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

ABSTRACT: Novel 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.

Clinical Benefits and Safety of Gemtuzumab Ozogamicin in Treating Acute Myeloid Leukemia in Various Subgroups: An Updated Systematic Review, Meta-Analysis, and Network Meta-Analysis.

Background: Previous trials demonstrated evidence involving the total effects of gemtuzumab ozogamicin (GO), an anti-CD33 humanized antibody, on treating acute myeloid leukemia (AML). In this updated systematic review, meta-analysis, and network meta-analysis (NMA), we aimed to comprehensively explore the clinical benefits and safety of GO in various subtypes of AML. Methods: PubMed, Embase, Cochrane, and Chinese databases were filtered to search randomized controlled trials (RCTs) and retrospective cohort studies that compared clinical efficiency and toxicity of GO with non-GO groups in AML. Random-effects models were used to calculate pooled effect sizes and 95% confidence intervals (CIs). Relative risk (RR) was used for estimating complete remission (CR), early death, and toxicity. Hazard risk (HR) was accomplished to evaluate survival. Results: Fifteen RCTs and 15 retrospective cohort studies were identified (GO: 4,768; Control: 6,466). GO tended to improve CR (RR 0.95, p = 0.084), followed by significantly improved survival (overall survival: HR 0.86, p = 0.003; event-free survival: HR 0.86, p = 0.015; relapse-free survival: HR 0.83, p = 0.001; cumulative incidence of relapse: HR 0.82, p < 0.001). GO benefits of CR and survival were evident in favorable- and intermediate-risk karyotypes (p ≤ 0.023). GO advantages were also associated with nucleophosmin 1 mutations (p ≤ 0.04), wild-type FMS-like tyrosine kinase 3 internal tandem duplication gene (p ≤ 0.03), age of <70 years (p < 0.05), de novo AML (p ≤ 0.017), and CD33(+) (p ≤ 0.021). Both adding GO into induction therapy (p ≤ 0.011) and a lower (<6 mg/m2) dose of GO (p ≤ 0.03) enhanced survival. Prognosis of combined regimens with GO was heterogeneous in both meta-analysis and NMA, with several binding strategies showing improved prognosis. Additionally, GO was related to increased risk of early death at a higher dose (≥6 mg/m2) (RR 2.01, p = 0.005), hepatic-related adverse effects (RR 1.29, p = 0.02), and a tendency of higher risk for hepatic veno-occlusive disease or sinusoidal obstruction syndrome (RR 1.56, p = 0.072). Conclusions: These data indicated therapeutic benefits and safety of GO in AML, especially in some subtypes, for which further head-to-head RCTs are warranted. Systematic Review Registration: [PROSPERO: https://www.crd.york.ac.uk/prospero/], identifier [CRD42020158540].

Hypoxia/ischemia impairs CD33 (Siglec-3)/TREM2 signaling: Potential role in Alzheimer's pathogenesis.

Recent genetic and molecular studies have indicated that the innate immune system, especially microglia, have a crucial role in the accumulation of ß-amyloid plaques in Alzheimer's disease (AD). In particular, the CD33 receptor, also called Siglec-3, inhibits the TREM2 receptor-induced phagocytic activity of microglia. CD33 receptors recognize the α2,3 and α2,6-linked sialic groups in tissue glycocalyx, especially sialylated gangliosides in human brain. The CD33 receptor triggers cell-type specific responses, e.g., in microglia, CD33 inhibits phagocytosis, whereas in natural killer cells, it inhibits the cytotoxic activity of the NKG2D receptor. Nonetheless, the regulation of the activity of CD33 receptor needs to be clarified. For example, it seems that hypoxia/ischemia, a potential cause of AD pathology, increases the expression of CD33 and its downstream target SHP-1, a tyrosine phosphatase which suppresses the phagocytosis driven by TREM2. Moreover, hypoxia/ischemia increases the deposition of sialylated gangliosides, e.g., GM1, GM2, GM3, and GD1, which are ligands for inhibitory CD33/Siglec-3 receptors. In addition, ß-amyloid peptides bind to the sialylated gangliosides in raft-like clusters and subsequently these gangliosides act as seeds for the formation of ß-amyloid plaques in AD pathology. It is known that senile plaques contain sialylated GM1, GM2, and GM3 gangliosides, i.e., the same species induced by hypoxia/ischemia treatment. Sialylated gangliosides in plaques might stimulate the CD33/Siglec-3 receptors of microglia and thus impede TREM2-driven phagocytosis. We propose that hypoxia/ischemia, e.g., via the accumulation of sialylated gangliosides, prevents the phagocytosis of ß-amyloid deposits by inhibiting CD33/TREM2 signaling.

