The histone modifying enzymes (HME) represent particularly promising targets for the development of alternatives to praziquantel, the only currently available drug to combat schistosomiasis. The inhibition of these enzymes frequently arrests the cell cycle or induces apoptosis in cancer cells, but not in normal cells and numerous HME inhibitors are under investigation as potential anticancer agents. The recent resolution of the genome sequences of Schistosoma mansoni and Schistosoma japonicum has allowed us to identify all the schistosome genes encoding histone acetyltransferases, deacetylases, methyltransferases and demethylases. We have chosen a strategy using phylogenetic screening with inhibitors of HME classes, screening of individual HME targets by both high-throughput and reasoned (in silico docking using resolved crystal structures) approaches in a project funded by the European Community, named SEtTReND (Schistosome Epigenetics: Targets, Regulation, New Drugs). The initial focus is on the class I histone deacetylase (HDAC) 8 since the comparison of the catalytic site of the schistosome and human enzymes shows crucial differences, rendering possible the development of inhibitors specific for SmHDAC8. However, phenotypic screening shows that inhibitors of all HME classes tested were able to induce apoptosis and death in parasites in vitro, indicating that other enzymes may prove to be viable targets.
SCHISTOSOMIASIS: IMPACT OF THE DISEASE AND THE NEED FOR NEW DRUGSThe impact of schistosomiasis on communities in endemic areas extends well beyond the classical signs of morbidity: Symmer's fibrosis leading to hepato-splenomegaly, ascites, oesophageal varices, and culminating in death. These overt and catastrophic symptoms affect only a relatively small percentage of infected individuals, even if absolute numbers of annual deaths (about 280 000) are high. However, more cryptic effects such as anaemia, undernutrition, diarrhoea and chronic pelvic or abdominal pain were consistently underevaluated until a meta-analysis of a large number of previous schistosomiasis morbidity studies by King et al.[1] allowed an objective assessment. This showed that the WHO's previously estimated disability weight for schistosomiasis of 0.5%, based essentially on mortality, should be markedly revised upwards to between 2 and 15% and that the years of life lost to schistosomiasis represented a relatively small proportion of the total of years lost to disability. This reassessment of the true disease burden represented by schistosomiasis has led to the realization of the importance of reinforcing control measures.In the continuing absence of an effective infection-preventing vaccine, the only viable strategy is the mass-treatment of populations in endemic areas using the currently available drug, praziquantel. Thus the Schistosomiasis Control Initiative in Africa [2] had dispensed more than 40 million praziquantel treatments in eight sub-Saharan countries by 2008. This ongoing programme will undoubtedly have a major impact, both on...