MICA: Development of new agents for the treatment of cryptosporidiosis

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A recent clinical study in Africa and South Asia has found that cryptosporidiosis is one of the most significant causes of death and illness from diarrheal diseases amongst children in the developing world. Cryptosporidiosis is caused by a single-celled protozoan parasite; the predominant species infecting humans are called Cryptosporidium hominis and Cryptosporidium parvum. This parasite mainly lives in the cells in the gut wall and has a complex life-cycle. Infection occurs due to consumption of water or food contaminated with the parasites. Parasites are spread from an infected individual through their faeces. In people who are healthy and well nourished, the disease clears naturally within a couple of weeks. However, in people who are malnourished (particularly in young children) and people with an immune system that is not functioning properly (for example HIV/AIDS victims), the disease can have a much more significant impact. It is the major contributor to life-threatening diarrhea in young children, with 2.9-4.7 million cases in children under 24 months in sub-Saharan Africa and the Indian sub-continent, leading to more than 200,000 deaths per year. Cryptosporidiosis is also associated with malnutrition and stunted growth in children and probably causes chronic infections, which last for weeks or months. The only drug registered for the treatment of this disease is nitazoxanide, which is not very effective, especially in those patients who are most severely affected due to a weak immune system and/ or malnutrition. Therefore there is an urgent need for the development of new drugs to treat: (1) children <24 months, especially those that are malnourished and with chronic diarrhea; and (2) immunocompromised children and adults with advanced AIDS and chronic diarrhea. Cryptosporidium may be the cause of as much as 75% of chronic diarrhea in this patient cohort. We have discovered some chemical starting points that can be used for a drug discovery programme. We have a series of compounds that kill the parasites and also are very effective in clearing the parasites from rodent models of cryptosporidiosis. The compounds are thought to work through preventing the parasite making proteins. The aim of this project is to take these starting points and optimise them to make a molecule which has the potential to be a drug. This will require us to optimise multiple features of the molecule: its ability to kill the parasite, its ability to reach the sites in the body where the parasite resides without being broken down, and its safety. At the end of this project we hope to have a "preclinical candidate". This is a compound that we think should be suitable to enter human clinical trials. The steps after this project, prior to human clinical trials will be to make the compound on a larger scale under properly defined conditions and to carry out formal safety testing.