T cell engaging bispecific antibodies targeting CD33 IgV and IgC domains for the treatment of acute myeloid leukemia.

BACKGROUND: Acute myeloid leukemia (AML) remains one of the most challenging hematological malignancies. Despite progress in therapeutics, majority of patients succumb to this neoplasm. CD33 is a proven therapeutic target, given its expression on most AML cells. Almost all anti-CD33 antibodies target the membrane distal immunoglobulin V (IgV) domain of the CD33 extracellular domain. METHODS: In this manuscript, we present data on three bispecific antibodies (BsAbs) against the CD33 IgV and membrane proximal immunoglobulin C (IgC) domains. We use in vitro binding and cytotoxicity assays to show the effect of these BsAbs on AML cell lines. We also use immunodeficient mice-bearing leukemias from cell lines and patient-derived xenografts to show the effect of these BsAbs in vivo. RESULTS: In vitro, the IgV-targeting BsAb had higher binding to AML cell lines using flow cytometry and delivered more potent cytotoxicity in T-cell-dependent cytotoxicity assays; importantly, the IgC domain-targeting outperformed the IgV domain-targeting BsAb in medullary and extramedullary leukemia animal models. CONCLUSIONS: These data support further clinical development of this BsAb for first-in-human phase I clinical trial.

The CD33 short isoform is a gain-of-function variant that enhances Aß1-42 phagocytosis in microglia.

BACKGROUND: CD33 is genetically linked to Alzheimer's disease (AD) susceptibility through differential expression of isoforms in microglia. The role of the human CD33 short isoform (hCD33m), preferentially encoded by an AD-protective CD33 allele (rs12459419T), is unknown. Here, we test whether hCD33m represents a loss-of-function or gain-of-function variant. METHODS: We have developed two models to test the role of hCD33m. The first is a new strain of transgenic mice expressing hCD33m in the microglial cell lineage. The second is U937 cells where the CD33 gene was disrupted by CRISPR/Cas9 and complemented with different variants of hCD33. Primary microglia and U937 cells were tested in phagocytosis assays and single cell RNA sequencing (scRNAseq) was carried out on the primary microglia. Furthermore, a new monoclonal antibody was developed to detect hCD33m more efficiently. RESULTS: In both primary microglia and U937 cells, we find that hCD33m enhances phagocytosis. This contrasts with the human CD33 long isoform (hCD33M) that represses phagocytosis, as previously demonstrated. As revealed by scRNAseq, hCD33m+ microglia are enriched in a cluster of cells defined by an upregulated expression and gene regulatory network of immediate early genes, which was further validated within microglia in situ. Using a new hCD33m-specific antibody enabled hCD33m expression to be examined, demonstrating a preference for an intracellular location. Moreover, this newly discovered gain-of-function role for hCD33m is dependent on its cytoplasmic signaling motifs, dominant over hCD33M, and not due to loss of glycan ligand binding. CONCLUSIONS: These results provide strong support that hCD33m represents a gain-of-function isoform and offers insight into what it may take to therapeutically capture the AD-protective CD33 allele.

Targeting the membrane-proximal C2-set domain of CD33 for improved CD33-directed immunotherapy.

