Development of novel JAK3 inhibitors for the treatment of autoimmunity.
Lead Research Organisation:
University of Dundee
Department Name: School of Life Sciences
Abstract
Chronic inflammatory and autoimmune disorders, such as rheumatoid arthritis, psoriasis and inflammatory bowel disease, represent a significant problem in the UK. For example, an estimated 0.4 million people in the UK suffer from rheumatoid arthritis while psoriasis affects 1.8 million and inflammatory bowel disease affects 260000. These diseases are often long term and can be severely debilitating. Current treatments focus on suppressing the body's immune system with the aim of arresting disease progression. There are however two main issues with the drugs currently available to treat these conditions. Long-term immunosuppressive therapy caries a risk of serious side effects that include, but are not limited to, serious and potentially life-threating infections as well as an increased incidence of cancer. In addition not all patients respond to the available 1st line drugs while the recently developed "biological" agents, such as anti-TNF therapy are expensive and must be administered by injection. An effective orally available drug would therefore represent a significant advance for the treatment of these diseases.
A common feature of autoimmune conditions is that the immune system loses that ability to react only to pathogens and starts to recognize components of the body as being foreign. This triggers immune activation leading to chronic inflammation and irreversible tissue damage. This process depends on the production of proteins termed cytokines that activate immune cells and drive inflammation. To activate an immune cell, cytokines must turn on specific signaling proteins inside the cell. One important example of this is a group of 4 related proteins referred to as "Janus kinases" or JAKs. Blocking the activity of JAKs would deactivate the immune cell and therefore prevent inflammation. Evidence to support this comes from a drug, Tofacitinib, which has proven effective in clinical trials for autoimmune diseases. Widespread use of Tofacitinib may however be prevented by the adverse side effects that can be seen in a minority of patients receiving the drug. Although Tofacitinib has been approved for use in the US for treating some forms of rheumatoid arthritis, concerns over these side effects have prevented its approval in the UK. Despite its drawbacks, Tofacitinib has demonstrated that inhibition of JAKs is a promising new way for treating some autoimmune diseases. A key question now is whether new JAK inhibitors could be found that have an improved ability to treat autoimmunity but have fewer side effects. Tofacitinib inhibits multiple members of the JAK family, and this broad inhibition may give rise to some of the off target effects. A more selective JAK inhibitor may be able to deliver the required benefits with less toxicity. JAK3 is an attractive target in this respect as, unlike JAK1 and JAK2 that are found in many cell types in the body, JAK3 is only found in cells in the immune system. Furthermore mutations that inactivate JAK3 are known to suppress the immune system. We have identified a new inhibitor that blocks JAK3 activity by targeting a site that is unique to JAK3 and not found in the other members of the family. The project will carry out "hit to lead" chemistry around this molecule with the aim of delivering lead molecules orally active in a mouse model of arthritis. We will also use a new technique, referred to as chemical genetics, to show that the action of the drug in mice is due to its ability to inhibit JAK3 and not an off target effect of the compound.
This work constitutes the early stages of drug development and the aim of the project will be to deliver a new potential drug that is suitable to advance in to late lead optimization, pre-clinical testing and then into clinical trials.
A common feature of autoimmune conditions is that the immune system loses that ability to react only to pathogens and starts to recognize components of the body as being foreign. This triggers immune activation leading to chronic inflammation and irreversible tissue damage. This process depends on the production of proteins termed cytokines that activate immune cells and drive inflammation. To activate an immune cell, cytokines must turn on specific signaling proteins inside the cell. One important example of this is a group of 4 related proteins referred to as "Janus kinases" or JAKs. Blocking the activity of JAKs would deactivate the immune cell and therefore prevent inflammation. Evidence to support this comes from a drug, Tofacitinib, which has proven effective in clinical trials for autoimmune diseases. Widespread use of Tofacitinib may however be prevented by the adverse side effects that can be seen in a minority of patients receiving the drug. Although Tofacitinib has been approved for use in the US for treating some forms of rheumatoid arthritis, concerns over these side effects have prevented its approval in the UK. Despite its drawbacks, Tofacitinib has demonstrated that inhibition of JAKs is a promising new way for treating some autoimmune diseases. A key question now is whether new JAK inhibitors could be found that have an improved ability to treat autoimmunity but have fewer side effects. Tofacitinib inhibits multiple members of the JAK family, and this broad inhibition may give rise to some of the off target effects. A more selective JAK inhibitor may be able to deliver the required benefits with less toxicity. JAK3 is an attractive target in this respect as, unlike JAK1 and JAK2 that are found in many cell types in the body, JAK3 is only found in cells in the immune system. Furthermore mutations that inactivate JAK3 are known to suppress the immune system. We have identified a new inhibitor that blocks JAK3 activity by targeting a site that is unique to JAK3 and not found in the other members of the family. The project will carry out "hit to lead" chemistry around this molecule with the aim of delivering lead molecules orally active in a mouse model of arthritis. We will also use a new technique, referred to as chemical genetics, to show that the action of the drug in mice is due to its ability to inhibit JAK3 and not an off target effect of the compound.
