15 June 2016

The recent outbreak of the mosquito-borne Zika virus in Brazil and French Polynesia has raised major public health concerns with the lack of available medical countermeasures. Most importantly, the spread of Zika virus is associated with the rise in abnormal birth defects including microcephaly and a reported rise Guillan-Barré Syndrome in the region. As a result, there is a need for effective diagnostic applications and therapeutic candidates to help alleviate the burden of Zika virus.

What is Zika Virus?

Zika virus (ZV) belongs to the Flaviviridae family of viruses, which include yellow fever, dengue, West Nile, and Japanese encephalitis viruses (Hemel et al. 2015). This RNA virus is transmitted via insect vectors including mosquitoes (Aedes spp.) and has been reported in minor epidemics across Africa and south Asia since 1947. However in recent years, the rate of infection has soared with some experts predicting a ‘Zika pandemic’ if no action is taken.

Once in the microcirculation, the virus is able to infect permissive cells. Data shows that neuronal cells, including astrocytes, neurons and neuronal progenitor cells are all susceptible to Zika infection, resulting in decreased proliferation and cell death via Caspase-3 activation and cell cycle arrest. Similarly, skin cells surrounding the site of infection are also prone to infection, with fibroblasts, keratinocytes and dendritic cells all showing upregulation of innate immune receptors including TLR3, RIG1, MDA5 and CCL5 (Ramos de Silva & Gao, 2016). Interestingly, Zika infection of skin cells has also been shown to promote autophagy which may promote viral replication and transmission (Hemel et al. 2015). Whilst the receptors and signalling pathways triggered are poorly characterised, several receptors have been shown to be involved including AXL, DC-SIGN and Tyro3 (Ramos de Silva & Gao, 2016).

Current diagnosis

A suspected case of ZV requires the presence of fever and/or rash accompanied by arthralgia, non-purulent conjunctivitis or arthritis. This is supported further via biochemical assays, detecting either anti-Zika IgM antibodies or ZV RNA via PCR. However, firm clinical diagnosis of ZV infection is difficult due to the acute similarities with other closely related viruses (Kelser, 2016).

More recently, the FDA issued an emergency use authorisation for the use of Zika MAC-ELISA to detect the presence of anti-Zika IgM in serum or cerebrospinal fluid to improve the speed of diagnosis. Whilst partially effective, the test is limited by poor specificity to distinguish between IgM raised by Zika infection and the antibodies raised by other closely related species.

New Diagnostics – Aptamers recognising Zika

Viral infections are difficult to detect, especially during early infection when viral copy number is low. The reliance of Zika MAC-ELISA on antibodies presents an opportunity for aptamers to enter the market – namely due to high specificity, affinity and low cost of production. By using aptamers, it is possible to devise biosensors or other diagnostic platforms to detect of early (genetic material, viral Protein) and late (own host antibodies) infection markers (Ruslinda et al. 2013) with a high degree of precision. Moreover, aptamers are also capable of distinguishing between infected and non-infected host cells which aids in recognising active forms of the virus (Labib et al. 2012).

Therapeutic aptamers targeting Zika

The targeting of virus is notoriously difficult for therapeutic providers. Reasons for the lack of effective medications include:

  1. High viral mutation rates
  2. Low specificity
  3. Ability to evade a host’s immune response

Aptamers are well placed to meet these limitations and to target proteins from infected cells and viral components. The host may also be targeted using aptamers to selectively stimulate the immune system and prevent viral infection by increasing anti-viral compounds e.g. IFNs (Wandtke, Wozniak, and Kopinski, 2015).

Several different strategies exist to target Zika using aptamers. These include:

  • Inhibition of viral fusion with the target cell: Aptamers binding to cell surface receptors can prevent viral internalisation. A similar approach has been demonstrated showing the infectious potential of HSV-1 to be reduced in an aptamer dose dependent manner (Gopinath, Hayashi, and Kumar, 2012).
  • Inhibition of viral proteins: The viral genome encodes several enzymes, including those essential for replication and by inhibiting these enzymes, viral replication can be prevented. HCV viral protein (nonstructural protein 5B), RNA-dependant – RNA polymerase is a promising target for aptamer treatment due to its significance for viral replication in the single stranded RNA virus. Studies have shown that an RNA aptamer with anti-polymerase activity reduced viral copy number which positively correlated with aptamer concentration in vitro (Biroccio et al. 2002).
  • Inhibition of nucleic acid sequences: Aptamers are also able to bind to nucleic acids with high specificity. By targeting the viral genome, aptamers can prevent translation or target RNA for degradation by the host cell.

