(PA-532) Targeting JAM-A to Prevent Multiple Myeloma Progression: Novel Peptide Inhibitors Block Proliferation and Offer a New Therapeutic Strategy for High-Risk Disease

Introduction:  Gain of chromosome 1q is a common high-risk (HR) abnormality in multiple myeloma (MM), linked to poor prognosis and extramedullary disease (EMD). F11R, which encodes Junctional Adhesion Molecule-A (JAM-A), is located on 1q and is frequently overexpressed in MM, especially in patients with adverse cytogenetics. JAM-A overexpression correlates with reduced progression-free and overall survival, and promotes proliferation, survival, motility, and invasion. Through cis-dimerization, JAM-A activates oncogenic signalling that drives early tumour growth. Given the incurable nature of MM, strategies that prevent progression in HR patients are urgently needed. This study aimed to develop second-generation peptide inhibitors that block JAM-A cis-dimerization and disrupt its oncogenic activity.

Methods:   F11R expression was analysed in patients using the CoMMpass dataset to assess correlations with cytogenetic risk and clinical outcome. JAM-A’s role in proliferation was validated by siRNA knockdown in KMS18 cells. A computationally designed peptide library targeting the JAM-A cis-dimer interface was developed to improve upon the first-generation inhibitor, optimising binding affinity and stability. Lead peptides were evaluated in vitro using proliferation and β-galactosidase senescence assays. In vivo efficacy was evaluated using the chick chorioallantoic membrane (CAM) model, a rapid and cost-effective screening platform previously developed by our lab (PMID: 35267611). Tumour mass, Ki67 proliferation index, and CD138⁺ plasma cell burden were assessed by IHC in pre-treated xenografts.

Results:   F11R expression was higher in MM patients with 1q gain than those without (mean 9.610 vs 7.138, p< 0.0001), and progressively increased from healthy donors to relapsed MM (mean 48.4 vs 87.83, p=0.0425). JAM-A expression above the median was linked to shorter progression-free survival (JAM-A^low 1106 days vs JAM-A^high 914 days, p=0.05) and overall survival (JAM-A^low 2922 days vs JAM-A^high 2356 days, p=0.0009). JAM-A overexpression in MM1.S enhanced proliferation (EV 115% vs JAM-A OE 169%, p=0.0152). Knockdown in KMS18 cells confirmed JAM-A’s role in proliferation. From the peptide library, P4 was the most potent, with an IC₅₀ of 11.88µM in KMS18 cells and efficacy in patient-derived CD138⁺ cells. P4 induced senescence and reduced adhesion to HS5 stromal cells (untreated 34,081 RFU vs P4 24,473 RFU, p=0.0024). JAM-A knockdown abrogated P4’s effects (siNeg IC₅₀ 14.53 µM vs siJAM-A IC₅₀ not reached), confirming specificity. Strikingly, when tested in the CAM model, P4 pre-treatment significantly reduced tumour size and mass (p< 0.0001), as well as Ki67 index and CD138⁺ content.

Conclusions:   This is the first in vivo demonstration of JAM-A inhibition via peptide therapy in MM. JAM-A is a key driver of MM proliferation, and P4 effectively disrupts its signalling in vivo. These findings support further development of P4 as a novel preventative strategy for HRMM, particularly in patients with 1q gain or EMD.