Heart failure, cancer therapies, protein kinases, hypertension, hypertrophy
Basic research; translational and applied research; maintenance of colonies of genetically altered animals
Cancer and heart diseases are leading causes of death and illness. Many cancer treatments target enzymes required for the heart to function properly. One group of enzymes forms the ERK1/2 pathway which protects the heart from damage and is required for the contractile heart cells to grow. This is necessary for the heart to increase its ability to pump blood around the body in "healthy" situations (e.g. regular exercise or pregnancy) or in pathological conditions (e.g. high blood pressure). However, the ERK1/2 pathway is important in cancer, and drugs targeting these enzymes are being used as cancer therapies. We aim to determine how the ERK1/2 pathway is regulated in the heart and establish how it elicits its effects. A second goal is to determine how cancer drugs that inhibit the pathway affect healthy hearts or hearts that are dysfunctional as a result of high blood pressure.
The study will increase our understanding of the regulation/role of the ERK1/2 pathway in the heart. This will enable us to identify ways in which the pathway may be manipulated to protect the heart (e.g. in patients with high blood pressure) or promote "healthy" growth (as in exercise or pregnancy) rather than pathological growth that leads to heart failure. The study will also aid in understanding whether/how cancer drugs that inhibit the ERK1/2 pathway cause cardiac dysfunction. This may help target cancer therapies to avoid cardiac problems, and may identify patient populations who should or should not be treated with these drugs.
We expect to use approximately 1200 rats and 1450 mice over 5 years.
Approximately 50% of the animals will be subjected only to terminal anaesthesia with removal of the heart immediately prior to death (i.e. non-recovery).
In all in vivo studies, we aim to study early stages of heart failure as heart function becomes impaired and before overt clinical signs of the disease develop. This will be achieved using echocardiography to monitor the hearts of live animals (as in patients) over time. Pilot studies will be conducted to determine the earliest end-point at which we can reliably detect functional changes in the heart. Thus, although the predicted level of severity for protocols 2-4 is moderate, the actual level of severity should be restricted to mild in most cases.
The rat model of high blood pressure develops an enlarged heart over ~6-8 weeks and heart failure over 11-12 weeks. The experiments will be conducted for a maximum of 8 weeks to permit study of early stages of heart failure, but restricting the level of severity as far as possible to mild.
We will use genetically-modified rodents that have the potential for heart problems and heart failure to develop, particularly over prolonged periods (several months). We will use the latest technology to ensure, as far as possible, that the highest level of severity is likely to be mild. However, unexpected cardiac complications could still develop and the level of severity may become moderate.
Animals will be exposed to drugs that induce changes in the heart (and are used to treat heart failure in humans), and/or drugs that are used to treat cancer in humans. To minimise adverse effects, concentrations of drugs will be based on previous work in rats/mice or use amounts that do not exceed those that are appropriate for humans. The duration of drug delivery will be minimised to restrict the severity to mild, as far as possible.
Animals that show signs of developing moderate heart failure or distress will be killed immediately. At the end of the experiments all animals will be killed.
Contractile cells of the heart (cardiomyocytes) do not divide and there are no cell lines that are representative of these cells. It is therefore necessary to use animals for their study. For studies of cardiomyocyte function within the intact heart, there are no non-animal alternatives.
For cardiomyocyte experiments, cells are prepared under conditions that produce the greatest yield. The data from the cells are used to inform experiments with adult hearts.
When necessary, or appropriate, a professional statistician will be consulted to ensure an experimental design is optimal and minimises the number of animals required, yet ensures an adequate level of precision and power, and the appropriate statistical analysis is performed. In all cases, the minimum number of experiments will be performed to detect meaningful differences in responses, if they occur, at an appropriate level of statistical significance.
In vivo studies will require pilot studies to determine the numbers of animals required. These will be informed by published data where possible. Otherwise, they will be informed by data from cultured cells and ex vivo perfused hearts. The pilot studies will be initiated with small numbers of animals. Power calculations will be performed using the pilot data to determine the minimum numbers to detect meaningful differences in responses, if they occur, at an appropriate level of statistical significance.
We will use rodents. Where possible, we will use rat models which have been used widely for studies of the heart and which represent the most suitable model for studies of, for example, hypertension. We have worked with rats for over 20 years and have a large body of data on ERK1/2 signalling in this species. For studies of hypertension, we will use pre-existing models with their appropriate controls since these have been well characterized over ~50 years.
For genetically-modified animals, we will use pre-existing mouse or rat models where possible. Where possible, the modification will be targeted to the cardiomyocytes for postnatal expression and we will use a drug-inducible system. Using these approaches, we can determine the effects of the ERK1/2 pathway and/or inhibition of the pathway in properly developed cardiomyocytes, thus avoiding confounding effects of, for example, kidney dysfunction or developmental defects. Echocardiography will be used to monitor cardiac function longitudinally in individual animals throughout the course of in vivo experiments. This reduces the number of animals required, brings end-point of the study forward (restricting heart failure development), and improves the quality of the data.