The Designed Ankyrin Repeat Protein Antiviral Ensovibep for Nonhospitalized Patients With Coronavirus Disease 2019: Results From EMPATHY, a Randomized, Placebo-Controlled Phase 2 Study.

Background: The coronavirus disease 2019 (COVID-19) pandemic was characterized by rapid evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, affecting viral transmissibility, virulence, and response to vaccines/therapeutics. EMPATHY (NCT04828161), a phase 2 study, investigated the safety/efficacy of ensovibep, a multispecific designed ankyrin repeat protein (DARPin) with multivariant in vitro activity, in ambulatory patients with mild to moderate COVID-19. Methods: Nonhospitalized, symptomatic patients (N = 407) with COVID-19 were randomized to receive single-dose intravenous ensovibep (75, 225, or 600 mg) or placebo and followed until day 91. The primary endpoint was time-weighted change from baseline in log10 SARS-CoV-2 viral load through day 8. Secondary endpoints included proportion of patients with COVID-19-related hospitalizations, emergency room (ER) visits, and/or all-cause mortality to day 29; time to sustained clinical recovery to day 29; and safety to day 91. Results: Ensovibep showed superiority versus placebo in reducing log10 SARS-CoV-2 viral load; treatment differences versus placebo in time-weighted change from baseline were -0.42 (P = .002), -0.33 (P = .014), and -0.59 (P < .001) for 75, 225, and 600 mg, respectively. Ensovibep-treated patients had fewer COVID-19-related hospitalizations, ER visits, and all-cause mortality (relative risk reduction: 78% [95% confidence interval, 16%-95%]) and a shorter median time to sustained clinical recovery than placebo. Treatment-emergent adverse events occurred in 44.3% versus 54.0% of patients in the ensovibep and placebo arms; grade 3 events were consistent with COVID-19 morbidity. Two deaths were reported with placebo and none with ensovibep. Conclusions: All 3 doses of ensovibep showed antiviral efficacy and clinical benefits versus placebo and an acceptable safety profile in nonhospitalized patients with COVID-19.

Ensovibep, a SARS-CoV-2 antiviral designed ankyrin repeat protein, is safe and well tolerated in healthy volunteers: Results of a first-in-human, ascending single-dose Phase 1 study.

AIMS: This study aimed to assess safety, tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) effects of ensovibep, a designed ankyrin repeat protein antiviral being evaluated as a COVID-19 treatment, in healthy volunteers in a first-in-human ascending single-dose study. METHODS: Subjects were dosed intravenously, in a randomized double-blinded manner, with either ensovibep at 3, 9 or 20 mg/kg or with placebo, and followed until Day 100. PK and safety were assessed throughout the study duration. Immunogenicity and PD via viral neutralization in serum were also assessed. RESULTS: All adverse events were of mild to moderate severity, and no serious adverse events were observed. One subject who received the 20-mg/kg dose presented with moderate hypersensitivity vasculitis 3 weeks after infusion, which fully resolved using standard procedures. In most subjects ensovibep showed expected mono-exponential decline with a half-life of around 2 weeks. Anti-drug antibodies were detected in 15 of 17 subjects, with the earliest onset detected on Day 29. Viral neutralization assays on subject serum showed effective viral neutralization over the first 3 weeks following dosing with titre values in a dose dependent manner. CONCLUSION: Ensovibep proved safe in this first-in-human safety study and exhibited PK and PD parameters consistent with the expected treatment period required for acute COVID-19 infection.

Viral clearance, pharmacokinetics and tolerability of ensovibep in patients with mild to moderate COVID-19: A phase 2a, open-label, single-dose escalation study.