Aptamers sit alongside other therapeutic candidates, including both low (siRNA) and high molecular weight molecules (Monoclonal antibodies). Due to their ability to bind to a wide range of targets – from small molecules through to cells, aptamers are well placed to act as therapeutic candidates, but can also serve to help target existing therapies e.g. siRNA or antibody-drug conjugates.

Aptamers selected as specific antiviral molecules have the potential to transform the diagnostic and therapeutic area for ZV. However no aptamers against ZV have entered the clinical setting and up to this point there are no approved therapeutic candidates to accurately detect and treat ZV. This remains an exciting and unexplored area of research with wide reaching impact.

Aptamer Group

Aptamer Group takes a high-throughput approach using liquid handling robotics and dedicated researchers to identify aptamers against novel and significant targets. We are committed to finding the perfect aptamers to your target and use a proprietary selection technique to identify high affinity aptamers with specificity in as short as 3 months.

Aptamer Group’s biomarker discovery, diagnostic and therapeutic divisions aim to conduct further research in the prevention, diagnosis, and treatment of zika. Through our know-how and key collaborators, we are able to help facilitate the development of aptamers as therapeutics or diagnostic devices for your target of interest, including Zika virus and other viral pathogens.

For enquiries, please contact us at  info@aptamergroup.co.uk

 

References

Centers for Disease Control and Prevention Zika MAC-ELISA Emergency Use Authorization. Fact Sheet for Health Care Providers:  Interpreting Zika MAC-ELISA Results, February, 2016

Gopinath, S. C. B., Hayashi, K., & Kumar, P. K. R. (2012). Aptamer That Binds to the gD Protein of Herpes Simplex Virus 1 and Efficiently Inhibits Viral Entry. Journal of Virology, 86(12), 6732–6744. http://doi.org/10.1128/JVI.00377-12

Hamel, R., Dejarnac, O., Wichit, S., Ekchariyawat, P., Neyret, A., Luplertlop, N., … Missé, D. (2015). Biology of Zika Virus Infection in Human Skin Cells. Journal of Virology, 89(17), 8880–8896. http://doi.org/10.1128/JVI.00354-15

Hwang, S.Y.; Sun, H.Y.; Lee, K.H.; Oh, B.H.; Cha, Y.J.; Kim, B.H.; Yoo, J.Y.  5′-triphosphate-RNA-independent activation of RIG-I via RNA aptamer with enhanced antiviral activity. Nucleic Acids Res. 2012, 40, 2724–2733.

Kelser,E.A., (2016) Meet dengue’s cousin, Zika. Microbes and infection, 18(3):163-6.doi:10.1016/j.micinf.2015.12.003

Labib, M.; Zamay, A.S.; Muharemagic, D.; Chechik, A.V.; Bell, J.C.; Berezovski, M.V.  Aptamer-based viability impedimetric sensor for viruses. Anal. Chem. 2012, 84, 1813–1816.

Malone, R. W., Homan, J., Callahan, M. V., Glasspool-Malone, J., Damodaran, L., Schneider, A. D. B., … Zika Response Working Group. (2016). Zika Virus: Medical Countermeasure Development Challenges. PLoS Neglected Tropical Diseases, 10(3), e0004530. http://doi.org/10.1371/journal.pntd.0004530

Ramos da Silva, S. & Gao, S. J. (2016). Zika virus: An update on epidemiology, pathology, molecular biology, and animal model. Journal of Medical virology, 88(8) p.1291-6

Ruslinda, R.A.; Tanabe, K.; Ibori, S.; Wang, X.; Kawarada, H. Effects of diamond-FET-based RNA aptamer sensing for detection of real sample of HIV-1 Tat protein. Biosens. Bioelectron. 2013, 40, 277–282.

Wandtke, T., Woźniak, J., & Kopiński, P. (2015). Aptamers in Diagnostics and Treatment of Viral Infections. Viruses, 7(2), 751–780. http://doi.org/10.3390/v7020751

World Health Organization. Zika situation report, April 7, 2016 http://apps.who.int/iris/bitstream/10665/204961/1/zikasitrep_7Apr2016_eng.pdf?ua=1