Clozapine Toxicity: Role Of Pharmacogenetic Variation In CYP Enzymes And Bioactivation Mechanisms In Patient Neutrophils
Funder
National Health and Medical Research Council
Funding Amount
$336,000.00
Summary
The treatment of mental disorders such as schizophrenia involves the administration of potent drug combinations to patients. Some individuals, however, do not respond to commonly-used antipsychotic drugs and their condition only improves with a unique drug called clozapine. The major problem with clozapine is its toxicity toward blood cells, heart and other organs. All people who receive clozapine must be monitored closely, especially in the first 3-4 months after starting therapy. Several new d ....The treatment of mental disorders such as schizophrenia involves the administration of potent drug combinations to patients. Some individuals, however, do not respond to commonly-used antipsychotic drugs and their condition only improves with a unique drug called clozapine. The major problem with clozapine is its toxicity toward blood cells, heart and other organs. All people who receive clozapine must be monitored closely, especially in the first 3-4 months after starting therapy. Several new drugs have been suggested to be safer versions of clozapine but these are all ineffective. Clozapine is the only agent that is effective in people who do not respond to the other drugs used to treat schizophrenia. Thus, clozapine toxicity, which necessitates discontinuation of the drug, is a devastating outcome because there is no alternative treatment that is available. Another significant problem with clozapine is that its rate of removal from the body is slowed down by many other drugs that are used concurrently. The problems with clozapine occur in some but not all individuals. This suggests that the patient's genetic makeup and their exposure to drugs and environmental agents determine the incidence of toxicity. The present project looks at how clozapine is removed from the body and how it is converted into a toxic product that damages cells. These processes will be examined, with emphasis on differences between individual patients, and strategies to protect cells from damage from the toxic derivative will be tested. Corresponding studies will be done in patients who are receiving clozapine as treatment for psychoses. We will be able to compare experimental and clinical findings in order to identify those patients who appear to be at risk. This will be possible before the toxic effects occur and will help us to identify subjects in whom the drug should only be used with great care. We may also devise strategies that will minimise the incidence of toxicity.Read moreRead less
Drugs are broken down in the body by the process of metabolism. Metabolism is important as both a detoxification and elimination mechanism, and determines dose rate for chronically administered drugs. Many drugs are metabolised by a reaction called glucuronidation. We will characterise the various components of the glucuronidation reaction in an integrated manner in order to understand and predict factors that influence an individual's capacity to metabolise drugs and other chemicals.
Predicting Drug-drug Interactions Due To Tyrosine Kinase Inhibitors: Inhibition Of Drug Metabolising Enzymes And Transporters
Funder
National Health and Medical Research Council
Funding Amount
$535,495.00
Summary
Tyrosine kinase inhibitors (TKIs) are a new class of anticancer agents. Cancer patients typically receive multiple drugs, for the treatment of cancer and other diseases, increasing the probability of interactions between coadministered drugs. Despite the widespread use of TKIs, their potential to cause drug interactions is poorly understood. Using novel in vitro approaches, this project will identify drug interactions precipitated by TKIs thereby improving drug efficacy and patient safety.
Quantitative In Vitro-in Vivo Extrapolation: Realising The Promise
Funder
National Health and Medical Research Council
Funding Amount
$529,509.00
Summary
Most drugs are 'broken down', or metabolised, in the body by enzymes which are located mainly in liver. Knowing the efficiency of drug metabolism in patients is important for the discovery of new drugs and for the rational use of established drugs. This project will develop in vitro, or test-tube, approaches that predict how well a drug is metabolised in humans and whether it will interact with coadminsitered drugs. In turn, this allows prediction of drug dosage and frequency of administration.
Interaction Of New Kinase Inhibitor Drugs With Multi-drug Resistance (MDR) Transporter Proteins.
Funder
National Health and Medical Research Council
Funding Amount
$411,000.00
Summary
Multidrug transporter proteins are remarkable molecular pumps that expel a wide variety of drugs and toxins from cells. They are located at strategic sites where they eliminate harmful substances from the body or prevent them being absorbed from our diet in the first place. Multidrug transporters are also found at natural barriers within the body where they protect vulnerable tissue compartments, including the brain, cerebrospinal fluid, testes and, in preganant women, the foetus. Nevertheless, ....Multidrug transporter proteins are remarkable molecular pumps that expel a wide variety of drugs and toxins from cells. They are located at strategic sites where they eliminate harmful substances from the body or prevent them being absorbed from our diet in the first place. Multidrug transporters are also found at natural barriers within the body where they protect vulnerable tissue compartments, including the brain, cerebrospinal fluid, testes and, in preganant women, the foetus. Nevertheless, multidrug transporters sometimes interfere with drug therapy. They can prevent efficient absorption of drugs, increase the rate of drug elimination from the body, or prevent drug access to some tissues . Moreover, the activity of the transporters is quite variable, both between patients and within the same patient over time. This makes it difficult to provide optimal drug doses, particularly when treating cancer, where the drugs must be given at the maximum tolerated dose. The presence of drug transporter proteins in tumour cells can prevent entry of anticancer drugs, rendering them resistant to treatment. This is the main cause of failure in chemotherapy. This project will investigate a class of very promising new anticancer drugs, kinase inhibitors, to determine whether they are pumped by multidrug transporters, whether they alter the amounts of drug transporters in cells, and whether they alter transporter activity. We will also determine the consequences that follow from this for drug therapy. This information will help clinicians to rationally optimise therapy with the new drugs, to identify in advance both favourable (synergistic) and unfavourable (harmful) drug interactions in combination chemotherapy, to optimise drug doses and to minimise toxic side effects. The information will also add to our general understanding of drug absorption and elimination, and to the basic science of the remarkable multidrug transporter proteins.Read moreRead less
The Molecular Basis Of Cytochrome P450 Ligand Binding: Towards Predicting Enzyme Substrate Selectivity And Drug-drug Interaction Potential
Funder
National Health and Medical Research Council
Funding Amount
$558,447.00
Summary
Cytochrome P450 (CYP) enzymes play a pivotal role in the metabolism (i.e. chemical breakdown) of drugs, a process that is essential for their detoxification and elimination from the body. This project will combine advanced computational and experimental approaches to elucidate the molecular basis for the binding of drugs to CYP enzymes, which is crucial for the design of drugs with favourable metabolic properties and decreased propensity for harmful interactions with co-administered drugs.
