Phase 1 study of anti-CD47 monoclonal antibody CC-90002 in patients with relapsed/refractory acute myeloid leukemia and high-risk myelodysplastic syndromes

CC-90002 is an anti-CD47 antibody that inhibits CD47-SIRPα interaction and enables macrophage-mediated killing of tumor cells in hematological cancer cell lines. In this first clinical, phase 1, dose-escalation and -expansion study (CC-90002-AML-001; NCT02641002), we evaluated CC-90002 in patients with relapsed/refractory acute myeloid leukemia (AML) or high-risk myelodysplastic syndromes (MDS). CC-90002 was administered in escalating doses of 0.1-4.0 mg/kg, using a modified 3 + 3 design. Primary endpoints included dose-limiting toxicities (DLTs), non-tolerated dose (NTD), maximum tolerated dose (MTD), and recommended phase 2 dose. Secondary endpoints included preliminary efficacy, pharmacokinetics, and presence/frequency of anti-drug antibodies (ADAs). Between March 2016 and July 2018, 28 patients were enrolled (24 with AML and 4 with MDS) at 6 sites across the USA. As of July 18, 2018, all patients had discontinued, mainly due to death or progressive disease. The most common treatment-emergent adverse events were diarrhea (46.4%), thrombocytopenia (39.3%), febrile neutropenia (35.7%), and aspartate aminotransferase increase (35.7%). Four patients experienced DLTs (1 patient had grade 4 disseminated intravascular coagulation and grade 5 cerebral hemorrhage, 1 had grade 3 purpura, 1 had grade 4 congestive cardiac failure and grade 5 acute respiratory failure, and another had grade 5 sepsis). The NTD and MTD were not reached. No objective responses occurred. CC-90002 serum exposure was dose-dependent. ADAs were present across all doses, and the proportion of ADA-positive patients in cycle 1 increased over time. Despite no unexpected safety findings, the CC-90002-AML-001 study was discontinued in dose escalation for lack of monotherapy activity and evidence of ADAs. However, as other anti-CD47 agents in clinical trials are showing promising early results for AML and MDS, understanding preclinical and clinical differences between individual agents in this class will be of high importance.

Population Pharmacokinetics and Exposure-Response Relationship of Luspatercept, an Erythroid Maturation Agent, in Anemic Patients With β-Thalassemia

β‐Thalassemia is an inherited blood disorder resulting from defects in hemoglobin production, leading to premature death of red blood cells (RBCs) or their precursors. Patients with transfusion‐dependent β‐thalassemia often need lifelong regular RBC transfusions to maintain adequate hemoglobin levels. Frequent transfusions may lead to iron overload and organ damage. Thus, there is a large unmet need for alternative therapies. Luspatercept, a first‐in‐class erythroid maturation agent, is the first approved therapy in the United States for the treatment of anemia in adult patients with β‐thalassemia who require regular RBC transfusions. The population pharmacokinetics and exposure‐response relationship of luspatercept were evaluated in 285 patients with β‐thalassemia. Luspatercept displayed linear and time‐invariant pharmacokinetics when administered subcutaneously once every 3 weeks. Body weight was the only clinically relevant covariate of luspatercept clearance, favoring weight‐based dosing. Magnitude and frequency of hemoglobin increase, if not influenced by RBC transfusions, was positively correlated with luspatercept area under the serum concentration‐time curve (AUC), 0.2‐1.25 mg/kg, whereas a significant reduction in RBC units transfused was observed in frequently transfused patients. The probability of achieving ≥33% or ≥50% reduction in RBC transfusion burden was similar across the time‐averaged AUC (0.6‐1.25 mg/kg), with the 1 mg/kg starting dose sufficient for most early responders (71%‐80%). Increasing luspatercept AUC (0.2‐1.25 mg/kg) did not increase incidence or severity of treatment‐emergent adverse events. These results provide a positive benefit‐risk profile for the recommended luspatercept doses (1‐1.25 mg/kg) in treating adult patients with β‐thalassemia who require regular RBC transfusions.

