Target In Acute Myeloid Leukemia Research Articles

The multi-CDK inhibitor dinaciclib reverses bromo- and extra-terminal domain (BET) inhibitor resistance in acute myeloid leukemia via inhibition of Wnt/β-catenin signaling

Acute myeloid leukemia (AML) is a highly aggressive hematologic cancer with poor survival across a broad range of molecular subtypes. Development of efficacious and well-tolerable therapies encompassing the range of mutations that can arise in AML remains an unmet need. The bromo- and extra-terminal domain (BET) family of proteins represents an attractive therapeutic target in AML due to their crucial roles in many cellular functions, regardless of any specific mutation. Many BET inhibitors (BETi) are currently in pre-clinical and early clinical development, but acquisition of resistance continues to remain an obstacle for the drug class. Novel methods to circumvent this development of resistance could be instrumental for the future use of BET inhibitors in AML, both as monotherapy and in combination. To date, many investigations into possible drug combinations of BETi with CDK inhibitors have focused on CDK9, which has a known physical and functional interaction with the BET protein BRD4. Therefore, we wished to investigate possible synergy and additive effects between inhibitors of these targets in AML. Here, we describe combination therapy with the multi-CDK inhibitor dinaciclib and the BETi PLX51107 in pre-clinical models of AML. Dinaciclib and PLX51107 demonstrate additive effects in AML cell lines, primary AML samples, and in vivo. Further, we demonstrate novel activity of dinaciclib through inhibition of the canonical/β-catenin dependent Wnt signaling pathway, a known resistance mechanism to BETi in AML. We show dinaciclib inhibits Wnt signaling at multiple levels, including downregulation of β-catenin, the Wnt co-receptor LRP6, as well as many Wnt pathway components and targets. Moreover, dinaciclib sensitivity remains unaffected in a setting of BET resistance, demonstrating similar inhibitory effects on Wnt signaling when compared to BET-sensitive cells. Ultimately, our results demonstrate rationale for combination CDKi and BETi in AML. In addition, our novel finding of Wnt signaling inhibition could have potential implications in other cancers where Wnt signaling is dysregulated and demonstrates one possible approach to circumvent development of BET resistance in AML.

Abstract P20: Anti-CD123 CAR NK cells and cam161533 Trispecific Killer Engager have synergistic activity against Acute Myeloid Leukemia

Abstract P20: Anti-CD123 CAR NK cells and cam161533 Trispecific Killer Engager have synergistic activity against Acute Myeloid Leukemia

Research Progress of Circular RNA in Acute Myeloid Leukemia --Review

Acute myeloid leukemia(AML) is a malignant tumor of the blood system that is highly heterogeneous in terms of pathogenesis, genetic background and prognostic outcome, with an extremely high fatality rate and recurrence rate. Therefore, exploring new treatment methods and diagnostic strategies is one of the ways to improve the survival rate of patients with acute myeloid leukemia. Circular RNA (circRNA) is a special kind of noncoding RNA, which plays an important role in gene transcription, translation and epigenetic modification, and participates in the disease progression and prognosis of multiple solid tumors. At present, it has found that the abnormal expression of circRNA is closely related to the occurrence, development, drug resistance and prognosis of acute myeloid leukemia.Clinically, it can be used as a new biomarker and potential therapeutic target for AML. This article briefly reviews the research progress of circRNA in acute myeloid leukemia, aiming to provide new strategies for optimizing the diagnosis, treatment and prognosis of leukemia.

Dual-targeting CD33/CD123 NANOBODY T-cell engager with potent anti-AML activity and good safety profile

AbstractNovel therapies are needed for effective treatment of acute myeloid leukemia (AML). Relapse is common and salvage treatment with cytotoxic chemotherapy is rarely curative. CD123 and CD33, 2 clinically validated targets in AML, are jointly expressed on blasts and leukemic stem cells in >95% of patients with AML. However, their expression is heterogenous between subclones and between patients, which may affect the efficacy of single-targeting agents in certain patient populations. We present here a dual-targeting CD33/CD123 NANOBODY T-cell engager (CD33/CD123-TCE) that was designed to decrease the risk of relapse from possible single antigen-negative clones and to increase coverage within and across patients. CD33/CD123-TCE killed AML tumor cells expressing 1 or both antigens in vitro. Compared with single-targeting control compounds, CD33/CD123-TCE conferred equal or better ex vivo killing of AML blasts in most primary AML samples tested, suggesting a broader effectiveness across patients. In a disseminated cell-line–derived xenograft mouse model of AML, CD33/CD123-TCE cleared cancer cells in long bones and in soft tissues. As cytokine release syndrome is a well-documented adverse effect of TCE, the compound was tested in a cytokine release assay and shown to induce less cytokines compared to a CD123 single-targeting control. In an exploratory single-dose nonhuman primate study, CD33/CD123-TCE revealed a favorable PK profile. Depletion of CD123 and CD33 expressing cells was observed, but there were neither signs of cytokine release syndrome nor clinical signs of toxicity. Taken together, the CD33/CD123 dual-targeting NANOBODY TCE exhibits potent and safe anti-AML activity and promises a broad patient coverage.

