Safety and efficacy of intra-erythrocyte dexamethasone sodium phosphate in children with ataxia telangiectasia (ATTeST): a multicentre, randomised, double-blind, placebo-controlled phase 3 trial.

BACKGROUND: Ataxia telangiectasia is a multisystem disorder with progressive neurodegeneration. Corticosteroids can improve neurological functioning in patients with the disorder but adrenal suppression and symptom recurrence on treatment discontinuation has limited their use, prompting the development of novel steroid delivery systems. The aim of the ATTeST study was to evaluate the efficacy and safety of intra-erythrocyte delivery of dexamethasone sodium phosphate compared with placebo in children with ataxia telangiectasia. METHODS: This multicentre, randomised, double-blind, placebo-controlled, phase 3 trial was done at 22 centres in 12 countries (Australia, Belgium, Germany, India, Israel, Italy, Norway, Poland, Spain, Tunisia, the UK, and the USA). Eligible participants were children aged 6 years or older weighing more than 15 kg who met clinical criteria for ataxia telangiectasia but who had preserved autonomous gait. Participants were randomly assigned (1:1:1) to low-dose (approximately 5-10 mg), or high-dose (approximately 14-22 mg) intra-erythrocyte dexamethasone sodium phosphate, or placebo, using an independent interactive web response system, with minimisation for sex and age (6-9 years vs ≥10 years). Intravenous intra-erythrocyte dexamethasone sodium phosphate was administered once a month for 6 months. Participants, employees of the sponsor, investigators, all raters of efficacy endpoints, and central reviewers were masked to treatment assignment and dose allocations. The primary efficacy endpoint was change in the modified International Cooperative Ataxia Rating Scale (mICARS) from baseline to month 6, assessed in the modified intention-to-treat (mITT) population, which included all randomly assigned participants who received at least one dose of study drug and had at least one post-baseline efficacy assessment. This trial is registered with Clinicaltrials.gov (NCT02770807) and is complete. FINDINGS: Between March 2, 2017, and May 13, 2021, 239 children were assessed for eligibility, of whom 176 were randomly assigned. One patient assigned to high-dose intra-erythrocyte dexamethasone sodium phosphate did not initiate treatment. 175 patients received at least one dose of treatment (59 patients received the low dose and 57 received the high dose of intra-erythrocyte dexamethasone sodium phosphate, and 59 received placebo). The mITT population comprised 164 participants (56 children in the low-dose group, 54 children in the high-dose group, and 54 in the placebo group). Compared with the placebo group, no differences were identified with regard to change in mICARS score from baseline to 6 months in the low-dose group (least squares mean difference -1·37 [95% CI -2·932 to 0·190]) or the high-dose group (-1·40 [-2·957 to 0·152]; p=0·0765). Adverse events were reported in 43 (73%) of 59 participants in the low-dose group, 47 (82%) of 57 participants in the high-dose group, and 43 (73%) of 59 participants in the placebo group. Serious adverse events were observed in six (10%) of 59 participants in the low-dose group, seven (12%) of 57 participants in the high-dose group, and seven (12%) of 59 participants in the placebo group. There were no reports of hyperglycaemia, hypertension, hirsutism, or Cushingoid appearance in any of the treatment groups, nor any treatment-related deaths. INTERPRETATION: Although there were no safety concerns, the primary efficacy endpoint was not met, possibly related to delays in treatment reducing the number of participants who received treatment as outlined in the protocol, and potentially different treatment effects according to age. Studies of intra-erythrocyte delivery of dexamethasone sodium phosphate will continue in participants aged 6-9 years, on the basis of findings from subgroup analyses from this trial. FUNDING: EryDel and Quince Therapeutics.

A Study of the Pharmacokinetic Properties and the In Vivo Kinetics of Erythrocytes Loaded With Dexamethasone Sodium Phosphate in Healthy Volunteers.