Population Pharmacokinetics and Exposure-Response of Luspatercept, an Erythroid Maturation Agent, in Anemic Patients With Myelodysplastic Syndromes

Luspatercept is a recombinant fusion protein that enhances late‐stage erythroid maturation. This report describes the population pharmacokinetics and exposure–response relationship of luspatercept in 260 patients with anemia due to myelodysplastic syndromes. Luspatercept displayed linear and time‐invariant pharmacokinetics over a dose range of 0.125–1.75 mg/kg administered subcutaneously once every 3 weeks. Body weight was the only clinically relevant covariate of luspatercept exposure, supporting the weight‐based dosing. The probability of achieving transfusion independence ≥ 8 weeks increased with time‐averaged luspatercept serum exposure, reaching the plateau at doses 1.0–1.75 mg/kg. The probability of achieving multiple efficacy end points increased with slower luspatercept clearance, independent of effects of luspatercept exposure or disease characteristics. The probability of experiencing severe treatment‐emergent adverse events decreased with increasing luspatercept exposure, especially during long‐term treatment. These results provide a positive benefit–risk profile for the titration‐to‐response dose regimen (1.0–1.75 mg/kg) recommended for this population.

Current Approaches for Absorption, Distribution, Metabolism, and Excretion Characterization of Antibody-Drug Conjugates: An Industry White Paper

An antibody-drug conjugate (ADC) is a unique therapeutic modality composed of a highly potent drug molecule conjugated to a monoclonal antibody. As the number of ADCs in various stages of nonclinical and clinical development has been increasing, pharmaceutical companies have been exploring diverse approaches to understanding the disposition of ADCs. To identify the key absorption, distribution, metabolism, and excretion (ADME) issues worth examining when developing an ADC and to find optimal scientifically based approaches to evaluate ADC ADME, the International Consortium for Innovation and Quality in Pharmaceutical Development launched an ADC ADME working group in early 2014. This white paper contains observations from the working group and provides an initial framework on issues and approaches to consider when evaluating the ADME of ADCs.

Antibiofilm activity of three irrigation protocols activated by ultrasonic, diode laser or Er:YAG laser in vitro

AIM

To investigate the impact of three irrigation protocols, activated by three different methods, on mature biofilms of Enterococcus faecalis in vitro.

METHODOLOGY

Root canals in 280 single-rooted teeth were instrumented using a rotary Ni-Ti system. Biofilms of E. faecalis were generated based on a previously established protocol. Samples were randomly divided into three experimental (n = 80) and one control (n = 40) group based on the irrigation protocol employed: group 1 (NaOCl + Etidronic acid), 1 : 1 mixture of 6% NaOCl and 18% etidronic acid; group 2 (NaOCl-EDTA), 3% NaOCl followed by 17% EDTA; group 3 (NaOCl-EDTA-NaOCl), 3% NaOCl followed by 17% EDTA and a final flush of 3% NaOCl. Saline served as the control. Samples were further divided into four subgroups (n = 20) based on the activation method: subgroup A, no activation; subgroup B, ultrasonic activation; group C, diode laser; group D, Er:YAG laser. Confocal laser scanning microscopy was used to assess bacterial viability in situ. Root dentine powder was obtained for determining the colony-forming units (CFU mL(-1) ). Data were analysed by appropriate statistical analyses with P = 0.05.

RESULTS

All experimental irrigation protocols caused complete destruction of the biofilm in the root canal lumen. Within the dentinal tubules, all groups had a significantly higher percentage of dead bacteria than the saline control (P < 0.05). There was no significant difference between NaOCl + etidronic acid and NaOCl-EDTA-NaOCl (P > 0.05), whereas both groups brought about more bacterial reduction than NaOCl-EDTA (P < 0.05). There was no significant difference between diode laser and Er:YAG laser in any of the groups (P > 0.05). Both diode and Er:YAG laser were more effective than ultrasonic activation and conventional syringe irrigation in reducing E. fecalis biofilms (P < 0.05).

CONCLUSIONS

The use of NaOCl after or in combination with a chelator caused the greatest reduction of E. faecalis. Diode laser and Er:YAG laser activation were superior to ultrasonics in dentinal tubule disinfection.