Dysregulated immune and metabolic pathways are associated with poor survival in adult acute myeloid leukemia with CEBPA bZIP in-frame mutations

Acute myeloid leukemia (AML) with CEBPA bZIP in-frame mutations (CEBPAbZIP-inf) is classified within the favorable-risk group by the 2022 European LeukemiaNet (ELN-2022). However, heterogeneous clinical outcomes are still observed in these patients. In this study, we aimed to investigate the mutation profiles and transcriptomic patterns associated with poor outcomes in patients with CEBPAbZIP-inf. One hundred and thirteen CEBPAbZIP-inf patients were identified in a cohort of 887 AML patients homogeneously treated with intensive chemotherapy. Concurrent WT1 or DNMT3A mutations significantly predicted worse survival in AML patients with CEBPAbZIP-inf. RNA-sequencing analysis revealed an enrichment of interferon (IFN) signaling and metabolic pathways in those with a shorter event-free survival (EFS). CEBPAbZIP-inf patients with a shorter EFS had higher expression of IFN-stimulated genes (IRF2, IRF5, OAS2, and IFI35). Genes in mitochondrial complexes I (NDUFA12 and NDUFB6) and V (ATP5PB and ATP5IF1) were overexpressed and were associated with poorer survival, and the results were independently validated in the TARGET AML cohort. In conclusion, concurrent WT1 or DNMT3A mutations and a dysregulated immune and metabolic state were correlated with poor survival in patients with CEBPAbZIP-inf, and upfront allogeneic transplantation may be indicated for better long-term disease control.

Targeting IDH2R140Q and other neoantigens in acute myeloid leukemia

AbstractFor patients with high-risk or relapsed/refractory acute myeloid leukemia (AML), allogeneic stem cell transplantation (allo-HSCT) and the graft-versus-leukemia effect mediated by donor T cells, offer the best chance of long-term remission. However, the concurrent transfer of alloreactive T cells can lead to graft-versus-host disease that is associated with transplant-related morbidity and mortality. Furthermore, ∼60% of patients will ultimately relapse after allo-HSCT, thus, underscoring the need for novel therapeutic strategies that are safe and effective. In this study, we explored the feasibility of immunotherapeutically targeting neoantigens, which arise from recurrent nonsynonymous mutations in AML and thus represent attractive targets because they are exclusively present on the tumor. Focusing on 14 recurrent driver mutations across 8 genes found in AML, we investigated their immunogenicity in 23 individuals with diverse HLA profiles. We demonstrate the immunogenicity of AML neoantigens, with 17 of 23 (74%) reactive donors screened mounting a response. The most immunodominant neoantigens were IDH2R140Q (n = 11 of 17 responders), IDH1R132H (n = 7 of 17), and FLT3D835Y (n = 6 of 17). In-depth studies of IDH2R140Q-specific T cells revealed the presence of reactive CD4+ and CD8+ T cells capable of recognizing distinct mutant-specific epitopes restricted to different HLA alleles. These neo–T cells could selectively recognize and kill HLA-matched AML targets endogenously expressing IDH2R140Q both in vitro and in vivo. Overall, our findings support the clinical translation of neoantigen–specific T cells to treat relapsed/refractory AML.

Regulatory function and mechanism research for m6A modification WTAP via SUCLG2-AS1- miR-17-5p-JAK1 axis in AML

Acute myeloid leukemia (AML), characterized by the abnormal accumulation of immature marrow cells in the bone marrow, is a malignant tumor of the blood system. Currently, the pathogenesis of AML is not yet clear. Therefore, this study aims to explore the mechanisms underlying the development of AML. Firstly, we identified a competing endogenous RNA (ceRNA) SUCLG2-AS1-miR-17-5p-JAK1 axis through bioinformatics analysis. Overexpression of SUCLG2-AS1 inhibits proliferation, migration and invasion and promotes apoptosis of AML cells. Secondly, luciferase reporter assay and RIP assay validated that SUCLG2-AS1 functioned as ceRNA for sponging miR-17-5p, further leading to JAK1 underexpression. Additionally, the results of MeRIP-qPCR and m6A RNA methylation quantification indicted that SUCLG2-AS1(lncRNA) had higher levels of m6A RNA methylation compared with controls, and SUCLG2-AS1 is regulated by m6A modification of WTAP in AML cells. WTAP, one of the main regulatory components of m6A methyltransferase complexes, proved to be highly expressed in AML and elevated WTAP is associated with poor prognosis of AML patients. Taken together, the WTAP-SUCLG2-AS1-miR-17-5p-JAK1 axis played essential roles in the process of AML development, which provided a novel therapeutic target for AML.

