CD38 Enzymatic Activity Modulates Drug Susceptibility in Multiple Myeloma Cells

Introduction. CD38, a membrane bound nicotinamide adenine dinucleotide (NAD+) degrading enzyme is highly expressed in bone marrow plasma cells and multiple myeloma (MM) cells. Anti-CD38 monoclonal antibodies, such as daratumumab and isatuximab, which exerts therapeutic effect against MM cells through direct cell damage, antibody dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), has shown its high efficacy in clinical practice. However, the role of CD38 enzyme activity in MM cell biology is still unclear. In the present study, we analyzed differences in multi-omics profile, cell proliferation and drug sensitivity between CD38 positive and negative MM cells. Moreover, changes in MM cell homeostasis according to CD38 enzyme activity was examined.

Materials and methods. MM cell lines harboring CD38 positive and negative fractions (KMS-12BM, KMS-11) were sorted according to CD38 expression. Intracellular NAD+ concentrations, cell cycle status and drug sensitivity (lenalidomide, bortezomib and glycolysis inhibitor) between CD38 positive and negative cells were analyzed. CD38 positive and negative cells from MM cell lines were subjected to metabolome and proteome analysis using Shimadzu TQ8050 GC-MS/MS and TripleTOF 5600 respectively. Metabolites and proteins significantly enriched in CD38 negative MM cells were analyzed using MetaboAnalyst and Metascape. CD138 positive bone marrow monoclonal plasma cells from patients of monoclonal plasma cell dyscrasias were submitted for proteome analysis. CD38 positive MM cell lines and patient derived bone marrow MM cells were treated with a CD38 NADase inhibitor (78c) and were analyzed for cell viability and cell cycle status. A CD38 NADase inhibitor resistant MM cell line (MOLP8) was developed by chronic exposure of 78c. Difference in drug sensitivity (isatuximab and lenalidomide) and proteomic analysis were performed between the control and 78c resistant MOLP8 cell line.

Results. CD38 negative cells of MM cell lines had higher NAD+ concentration, higher glycolytic activity and reduced cell proliferation compared to their CD38 positive counterparts. Proteomic analysis of CD38 low-expressing monoclonal plasma cells from patients also demonstrated higher glycolytic related protein expression compared to CD38 high-expressing MM cells. Interestingly, CD38 negative cells had relatively low sensitivity to lenalidomide compared to CD38 positive cells, which could be explained by reduced expression of IKZF1 protein expression in CD38 low-negative cells. High sensitivity to glycolytic inhibitor in CD38 negative MM cells were observed, reflecting the high glycolytic activity. CD38 NADase inhibitor resistant MOLP8 cells were less sensitive to direct isatuximab effect compared to control cells, proving that importance of CD38 NADase activity in CD38 therapeutic antibody sensitivity. Moreover, CD38 NADase inhibitor resistant MOLP8 cells were less sensitive to lenalidomide compared to control cells, reflecting the reduced IKZF1 protein expression.

Conclusions. CD38 is the major NADase in mammalian tissues, involved in catabolism of NAD⁺. Although CD38 is highly expressed in normal plasma cells and MM cells, its role in MM cell biology has not been studied in detail. We showed that CD38 NADase activity is associated with cell metabolism, proliferation, anti-MM drug sensitivity and direct effect of CD38 therapeutic antibody of MM cells. The present study sheds light on the significance of CD38 enzyme activity in MM cell biology and may also contribute to understanding the mechanism of resistance to CD38 targeted therapy.

Kawano:Sanofi: Honoraria; Ono Pharmaceutical: Honoraria; Bristol Myers Squibb Co.: Honoraria; Sebia: Honoraria; Takeda Pharmaceutical Co. Ltd.: Honoraria; Janssen Pharmaceuticals Inc: Honoraria.