Abstract 721: The role of NCAM1(CD56) in mediating venetoclax resistance

Abstract Background: NCAM1 (CD56) is a neural cell adhesion molecule that is expressed on immune cells including NK cells, T cells, dendric cells and monocytes. Acute myeloid leukemia (AML) patients also aberrantly express NCAM1 in around 30% of cases which may impact treatment response. Our group recently found that CD56 expression on myeloid blasts is associated with worse overall survival to treatment with the BCL2 inhibitor, Venetoclax (VEN), including VEN combined with hypomethylating agents or with the JAK inhibitor, Ruxolitinib. Within molecular prognostic risk score (mPRS) defined higher and intermediate- risk groups, CD56 positivity further stratified survival in addition to genetics. The functional role of CD56 in VEN resistance is unknown. Methods: We used 2 different AML cell lines showing high and intermediate expression of CD56, MOLM14 and OCI-AML2 respectively. Utilizing CRISPR Cas9 gene editing technology we generated stable NCAM1 knockouts. Multiparameter flow cytometry was used to access changes in surface CD56 expression. Ex-vivo drug sensitivity assays were performed on parental, NCAM1 knockout, and non-targeting cells to investigate VEN response at baseline and upon NCAM1 knockout. Western blot as well as single-cell imaging analysis were performed to elucidate changes in protein expression. Results: VEN sensitivity is associated with relative CD56 expression in MOLM14 and OCI-AML2. MOLM14 cell with high CD56 expression are more resistant to VEN than OCI-AML2 showing intermediate expression. Additionally, upon acquisition of VEN resistance through long-term drug exposure, MOLM14 and OCI-AML2 increase expression of CD56, phospho-MAPK1/3 (pERK), and have a higher ratio of MCL1/BCL2. To understand the impact of genetic deletion, we utilized CRISPR Cas9 to knockout NCAM1 in MOLM14 and OCI-AML2 and found that absence/or knockdown of CD56 sensitizes cells to VEN, as well as decreases protein levels of BCL2, pMAPK1/3, MCL1 and FGFR1. Of note, we saw no changes in surface markers associated with myeloid cell differentiation state (ie. CD11b, CD14, CD117) in our NCAM1 knockout lines compared to non-targeted control. Conclusions: Genetic deletion of CD56 sensitizes AML cells to VEN treatment and decreases pMAPK1/3 as well as BCL2 protein levels. CD56 signaling occurs through the PTK2/RAS/MAPK signaling pathway, however a direct regulatory role of CD56 on BCL2 expression has not yet been reported. Future therapeutics targeting CD56 may be able to improve response and survival in patients with CD56 positive AML particularly after VEN resistance. Further research to delineate the underlying mechanisms associated with CD56 and BCL2 family profiles are underway which may enhance current treatment approaches. Citation Format: Bernhard Alber, Tania Q. Vu, Bridget Robinson, Daniel Chandra, Jessica Mulkey, Yoko Kosaka, Evan Lind, Jeffrey W. Tyner, Jennifer N. Saultz. The role of NCAM1(CD56) in mediating venetoclax resistance [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 721.