Oncogenic lncRNA FAM215A promotes the malignant cell phenotypes of acute myeloid leukemia (AML) cell lines.

Acute myeloid leukemia (AML) is a form of blood cancer that arise as a result of clonal proliferation of malignant myeloid precursors acquiring genetic abnormalities. Primary resistance to initial treatment and disease recurrence continues to be huge challenge in treating AML. Herein, GSE114868 was analyzed for differentially-expressed lncRNAs between AML patients' mononucleated cells and healthy normal control mononucleated cells and 191 lncRNAs were significantly deregulated in AML patients' mononucleated cells. The correlation between candidate lncRNAs and AML patients' overall survival was analyzed and 6 lncRNAs, including MIR181A1HG, TRAF3IP2-AS1, STARD4-AS1, E2F3-IT1, FAM215A, and HHIP-AS1 were dramatically linked to AML patients' OS. Using a Cox proportional-hazards model, we identified risk factors and found FAM215A as a risk factor for AML patients' prognosis. The expression level of FAM215A showed to be upregulated within blood samples and cells. Genes correlated with FAM215A were correlated to cell division, modulation of cell apoptosis, and modulation of programmed cell death. FAM215A knockdown inhibited AML cell viability, elicited G0/G1-phase arrest of cell cycle, enhanced cell apoptosis, increased proapoptotic Bax and cleaved-caspase3 levels, and decreased antiapoptotic Bcl2. FAM215A overexpression exerted opposite effects on AML cells. Conclusively, FAM215A serves as an oncogenic lncRNA in AML, promoting cell viability, relieving cell cycle arrest, and suppressing cell apoptosis. FAM215A might be un underlying biological prognostic marker and therapeutic target for AML.

MiR-133a and miR-135a Regulate All-Trans Retinoic Acid-Mediated Differentiation in Pediatric Acute Myeloid Leukemia by Inhibiting CDX2 Translation and Serve as Prognostic Biomarkers.

Background: Acute myeloid leukemia (AML) is a type of blood cancer characterized by excessive growth of immature myeloid cells. Unfortunately, the prognosis of pediatric AML remains unfavorable. It is imperative to further our understanding of the mechanisms underlying leukemogenesis and explore innovative therapeutic approaches to enhance overall disease outcomes for patients with this condition. Methods: Quantitative reverse-transcription PCR was used to quantify the expression levels of microRNA (miR)-133a and miR-135a in 68 samples from 59 pediatric patients with AML. Dual-luciferase reporter transfection assay, Cell Counting Kit-8 assay, and western blot analysis were used to investigate the functions of miR-133a and miR-135a. Results: Our study found that all-trans-retinoic acid (ATRA) promoted the expression of miR-133a and miR-135a in AML cells, inhibited caudal type homeobox 2 (CDX2) expression, and subsequently inhibited the proliferation of AML cells. Additionally, miR-133a and miR-135a were highly expressed in patients with complete remission and those with better survival. Conclusions: miR-133a and miR-135a may play an antioncogenic role in pediatric AML through the ATRA-miRNA133a/135a-CDX2 pathway. They hold promise as potentially favorable prognostic indicators and novel therapeutic targets for pediatric AML.

LncRNA LBX2-AS1 inhibits acute myeloid leukemia progression through miR-455-5p/MYLIP axis

Acute myeloid leukemia (AML) is a common blood cancer primarily affecting the bone marrow and blood cells, which is prevalent among adults. Long non-coding RNAs (lncRNAs) have been shown to play a crucial role in the development and progression of AML. LBX2-AS1 is a recently discovered lncRNA that has been linked to the pathogenesis and progression of several types of cancer. This study aimed to investigate the role and possible mechanisms of LBX2-AS1 in AML. Expression levels of LBX2-AS1, miR-455-5p, and their target genes were detected in AML samples and cells by RT-qPCR. Cell proliferation and apoptosis were determined by Cell Counting Kit-8 and 5-ethynyl-2′-deoxyuridine assays, and flow cytometry, respectively. LBX2-AS1 was downregulated in AML specimens and cells, and overexpression of LBX2-AS1 significantly inhibited cell proliferation and enhanced apoptosis in vitro. We also determined the effects of LBX2-AS1 overexpression in an AML mouse model by in vivo bioluminescence imaging. Mechanistically, LBX2-AS1 acts as a competitive endogenous RNA, which promotes myosin regulatory light chain interacting protein (MYLIP) expression by sponging miR-455-5p. Knockdown of MYLIP or upregulation of miR-455-5p antagonized the effect of LBX2-AS1 overexpression on the progression of AML. LBX2-AS1 may thus be a valuable therapeutic target for AML.