There is increasing interest in targeting CD33 in malignant and non-malignant disorders. In acute myeloid leukemia, longer survival with the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO) validates this strategy. Still, GO benefits only some patients, prompting efforts to develop more potent CD33-directed therapeutics. As one limitation, CD33 antibodies typically recognize the membrane-distal V-set domain. Using various artificial CD33 proteins, in which this domain was differentially positioned within the extracellular portion of the molecule, we tested whether targeting membrane-proximal epitopes enhances the effector functions of CD33 antibody-based therapeutics. Consistent with this idea, a CD33V-set/CD3 bispecific antibody (BsAb) and CD33V-set-directed chimeric antigen receptor (CAR)-modified T cells elicited substantially greater cytotoxicity against cells expressing a CD33 variant lacking the entire C2-set domain than cells expressing full-length CD33, whereas cytotoxic effects induced by GO were independent of the position of the V-set domain. We therefore raised murine and human antibodies against the C2-set domain of human CD33 and identified antibodies that bound CD33 regardless of the presence/absence of the V-set domain ("CD33PAN antibodies"). These antibodies internalized when bound to CD33 and, as CD33PAN/CD3 BsAb, had potent cytolytic effects against CD33+ cells. Together, our data provide the rationale for further development of CD33PAN antibody-based therapeutics.

Development of Highly Optimized Antibody-Drug Conjugates against CD33 and CD123 for Acute Myeloid Leukemia.

PURPOSE: Mortality due to acute myeloid leukemia (AML) remains high, and the management of relapsed or refractory AML continues to be therapeutically challenging. The reapproval of Mylotarg, an anti-CD33-calicheamicin antibody-drug conjugate (ADC), has provided a proof of concept for an ADC-based therapeutic for AML. Several other ADCs have since entered clinical development of AML, but have met with limited success. We sought to develop a next-generation ADC for AML with a wide therapeutic index (TI) that overcomes the shortcomings of previous generations of ADCs. EXPERIMENTAL DESIGN: We compared the TI of our novel CD33-targeted ADC platform with other currently available CD33-targeted ADCs in preclinical models of AML. Next, using this next-generation ADC platform, we performed a head-to-head comparison of two attractive AML antigens, CD33 and CD123. RESULTS: Our novel ADC platform offered improved safety and TI when compared with certain currently available ADC platforms in preclinical models of AML. Differentiation between the CD33- and CD123-targeted ADCs was observed in safety studies conducted in cynomolgus monkeys. The CD33-targeted ADC produced severe hematologic toxicity, whereas minimal hematologic toxicity was observed with the CD123-targeted ADC at the same doses and exposures. The improved toxicity profile of an ADC targeting CD123 over CD33 was consistent with the more restricted expression of CD123 in normal tissues. CONCLUSIONS: We optimized all components of ADC design (i.e., leukemia antigen, antibody, and linker-payload) to develop an ADC that has the potential to translate into an effective new therapy against AML.

CD33 directed bispecific antibodies in acute myeloid leukemia.

Despite the approval of a number of new targeted therapies for acute myeloid leukemia (AML), median overall survival still remains poor, ranging from 12 to 18 months in most patients. Based on the success of blinatumomab, the CD19-targeted bispecific antibody for the treatment of acute lymphoblastic leukemia, the development of several CD33-targeted bispecific antibodies for AML are being investigated in clinical trials. In this review article of CD33-targeted bispecific antibodies, we describe the rationale for targeting CD3 x CD33, summarize the data from four ongoing phase 1 studies, review the major toxicity associated with CD33-targeted bispecific antibody therapy of cytokine release syndrome (CRS) and steps to mitigate CRS, and describe possible mechanisms of resistance to CD33-targeted bispecific antibody therapy. Future development to try to improve outcomes include combination therapies to reduce the tumor burden prior to starting treatment, combining with immune checkpoint inhibition therapy such as anti-PD-1/PDL1 antibodies, and the use of second generation bispecific antibodies that target two different antigens and recruit other effector cells such as nature killer cells and macrophages.