AIM: To assess viral clearance, pharmacokinetics, tolerability and symptom evolution following ensovibep administration in symptomatic COVID-19 outpatients. METHODS: In this open-label, first-in-patient study a single dose of either 225 mg (n = 6) or 600 mg (n = 6) of ensovibep was administered intravenously in outpatients with mild-to-moderate COVID-19 symptoms. Pharmacokinetic profiles were determined (90-day period). Pharmacodynamic assessments consisted of viral load (qPCR and cultures) and symptom questionnaires. Immunogenicity against ensovibep and SARS-CoV-2-neutralizing activity were determined. Safety and tolerability were assessed throughout a 13-week follow-up. RESULTS: Both doses showed similar pharmacokinetics (first-order) with mean half-lives of 14 (SD 5.0) and 13 days (SD 5.7) for the 225- and 600-mg groups, respectively. Pharmacologically relevant serum concentrations were maintained in all subjects for at least 2 weeks postdose, regardless of possible immunogenicity against ensovibep. Viral load changes from baseline at day 15 were 5.1 (SD 0.86) and 5.3 (SD 2.2) log10 copies/mL for the 225- and 600-mg doses, respectively. COVID-19 symptom scores decreased from 10.0 (SD 4.1) and 11.3 (SD 4.0) to 1.6 (SD 3.1) and 3.3 (SD 2.4) in the first week for the 225- and 600-mg groups, respectively. No anti-SARS-CoV-2 neutralizing activity was present predose and all patients had SARS-CoV-2 antibodies at day 91. Adverse events were of mild-to-moderate severity, transient and self-limiting. CONCLUSION: Single-dose intravenous administration of 225 or 600 mg of ensovibep appeared safe and well tolerated in patients with mild-to-moderate COVID-19. Ensovibep showed favourable pharmacokinetics in patients and the pharmacodynamic results warrant further research in a larger phase 2/3 randomized-controlled trail.

Bone Marrow Mesenchymal Stem Cells Support Acute Myeloid Leukemia Bioenergetics and Enhance Antioxidant Defense and Escape from Chemotherapy.

Like normal hematopoietic stem cells, leukemic stem cells depend on their bone marrow (BM) microenvironment for survival, but the underlying mechanisms remain largely unknown. We have studied the contribution of nestin+ BM mesenchymal stem cells (BMSCs) to MLL-AF9-driven acute myeloid leukemia (AML) development and chemoresistance in vivo. Unlike bulk stroma, nestin+ BMSC numbers are not reduced in AML, but their function changes to support AML cells, at the expense of non-mutated hematopoietic stem cells (HSCs). Nestin+ cell depletion delays leukemogenesis in primary AML mice and selectively decreases AML, but not normal, cells in chimeric mice. Nestin+ BMSCs support survival and chemotherapy relapse of AML through increased oxidative phosphorylation, tricarboxylic acid (TCA) cycle activity, and glutathione (GSH)-mediated antioxidant defense. Therefore, AML cells co-opt energy sources and antioxidant defense mechanisms from BMSCs to survive chemotherapy.

The Impact of the Cellular Origin in Acute Myeloid Leukemia: Learning From Mouse Models.

Acute myeloid leukemia (AML) is a genetically heterogeneous disease driven by a limited number of cooperating mutations. There is a long-standing debate as to whether AML driver mutations occur in hematopoietic stem or in more committed progenitor cells. Here, we review how different mouse models, despite their inherent limitations, have functionally demonstrated that cellular origin plays a critical role in the biology of the disease, influencing clinical outcome. AML driven by potent oncogenes such as mixed lineage leukemia fusions often seem to emerge from committed myeloid progenitors whereas AML without any major cytogenetic abnormalities seem to develop from a combination of preleukemic initiating events arising in the hematopoietic stem cell pool. More refined mouse models may serve as experimental platforms to identify and validate novel targeted therapeutic strategies.

Ontogenic Changes in Hematopoietic Hierarchy Determine Pediatric Specificity and Disease Phenotype in Fusion Oncogene-Driven Myeloid Leukemia.

Fusion oncogenes are prevalent in several pediatric cancers, yet little is known about the specific associations between age and phenotype. We observed that fusion oncogenes, such as ETO2-GLIS2, are associated with acute megakaryoblastic or other myeloid leukemia subtypes in an age-dependent manner. Analysis of a novel inducible transgenic mouse model showed that ETO2-GLIS2 expression in fetal hematopoietic stem cells induced rapid megakaryoblastic leukemia whereas expression in adult bone marrow hematopoietic stem cells resulted in a shift toward myeloid transformation with a strikingly delayed in vivo leukemogenic potential. Chromatin accessibility and single-cell transcriptome analyses indicate ontogeny-dependent intrinsic and ETO2-GLIS2-induced differences in the activities of key transcription factors, including ERG, SPI1, GATA1, and CEBPA. Importantly, switching off the fusion oncogene restored terminal differentiation of the leukemic blasts. Together, these data show that aggressiveness and phenotypes in pediatric acute myeloid leukemia result from an ontogeny-related differential susceptibility to transformation by fusion oncogenes. SIGNIFICANCE: This work demonstrates that the clinical phenotype of pediatric acute myeloid leukemia is determined by ontogeny-dependent susceptibility for transformation by oncogenic fusion genes. The phenotype is maintained by potentially reversible alteration of key transcription factors, indicating that targeting of the fusions may overcome the differentiation blockage and revert the leukemic state.See related commentary by Cruz Hernandez and Vyas, p. 1653.This article is highlighted in the In This Issue feature, p. 1631.

