Abstract 1126: Concurrent degradation of BTK and IMiD neosubstrates by NX-2127 enhances multiple mechanisms of tumor killing

Abstract B-cell receptor (BCR) signaling is integral for the development, adhesion, growth, and survival of human B cells. Chronic activation of BTK-mediated BCR signaling is a hallmark of many B cell lymphoid malignancies, making BTK an attractive therapeutic target. While covalent inhibitors of BTK have proven effective, they have been associated with the occurrence of acquired resistance mutations. IMiDs (immunomodulatory imide drugs) exert direct anti-cancer effects in B cell malignancies as well as enhance the activity of T cells. Based on clinical data of BTK covalent inhibitors and IMiDs in B-cell malignancies, a strategy combining BTK and IMiD targeting in a single oral, small molecule may improve anti-tumor activity. Here we describe NX-2127, a bifunctional molecule that catalyzes the degradation of BTK and IMiD neosubstrates Aiolos and Ikaros. In primary human T cells, NX-2127 degrades Aiolos (DC50=25 nM) and Ikaros (DC50=54 nM) and enhances IL-2 secretion. NX-2127 promotes superior in vitro killing of a DLBCL cell line, TMD8, and a MCL cell line, REC-1, as compared to BTK inhibitors ibrutinib, acalabrutinib, and pirtobrutinib, or IMiDs pomalidomide and lenalidomide. BTK inhibitors promote partial death of TMD8 cells (Emax = 17-33% viable) and REC-1 cells (Emax = 46-52% viable). By contrast, the dual BTK and IMiD activity of NX-2127 promotes complete killing of TMD8 and REC-1 cells and does so more potently than IMiDs alone. In REC-1 cells, suppression of Ikaros protein levels by IMiDs, BTK inhibitors, and NX-2127 correlates closely with downstream viability reduction, independent of drug mechanism. In vivo, oral administration of NX-2127 demonstrates dose proportional degradation of BTK and Aiolos protein in a TMD8 xenograft model, closely correlating with the degree of tumor control. RNA-seq analysis performed on REC-1 cells demonstrates that NX-2127 exhibits distinct regulation of gene expression when compared to ibrutinib or pomalidomide. Gene set enrichment analysis (GSEA) of these uniquely modulated genes reveals that NX-2127 downregulates gene sets involved in cell cycle, DNA replication, DNA repair, and survival signaling pathways. Furthermore, a key mediator of T cell recognition is more strongly upregulated by NX-2127 than pomalidomide and ibrutinib at both the transcript and cell surface expression levels in REC-1 cells, implying a potential immune-mediated anti-neoplastic mechanism. The gene expression signature of NX-2127 exposure supports the hypothesis that its anti-tumor effects include both tumor cell-intrinsic and tumor cell-extrinsic mechanisms and suggests that the combination of BTK degradation and IMiD activity may be more efficacious in treating certain B-cell malignancies than either activity alone. A phase 1a/b trial of NX-2127 for patients with relapsed or refractory B-cell malignancies is ongoing. Citation Format: Mark A. Noviski, Jun Ma, Ernestine Lee, Nivetha Brathaban, May Tan, Luz Perez, Daniel W. Robbins, Austin Tenn-McClellan, Janine Powers, Gwenn Hansen, Cristiana Guiducci, Ryan Rountree. Concurrent degradation of BTK and IMiD neosubstrates by NX-2127 enhances multiple mechanisms of tumor killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1126.