Gemtuzumab ozogamicin in acute myeloid leukemia: past, present and future.

After being in the therapeutic wilderness for several decades, acute myeloid leukemia has been recently thrust into the limelight with a series of drug approvals. Technical refinements in production, genetic manipulation and chemical modification of monoclonal antibodies led to growing interest in antibodies-based treatment strategies. Much of the focus of these efforts in acute myeloid leukemia has been on CD33 as a target. On September 2, 2017, the U.S. Food and Drug Administration approved gemtuzumab ozogamicin for treatment of relapsed or refractory CD33+ acute myeloid leukemia. This signals a new chapter in the long and unusual story of gemtuzumab ozogamicin, which was the first antibody-drug conjugate approved for human use by the Food and Drug Administration. In this review we have analyzed the history of this drug which, among several mishaps, is experiencing a second youth and still represents a field to be further explored.

Gene therapy for Alzheimer's disease targeting CD33 reduces amyloid beta accumulation and neuroinflammation.

Neuroinflammation is a key contributor to the pathology of Alzheimer's disease (AD). CD33 (Siglec-3) is a transmembrane sialic acid-binding receptor on the surface of microglial cells. CD33 is upregulated on microglial cells from post-mortem AD patient brains, and high levels of CD33 inhibit uptake and clearance of amyloid beta (Aß) in microglial cell cultures. Furthermore, knockout of CD33 reduces amyloid plaque burden in mouse models of AD. Here, we tested whether a gene therapy strategy to reduce CD33 on microglia in AD could decrease Aß plaque load. Intracerebroventricular injection of an adeno-associated virus (AAV) vector-based system encoding an artificial microRNA targeting CD33 (miRCD33) into APP/PS1 mice reduced CD33 mRNA and TBS-soluble Aß40 and Aß42 levels in brain extracts. Treatment of APP/PS1 mice with miRCD33 vector at an early age (2 months) was more effective at reducing Aß plaque burden than intervening at later times (8 months). Furthermore, early intervention downregulated several microglial receptor transcripts (e.g. CD11c, CD47 and CD36) and pro-inflammatory activation genes (e.g. Tlr4 and Il1b). Marked reductions in the chemokine Ccl2 and the pro-inflammatory cytokine Tnfα were observed at the protein level in the brain of APP/PS1 mice treated with miRCD33 vector. Overall, our data indicate that CD33 is a viable target for AAV-based knockdown strategies to reduce AD pathology. One Sentence Summary: A gene therapy approach for Alzheimer's disease using adeno-associated virus vector-based knockdown of CD33 reduced amyloid beta accumulation and neuroinflammation.

[Preparation of monoclonal antibody against human CD33 by immunizing mice with recombinant vector].

Objective To prepare a monoclonal antibody (mAb) against human CD33 by immunizing mice with recombinant vector and analyze its characteristics and clinical application. Methods The eukaryotic expression vector pcDNA3.1(+)/CD33 was constructed and used to immunize mice. The mouse monoclonal antibody against human CD33 was then harvested using the hybridoma technique. Its properties were evaluated and the clinical performance was validated. Results One hybridoma cell line capable of secreting mouse anti-human CD33 monoclonal antibody was successfully obtained, which was named HI33a for clone identification with a subclass of IgG2a, κ. Flow Cytometry analysis revealed that the antibody could stain myeloid cell lines but not lymphoid cell lines, and it could inhibit the binding of similar imported antibodies with HL-60 cells competitively. Western blotting verified that it could bind a Mr 67 000 membrane protein extracted from HL-60 cells, which was a strong indication of the characteristics of CD33 protein molecule. Labeled with PE fluorescein, CD33-PE was tested as an antibody reagent in comparison with other similar imported products. Its overall performance including the accuracy, linearity, and precision all met the industrial standard. Further clinical evaluation of 558 bone marrow samples showed that the results were highly consistent with those by the imported reagents used as controls. Conclusion A hybridoma cell line stably secreting anti-human CD33 mAb was prepared.

