Understanding BK virus in kidney transplantation
Lead Research Organisation:
University of Leeds
Department Name: Astbury Centre
Abstract
Each year, over 90,000 patients worldwide suffering from kidney disease receive a life transforming kidney transplant. These patients take immunosuppression medications to prevent rejection of the transplanted kidney, but those medications increase the risk of infection. Of growing importance in this regard is BK virus, a harmless virus in a healthy person, but one that can cause severe disease in kidney transplant patients.
Uncontrolled BK infection can trigger serious damage to the kidney in a person taking immunosuppression, limiting transplant function and potentially leading to premature kidney loss and return to dialysis. There are no effective treatments for BK infection, other than reducing anti-rejection medications to allow the immune system to fight BK, which increases the risk of transplant rejection and loss.
As kidney transplantation has become more complex over time, an increasing number of patients need strong immunosuppression combinations to prevent their kidney transplant from rejecting. This means the number of patients with kidney transplants affected by BK virus is expected to grow, For this reason it is increasingly important that we have a clear understanding of the molecular mechanisms of BK virus and use this to develop new treatments.
BK virus is present in the vast majority of people by the time they are adults. We recently showed that a protein made by BK virus (called agnoprotein) forms a channel and that by a mechanism that we do not understand, this channel-forming ability is necessary to allow the virus to exit from infected cells - this is referred to as a "viroporin". Since the virus is present in almost every person receiving a kidney transplant, how it leaves the cells is thought to be critical to the problems it can cause for a kidney transplant.
This project will examine the structure and function of agnoprotein in the way the virus leaves the cells and seek to identify targets for medications that could stop the BK virus from damaging the kidney transplant.
Specific aims of the project are:
1) Understand agnoprotein viroporin structure and function:
o Determine the 3D molecular structure of the agnoprotein viroporin using advanced electron microscopy
o Define molecular target sites in the structure creating a platform for functional analysis and for screening of compounds for the ability to disrupt the viroporin function
2) Develop potent agnoprotein inhibitors
o Use our novel structural knowledge of the agnoprotein viroporin to understand the binding of known low potency inhibitors
o Use this information to screen virtual libraries of compounds for high potency inhibitors
o Test these inhibitors in vitro and in cell culture models to generate a suite of compounds for further functional studies and potential future clinical use
3) Validate viroporin function, and novel inhibitors in primary cell culture models
o Use two complementary cell culture systems to model the antiviral activity of the high potency inhibitor compounds
We will work with expert collaborators in Structural Biology and Medicinal Chemistry, and other BK researchers who use different cell culture models, to ensure our results are robust and can be taken forward to find new treatments for BK virus.
Ultimately, this will benefit patients by reducing the problems caused by BK virus, which will make kidney transplants affected by BK virus last longer.
Uncontrolled BK infection can trigger serious damage to the kidney in a person taking immunosuppression, limiting transplant function and potentially leading to premature kidney loss and return to dialysis. There are no effective treatments for BK infection, other than reducing anti-rejection medications to allow the immune system to fight BK, which increases the risk of transplant rejection and loss.
As kidney transplantation has become more complex over time, an increasing number of patients need strong immunosuppression combinations to prevent their kidney transplant from rejecting. This means the number of patients with kidney transplants affected by BK virus is expected to grow, For this reason it is increasingly important that we have a clear understanding of the molecular mechanisms of BK virus and use this to develop new treatments.
BK virus is present in the vast majority of people by the time they are adults. We recently showed that a protein made by BK virus (called agnoprotein) forms a channel and that by a mechanism that we do not understand, this channel-forming ability is necessary to allow the virus to exit from infected cells - this is referred to as a "viroporin". Since the virus is present in almost every person receiving a kidney transplant, how it leaves the cells is thought to be critical to the problems it can cause for a kidney transplant.
This project will examine the structure and function of agnoprotein in the way the virus leaves the cells and seek to identify targets for medications that could stop the BK virus from damaging the kidney transplant.