Ligand binding assay critical reagents and their stability: recommendations and best practices from the Global Bioanalysis Consortium Harmonization Team

The L4 Global Harmonization Team on reagents and their stability focused on the management of critical reagents for pharmacokinetic, immunogenicity, and biomarker ligand binding assays. Regulatory guidance recognizes that reagents are important for ligand binding assays but do not address numerous aspects of critical reagent life cycle management. Reagents can be obtained from external vendors or developed internally, but regardless of their source, there are numerous considerations for their reliable long-term use. The authors have identified current best practices and provided recommendations for critical reagent lot changes, stability management, and documentation.

Target-mediated drug disposition and prolonged liver accumulation of a novel humanized anti-CD81 monoclonal antibody in cynomolgus monkeys

CD81 is an essential receptor for hepatitis C virus (HCV). K21 is a novel high affinity anti-CD81 antibody with potent broad spectrum anti-HCV activity in vitro. The pharmacokinetics (PK), pharmacodynamics and liver distribution of K21 were characterized in cynomolgus monkeys after intravenous (i.v.) administration of K21. Characteristic target-mediated drug disposition (TMDD) was shown based on the PK profile of K21 and a semi-mechanistic TMDD model was used to analyze the data. From the TMDD model, the estimated size of the total target pool at baseline (V(c) • R(base)) is 16 nmol/kg and the estimated apparent Michaelis-Menten constant (KM) is 4.01 nM. A simulation using estimated TMDD parameters indicated that the number of free receptors remains below 1% for at least 3 h after an i.v. bolus of 7 mg/kg. Experimentally, the availability of free CD81 on peripheral lymphocytes was measured by immunostaining with anti-CD81 antibody JS81. After K21 administration, a dose- and time-dependent reduction in free CD81 on peripheral lymphocytes was observed. Fewer than 3% of B cells could bind JS81 3 h after a 7 mg/kg dose. High concentrations of K21 were found in liver homogenates, and the liver/serum ratio of K21 increased time-dependently and reached ~160 at 168 h post-administration. The presence of K21 bound to hepatocytes was confirmed by immunohistochemistry. The fast serum clearance of K21 and accumulation in the liver are consistent with TMDD. The TMDD-driven liver accumulation of the anti-CD81 antibody K21 supports the further investigation of K21 as a therapeutic inhibitor of HCV entry.

High-throughput phagocytosis assay utilizing a pH-sensitive fluorescent dye

We describe a development of a novel high-throughput phagocytosis assay based on a pH-sensitive cyanine dye, CypHer5E™, which is maximally fluorescent in an acidic environment. This dye is ideally suited for the study of phagocytosis because of the acidic conditions generated in the intracellular phagocytic vesicles after particle uptake. Use of CypHer5E-labeled particles results in greatly reduced background from noninternalized particles and makes the assay more robust. Additionally, CypHer5E-labeled particles are resistant to fluorescence quenching observed in the aggressive and acidic environment of the phagosome with traditional dyes. The CypHer5E-based assay has been shown to work reliably in a variety of cell types, including primary human monocytes, primary human dendritic cells, primary human endothelial cells, human monocytic THP-1 cell line, and human/mouse hybrid macrophage cell line WBC264-9C. Inhibition of CypHer5E bead uptake by cytochalasin D was studied, and the 50% inhibition concentration (IC50) was determined. The assay was performed in 96- and 384-well formats, and it is appropriate for high-throughput cellular screening of processes and compounds affecting phagocytosis. The CypHer5E phagocytosis assay is superior to existing protocols because it allows easy distinction of true phagocytosis from particle adherence and can be used in microscopy-based measurement of phagocytosis.

Unique architecture of the plastid ribosomal RNA operon promoter recognized by the multisubunit RNA polymerase in tobacco and other higher plants

Expression of the plastid rRNA operon (rrn) during development is highly regulated at the level of transcription. The plastid rrn operon in most higher plants is transcribed by the plastid-encoded RNA polymerase (PEP), the multisubunit plastid RNA polymerase from PrrnP1, a sigma(70)-type promoter with conserved -10 and -35 core promoter elements. To identify functionally important sequences, the tobacco PrrnP1 was dissected in vivo and in vitro. Based on in vivo deletion analysis, sequences upstream of nucleotide -83 do not significantly contribute to promoter function. The in vitro analyses identified an essential hexameric sequence upstream of the -35 element (GTGGGA; the rRNA operon upstream activator [RUA]) that is conserved in monocot and dicot species and suggested that the -10 element plays only a limited role in PrrnP1 recognition. Mutations in the initial transcribed sequence (+9 to +14) enhanced transcription, the characteristic of strong promoters in prokaryotes. We propose that sigma interaction with the -10 element in PrrnP1 is replaced in part by direct PEP-RUA (protein-DNA) interaction or by protein-protein interaction between the PEP and an RUA binding transcription factor.