How I treat acute myeloid leukemia in the era of new drugs.

The acute myeloid leukemia (AML) treatment landscape has changed substantially since 2017. New targeted drugs have emerged, including venetoclax to target B-cell lymphoma 2, midostaurin and gilteritinib to target FLT3, and ivosidenib and enasidenib to target mutant isocitrate dehydrogenase 1 and 2, respectively. Other additions include reapproval of gemtuzumab ozogomycin to target CD33, glasdegib to target the hedgehog pathway, and a liposomal formulation of daunorubicin and cytarabine (CPX-351). Genomically heterogeneous AML has a tendency to evolve, particularly under selective treatment pressure. For decades, treatment decisions have largely centered around chemotherapy drug intensity. Physicians now have access to an increasing number of drugs with novel mechanisms of action and distinctive side-effect profiles. Key issues faced by hematologists in this era of new drugs include (1) the timely identification of actionable mutations at diagnosis and at relapse; (2) deciding which drug to use among several therapeutic options; and (3) increasing awareness of how to anticipate, mitigate, and manage common complications associated with these new agents. This article will use 3 case presentations to discuss some of the new treatment challenges encountered in AML management, with the goal of providing practical guidance to aid the practicing physician.

ImmunoPET, [64Cu]Cu-DOTA-Anti-CD33 PET-CT, Imaging of an AML Xenograft Model.

PURPOSE: Acute myeloid leukemia (AML) is a highly aggressive form of leukemia, which results in poor survival outcomes. Currently, diagnosis and prognosis are based on invasive single-point bone marrow biopsies (iliac crest). There is currently no AML-specific noninvasive imaging method to detect disease, including in extramedullary organs, representing an unmet clinical need. About 85% to 90% of human myeloid leukemia cells express CD33 cell surface receptors, highlighting CD33 as an ideal candidate for AML immunoPET. EXPERIMENTAL DESIGN: We evaluated whether [64Cu]Cu-DOTA-anti-CD33 murine mAb can be used for immunoPET imaging of AML in a preclinical model. MicroCT was adjusted to detect spatial/anatomical details of PET activity. For translational purposes, a humanized anti-CD33 antibody was produced; we confirmed its ability to detect disease and its distribution. We reconfirmed/validated CD33 antibody-specific targeting with an antibody-drug conjugate (ADC) and radioimmunotherapy (RIT). RESULTS: [64Cu]Cu-DOTA-anti-CD33-based PET-CT imaging detected CD33+ AML in mice with high sensitivity (95.65%) and specificity (100%). The CD33+ PET activity was significantly higher in specific skeletal niches [femur (P < 0.00001), tibia (P = 0.0001), humerus (P = 0.0014), and lumber spine (P < 0.00001)] in AML-bearing mice (over nonleukemic control mice). Interestingly, the hybrid PET-CT imaging showed high disease activity in the epiphysis/metaphysis of the femur, indicating regional spatial heterogeneity. Anti-CD33 therapy using newly developed humanized anti-CD33 mAb as an ADC (P = 0.02) and [225Ac]Ac-anti-CD33-RIT (P < 0.00001) significantly reduced disease burden over that of respective controls. CONCLUSIONS: We have successfully developed a novel anti-CD33 immunoPET-CT-based noninvasive modality for AML and its spatial distribution, indicating a preferential skeletal niche.

A glycal-based photoaffinity probe that enriches sialic acid binding proteins.

To identify sialic acid binding proteins from complex proteomes, three photocrosslinking affinity-based probes were constructed using Neu5Ac (5 and 6) and Neu5Ac2en (7) scaffolds. Kinetic inhibition assays and Western blotting revealed the Neu5Ac2en-based 7 to be an effective probe for the labeling of a purified gut microbial sialidase (BDI_2946) and a purified human sialic acid binding protein (hCD33). Additionally, LC-MS/MS affinity-based protein profiling verified the ability of 7 to enrich a low-abundance sialic acid binding protein (complement factor H) from human serum thus validating the utility of this probe in a complex context.