Specific aims of the project are:
1) Understand agnoprotein viroporin structure and function:
o Determine the 3D molecular structure of the agnoprotein viroporin using advanced electron microscopy
o Define molecular target sites in the structure creating a platform for functional analysis and for screening of compounds for the ability to disrupt the viroporin function
2) Develop potent agnoprotein inhibitors
o Use our novel structural knowledge of the agnoprotein viroporin to understand the binding of known low potency inhibitors
o Use this information to screen virtual libraries of compounds for high potency inhibitors
o Test these inhibitors in vitro and in cell culture models to generate a suite of compounds for further functional studies and potential future clinical use
3) Validate viroporin function, and novel inhibitors in primary cell culture models
o Use two complementary cell culture systems to model the antiviral activity of the high potency inhibitor compounds
We will work with expert collaborators in Structural Biology and Medicinal Chemistry, and other BK researchers who use different cell culture models, to ensure our results are robust and can be taken forward to find new treatments for BK virus.
Ultimately, this will benefit patients by reducing the problems caused by BK virus, which will make kidney transplants affected by BK virus last longer.
Technical Summary
Transplantation represents the treatment of choice for patients with end stage kidney disease. Following transplantation, the risk of organ rejection is reduced by immunosuppressive medicines. However, these drugs also increase the likelihood of reactivation of BK polyomavirus (BKPyV), an opportunistic pathogen that causes a persistent infection of the kidneys. Of the 90,000 kidney transplants occurring annually, 30-40% will experience clinically relevant viraemia and approximately 10% of cases will develop extensive kidney damage known as BKPyV-associated nephropathy (BKVAN).
Treatment for BKVAN is limited to reduced immunosuppression, which enhances the risk of graft rejection, reducing transplant life. Use of generic antivirals shows only questionable efficacy and nephrotoxicity. A clear and unmet need exists to study BKPyV and identify new BKPyV-specific antiviral therapeutic strategies. Ion channels comprise one of the most successfully exploited targets for pharmaceuticals, yet those encoded by viruses - viroporins - remain poorly characterised in terms of their structure and biology, leaving a wealth of potential drug targets untapped. Despite this, clinical precedent exists for adamantanes targeting Influenza A virus M2, yet these are now redundant due to poor drug like properties. We demonstrated that the BKPyV encoded agnoprotein possesses viroporin qualities, which is required for virus release from infected cells in culture. We will now conduct structural and functional studies on agnoprotein, coupled with the discovery of newer, more potent inhibitor compounds targeting viroporin activity. We will use these inhibitor compounds to assess the role of agnoprotein in virus release from renal cells and the urothelium, which remains a very poorly understood cellular niche for BKPyV. Completion of the project will deliver new insight, plus a suite of inhibitor compounds with which to investigate viroporin function, to take forward for future translation.
Treatment for BKVAN is limited to reduced immunosuppression, which enhances the risk of graft rejection, reducing transplant life. Use of generic antivirals shows only questionable efficacy and nephrotoxicity. A clear and unmet need exists to study BKPyV and identify new BKPyV-specific antiviral therapeutic strategies. Ion channels comprise one of the most successfully exploited targets for pharmaceuticals, yet those encoded by viruses - viroporins - remain poorly characterised in terms of their structure and biology, leaving a wealth of potential drug targets untapped. Despite this, clinical precedent exists for adamantanes targeting Influenza A virus M2, yet these are now redundant due to poor drug like properties. We demonstrated that the BKPyV encoded agnoprotein possesses viroporin qualities, which is required for virus release from infected cells in culture. We will now conduct structural and functional studies on agnoprotein, coupled with the discovery of newer, more potent inhibitor compounds targeting viroporin activity. We will use these inhibitor compounds to assess the role of agnoprotein in virus release from renal cells and the urothelium, which remains a very poorly understood cellular niche for BKPyV. Completion of the project will deliver new insight, plus a suite of inhibitor compounds with which to investigate viroporin function, to take forward for future translation.