Recent advances in CAR-T therapy for the treatment of acute myeloid leukemia.

Chimeric antigen receptor T-cell (CAR-T) therapy, which has demonstrated notable efficacy against B-cell malignancies and is approved by the US Food and Drug Administration for clinical use in this context, represents a significant milestone in cancer immunotherapy. However, the efficacy of CAR-T therapy for the treatment of acute myeloid leukemia (AML) is poor. The challenges associated with the application of CAR-T therapy for the clinical treatment of AML include, but are not limited to, nonspecific distribution of AML therapeutic targets, difficulties in the production of CAR-T cells, AML blast cell heterogeneity, the immunosuppressive microenvironment in AML, and treatment-related adverse events. In this review, we summarize the recent findings regarding various therapeutic targets for AML (CD33, CD123, CLL1, CD7, etc.) and the results of the latest clinical studies on these targets. Thereafter, we also discuss the challenges related to CAR-T therapy for AML and some promising strategies for overcoming these challenges, including novel approaches such as gene editing and advances in CAR design.

Suppression of DNMT1 combined with ATM or ATR inhibitor as a therapeutic combination of acute myeloid leukemia.

The potential treatment option of targeting DNA methyltransferase 1 (DNMT1) has been explored, but further investigation is required to assess the efficacy of combination therapy in acute myeloid leukemia (AML). In this study, bioinformatics and online databases were utilized to select the combined therapeutic targets. The potential kinases associated with DNMT1-related genes in AML were analyzed using the Cancer Genome Atlas (TCGA) database and X2K Appyter (Expression2Kinases) database. In-vitro evaluations were conducted to assess the synergistic effects between DNMT1 and ATR/ATM in five AML cell lines (MOLM-16, NB-4, HEL 92.1.7, HEL, EOL-1). In our study, ATR and ATM are primarily the kinases associated with DNMT1-related genes in AML. We observed a significant upregulation of DNMT1, ATR, and ATM expression in AML tissues and cell lines. The five AML cell lines demonstrated sensitivity to monotherapy with GSK-368, AZD-1390, or AZD-6738 (EC50 value ranges from 5.461 to 7.349 nM, 5.821 to 10.120 nM, and 7.618 to 10.100 nM, respectively). A considerable synergistic effect was observed in AML cell lines when combining GSK-368 and AZD-1390, GSK-368 and AZD-6738, or AZD-1390 and AZD-6738, resulting in induced cell apoptosis and inhibited cell growth. DNMT1, ATM, and ATR possess potential as therapeutic targets for AML. Both individual targeting and combination targeting of these molecules have been confirmed as promising therapeutic approaches for AML.

The PedAL/EuPAL Project: A Global Initiative to Address the Unmet Medical Needs of Pediatric Patients with Relapsed or Refractory Acute Myeloid Leukemia.

The prognosis of children with acute myeloid leukemia (AML) has improved incrementally over the last few decades. However, at relapse, overall survival (OS) is approximately 40-50% and is even lower for patients with chemo-refractory disease. Effective and less toxic therapies are urgently needed for these children. The Pediatric Acute Leukemia (PedAL) program is a strategic global initiative that aims to overcome the obstacles in treating children with relapsed/refractory acute leukemia and is supported by the Leukemia and Lymphoma Society in collaboration with the Children's Oncology Group, the Innovative Therapies for Children with Cancer consortium, and the European Pediatric Acute Leukemia (EuPAL) foundation, amongst others. In Europe, the study is set up as a complex clinical trial with a stratification approach to allocate patients to sub-trials of targeted inhibitors at relapse and employing harmonized response and safety definitions across sub-trials. The PedAL/EuPAL international collaboration aims to determine new standards of care for AML in a first and second relapse, using biology-based selection markers for treatment stratification, and deliver essential data to move drugs to front-line pediatric AML studies. An overview of potential treatment targets in pediatric AML, focused on drugs that are planned to be included in the PedAL/EuPAL project, is provided in this manuscript.