Aggressive leukemia driven by MLL-AF9.

We recently showed that cellular origin impacts the aggressiveness and the phenotype of acute myeloid leukemia (AML). Direct induction of the MLL-AF9 fusion in various hematopoietic compartments in vivo using a doxycycline (DOX) regulated mouse model (iMLL-AF9) led to an invasive chemoresistant AML expressing several genes known to be involved in epithelial to mesenchymal transition (EMT) in solid cancers. Many of these genes play important roles in migration and invasion and are significantly associated with poor overall survival in AML patients.

A Novel Inducible Mouse Model of MLL-ENL-driven Mixed-lineage Acute Leukemia.

Previous retroviral and knock-in approaches to model human t(11;19)+ acute mixed-lineage leukemia in mice resulted in myeloproliferation and acute myeloid leukemia not fully recapitulating the human disease. The authors established a doxycycline (DOX)-inducible transgenic mouse model "iMLL-ENL" in which induction in long-term hematopoietic stem cells, lymphoid primed multipotent progenitor cells, multipotent progenitors (MPP4) but not in more committed myeloid granulocyte-macrophage progenitors led to a fully reversible acute leukemia expressing myeloid and B-cell markers. iMLL-ENL leukemic cells generally expressed lower MLL-ENL mRNA than those obtained after retroviral transduction. Disease induction was associated with iMLL-ENL levels exceeding the endogenous Mll1 at mRNA and protein levels. In leukemic cells from t(11;19)+ leukemia patients, MLL-ENL mRNA also exceeded the endogenous MLL1 levels suggesting a critical threshold for transformation. Expression profiling of iMLL-ENL acute leukemia revealed gene signatures that segregated t(11;19)+ leukemia patients from those without an MLL translocation. Importantly, B220+ iMLL-ENL leukemic cells showed a higher in vivo leukemia initiation potential than coexisting B220- cells. Collectively, characterization of a novel transgenic mouse model indicates that the cell-of-origin and the fusion gene expression levels are both critical determinants for MLL-ENL-driven acute leukemia.

MLL-AF9 Expression in Hematopoietic Stem Cells Drives a Highly Invasive AML Expressing EMT-Related Genes Linked to Poor Outcome.

To address the impact of cellular origin on acute myeloid leukemia (AML), we generated an inducible transgenic mouse model for MLL-AF9-driven leukemia. MLL-AF9 expression in long-term hematopoietic stem cells (LT-HSC) in vitro resulted in dispersed clonogenic growth and expression of genes involved in migration and invasion. In vivo, 20% LT-HSC-derived AML were particularly aggressive with extensive tissue infiltration, chemoresistance, and expressed genes related to epithelial-mesenchymal transition (EMT) in solid cancers. Knockdown of the EMT regulator ZEB1 significantly reduced leukemic blast invasion. By classifying mouse and human leukemias according to Evi1/EVI1 and Erg/ERG expression, reflecting aggressiveness and cell of origin, and performing comparative transcriptomics, we identified several EMT-related genes that were significantly associated with poor overall survival of AML patients.

Estrogen signaling selectively induces apoptosis of hematopoietic progenitors and myeloid neoplasms without harming steady-state hematopoiesis.

Estrogens are potent regulators of mature hematopoietic cells; however, their effects on primitive and malignant hematopoietic cells remain unclear. Using genetic and pharmacological approaches, we observed differential expression and function of estrogen receptors (ERs) in hematopoietic stem cell (HSC) and progenitor subsets. ERα activation with the selective ER modulator (SERM) tamoxifen induced apoptosis in short-term HSCs and multipotent progenitors. In contrast, tamoxifen induced proliferation of quiescent long-term HSCs, altered the expression of self-renewal genes, and compromised hematopoietic reconstitution after myelotoxic stress, which was reversible. In mice, tamoxifen treatment blocked development of JAK2(V617F)-induced myeloproliferative neoplasm in vivo, induced apoptosis of human JAK2(V617F+) HSPCs in a xenograft model, and sensitized MLL-AF9(+) leukemias to chemotherapy. Apoptosis was selectively observed in mutant cells, and tamoxifen treatment only had a minor impact on steady-state hematopoiesis in disease-free animals. Together, these results uncover specific regulation of hematopoietic progenitors by estrogens and potential antileukemic properties of SERMs.

Insights into molecular pathways for targeted therapeutics in acute leukemia.