Early T precursor acute lymphoblastic leukaemia/lymphoma shows differential immunophenotypic characteristics including frequent CD33 expression and in vitro response to targeted CD33 therapy.

The differential immunophenotypic characteristics of early T precursor (ETP) acute lymphoblastic leukaemia/lymphoma (ALL) remain incompletely characterized. The study group (n = 142) included 106 (74·7%) men and 36 (25·3%) women with a median age of 34·9 years (range, 2-79) at diagnosis. Patients were subtyped by flow cytometry immunophenotyping as follows: 33 (23·2%) ETP; 32 (22·5%) early non-ETP; 60 (42·2%) thymic; and 17 (12·1%) mature. Excepting definitional markers, there was a significant differential expression of the markers CD2, CD10, CD33 and TdT between ETP-ALL and non-ETP-ALL. Positive CD33 expression (≥20% of leukaemic blasts) was detected in 21/33 (63%) ETP-ALL compared with 17/95 (17·9%) non-ETP-ALL (P < 0·001). Notably, targeted anti-CD33 therapy with IMGN779 resulted in significant growth inhibition and increased apoptosis in ETP-ALL cells in vitro. An 11-marker T-ALL immunophenotype score discriminated reliably between ETP and non-ETP ALL. Longitudinal analysis of ETP-ALL cases in this study demonstrated that the immunophenotype may be occasionally dynamic but is largely stable over the disease course. In summary, identification of ETP-ALL might be enhanced by using an 11-marker T-ALL immunophenotype score. CD33 expression is frequent in ETP-ALL, and in vitro data suggest that exploring anti-CD33 therapy in ETP-ALL is warranted.

The EMA Review of Mylotarg (Gemtuzumab Ozogamicin) for the Treatment of Acute Myeloid Leukemia.

On February 22, 2018, the Committee for Medicinal Products for Human Use (CHMP) adopted a positive opinion, recommending the granting of a marketing authorization for the medicinal product gemtuzumab ozogamicin (Mylotarg; Pfizer, New York City, NY), intended for the treatment of acute myeloid leukemia. Mylotarg was designated as an orphan medicinal product on October 18, 2000. The applicant for this medicinal product was Pfizer Limited (marketing authorization now held by Pfizer Europe MA EEIG).The demonstrated benefit with Mylotarg is improvement in event-free survival. This has been shown in the pivotal ALFA-0701 (MF-3) study. In addition, an individual patient data meta-analysis from five randomized controlled trials (3,325 patients) showed that the addition of Mylotarg significantly reduced the risk of relapse (odds ratio [OR] 0.81; 95% CI: 0.73-0.90; p = .0001), and improved overall survival at 5 years (OR 0.90; 95% CI: 0.82-0.98; p = .01) [Lancet Oncol 2014;15:986-996]. The most common (>30%) side effects of Mylotarg when used together with daunorubicin and cytarabine are hemorrhage and infection.The full indication is as follows: "Mylotarg is indicated for combination therapy with daunorubicin (DNR) and cytarabine (AraC) for the treatment of patients age 15 years and above with previously untreated, de novo CD33-positive acute myeloid leukemia (AML), except acute promyelocytic leukemia (APL)."The objective of this article is to summarize the scientific review done by the CHMP of the application leading to regulatory approval in the European Union. The full scientific assessment report and product information, including the Summary of Product Characteristics, are available on the European Medicines Agency website (www.ema.europa.eu). IMPLICATIONS FOR PRACTICE: This article reflects the scientific assessment of Mylotarg (gemtuzumab ozogamicin; Pfizer, New York City, NY) use for the treatment of acute myeloid leukemia based on important contributions from the rapporteur and co-rapporteur assessment teams, Committee for Medicinal Products for Human Use members, and additional experts following the application for a marketing authorization from the company. It's a unique opportunity to look at the data from a regulatory point of view and the importance of assessing the benefit-risk.

