Optimisation of UHPLC conditions and MS collision parameters allowed the resolution and detection of the four derivatised active metabolite isomers (MP-H1 to MP-H4). The stereoselective assay was extensively validated, and was accurate and precise over the concentration range 0.5–250 ng/ml. Only MP-H3 and MP-H4 were quantifiable in incurred clinical samples. Based on in vitro pharmacodynamic data and found concentrations, the active metabolite isomer H4 is the only diastereoisomer of clinical relevance for documenting the pharmacokinetic profile of the active metabolite of clopidogrel.