Iberdomide (CC-220) is a potent cereblon E3 ligase modulator with antitumor and immunostimulatory activities in lenalidomide- and pomalidomide-resistant multiple myeloma cells with dysregulated CRBN

Abstract

Immunomodulatory compounds, IMiDs® lenalidomide and pomalidomide mediate their anti-myeloma activities via cereblon, a component of the Cul4A CRBN E3 ligase complex [ 1 , 2 ]. Here we describe preclinical experiments with a next generation cereblon targeting agent, iberdomide (CC-220) and explore its activity in lenalidomide- and pomalidomide-sensitive and -resistant multiple myeloma (MM) cell lines, and its pharmacodynamic effects in the bone marrow from relapsed/refractory MM (RRMM) patients. We observed order of antiproliferative activity of iberdomide > pomalidomide > lenalidomide in matched lenalidomide-sensitive (H929) and an acquired lenalidomide-resistant (H929/LR) cell line (Fig. S 1A ). In a panel of MM cell lines across a range of concentrations, iberdomide had pronounced antiproliferative effects (Fig. S 1B ) compared to lenalidomide and pomalidomide measured by a ‘sensitivity shift’ of the relative percentage of AUC reduction ( Supplementary Methods ) (Fig. S 1C ). Analysis of the substrates Aiolos/Ikaros show degradation by both pomalidomide and iberdomide in the H929/LR cells (not shown), consistent with previous observations [ 3 ]. Further, treatment of H929 cells, with either pomalidomide or iberdomide resulted in time-dependent increases in G0/G1 and sub-G1 cell cycle fractions (Fig. S 1D ). Consistently, iberdomide induced greater apoptosis than pomalidomide in all MM cell lines tested, at a tenfold lower concentration, estimated to be in the range of clinical activity [ 4 ] (Fig. S 1E ). Pomalidomide and lenalidomide bind cereblon with similar affinity (~3 µM) [ 5 ]. We previously reported that faster rate of degradation of targeted substrates, Ikaros and Aiolos, and the down regulation of c-Myc/IRF4 expression were associated with greater antitumor effects of pomalidomide [ 6 ]. Treatment with 0.1 µM iberdomide led to a faster decrease in the relative abundance of these proteins than with pomalidomide (1 µM) (Fig. S 1F ). Cereblon-binding affinity IC50 of iberdomide is ~150 nM [ 5 ]. Thus the faster degradation of the substrates may be due to increased cereblon-binding affinity and/or improved processivity of the iberdomide-bound E3 ligase. Current clinical application of IMiDs compounds include doublet and triplet combinations with dexamethasone, bortezomib, and/or daratumumab. We initially compared the antiproliferative and pro-apoptotic activity of iberdomide to pomalidomide in combination with bortezomib in MM1.S cells. Due to the potent cytotoxic effects of bortezomib, pomalidomide, and iberdomide, and the narrow window of observable combinatorial effects, we titrated either pomalidomide (0.001–10 μM) or iberdomide (0.0001–1 μM) against bortezomib (0.0625–1 nM) (Figs. S 2A , S 3A , left). Using these concentrations, inhibition of proliferation induced by the combinations of iberdomide/bortezomib and pomalidomide/bortezomib were both synergistic [ 7 ] (Fig. S 2B ). In MM1.S cells, while single agent bortezomib, pomalidomide, or iberdomide induced apoptosis at 11%, 77%, and 89% respectively, the combination of iberdomide/bortezomib increased the apoptotic fraction to 95%, compared to pomalidomide/bortezomib at 87% (Fig. S 2C ). Utilizing similar concentrations where we observed synergy with bortezomib, we evaluated the potential inhibitory effect on substrate degradation of Aiolos, Ikaros, and ZFP91, and found no apparent inhibition by bortezomib with either pomalidomide or iberdomide (Fig. S 2D ). While the combination of iberdomide with bortezomib displayed strong antitumor effects, a potential clinical combination would likely include dexamethasone. Proliferative inhibition in MM1.S cells with the combination of iberdomide/bortezomib (Fig. S 3A , left), followed by the addition of 1 nM dexamethasone increased the sensitivity (Fig. S 3A , middle), and addition of 10 nM dexamethasone nearly completely stopped all proliferation (Fig. S 3A , right). Combination index calculations [ 7 ] showed a synergistic antiproliferative effect across the concentration range for the three drugs (Fig. S 3B ). In presence of human-derived complement, iberdomide plus daratumumab had a greater inhibitory effect on H929 cells than either drug alone (Fig. S 3C ). While complement-dependent cytotoxicity (CDC) was reported to be the primary mechanism of action for daratumumab, it also exerts activity through antibody-derived cellular cytotoxicity (ADCC) [ 8 ]. We evaluated the effects of iberdomide and daratumumab, alone and in combination in an ADCC assay. First, we incubated isolated PBMCs (effector) with either vehicle (DMSO), daratumumab (Dara (0.1 μg/mL)), iberdomide (Iber (0.008 μM)), or both drugs (Fig. S 3D ), and measured ADCC on the target H929 cells ( Supplemental Methods ). H929 only, PBMCs alone and PBMCs treated with daratumumab had similar killing effects on the target cells (purple and blue bars), while iberdomide (green) and iberdomide/daratumumab (red) had more cell killing activity (Fig.