This work constitutes the early stages of drug development and the aim of the project will be to deliver a new potential drug that is suitable to advance in to late lead optimization, pre-clinical testing and then into clinical trials.
Technical Summary
This project will carry out hit-to-lead optimization on a novel JAK3 inhibitor we have identified as a potential lead compound for development to treat autoimmunity. Our compound inhibits JAK3 kinase activity in vitro with an IC50 of 4.8nM in a fixed time-point assay and has at least 180-fold selectivity over other JAK isoforms. It is a covalent inhibitor and exhibits the expected time-dependent inhibition of JAK3 kinase activity. Profiling against extended kinase panels has confirmed its in vitro selectivity. In primary immune cells the compound inhibits signaling by JAK3 dependent cytokines at 500nM but not signaling by cytokines requiring JAK1, JAK2 or Tyk2 independently of JAK3. Preliminary DMPK analysis has found that the lead compound has good aqueous solubility, good metabolic stability in vitro when incubated with human liver microsomes and good oral bioavailability in mice.
The project will be divided into 3 sections; hit-to-lead optimization, testing of selected compounds in mouse arthritis models and the development of a chemical genetic model to validate the in vivo on target action of the inhibitors.
The project will bring together the groups of Simon Arthur, Kevin Read (Dundee), Nathanael Gray (Boston) and Iain McInnes (Glasgow) to form a consortium that has all the required expertise to support the project. Hit-to-lead chemistry will be carried out by Nathanael Gray, whose lab in Boston identified the lead compound. This will be aided by the availability of a JAK3/lead compound crystal structure and supported by kinase profiling and DMPK analysis carried out in Dundee. Selected compounds will be analyzed for their effect in vivo on Jak3 dependent biomarkers and in mouse arthritis models (Dundee and Glasgow). The chemical genetic mouse model will use a point mutation that does not affect catalytic activity but which blocks inhibitor binding. Once validated, a mouse knockin for this mutation will be generated to provide the chemical model (Dundee).
The project will be divided into 3 sections; hit-to-lead optimization, testing of selected compounds in mouse arthritis models and the development of a chemical genetic model to validate the in vivo on target action of the inhibitors.
The project will bring together the groups of Simon Arthur, Kevin Read (Dundee), Nathanael Gray (Boston) and Iain McInnes (Glasgow) to form a consortium that has all the required expertise to support the project. Hit-to-lead chemistry will be carried out by Nathanael Gray, whose lab in Boston identified the lead compound. This will be aided by the availability of a JAK3/lead compound crystal structure and supported by kinase profiling and DMPK analysis carried out in Dundee. Selected compounds will be analyzed for their effect in vivo on Jak3 dependent biomarkers and in mouse arthritis models (Dundee and Glasgow). The chemical genetic mouse model will use a point mutation that does not affect catalytic activity but which blocks inhibitor binding. Once validated, a mouse knockin for this mutation will be generated to provide the chemical model (Dundee).
Planned Impact
Autoimmune diseases such as rheumatoid arthritis represent a significant clinical problem and result in major costs to the healthcare system. As these diseases are often chronic and debilitating, long-term treatment is normally required. This carries with it risks of serious side effects, including infection and cancer. While the treatment options have expanded for these diseases with the advent of biological therapies such as anti-TNF, further improvements are still required. Biologic therapies remain expensive and must be administered by injection. New orally available small molecule drugs will therefore be of considerable benefit.
The recent development of Tofacitinib by Pfizer has renewed interest in the use of kinase inhibitors for autoimmunity and has validated the JAK family as targets for the treatment of autoimmunity. The efficacy to toxicity ratio of Tofacitinib however is not ideal, and this has prevented its approval in the UK. Despite this, improved JAK inhibitors have significant potential. Most current JAK inhibitors inhibit multiple JAK isoforms and this may be a disadvantage as it could increase likelihood of unwanted side effects. A key, and as yet unresolved question, is what the optimal profile of a JAK inhibitor would be.