Mezigdomide is effective alone and in combination with menin inhibition in preclinical models of KMT2A-r and NPM1c AML

AbstractSmall molecules that target the menin-KMT2A protein-protein interaction (menin inhibitors) have recently entered clinical trials in lysine methyltransferase 2A (KMT2A or MLL1)–rearranged (KMT2A-r) and nucleophosmin-mutant (NPM1c) acute myeloid leukemia (AML) and are demonstrating encouraging results. However, rationally chosen combination therapy is needed to improve responses and prevent resistance. We have previously identified IKZF1/IKAROS as a target in KMT2A-r AML and shown in preclinical models that IKAROS protein degradation with lenalidomide or iberdomide has modest single-agent activity yet can synergize with menin inhibitors. Recently, the novel IKAROS degrader mezigdomide was developed with greatly enhanced IKAROS protein degradation. In this study, we show that mezigdomide has increased preclinical activity in vitro as a single-agent in KMT2A-r and NPM1c AML cell lines, including sensitivity in cell lines resistant to lenalidomide and iberdomide. Further, we demonstrate that mezigdomide has the greatest capacity to synergize with and induce apoptosis in combination with menin inhibitors, including in MEN1 mutant models. We show that the superior activity of mezigdomide compared with lenalidomide or iberdomide is due to its increased depth, rate, and duration of IKAROS protein degradation. Single-agent mezigdomide was efficacious in 5 patient-derived xenograft models of KMT2A-r and 1 NPM1c AML. The combination of mezigdomide with the menin inhibitor VTP-50469 increased survival and prevented and overcame MEN1 mutations that mediate resistance in patients receiving menin inhibitor monotherapy. These results support prioritization of mezigdomide for early phase clinical trials in KMT2A-r and NPM1c AML, either as a single agent or in combination with menin inhibitors.

Reduced Proteolipid Protein 2 promotes endoplasmic reticulum stress-related apoptosis and increases drug sensitivity in acute myeloid leukemia.

The Proteolipid Protein 2 (PLP2), a protein in the Endoplasmic Reticulum (ER) membrane, has been reported to be highly expressed in various tumors. Previous studies have demonstrated that the reduced PLP2 can induce apoptosis and autophagy through ER stress-related pathways, leading to a decreased proliferation and aggressiveness. However, there is no research literature on the role of PLP2 in Acute Myeloid Leukemia (AML). PLP2 expression, clinical data, genetic mutations, and karyotype changes from GEO, TCGA, and timer2.0 databases were analyzed through the R packages. The possible functions and pathways of cells were explored through GO, KEGG, and GSEA enrichment analysis using the clusterProfiler R package. Immuno-infiltration analysis was conducted using the Cibersort algorithm and the Xcell R package. RT-PCR and western blot techniques were employed to identify the PLP2 expression, examine the knockdown effects in THP-1 cells, and assess the expression of genes associated with endoplasmic reticulum stress and apoptosis. Flow cytometry was utilized to determine the apoptosis and survival rates of different groups. PLP2 expression was observed in different subsets of AML and other cancers. Enrichment analyses revealed that PLP2 was involved in various tumor-related biological processes, primarily apoptosis and lysosomal functions. Additionally, PLP2 expression showed a strong association with immune cell infiltration, particularly monocytes. In vitro, the knockdown of PLP2 enhanced endoplasmic reticulum stress-related apoptosis and increased drug sensitivity in THP-1 cells. PLP2 could be a novel therapeutic target in AML, in addition, PLP2 is a potential endoplasmic reticulum stress regulatory gene in AML.

Enhancing anti-AML activity of venetoclax by isoflavone ME-344 through suppression of OXPHOS and/or purine biosynthesis in vitro

Venetoclax (VEN), in combination with low dose cytarabine (AraC) or a hypomethylating agent, is FDA approved to treat acute myeloid leukemia (AML) in patients who are over the age of 75 or cannot tolerate standard chemotherapy. Despite high response rates to these therapies, most patients succumb to the disease due to relapse and/or drug resistance, providing an unmet clinical need for novel therapies to improve AML patient survival. ME-344 is a potent isoflavone with demonstrated inhibitory activity toward oxidative phosphorylation (OXPHOS) and clinical activity in solid tumors. Given that OXPHOS inhibition enhances VEN antileukemic activity against AML, we hypothesized that ME-344 could enhance the anti-AML activity of VEN. Here we report that ME-344 enhanced VEN to target AML cell lines and primary patient samples while sparing normal hematopoietic cells. Cooperative suppression of OXPHOS was detected in a subset of AML cell lines and primary patient samples. Metabolomics analysis revealed a significant reduction of purine biosynthesis metabolites by ME-344. Further, lometrexol, a purine biosynthesis inhibitor, synergistically enhanced VEN-induced apoptosis in AML cell lines. Interestingly, AML cells with acquired AraC resistance showed significantly increased purine biosynthesis metabolites and sensitivities to ME-344. Furthermore, synergy between ME-344 and VEN was preserved in these AraC-resistant AML cells. In vivo studies revealed significantly prolonged survival upon combination therapy of ME-344 and VEN in NSGS mice bearing parental or AraC-resistant MV4-11 leukemia compared to the vehicle control. This study demonstrates that ME-344 enhances VEN antileukemic activity against preclinical models of AML by suppressing OXPHOS and/or purine biosynthesis.

