Evaluation of cytokine release syndrome (CRS) in patients with relapsed or refractory multiple myeloma (RRMM) receiving step-up priming doses and longer dosing intervals of elranatamab: MagnetisMM-9.
Authors: Sborov Douglas W. , Pawlyn Charlotte , Ishida Tadao , Huang Jeffrey S.Y. , Benjamin Reuben , Iida Shinsuke , Popat Rakesh , Kuroda Junya , Pianko Matthew James , Ramakrishnan Aravind , Schuster Steven Robert , Dabak Vrushali S. , Lesokhin Alexander M. , Conte Umberto , Soltantabar Pooneh , Hong Fangxin , Vandendries Erik , Fonseca Rafael 
Published: June 2024

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Background: Elranatamab (ELRA) is a humanized BCMA-CD3 bispecific antibody. In the phase 2 registrational MagnetisMM-3 (MM-3) trial, SC ELRA was given as 2 step-up priming doses (12 mg on C1D1 and 32 mg on C1D4) followed by 76 mg QW in patients (pts) with RRMM. Overall, 56.3% of pts had CRS (grade 2, 14.3%; no grade ≥3). Most events occurred after doses 1 (44.5%), 2 (20.2%), and 3 (5.9%); 0.8% (1 pt) had CRS with doses 4+. Recurrent CRS (>1 event) occurred in 15.1% of pts (Lesokhin Nat Med 2023). Methods: MagnetisMM-9 (MM-9; NCT05014412) is a phase 1/2, open-label, nonrandomized study of ELRA examining an alternative 2-dose step-up priming regimen (4 and 20 mg on C1D1 and C1D4, respectively). Eligible pts had RRMM and were refractory to ≥1 IMiD, ≥1 PI, and ≥1 anti-CD38 antibody. After the priming doses, ELRA 76 mg was given QW for 6 cycles (Part 1) or for 1 cycle followed by 116 or 152 mg Q2W for 5 cycles (Part 2A). The RP2D from Part 2A (152 mg) was evaluated in Part 2B (dose expansion). The rate of grade ≥2 CRS per ASTCT criteria during C1 is the primary endpoint for both parts. Secondary endpoints include evaluation of AEs and PK. Here, we report the overall safety and CRS profile associated with the 4/20 mg priming regimen. Results: For 85 treated pts, median age was 64.0 y; 49.4% were male; 23.5% had EMD; 31.8% had high-risk cytogenetics. Pts had a median of 5.0 (range, 1-12) prior LOTs; 85.9% had triple-class refractory disease. After a median follow-up of 7.4 mo, the most common (>50%) AEs were CRS (63.5%; grade ≥2, 15.3%) and neutropenia (54.1%; all grade ≥2). ICANS occurred in 4.7% of pts (all grade ≤2). The grade ≥2 CRS rate in C1 was 14.1% (90% CI, 8.4-21.9). CRS rates after the first 3 doses are in the the table. For doses 4+, any grade (grade ≥2) CRS was observed in 10.6% (3.5%) of pts overall, 12.1% (3.0%) of pts continuing to receive 76 mg (n=33), 25.0% (0%) of pts receiving 116 mg (n=12), and 5.0% (5.0%) of pts receiving 152 mg (RP2D; n=40). Overall, recurrent CRS was observed in 20.0% of pts. The geometric means (CV%) of free ELRA concentrations 24 h (Cmax-24h) after step-up doses 1 and 2 were 85.64 (48%) and 242.8 (55%). Conclusions: The 4/20 mg step-up priming regimen and alternative dosing schedules resulted in similar safety and incidence of overall and grade ≥2 CRS events vs the regimen used in MM-3 (12/32 mg), with no new safety signals identified. However, the CRS profile in this study differed, with more CRS after doses 2, 3, and 4+ and a higher prevalence of recurrent CRS. The Cmax-24h of free ELRA (CV%) after the priming doses were lower than those in MM-3 (107.4 [47%] and 405.1 [72%], respectively). Thus, the priming regimen used in MM-3 remains the optimal regimen for mitigating CRS. Future analyses of ongoing studies will be used to confirm these results. Clinical trial information: NCT05014412 . [Table: see text]