Epigenetic inhibition of lysyl oxidase transcription after transformation by ras oncogene

Lysyl oxidase is an extracellular enzyme involved in connective tissue maturation that also acts as a phenotypic suppressor of the ras oncogene. To understand how this suppressor is controlled, gene transcription was studied and the promoter was characterized. Nuclear runoff transcription assays indicated that the markedly reduced amounts of lysyl oxidase message detected after ras transformation resulted from inhibition of lysyl oxidase transcription. Interferon-mediated phenotypic reversion of ras transformed cells, in which the ras oncogene continued to be expressed, was accompanied by the restoration of lysyl oxidase transcription. Reporter gene assay of a transfected mouse lysyl oxidase promoter indicated that it was active in the transformed background, despite the silencing of the endogenous lysyl oxidase promoter. The detection of comparable amounts of mRNA for transcription factors IRF-1 and IRF-2 in normal and ras-transformed cell lines suggests that the differential transcription of lysyl oxidase was not due to regulation of IRFs. Lysyl oxidase promoter activity was localized to a 126 bp region that includes two consensus TATA boxes with associated confirmed cap signals. Analysis of a human lysyl oxidase promoter sequence indicated similar promoter elements and extensive sequence identity with the mouse promoter. The binding of transcription factor AP2 to sites predicted in the control region was confirmed by DNase footprinting. Lysyl oxidase transcription was stimulated by dexamethasone treatment of cells, but this effect could not be assigned within the approximately 3 kb region tested in reporter gene constructs. The promoter activity of the lysyl oxidase reporter gene construct was completely abolished by in vitro DNA methylation, suggesting that the transcriptional suppression after transformation by the ras oncogene may involve DNA methylation.

The phage-type PclpP-53 plastid promoter comprises sequences downstream of the transcription initiation site

The existence of a phage-type plastid transcription machinery (NEP), related to the mitochondrial RNA polymerase, has been recognized only recently. Here we report the cis sequences required for transcription initiation by the phage-type enzyme. The promoter chosen for the study, PclpP-53, is well expressed in tobacco leaves, unlike most NEP promoters. Promoter definition was carried out in vivo , in transplastomic tobacco plants expressing a uidA reporter gene from PclpP-53 promoter derivatives. We report here that sequences from -5 to +25 (relative to the transcription initiation site) are sufficient to support specific transcription initiation. Requirement of sequences downstream of the transcription initiation site contrasts with mitochondrial promoters, which have conserved sequences predominantly upstream. The promoter defined here is conserved in liverworts and conifers, indicating that the phage-type transcription machinery appeared in plastids early on during the evolution of land plants. The PclpP-53 promoter sequences are present in rice but do not function, suggesting that PclpP-53 recognition specificity is absent in some monocots.

Transcription from heterologous rRNA operon promoters in chloroplasts reveals requirement for specific activating factors

The plastid rRNA (rrn) operon in chloroplasts of tobacco (Nicotiana tabacum), maize, and pea is transcribed by the plastid-encoded plastid RNA polymerase from a sigma70-type promoter (P1). In contrast, the rrn operon in spinach (Spinacia oleracea) and mustard chloroplasts is transcribed from the distinct Pc promoter, probably also by the plastid-encoded plastid RNA polymerase. Primer-extension analysis reported here indicates that in Arabidopsis both promoters may be active. To understand promoter selection in the plastid rrn operon in the different species, we have tested transcription from the spinach rrn promoter in transplastomic tobacco and from the tobacco rrn promoter in transplastomic Arabidopsis. Our data suggest that transcription of the rrn operon depends on species-specific factors that facilitate transcription initiation by the general transcription machinery.