Current status and future perspectives in targeted therapy of NPM1-mutated AML

Abstract

Nucleophosmin 1 (NPM1) is a nucleus-cytoplasmic shuttling protein which is predominantly located in the nucleolus and exerts multiple functions, including regulation of centrosome duplication, ribosome biogenesis and export, histone assembly, maintenance of genomic stability and response to nucleolar stress. NPM1 mutations are the most common genetic alteration in acute myeloid leukemia (AML), detected in about 30-35% of adult AML and more than 50% of AML with normal karyotype. Because of its peculiar molecular and clinico-pathological features, including aberrant cytoplasmic dislocation of the NPM1 mutant and wild-type proteins, lack of involvement in driving clonal hematopoiesis, mutual exclusion with recurrent cytogenetic abnormalities, association with unique gene expression and micro-RNA profiles and high stability at relapse, NPM1-mutated AML is regarded as a distinct genetic entity in the World Health Organization (WHO) classification of hematopoietic malignancies. Starting from the structure and functions of NPM1, we provide an overview of the potential targeted therapies against NPM1-mutated AML and discuss strategies aimed at interfering with the oligomerization (compound NSC348884) and the abnormal traffic of NPM1 (avrainvillamide, XPO1 inhibitors) as well as at inducing selective NPM1-mutant protein degradation (ATRA/ATO, deguelin, (-)-epigallocatechin-3-gallate, imidazoquinoxaline derivatives) and at targeting the integrity of nucleolar structure (actinomycin D). We also discuss the current therapeutic results obtained in NPM1-mutated AML with the BCL-2 inhibitor venetoclax and the preliminary clinical results using menin inhibitors targeting HOX/MEIS1 expression. Finally, we review various immunotherapeutic approaches in NPM1-mutated AML, including immune check-point inhibitors, CAR and TCR T-cell-based therapies against neoantigens created by the NPM1 mutations.

Fig. 1. Targeting the structure, localization and levels of the wild-type and mutant NPM1 proteins.

Mechanisms of targeting include: interference with protein folding, prevention of NPM1 oligomerization, inhibition of protein–protein interactions (PPIs), promotion of nucleolar stress, block of nuclear export, and induction of protein degradation.

Fig. 2. Other approaches to target NPM1-mutated AML.

NPM1-mutated AML can be targeted with selective inhibitors of menin to downregulate HOX/MEIS, with BCL-2 (venetoclax) to induce apoptosis and with inhibitors of the SYK pathway (entospletinib).

Fig. 3. Venetoclax in NPM1-mutated AML.

A Algorithm for the treatment of NPM1-mutated AML patients older than 60 years. ^Based on the presence or absence of FLT3 mutations. CR complete remission, FLT3i FLT3 inhibitors, HMA hypomethylating agents, LDAC low-dose cytarabine, allo-HSCT allogeneic hematopoietic stem cell transplantation. B Examples of preemptive therapy with venetoclax as bridging to allo-HSCT. All three patients achieved molecular CR (negativity for NPM1 mutant transcripts) before allo-HSCT. VTX venetoclax, 5-AZA 5-azacytidine, CHT chemotherapy.

Fig. 4. Immunotherapeutic approaches to NPM1-mutated AML.

NPM1-mutated AML can be targeted using antibody-drug conjugates (e.g., gentuzumab ozogamicin, anti-CD33), immune check-point inhibitors, CAR and TCR-based adoptive T-cell therapies directed against NPM1 mutated epitope/HLA complex. CAR chimeric antigen receptor, TCR T-cell receptor.

Fig. 5. Dual CAR targeting of CD33 and CD123.

The rationale of CD123/CD33 dual targeting trans-signaling strategy is to induce a full cell activation against only CD123/CD33+ leukemic cells while reducing cell stimulation against CD33+ HSPCs and CD123+ endothelial cells [144].

Fig. 6. High-throughput screening for novel drugs in NPM1-mutated AML.

A Workflow of microscopy-based screening strategy (created with BioRender.com). B Example of 96 well plate subjected to image and data processing (generated with ShinyHTM software). Arrows indicate results obtained with XPO1 inhibitors (KPT-185, KPT-276 and KPT-330). The higher number of points for selinexor (KPT-330) results from its use as a positive control.