Abstract 5277: The ROCK-2 inhibitor belumosudil exerts a direct antimyeloma effect and improves isatuximab-mediated cytotoxicity against multiple myeloma cells
Authors: Meloni Marco , Perrin Pauline , Nouguier Claire , Poirier Stephane , Bouaboula Monsif , Bisht Kamlesh , de Velde Helgi Van , Virone-Oddos Angela , Chiron Marielle 
Published: March 2024

Abstract
Multiple myeloma (MM) is a plasma cell malignancy characterized by clonal accumulation of malignant plasma cells in the bone marrow. Isatuximab (Sarclisa®) is a monoclonal antibody used for the treatment of MM. Isatuximab binds to CD38 (highly expressed on MM cells) and induces tumor cell killing via several mechanisms including antibody dependent cellular cytotoxicity (ADCC) and direct apoptosis. Belumosudil (RezurockTM) is a ROCK2 inhibitor that is approved for the treatment of chronic graft versus host disease (cGVHD). Recent reports suggest that inhibition of ROCK2 induces apoptosis and prevents growth of MM cells. Here, we investigated the potential antimyeloma effect of belumosudil alone or in combination with isatuximab with different readouts of viability, apoptosis and cytotoxicity.
The potential cytotoxic effect of belumosudil (as single agent or in combination with isatuximab) against MM cells was assessed in vitro by flow cytometry apoptosis assay, CellTiter-Glo® luminescent cell viability assay or long-term cytotoxic assay (Incucyte). The effect of belumosudil on healthy donor-derived NK cells viability was also assessed by flow cytometry.
Belumosudil reduced the number and viability of several MM cell lines without affecting healthy donor NK cell number and viability. Moreover, belumosudil induced apoptosis of MOLP-8 MM cells in a dose-dependent manner and further increased MOLP-8 cell apoptosis when combined with isatuximab after 2, 3 and 4 days of in vitro treatment. Belumosudil induced killing of MM cells in a dose-dependent manner over time (up to 4 days), independently of the presence of NK cells, as measured by Incucyte-based cytotoxicity assay. In addition, the combination of belumosudil (3.3 µM) with isatuximab (10 µg/ml) in presence of NK cells enhanced the killing of different MM cell lines over time compared to single agents.Finally, the expression of CD38 on MM cells has been documented to be decreased after treatment with anti-CD38 antibodies. Interestingly, analysis of CD38 expression on MM cells indicated that belumosudil induces an increase of CD38 on the surface of MOLP-8 MM cells and prevents isatuximab-induced decrease of CD38 expression.
These data suggest that belumosudil has a direct antimyeloma effect and increases isatuximab-mediated cytotoxicity against MM cells, without affecting the viability of NK cells. Taken together, this study provides evidence of the therapeutic potential of belumosudil in combination with isatuximab in the setting of MM.
Citation Format: Marco Meloni, Pauline Perrin, Claire Nouguier, Stephane Poirier, Monsif Bouaboula, Kamlesh Bisht, Helgi Van de Velde, Angela Virone-Oddos, Marielle Chiron. The ROCK-2 inhibitor belumosudil exerts a direct antimyeloma effect and improves isatuximab-mediated cytotoxicity against multiple myeloma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5277.