Immunoproteasome function maintains oncogenic gene expression in KMT2A-complex driven leukemia

Pharmacologic targeting of chromatin-associated protein complexes has shown significant responses in KMT2A-rearranged (KMT2A-r) acute myeloid leukemia (AML) but resistance frequently develops to single agents. This points to a need for therapeutic combinations that target multiple mechanisms. To enhance our understanding of functional dependencies in KMT2A-r AML, we have used a proteomic approach to identify the catalytic immunoproteasome subunit PSMB8 as a specific vulnerability. Genetic and pharmacologic inactivation of PSMB8 results in impaired proliferation of murine and human leukemic cells while normal hematopoietic cells remain unaffected. Disruption of immunoproteasome function drives an increase in transcription factor BASP1 which in turn represses KMT2A-fusion protein target genes. Pharmacologic targeting of PSMB8 improves efficacy of Menin-inhibitors, synergistically reduces leukemia in human xenografts and shows preserved activity against Menin-inhibitor resistance mutations. This identifies and validates a cell-intrinsic mechanism whereby selective disruption of proteostasis results in altered transcription factor abundance and repression of oncogene-specific transcriptional networks. These data demonstrate that the immunoproteasome is a relevant therapeutic target in AML and that targeting the immunoproteasome in combination with Menin-inhibition could be a novel approach for treatment of KMT2A-r AML.

Pyrimidine Starvation Is a Targetable Cancer Vulnerability: Mechanisms of Nucleotide Homeostasis

Introduction: Acute myeloid leukemia (AML) is a heterogeneous disease, though all AML exhibit a characteristic block in differentiation. Hence, much effort has been made to develop small molecules that promote leukemic cell differentiation in the treatment of AML. In 2016 we identified the enzyme dihydroorotate dehydrogenase (DHODH) as a therapeutic target in AML. DHODH is a mitochondrial enzyme that converts dihydroorotate to orotate in the 4th step of de novo pyrimidine synthesis. Without DHODH enzymatic activity, a cell is forced to rely on autophagy or extracellular salvage to maintain its intracellular pyrimidine pool. DHODH inhibitor therapy has shown broad preclinical efficacy across multiple cancer types including, glioma, neuroblastoma, breast, small cell lung and pancreatic cancer suggesting that malignant cells are specifically impaired in their ability to maintain nucleotide homeostasis during periods of limited availability. Despite these very encouraging pre-clinical results, the translation into human clinical trials has been met with limited anti-cancer activity and therapeutic success. This discordance between pre-clinical and clinical benefit likely speaks to our limited understanding of how normal and malignant cells respond to pyrimidine starvation. Methods: Using in vitro and in vivo assays to compare normal hematopoietic progenitor and leukemic cells we interrogated key nodes in pyrimidine synthesis to identify the mechanisms behind this selective, anti-leukemic activity in the context of nucleotide starvation: [1] Nucleotide measurement by HPLC, [2] Flux experiments by isotopic tracing, [3] Polysome profiling to compare the transcriptome and translatome, [4] Quantification of ribosome recycling by examining the lysosomes following ultracentrifugation and [5] Direct visualization of lysosomes using new techniques in cryogenic electron microscopy. Results: Treatment of leukemia cells with brequinar blocked de novo synthesis and led to the rapid depletion of intracellular pyrimidines. In comparison, normal hematopoietic CD34 positive progenitor cells had less depletion, suggesting a selective vulnerability of leukemic cells over normal cells. We used isotopically labeled glutamine (15N) and uridine (13C) to quantify the contribution of de novo synthesis and extracellular salvage under control and starvation conditions. The leukemia cell line THP1 showed a higher reliance on de novo synthesis than normal CD34 positive hematopoietic progenitors ( Figure 1A, left graphs). Furthermore, following DHODH inhibition, THP1 cells were less capable of extracellular salvage compared to normal cells ( Figure 1A, right graphs). Polysome profiling analysis in THP1 cells showed a dramatic decrease in translating ribosomes as well as dramatic decrease in ribosomal RNA. We identified a short-list of 22 genes whose translation is prioritized during nucleotide deprivation. Following DHODH inhibition and nucleotide starvation, cells upregulate their number of lysosomes, as quantified by flow cytometry. In addition, the contents of the lysosome include ribosomal proteins, whose abundance increased during nucleotide starvation, suggesting an ongoing recycling of ribosomes to meet the nucleotide demand of leukemic cells during starvation. Finally, for the first time we have been able to directly visualize (by cryogenic electron microscopy) ribosomes within lysosomes during periods of nucleotide starvation, a finding that was completely absent in leukemia cells cultured under normal conditions ( Figure 1B). Conclusion: We hypothesized that the transformation from normal to malignant cell is accompanied by changes in nucleotide metabolism that render the transformed cells more reliant on de novo synthesis, establishing a metabolic vulnerability (and inherent therapeutic window) in the use of DHODH inhibitors. Our work confirms that leukemic blasts differ in their dependence on de novo nucleotide synthesis and its ability to garner nucleotides via salvage or autophagy pathways. This balance appears to be disturbed in the setting of malignancy such that leukemic cells are empirically more sensitive to treatment targeting pyrimidine synthesis. Understanding the differences in how leukemic and normal cells handle their nucleotide pools at baseline, and under starvation conditions, will guide the clinical utility of this class of inhibitors.