Despite the development of modern chemotherapeutic regimens, acute leukaemia remains incurable in the majority of adult patients and potential cure is associated with considerable side effects. Clinical and experimental research of the last two decades has demonstrated that acute leukaemia is the consequence of multiple collaborative molecular aberrations affecting protein kinases and transcriptional regulators induced by genetic alterations and/or epigenetic mechanisms. New technologies have been developed to detect aberrations of the entire (epi)genome of a leukaemic blast that will result in a long list of potential therapeutic targets needing to be functionally validated in cellular and animal leukaemia models. Using these methods, several "druggable" protein kinases have been identified. These kinases exert their oncogenic potential not only through expansion of the leukaemic clone, but also by regulating critical interactions of leukaemic stem cells with the microenvironment. Due to the molecular complexity of acute leukaemia, new functional genome-wide screens have been established and may help to identify targets that when blocked result in synthetic lethality of the leukaemic blasts harbouring distinct (epi)genomic lesions. A close interaction between the academic and the pharmaceutical biomedical research will be essential to translate these exciting new molecular findings into improved therapies for acute leukaemia.

The MAPK signaling cascade is a central hub in the regulation of cell cycle, apoptosis and cytoskeleton remodeling by tripeptidyl-peptidase II.

Tripeptidyl-peptidase II (TPPII) is a serine peptidase highly expressed in malignant Burkitt's lymphoma cells (BL). We have previously shown that overexpression of TPPII correlates with chromosomal instability, centrosomal and mitotic spindle abnormalities and resistance to apoptosis induced by spindle poisons. Furthermore, TPPII knockdown by RNAi was associated with endoreplication and the accumulation of polynucleated cells that failed to complete cell division, indicating a role of TPPII in the cell cycle. Here we have applied a global approach of gene expression analysis to gain insights on the mechanism by which TPPII regulates this phenotype. mRNA profiling of control and TPPII knockdown BL cells identified one hundred and eighty five differentially expressed genes. Functional categorization of these genes highlighted major physiological functions such as apoptosis, cell cycle progression, cytoskeleton remodeling, proteolysis, and signal transduction. Pathways and protein interactome analysis revealed a significant enrichment in components of MAP kinases signaling. These findings suggest that TPPII influences a wide network of signaling pathways that are regulated by MAPKs and exerts thereby a pleiotropic effect on biological processes associated with cell survival, proliferation and genomic instability.

TPPII promotes genetic instability by allowing the escape from apoptosis of cells with activated mitotic checkpoints.

Overexpression of TPPII correlates with accelerated growth and the appearance of centrosome and chromosome aberrations, suggesting that the activity of this enzyme may be critical for the induction and/or maintenance of genetic instability in malignant cells. We now find that the length of mitosis and of the entire cell cycle is significantly reduced in TPPII overexpressing HEK293 cells compared to untransfected and control transfected cells. Functional TPPII knockdown by shRNA interference caused a significant slowdown in cell growth and the accumulation of cells that delayed or failed to complete mitosis. TPPII overexpressing cells evade mitotic arrest induced by spindle poisons and display high levels of polyploidy despite the constitutively high expression of major components of the spindle checkpoint. TPPII overexpression correlated with upregulation of IAPs and with resistance to mitochondria dependent apoptosis induced by p53 stabilization. Thus, TPPII appears to promote malignant cell growth by allowing exit from mitosis and the survival of cells with severe mitotic spindle damage.

Mitotic infidelity and centrosome duplication errors in cells overexpressing tripeptidyl-peptidase II.

The oligopeptidase tripeptidyl-peptidase II (TPP II) is up-regulated Burkitt's lymphoma (BL) cells that overexpress the c-myc proto-oncogene and is required for their growth and survival. Here we show that overexpression of TPP II induces accelerated growth and resistance to apoptosis in human embryonic kidney 293 cells. This correlates with the appearance of multiple chromosomal aberrations, numerical and structural centrosome abnormalities, and multipolar cell divisions. Similar mitotic aberrations were also observed in a panel of BL lines and were suppressed, in parallel with TPP II down-regulation, upon reversion of BL-like characteristics in EBV-immortalized B lymphocytes carrying a tetracycline-regulated c-myc. Functional TPP II knockdown by small interfering RNA expression in BL cells caused the appearance of giant polynucleated cells that failed to complete cell division. Collectively, these data point to a role of TPP II in the regulation of centrosome homeostasis and mitotic fidelity suggesting that this enzyme may be a critical player in the induction and/or maintenance of genetic instability in malignant cells.