Cathelicidins As Novel Therapeutic Antivirals For Dengue Infection

A significant challenge faced by modern society is the lack of therapeutics for a large number of infections, particularly those that are endemic or widely spread in developing countries. Dengue is one such infection which is endemic in Indonesia - it is transmitted by mosquitoes and infects approximately 100 million people per year, potentially causing death in the most severe cases. There is no treatment for dengue fever and given the spread of the disease around the globe, new treatment approaches are urgently required. We propose that small molecules present in the immune systems of humans and animals could be modified and exploited to fight this infection.

Our immune system contains substances that are some of the most complex and effective molecules to defeat infections. One of the ways in which the immune system can destroy invading pathogens is by the production of small peptides called cathelicidins. These peptides are present in many cells, fluids and tissues. We, and others, have shown cathelicidins to have powerful antiviral potential. They can play a key role in eliminating pathogens and controlling inflammation. We have shown that, in their natural state, cathelicidins can kill viruses such as influenza virus just as effectively as common antiviral drugs. One study has also shown that cathelicidins can kill Dengue virus, and may play in role in the immune response against this infection. Thus, we believe that developing new antimicrobial medicines based on the structure of cathelicidins offers promise as a novel way to fight pathogens such as dengue.

This study aims to understand how cathelicidins contribute to the immune response against dengue virus, and to find ways of harnessing this powerful activity to develop a treatment for dengue infection. In addition, given that cathelicidins are naturally occurring antiviral molecules in the body, stimulating their production through substances such as Vitamin D, which is incredibly effective at increasing cathelicidin release, may also be an effective way of defeating the infection. We will use both cells grown in the lab, and mouse models, to examine how cathelicidins, and stimulators of cathelicidin production, like Vitamin D, can be used to treat dengue infection. We will also study whether dengue stimulates or prevents cathelicidin release, and will also use samples from human patients who have contracted mild or severe dengue, and measure cathelicidin concentrations in their blood. We believe we can then examine the association between cathelicidin status, and severity of disease.

Furthermore, we will use cell models to understand how cathelicidins could be used to treat dengue infection, not just through their antiviral activity towards the virus, but by suppressing virus replication in the cells it infects. We know that dengue can hijack normal cell processes to replicate. One process, called autophagy, is required by healthy cells to recycle old or damaged cell proteins, so that the cell can break them down in order to survive. When dengue virus infects a cell, it hijacks the autophagy system, and uses it to replicate and release more virus, spreading to other cells. We will examine whether cathelicidins can prevent the virus from hijacking the autophagy machinery. We know that cathelicidins can induce a controlled form of cell death called apoptosis, and that in instances of infection, this can be beneficial in stopping infected cells from being used to generate more infectious virus particles. Thus we believe that by using cathelicidins to shift the balance from autophagy to apoptosis in dengue infection, this will be an effective and targeted way of treating this virus.

This project represents an unprecedented opportunity to gain a better understanding of how key molecules in the immune system can be harnessed to treat viruses, like dengue, that currently do not have an effective treatment.

Characterisation of the antiviral and immunomodulatory activity of the cathelicidin family of host defence peptides in Dengue infection may represent a novel approach that would inform the development of highly effective antiviral therapeutics. This study will characterise the impact of dengue infection on cathelicidin expression in vitro and in samples from patients diagnosed with mild or severe dengue fever, associating cathelicidin status with inflammatory markers and disease severity. Given that dengue virus is known to utilise autophagy induction to facilitate replication, and that cathelicidins are known to have the potential to induce apoptosis in infected cells, we aim to assess whether cathelicidin treatment can shift the balance from autophagy to apoptosis in dengue infected cells, as a way of halting viral replication and facilitating infected cell clearance. We will also use in vivo and in vitro models of dengue infection to provide a comparative assessment of the potential for exogenous peptide treatment, and upregulation of endogenous peptide, to be used as adjunct therapeutic approaches for dengue infection.

Key Research Deliverables

1. This study will provide a full translational characterisation of the impact of dengue infection on cathelicidin expression, in vitro and will assess cathelicidin and inflammatory status in patients diagnosed with mild or severe dengue fever.
2. We will provide a mechanistic characterisation of the immunomodulatory roles of cathelicidins in the context of the modulation of cell autophagy/apoptosis pathways in dengue infection.
3. We will provide in vitro and in vivo characterisation of the potential for either exogenous cathelicidin treatment, or vitamin D/butyrate mediated endogenous cathelicidin production to be used as an adjunct therapeutic approach for dengue infection.

This study is designed to characterise the potential for cathelicidins, a key component of the innate immune system, to be used as a novel therapeutic approach dengue virus. The work will provide a understanding of the pluripotent roles that cathelicidins can play in the response to dengue infection, will illuminate a novel approach for limiting dengue virus replication in the context of cathelicidin-mediated modulation of cell death/survival pathways, and assess the potential for stimulation of endogenous peptide production in the context of an adjunct therapeutic approach for dengue infection.

The healthcare burden and mortality associated with mild and severe dengue fever, particularly in developing countries and countries in receipt of ODA, has substantial implications, both financially, and in terms of global population morbidity/mortality. With over 100 million dengue infections estimated by the WHO each year, and with no effective therapeutic approach for this infection, the impact of the work proposed is extensive. Our work will map the effects of dengue viral infection on a key host defence peptide of the immune system, providing comprehensive characterisation of host defence mechanisms involved, and allowing us mechanistic insight into the design of novel peptide therapeutics. We believe that our strategy will not only provide insight into treating the pathogen used herein, but also for a number of other viral pathogens who employ autophagy to facilitate replication.

Furthermore, our work will inform a roadmap for the design and synthesis of novel peptide approaches for treating dengue infection. Our line-of-sight approach using primary cell in vitro models and in vivo models will allow us to conduct basic biological characterisation of a highly translational nature which is strongly emphasised through the use of primary clinical samples from patients who have experienced mild and severe dengue infection, and the use of translational in vivo infection models for efficacy assessment of the proposed peptide treatments and cathelicidin inducers.

The postdoctoral researcher who will be employed on this project will be supported to give them the best chance of developing as an independent researcher, and will also be given the experience of living and working in a centre of excellence for dengue research in Jakarta, seeing first hand the impact of dengue fever on the lives of those it affects. They will generate new skills both in vitro and in vivo and be able to publish high quality papers in journals of international esteem. More broadly, the potential for knowledge exchange between the UK and Indonesia that will be generated as part of this study in terms of expertise in Dengue viral infection models will be of key importance going forward.

The advances made in this study will impact upon a number of groups around the world who are focused upon elucidating novel pathways for the use of peptide-based therapeutics for treating viral infections such as dengue. In the context of pushing forward the global agenda on the development of therapeutics to address the fundamental challenge of vector borne infectious diseases, particularly in developing countries, this work will yield valuable information for future therapeutic design.