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.

Dimeric Ankyrin with Inverted Module Promotes Bifunctional Property in Capturing Capsid to Impede HIV-1 Replication.

Several anti-HIV scaffolds have been proposed as complementary treatments to highly active antiretroviral therapy. AnkGAG1D4, a designed ankyrin repeat protein, formerly demonstrated anti-HIV-1 replication by interfering with HIV-1 Gag polymerization. However, the improvement of the effectiveness was considered. Recently, the dimeric molecules of AnkGAG1D4 were accomplished in enhancing the binding activity against HIV-1 capsid (CAp24). In this study, the interaction of CAp24 against the dimer conformations was elucidated to elaborate the bifunctional property. The accessibility of the ankyrin binding domains was inspected by bio-layer interferometry. By inverting the second module of dimeric ankyrin (AnkGAG1D4NC-CN), the CAp24 interaction KD was significantly reduced. This reflects the capability of AnkGAG1D4NC-CN in simultaneously capturing CAp24. On the contrary, the binding activity of dimeric AnkGAG1D4NC-NC was indistinguishable from the monomeric AnkGAG1D4. The bifunctional property of AnkGAG1D4NC-CN was subsequently confirmed in the secondary reaction with additional p17p24. This data correlates with the MD simulation, which suggested the flexibility of the AnkGAG1D4NC-CN structure. The CAp24 capturing capacity was influenced by the distance of the AnkGAG1D4 binding domains to introduce the avidity mode of AnkGAG1D4NC-CN. Consequently, AnkGAG1D4NC-CN showed superior potency in interfering with HIV-1 NL4-3 WT and HIV-1 NL4-3 MIRCAI201V replication than AnkGAG1D4NC-NC and an affinity improved AnkGAG1D4-S45Y.

Thermostable designed ankyrin repeat proteins (DARPins) as building blocks for innovative drugs.

Designed ankyrin repeat proteins (DARPins) are antibody mimetics with high and mostly unexplored potential in drug development. By using in silico analysis and a rationally guided Ala scanning, we identified position 17 of the N-terminal capping repeat to play a key role in overall protein thermostability. The melting temperature of a DARPin domain with a single full-consensus internal repeat was increased by 8 °C to 10 °C when Asp17 was replaced by Leu, Val, Ile, Met, Ala, or Thr. We then transferred the Asp17Leu mutation to various backgrounds, including clinically validated DARPin domains, such as the vascular endothelial growth factor-binding domain of the DARPin abicipar pegol. In all cases, these proteins showed improvements in the thermostability on the order of 8 °C to 16 °C, suggesting the replacement of Asp17 could be generically applicable to this drug class. Molecular dynamics simulations showed that the Asp17Leu mutation reduces electrostatic repulsion and improves van-der-Waals packing, rendering the DARPin domain less flexible and more stable. Interestingly, this beneficial Asp17Leu mutation is present in the N-terminal caps of three of the five DARPin domains of ensovibep, a SARS-CoV-2 entry inhibitor currently in clinical development, indicating this mutation could be partly responsible for the very high melting temperature (>90 °C) of this promising anti-COVID-19 drug. Overall, such N-terminal capping repeats with increased thermostability seem to be beneficial for the development of innovative drugs based on DARPins.