MDM2-p53 Inhibitor Alrizomadlin (APG-115) Enhances Antitumor Activity of Pomalidomide in Multiple Myeloma (MM)

Introduction Multiple myeloma is a hematologic malignancy characterized by clonal expansion of cancerous plasma cells in the bone marrow. Treatment responses have been improved via contemporary regimens including immunomodulatory drugs (IMiDs), proteasome inhibitors, anti-CD38, and anti-B-cell maturation antigen monoclonal antibodies (in triplet or quadruplet combinations) in frontline or relapsed/refractory settings. Deregulated activities of different transcription factors associated with MM have been identified , including interferon regulatory factor 4 (IRF4), NF-κB, and c-MYC. IMiDs are known to exert direct antitumor activity by binding to cereblon, with subsequent proteasomal degradation of transcription factors Ikaros (IKZF-1) and Aiolos (IKZF-3) zinc fingers, which leads to decreased expression of IRF4 and c-MYC. A previous study demonstrated that p53 modulates IKZF1/3 expression via the p53-c-MYC axis, suggesting crosstalk of p53/c-MYC/IRF4. Therefore, activation of p53 in combination with IMiDs might provide an enhanced therapeutic approach to manage MM. Alrizomadlin is a novel, orally active small-molecule inhibitor that selectively targets p53/MDM2 interaction and is under clinical development for both hematologic and solid malignancies. The aim of this preclinical research was to evaluate whether alrizomadlin combined with IMiDs has synergistic antitumor effects on MM.

Methods A series of preclinical studies have been conducted to assess effects of alrizomadlin in combination with other contemporary therapies. These included cell-based antiproliferation assays; cell cycle and apoptosis detection with flow cytometry; tumor growth in xenograft models; and western blot assay to assess associations between exposure to these agents and a range of transcription factors and biomarkers.

Results The cell-based antiproliferation studies suggested synergistic activity between alrizomadlin and IMiDs against wild-type TP53 (TP53^WT) MM cell lines, including MOLP-8, H929, and MM1S. In vivo studies further revealed that co-administration of alrizomadlin with pomalidomide enhanced tumor growth inhibition (vs either agent). Tumor growth inhibition rates of 50% in H929 and 36.2% in MOLP-8 xenograft models were also observed in response to combination treatment. Mechanistically, pomalidomide likely induces dose-dependent decreases in IKZF1 and IKZF3, downregulating c-MYC and IRF4 while upregulating proapoptotic protein BCL-2 interacting mediator of cell death (BIM). Alrizomadlin induced accumulation of p53, MDM2, and downstream p21, and also inhibited phosphorylation of serine/threonine protein kinase Akt (protein kinase B; AKT) and extracellular signal-regulated kinase (ERK). Of note, alrizomadlin also downregulated IKZF1/3 and IRF4 while inhibiting activation of AKT and ERK pathways. More importantly, alrizomadlin plus pomalidomide further 1) enhanced accumulation of p21 and decreased phosphorylation of retinoblastoma tumor suppressor protein (RB), which culminated in cell cycle arrest at G0/G1; 2) augmented BIM as well as cleavage of caspase-3 and poly (ADP-ribose) polymerase-1 (PARP-1), which trigger and/or serve as a hallmark of apoptosis (respectively); and 3) promoted antiproliferative effects by disrupting mitogen-activated protein kinase (MAPK)/ERK and phosphoinositide 3-kinase (PI3K)/AKT pathways.

Conclusions Preclinical research suggests that MDM2 inhibitor alrizomadlin in combination with pomalidomide has synergistic antitumor effects in MM tumors harboring TP53^WT. These findings support further clinical evaluation of this novel combination for patients with relapsed/refractory MM.

Wang:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Liang:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Min:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Ge:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Wu:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Yu:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company. Yang:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company, Other: Leadership, Patents & Royalties. Zhai:Ascentage Pharma: Current Employment, Current equity holder in publicly-traded company, Other: Leadership, Patents & Royalties.