Population Pharmacokinetic Modeling of Gemtuzumab Ozogamicin in Adult Patients with Acute Myeloid Leukemia.

BACKGROUND AND OBJECTIVE: Gemtuzumab ozogamicin is an antibody-drug conjugate composed of the anti-CD33 monoclonal antibody hP67.6 covalently linked to N-acetyl-gamma-calicheamicin dimethylhydrazide, a potent cytotoxic antibiotic. The aim of this study was to characterize the population pharmacokinetics of gemtuzumab ozogamicin, represented by total hP67.6 antibody and unconjugated calicheamicin, in adult patients with acute myeloid leukemia to support drug dosing strategies and explore intrinsic and extrinsic factors that may influence exposure. Pharmacokinetic data from seven previous phase I and II studies in adult patients with relapsed, refractory, or de novo acute myeloid leukemia were integrated and analyzed using nonlinear mixed-effects modeling. METHODS: The pharmacokinetics of total hP67.6 antibody was described in 407 patients (5643 concentrations) who received gemtuzumab ozogamicin doses ranging from 0.25 to 9 mg/m2 using a two-compartment model with linear and time-dependent clearance components. The pharmacokinetics of unconjugated calicheamicin was characterized in 338 patients (4281 concentrations) using a two-compartment model with an input rate of formation dependent on the amount of hP67.6 eliminated. No statistically significant baseline covariates (sex, albumin, bone marrow, and peripheral blast percentage) demonstrated a clinically meaningful impact. RESULTS AND CONCLUSION: Total hP67.6 antibody disposition did not appear altered in patients with mild or moderate renal disease or hepatic impairment. Gemtuzumab ozogamicin was approved for the treatment of acute myeloid leukemia by the US Food and Drug Administration in September 2017. The model-based simulations described here provided a pharmacokinetic rationale for the approved dosing regimen of 3 mg/m2 on days 1, 4, and 7, and served as the basis for all exposure-response modeling included in the recent Biologics License Application submission. Clinical trials identifiers: 0903A1-101-US; 0903A1-103-JA; 0903B1-201-US/CA (NCT00003131); 0903B1-202-EU; 0903B1-203-US/EU (NCT00003673); 0903B1-205-US/EU/AU (NCT00037596); and 0903B1-206-US/EU/AU (NCT00037583).

Population Pharmacokinetics of Gemtuzumab Ozogamicin in Pediatric Patients with Relapsed or Refractory Acute Myeloid Leukemia.

BACKGROUND AND OBJECTIVE: To date, the population pharmacokinetics (popPK) of gemtuzumab ozogamicin (GO), a CD33-directed antibody-drug conjugate consisting of hP67.6 antibody linked to N-acetyl gamma calicheamicin used in the treatment of acute myeloid leukemia (AML), has not been characterized in pediatric patients. This report describes the popPK of GO following intravenous administration in 29 pediatric patients aged ≤ 17 years with relapsed or refractory AML who were enrolled in the 0903A1-102-US phase I/II study. METHODS: The pharmacokinetics (PK) of GO, as represented by total hP67.6 antibody, were described by a two-compartment model with two clearance components: a linear clearance (CL1) and time-dependent clearance that includes a decay coefficient. The PK of unconjugated calicheamicin (UC; payload) were described by a two-compartment model with CL1 and an input rate of formation based on antibody rate of elimination. Allometric scaling was included in both models, with baseline body weight as a fixed effect on CL1 and central volume. RESULTS AND CONCLUSIONS: PK parameters for hP67.6 and UC were not significantly affected by any of the available demographic factors and safety laboratory values tested as covariates (except baseline body weight). Simulations to compare GO dosing regimens (6, 7.5, and 9 mg/m2 on days 1 and 15 versus, 3 mg/m2 fractionated dosing on days 1, 4, and 7) were performed, showing that total antibody and UC trough concentrations were maintained at higher concentrations during treatment following the more frequent dosing than following the original regimen. STUDY IDENTIFIER: 0903A1-102-US.