We have identified a lead compound that acts as a highly selective inhibitor of JAK3. The proposed work will carry out further chemistry to optimize this compound and to deliver lead molecules active in mouse models of rheumatoid arthritis. In addition chemical genetics will be used to validate its in vivo mode of action. In addition to the development of the lead compound, this work will also provide important information on the ability of JAK3 inhibition to prevent autoimmunity. This will have an impact not just on the current work but also inform future development of other drugs targeted against JAKs.
The goal of this project is to generate a compound that could advance into late lead optimization and towards preclinical development. If successful, and if the compound then advances through clinical trials, it could have a major impact on the treatment of autoimmunity. It may also prove useful for treatment of leukemias that are driven by JAK3.
Given the translational aspect of this proposal, a key component to maximize the potential downstream impact of this research will be effective communication with the pharmaceutical industry. This will also be especially important towards the end of the project as we seek the next round of funding to progress compounds in preclinical studies. With respect to this we are fortunate to be in a good position as a consortium of several pharma companies including GSK, Merck Serono, Pfizer, AstraZeneca, Boehringer Ingelheim and Janssen Pharmaceutica currently fund work in multiple labs in Dundee, including work in Simon Arthur's group. This provides us with initial contacts with these companies, however we would we also explore options with other companies. The Office of Technology Transfer (ORTV) of Dana Farber has strong engagement with pharmaceutical and biotechnology companies in the Boston area and beyond and has a successful track-record of commercializing technologies.
Finally we will also continue to play an active role in informing the public about biomedical research and its importance. To do this we will continue our participation in science festivals in Dundee and Edinburgh that are focused on engaging children in science. SA's group also receives funding from Arthritis Research UK, and we have had several meetings with the fundraising division of this charity to talk to current and potential donors about the type of work we undertake and what its benefits are. This is something we are keen to continue with in the future.
The recent development of Tofacitinib by Pfizer has renewed interest in the use of kinase inhibitors for autoimmunity and has validated the JAK family as targets for the treatment of autoimmunity. The efficacy to toxicity ratio of Tofacitinib however is not ideal, and this has prevented its approval in the UK. Despite this, improved JAK inhibitors have significant potential. Most current JAK inhibitors inhibit multiple JAK isoforms and this may be a disadvantage as it could increase likelihood of unwanted side effects. A key, and as yet unresolved question, is what the optimal profile of a JAK inhibitor would be.
We have identified a lead compound that acts as a highly selective inhibitor of JAK3. The proposed work will carry out further chemistry to optimize this compound and to deliver lead molecules active in mouse models of rheumatoid arthritis. In addition chemical genetics will be used to validate its in vivo mode of action. In addition to the development of the lead compound, this work will also provide important information on the ability of JAK3 inhibition to prevent autoimmunity. This will have an impact not just on the current work but also inform future development of other drugs targeted against JAKs.
The goal of this project is to generate a compound that could advance into late lead optimization and towards preclinical development. If successful, and if the compound then advances through clinical trials, it could have a major impact on the treatment of autoimmunity. It may also prove useful for treatment of leukemias that are driven by JAK3.
Given the translational aspect of this proposal, a key component to maximize the potential downstream impact of this research will be effective communication with the pharmaceutical industry. This will also be especially important towards the end of the project as we seek the next round of funding to progress compounds in preclinical studies. With respect to this we are fortunate to be in a good position as a consortium of several pharma companies including GSK, Merck Serono, Pfizer, AstraZeneca, Boehringer Ingelheim and Janssen Pharmaceutica currently fund work in multiple labs in Dundee, including work in Simon Arthur's group. This provides us with initial contacts with these companies, however we would we also explore options with other companies. The Office of Technology Transfer (ORTV) of Dana Farber has strong engagement with pharmaceutical and biotechnology companies in the Boston area and beyond and has a successful track-record of commercializing technologies.
Finally we will also continue to play an active role in informing the public about biomedical research and its importance. To do this we will continue our participation in science festivals in Dundee and Edinburgh that are focused on engaging children in science. SA's group also receives funding from Arthritis Research UK, and we have had several meetings with the fundraising division of this charity to talk to current and potential donors about the type of work we undertake and what its benefits are. This is something we are keen to continue with in the future.
