New nanoligomer approach to treat severe COVID-19

The lack of antiviral treatments for respiratory infections has become evident with the emergence and global spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Study: Nanoligomers targeting human miRNA for treatment of severe COVID-19 are safe and non-toxic in mice. Image Credit: cherezoff/Shutterstock.com

Background

SARS-CoV-2 is a positive-strand enveloped ribonucleic acid (RNA) virus that binds to human angiotensin-converting enzyme receptor 2 (ACE2) and transmembrane protease serine receptor 2 (TMPRSS2 ), both of which are primarily located in the airways and lungs. SARS-CoV-2 infection then leads to coronavirus disease 2019 (COVID-19).

Severe cases of COVID-19 can lead to acute respiratory distress syndrome, cytokine storm syndrome, and respiratory failure. COVID-19 can also damage the liver, cardiovascular system, kidneys, gastrointestinal tract, and nervous system.

Although several vaccines have been developed against SARS-CoV-2, the continued emergence of new variants, lack of vaccine availability, and/or low vaccination rates continue to threaten the safety of the global population against COVID- 19. In addition to the high mortality rates of COVID-19, the potential long-term effects that have been reported in people who have recovered from the disease also constitute a considerable public health concern.

Antisense oligonucleotides (ASO) are synthetic single-stranded nucleotides that can bind to organic nucleic acids and molecules such as synthetic small interfering RNAs (siRNAs), peptide nucleic acids (PNAs), and morpholinos.

PNAs consist of nucleobases on a pseudo-peptide backbone and have a long live half life. Additionally, PNAs can bind strongly to both RNA and DNA due to an uncharged backbone and therefore can be used as inhibitory therapeutics that bind much more tightly to their target compared to technologies DNA based.

MicroRNAs (miRNAs) are small non-coding RNAs that perform many functions, including post-transcriptional regulation of genes associated with infections. Elevated levels of miRNA 2392 (miR-2392) have been observed in humans following severe SARS-CoV-2 infection.

Additionally, miR-2392 has also been reported to aid viral replication and limit host immune response to SARS-Cov-2. Hypoxia, upregulation of inflammation, glycolysis, and mitochondrial suppression have also been observed with elevated levels of miR-2392.

Previous studies have reported that PNAs can bind miRNAs and modulate immune responses, detect biomarkers, fight tumors, or serve as bio-supramolecular tags. However, the use of antisense technologies presents several challenges, as nucleic acids require a delivery vehicle in order to pass into cells.

One approach to overcome this challenge may be the use of nanoligomers. Nanoligomers contain gold nanoparticles that improve their transport and distribution throughout the body.

Previous studies with nanoligomers have indicated lower levels of SARS-CoV-2, as well as no toxicity, making it a suitable treatment option. However, more knowledge is needed about their live biodistribution, safety and pharmacokinetics (PK).

A new ACS Sciences and engineering of biomaterials The study discusses the biodistribution and safety of a novel nanoligomer called SBCoV207, which was used to target miR-2392 in a mouse model.

About the study

The current study involved the design and synthesis of nanoligomers followed by surface plasmon resonance (SPR) measurements. SARS-CoV-2 was propagated and viral titers were determined by plaque assay in Vero E6 cells. This was followed by a quantitative reverse transcription polymerase chain reaction (PCR) assay for measurement of SARS-CoV-2 RNA levels, as well as immunofluorescence of the viral nucleocapsid protein ( NOT).

A five-day intranasal safety study was performed in eight- to 12-week-old female BALB/c mice. Doses of SBCoV207 of 1, 2, 5 or 10 mg/kg were administered to each group intranasally and monitored for five days before being euthanized.

Blood and urine samples were taken before euthanasia, while tissue samples were taken afterwards. An enzyme immunoassay (ELISA) was used to determine serum levels of tumor necrosis factor α (TNF-α), albumin and interleukin 6 (IL-6). Histological analysis of the spleen, lungs, kidneys and liver was carried out on mice having received either 10 mg/kg of SBCoV207, or the control treatment.

A 24-hour intranasal biodistribution study was performed using blood and urine samples collected prior to euthanasia at one, three, six, or 24 hours after administration of SBCoV207. Subsequently, intraperitoneal and intravenous safety and biodistribution studies were conducted. Finally, the concentrations of SBCoV207 in different organic tissues were calculated.

Study results

SBCoV207 was found to inhibit viral infection, as well as lead to a ten-fold reduction in viral messenger RNA (mRNA) levels compared to missense nanoligomers. SPR measurements indicated strong binding of SBCoV207 to the miR2392 binding sequence compared to missense nanoligomers. However, none of the mice showed weight change and continued to drink and eat normally after SBCoV207 administration.

Histological studies indicated alveolar hemorrhage in the lungs, as well as subacute inflammation in the liver of SBCoV207-treated and control mice. Albumin, TNF-α and IL-6 levels were normal in treated and control mice. Additionally, most chemokine and cytokine levels were below the limit of detection (LOD), even 24 hours after SBCoV207 administration.

The highest levels of nanoligomers were found in kidneys, urine, lungs and whole blood. SBCoV207 was eliminated by urinary excretion a few hours after administration and showed low accumulation in organs after five days, regardless of the route of administration. Notably, no toxicity was observed at any time between one hour and five days after administration.

Steady-state concentration of SBCoV207 was achieved in spleen and liver by intraperitoneal and intravenous routes. Between 500 and 700 ng/g of SBCoV207 tissue was observed after five days in liver, urine and spleen, while even lower concentrations were reported in other organic tissues. Additionally, two mice showed elevated levels of SBCoV207 in the lungs and one in the kidneys five days after administration.

conclusion

The present study determined that SBCoV207 nanoligomer treatment showed no toxicity in mice regardless of their routes of administration. SBCoV207 exhibited high biodistribution in the lungs and site of infection; however, its accumulation in organs has been observed to be low.

Taken together, nanoligomer therapy has the potential to be effective and safe for treating severe COVID-19, especially in areas with low vaccination rates or where new variants have been detected. This approach can also help provide a strategy to mitigate future pandemics.[if–>

Journal reference:

  • McCollum, CR, Courtney, CM, O’Connor, NJ, et al. (2022). Nanoligomers targeting human miRNA for the treatment of severe COVID-19 are safe and non-toxic in mice. ACS Sciences and engineering of biomaterials. doi:10.1021/acsbiomaterials.2c00510.

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