Dual-Targeting CD33/CD123 NANOBODY ® T Cell Engager Targeting Leukemia Blasts and Stem/Progenitor Cells in Relapsed AML

Acute myeloid leukemia (AML) is the most common adult hematologic malignancy. Relapse is common and salvage treatment with cytotoxic chemotherapy is rarely curative. Immunotherapy targeting surface antigens expressed in leukemia cells has emerged as an effective approach for AML treatment for patients who are older/unfit for or relapsed from/refractory to current regimens (Isidori A, et al. Frontiers Oncol. 2021). CD123 and CD33, two clinically validated targets in AML, are jointly expressed on blasts and leukemic stem cells (LSC) in >95% of AML patients. However, their expression is heterogenous between subclones and between patients which may impact the efficacy of single-targeting agents in certain patient populations. We recently reported a novel dual-targeting CD33/CD123 NANOBODY® T-cell engager (CD33/CD123-TCE) and demonstrated the anti-leukemia activity of CD33/CD123-TCE in AML with good safety profile in vivo (Dullaers M, et. al, JITC. 2022). Here we showed that CD33/CD123-TCE effectively targets AML blasts and LSC in relapsed AML. The cell surface expression profiling of samples from 55 patients with relapsed/refractory AML showed that all samples were positive for CD123 and CD33. The frequency of subpopulations in all samples co-expressing CD33 and CD123 is the most prominent, followed by single expression of CD123, and CD33. CD33-CD123- subset represented a minority. To investigate the anti-leukemia effect of CD33/CD123 TCE, we treated 18 primary samples for 7 days and assessed apoptosis by flow cytometry. Treatment of CD33/CD123 TCE at 2.5nM (low dose) and 25nM (high dose) induced more than 50% specific apoptosis in majority of bulk AML, with no significant difference between low and high dose of CD33/123 TCE. Analysis of cytotoxicity towards CD34+ AML-LSC revealed that CD33/CD123 TCE at low and high doses resulted in similar specific apoptosis of CD34+ cells, half of samples reached higher than 50% of apoptosis. Colony-forming assay in 2 primary samples further confirmed that CD33/CD123 TCE effectively inhibited the clonogenicity of primary AML cells expressing CD123 and CD33. While the average activity of CD33/CD123 TCE was comparable to single-targeting CD33-TCE and CD123-TCE reagents, in a subset of patient samples (11% of all samples), the dual-targeting CD33/CD123-TCE induced higher apoptosis in bulk and CD34+ AML cells compared to single-targeting controls, supporting utility of dual targeting. Concomitantly, CD3+ T cell expansion was observed in all dual- and single treatment groups, with a trend toward stronger amplification by CD33/CD123-TCE. Next, we examined AML and T cell phenotypes using mass cytometry (CyTOF) to characterize the impact of the TCE treatments. UMAP plus FlowSOM analysis revealed heterogenous subsets of LSC within samples and across patients. LSC subsets defined by CD34+ are known to co-express various surface markers associated with LSC-drug resistance and disease relapse including CD135 (FLT3), CD117 (c-kit), CLL-1, PD-L1 and TIM-3. These subsets were found highly sensitive to CD33/CD123-TCE, with subset CD34+CD38+CD117+PD-L1+CD123+ and CD34+CD38- showing greater sensitivity to CD33/CD123-TCE. Despite diverse expression of leukemic markers, CD33/CD123-TCE depleted CD34+ AML-LSC in all 3 samples tested by CyTOF, whereas single-targeting CD123-TCE and CD33-TCE were only effective in 2/3 samples. Analysis of T cell subsets revealed that dual- or single- targeting TCE expanded CD4+ helper and CD8+ cytotoxic subsets in all samples compared to control. CD4+ and CD8+ cells co-expressing CD69, TIM-3 or PD-1 were expanded by TCE in all three samples. Expansion of central and effector memory T cells defined by CCR7+CD45RA- and CCR7-CD45RA- in CD4+ and CD8+ subsets were seen in all treatment groups in 2 samples, whereas the highest expansion of CCR7-CD45RA-CD4+ effector memory subsets by CD33/CD123-TCE was seen in 1 sample. Taken together, the CD33/CD123 dual-targeting NANOBODY® TCE exhibits potent anti-AML activity and offers a broad patient coverage. Immunophenotypic profiling confirmed the effectiveness of CD33/CD123-TCE in eliminating various blast- and LSC-subsets, activating CD4+ and CD8+ T cells or expanding central/effector memory CD4+ and CD8+ T cells. These dual-targeting immune engagers may constitute an effective treatment option for patients who are older/unfit for or relapsed from/refractory to current regimens.