The objectives of this 2-phase study were to elucidate pharmacokinetics (PK), in vivo 24-hour recovery, and red blood cell (RBC) survival properties of RBC-encapsulated dexamethasone sodium phosphate (DSP) prepared using the EryDex System (EDS). The 24-hour RBC recovery and T50 survival phase studied subjects were randomized to receive autologous RBCs loaded with either 15-20 mg DSP (Group 1A) or sham saline (Group 2A). Loaded RBCs were radiolabeled with 51-Cr, and the labeled RBCs were followed over time in vivo. The PK phase evaluated dose levels of 2.5-5 mg (Group 1B) and 15-20 mg (Group 2B) DSP encapsulated in RBCs infused into healthy randomized subjects. The mean ± SD 24-hour RBC recovery was 77.9% ± 3.3% and 72.7% ± 10.5% for Groups 1A and 2A, respectively. The mean ± SD RBC life span was 84.3 ± 8.3 days in Group 1A and 88.9 ± 6.2 days in Group 2A. The PK phase actual DSP loading doses (mean ± SEM) were 4.2 ± 0.27 mg and 16.9 ± 0.90 mg in Groups 1B and 2B, respectively. Release of dexamethasone from RBCs in vivo peaked at 1 hour, and a sustained release of dexamethasone could be detected until 35 days after the single intravenous infusion in Group 2B. The mean RBC in vivo recovery for DSP-loaded processed cells compares similarly to the 24-hour recovery of regulated RBC products intended for transfusion. There was a minimal but acceptable adverse impact on the survival of EDS-processed RBCs. DSP-loaded autologous RBCs, prepared using the EDS, delivered a sustained dose of dexamethasone in vivo.

Ex vivo encapsulation of dexamethasone sodium phosphate into human autologous erythrocytes using fully automated biomedical equipment.

Erythrocyte-based drug delivery systems are emerging as potential new solutions for the release of drugs into the bloodstream. The aim of the present work was to assess the performance of a fully automated process (EDS) for the ex-vivo encapsulation of the pro-drug dexamethasone sodium phosphate (DSP) into autologous erythrocytes in compliance with regulatory requirements. The loading method was based on reversible hypotonic hemolysis, which allows the opening of transient pores in the cell membrane to be crossed by DSP. The efficiency of encapsulation and the biochemical and physiological characteristics of the processed erythrocytes were investigated in blood samples from 34 healthy donors. It was found that the processed erythrocytes maintained their fundamental properties and the encapsulation process was reproducible. The EDS under study showed greater loading efficiency and reduced variability compared to previous EDS versions. Notably, these results were confirmed using blood samples from Ataxia Telangiectasia (AT) patients, 9.33±1.40 and 19.41±2.10mg of DSP (mean±SD, n=134) by using 62.5 and 125mg DSP loading quantities, respectively. These results support the use of the new EDS version 3.2.0 to investigate the effect of erythrocyte-delivered dexamethasone in regulatory trials in patients with AT.

Tissue expression and translational control of rat kynurenine aminotransferase/glutamine transaminase K mRNAs.

Kynurenic acid (KA) is an endogenous glutamate receptor antagonist at the level of the different ionotropic glutamate receptors. One of the enzymes responsible for the production of KA, kynurenine aminotransferase I (KATI), also catalyses the reversible transamination of glutamine to oxoglutaramic acid (GTK, EC 2.6.1.15). The enzyme exists in a cytosolic and in a mitochondrial form because of the presence of two different KATI mRNAs coding for a protein respectively with and without leader sequence targeting the protein into mitochondria. We have cloned from a phage library of rat kidney cDNA four new KATI cDNAs containing different 5' untranslated regions (UTRs). One of the transcripts (+14KATI cDNA) contains an alternative site of initiation of translation. The tissue distribution of the different transcripts was studied by RT-PCR. The study demonstrated that several KATI mRNAs are constitutively expressed in ubiquitous manner, while +14KATI mRNA is present only in kidney. The translational efficiency of the different transcripts was studied in vitro and enzymatic activities were measured in transiently transfected Cos-1 cells. Each KATI mRNA exhibits a different in vitro translational efficiency, which corresponds to different levels of KAT enzymatic activity in transfected cells. Both findings correlate with the predicted accessibility of the ribosomal binding sites of the different mRNAs. The structure of the rat KATI/GTK gene was also studied. The expression of several KATI mRNAs with different 5'UTRs represents an interesting example of transcriptional/translational control on the expression of pyridoxal phosphate (PLP)-dependent aminotransferases.