Novel Fluorescent Probes Of Cellular Microenvironments To Study The Mechanism Of Action Of Endoperoxide Antimalarials
Funder
National Health and Medical Research Council
Funding Amount
$983,305.00
Summary
Malaria is responsible for the deaths of about two million children each year. As current drugs become increasingly useless due to the development of parasite resistance, there is an urgent need for new antimalarials. Artemisinin, an ancient Chinese drug that is extracted from wormwood, is now a front-line antimalarial, however its mechanism of action is not clear. Information about how artemisinin works is needed to help design cheap synthetic drugs that work in the same way.
Drug Interactions Involving Complementary Medicines: Effects Of Phytoestrogenic Isoflavones.
Funder
National Health and Medical Research Council
Funding Amount
$196,018.00
Summary
Isoflavones are naturally occurring chemicals that have become widely recognised as 'phytoestrogens'. These are plant-derived compounds with a biological activity that resembles that of the human hormone, estrogen. Pharmaceutical preparations containing isoflavones, as herbal extracts, are currently available over-the-counter from pharmacies and health-food outlets and are being heavily promoted in the lay press. For example, Promensil, which contains 40mg of isoflavones per tablet, is being pro ....Isoflavones are naturally occurring chemicals that have become widely recognised as 'phytoestrogens'. These are plant-derived compounds with a biological activity that resembles that of the human hormone, estrogen. Pharmaceutical preparations containing isoflavones, as herbal extracts, are currently available over-the-counter from pharmacies and health-food outlets and are being heavily promoted in the lay press. For example, Promensil, which contains 40mg of isoflavones per tablet, is being promoted for use in women over the age of 45 years and Trinovin is being promoted for men over 50. It is well recognised that patients taking more than one drug may experience an adverse event as a consequence of one drug altering the way in which the body handles another. Therefore, a new 'conventional' drug cannot be marketed unless information on its ability to alter the handling of other drugs is provided to the relevant regulatory body. In stark contrast, there is comparatively little information required for the marketing of herbal products such as isoflavones, despite the fact that these products will be made available over-the-counter for self-medication. We hypothesise that isoflavones will be capable of interacting with conventional drugs and we will be conducting a range of experiments to address this hypothesis. At present little or no consideration is given to the safety issues that arise from the use of herbal remedies in general, not only the isoflavones. Therefore a patient taking a range of conventional drugs is able to purchase a herbal remedy, over-the-counter, with no consultation with a health professional. If we discover that isoflavones can alter the handling of conventional drugs by the body, then certain precautions will need to be taken in defining their safety in humans. The result may also have implications for the use of other complementary medicines.Read moreRead less
Developing Synergisers Of The Antimalarial Drug, Chloroquine, For The Treatment Of Chloroquine-resistant P. Falciparum.
Funder
National Health and Medical Research Council
Funding Amount
$243,000.00
Summary
Malaria is a debilitating parasitic disease that is responsible for the deaths of about two million children each year. As drugs, such as chloroquine, become increasingly useless due to the development of parasite resistance, there is an urgent need to understand the mode of action of and the molecular basis of resistance to existing antimalarials and to design affordable treatments that can replace chloroquine. It is known that some compounds, that have only poor antimalarial activity themselve ....Malaria is a debilitating parasitic disease that is responsible for the deaths of about two million children each year. As drugs, such as chloroquine, become increasingly useless due to the development of parasite resistance, there is an urgent need to understand the mode of action of and the molecular basis of resistance to existing antimalarials and to design affordable treatments that can replace chloroquine. It is known that some compounds, that have only poor antimalarial activity themselves, can synergise the action of chloroquine. This may involve the inhibition of the activity of proteins that directly or indirectly extrude chloroquine from its site of action in the parasite's digestive apparatus. Unfortunately, thechloroquine synergisers examined to date have been too toxic to be useful in vivo. In preliminary studies we have identified some compounds that would be suitable for use in malaria patients, including a widely used antimalarial drug, primaquine, that can synergise the activity of chloroquine against chloroquine-resistant parasites. We will attempt to understand the molecular basis of this interaction. This will allow us to define optimal combinations of chloroquine and a resistance-reversing quinoline for use treating malaria. This could extend the clinical life of this important antimalarial drug. The information obtained may also help to design novel antimalarial drugs.Read moreRead less