Pharmacology of a CpG-Linked Anti-Mir-126 Oligonucleotide Targeting Acute Myeloid Leukemia (AML) in Rats and Non-Human Primates (NHP)

Introduction: Acute myeloid leukemia (AML) is a lethal hematopoietic malignancy, characterized by the accumulation of clonal myeloid progenitor cells arrested in development. AML patients have dismal outcomes with a 5-year overall survival (2011 - 2017) of 29.5% (SEER). The persistence of leukemia stem cells (LSCs), a treatment-resistant primitive cell population able to inititiate and maintain AML, is thought to underlie relapse. Even newly approved drugs do not target LSCs efficiently. MicroRNA (miR)-126 is a non-coding regulatory RNA that contributes to LSC homeostasis in the bone marrow niche. Several lines of evidence validate miR-126 as a target in AML. Thus, we designed and made a novel anti-miR-126 oligonucleotide (oligo) linked to a CpG moiety, termed miRisten. miRisten incorporates modifications such as 2'-fluoro and phosphorothioate substituting phosphodiester in the sugar moiety of the nucleotide to enhance in vivo stability. miRisten eradicates LSCs in mouse models of AML and synergizes with FDA-approved AML drugs (PMID: 29505034, 34372909). Here, the results of IND-enabling toxicokinetic (TK) studies of miRisten in rats and NHP are presented. Objective: To investigate the pharmacological properties of miRisten to establish a safe dosing strategy to achieve prolonged knockdown of miR-126 for a first-in-human trial. Experimental Plan and Results: Good laboratory practice (GLP) TK studies were carried out in Sprague-Dawley rats. miRisten was given IV b.i.d. for 19 days at human equivalent doses (HED) of 1.6 and 4 mg/kg. miRisten was measured in plasma after the first dose. Plasma miRisten C max average was 3622 ± 335 and 6010 ± 175 nM post first doses of 1.6 and 4mg/kg, respectively. Plasma t 1/2 averaged 20.0 ± 3.8 minutes across both doses. The area under the curve (AUC 0 - ¥) were 638.9 ± 32 nMxhr (1.6 mg/kg) and 1313.5 ± 439 (4 mg/kg). A parallel toxicology study was undertaken documenting cage-side observations and body weight; complement activation, blood chemistries, urine and hematology were also evaluated. There were no unscheduled deaths in the toxicology segment. Four single NHP exploratory studies were also carried out (Fig. 1: Treatment schema). In each study, miRisten was given IV as a slow bolus (~5') b.i.d. and PK parameters evaluated in plasma. Study #1 & #2: 1 wk at 4mg/kg; #3: 1 wk at 5 mg/kg; #4: 18 days at 4 mg/kg. In all studies, miRisten dosage was ramped up (1, 2, 4 mg/kg for all and 5 mg/kg at dose 4 for Study #3). Solumedrol was given as premedication for the first 3 doses in all studies to prevent known phosphorothioate-mediated complement activation and cytokine release syndrome. Blood draws for PK were carried out immediately following doses 3 and 12 (Studies 1 - 3) and after the last dose on Day 18 (Study 4). The average area under the curve AUC was 3860 ± 1189 (4 mg/kg) and 3954 ± 1569 nMxhr (5 mg/kg) which was greater than observed in mice given the equivalent HED in bolus doses (~6x, 465.0). The t 1/2 of plasma miRisten was 11.7 min on Day 3 and 12.0 min on Day 7, comparable to mouse (9.6 min) and rat (20 min). Cage-side observations, body weight, complement activation, blood chemistries, urine and hematology were also evaluated. There was no terminal sacrifice of NHP however, all animals tolerated the treatment without observable adverse events. Conclusion: The dose ramp-up in NHP combined with pre-medication with solumedrol were undertaken to prevent possible acute inflammatory reactivity leading potentially to death. There were no unscheduled deaths in any species studied. These data are consistent with the safety of miRisten given IV with a dose ramping regimen combined with solumedrol. The greater AUC in NHP may predict better potency in humans. In mice, miRisten at 1.6 mg/kg HED q.d. effectively eradicated LSCs [PMID 29505034].