Abstract 5689: Proliferating cell nuclear antigen as a new therapeutic target in multiple myeloma

Background: Multiple myeloma (MM), a plasma cell cancer, is the second most common hematologic malignancy. Despite advances in treatment (proteasome inhibitors, cereblon-targeting immunomodulatory drugs, and anti-CD38 and anti-BCMA immunotherapies) MM remains incurable. Proliferating cell nuclear antigen (PCNA) is an essential protein which is involved in chromatin remodeling, cell cycle progression, and DNA repair and replication, plays a key role in regulation of cell growth and proliferation. A post-translationally modified isoform of PCNA plays a critical role in the pathogenesis of a wide variety of malignant diseases including MM. Increased expression of PCNA has been shown to be associated with an aggressive MM phenotype, making it an attractive therapeutic target. Methods: We tested the anti-tumor activity of the novel small molecule PCNA inhibitor AOH-1996 (alone and in combination with either bortezomib or venetoclax) against MM cell lines (MM1.S, SKMM2, RPMI-8226). We assessed the cytotoxic anti-MM effects of varying doses AOH-1996 using standard viability assays and also 3D spheroid degradation assays. Changes in gene expression relevant to cell growth, cell-cycle progression, apoptosis, methylation status, and cytokine production following AOH-1996 exposure were analyzed using RT-PCR and Western blotting, as appropriate. We also evaluated the impact of AOH-1996 exposure on miRNA levels. The anti-MM effect of AOH-1996 monotherapy and combinations versus the same cell lines was then further evaluated in xenograft animal model. Results: AOH-1996 demonstrated dose-dependent reduction of cell growth (2D) and CSC-like sphere formation (3D) of MM1.S, SKMM2, and RPMI-8226 MM cell lines. Either short (2 days) or long (7 days) incubation with AOH-1996 significantly down-regulated the gene expression of selected anti-apoptotic markers (PCNA, CDK4/6, BCL2), cancer stem cell markers (EZH2, vimentin), and inflammatory and pro-survival cytokines (IL-6, VEGF, MIP-1alpha). AOH-1996 treatment down-regulated miR-21, miR-142, and miR-222 levels along with the reduced cytokine production of VEGF. There was a synergic effect on cell growth and CSC-like sphere formation when either bortezomib or venetoclax was added to AOH-1996. AOH-1996 significantly inhibited MM.1S cell line-derived xenograft tumor growth. Additional xenograft studies using other MM cell lines, as well as AOH-1996/bortezomib and AOH-1996/venetoclax combinations are ongoing. Conclusions: These findings clearly suggest that PCNA is a potential therapeutic target in MM. We have demonstrated for the first time that the PCNA inhibitor AOH-1996 shows potent anti-myeloma activity through its effects on several key tumor-associated genes and miRNAs. AOH-1996 is currently being evaluated in a Phase I trial. Citation Format: Jeffrey Zonder, Bin Bao, Amro Aboukameel, Sahar Bannoura, Husain Y. Khan, Hafiz Uddin, Mohamad B. Hamami, Ali Rehman, Ramzi Mohammad, Long Gu, Linda Malkas, Asfar Azmi. Proliferating cell nuclear antigen as a new therapeutic target in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5689.