Schistosoma mansoni Sirtuins: characterization and potential as chemotherapeutic targets.

BACKGROUND: The chemotherapy of schistosomiasis currently depends on the use of a single drug, praziquantel. In order to develop novel chemotherapeutic agents we are investigating enzymes involved in the epigenetic modification of chromatin. Sirtuins are NAD+ dependent lysine deacetylases that are involved in a wide variety of cellular processes including histone deacetylation, and have been demonstrated to be therapeutic targets in various pathologies, including cancer. METHODOLOGY PRINCIPAL FINDINGS: In order to determine whether Schistosoma mansoni sirtuins are potential therapeutic targets we first identified and characterized their protein sequences. Five sirtuins (SmSirt) are encoded in the S. mansoni genome and phylogenetic analysis showed that they are orthologues of mammalian Sirt1, Sirt2, Sirt5, Sirt6 and Sirt7. Both SmSirt1 and SmSirt7 have large insertion in the catalytic domain compared to their mammalian orthologues. SmSirt5 is the only mitochondrial sirtuin encoded in the parasite genome (orthologues of Sirt3 and Sirt4 are absent) and transcripts corresponding to at least five splicing isoforms were identified. All five sirtuins are expressed throughout the parasite life-cycle, but with distinct patterns of expression. Sirtuin inhibitors were used to treat both schistosomula and adult worms maintained in culture. Three inhibitors in particular, Sirtinol, Salermide and MS3 induced apoptosis and death of schistosomula, the separation of adult worm pairs, and a reduction in egg laying. Moreover, Salermide treatment led to a marked disruption of the morphology of ovaries and testes. Transcriptional knockdown of SmSirt1 by RNA interference in adult worms led to morphological changes in the ovaries characterized by a marked increase in mature oocytes, reiterating the effects of sirtuin inhibitors and suggesting that SmSirt1 is their principal target. CONCLUSION SIGNIFICANCE: Our data demonstrate the potential of schistosome sirtuins as therapeutic targets and validate screening for selective sirtuin inhibitors as a strategy for developing new drugs against schistosomiasis.

Targeting schistosome histone modifying enzymes for drug development.

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.

Chromatin regulation in schistosomes and histone modifying enzymes as drug targets.

Only one drug is currently available for the treatment and control of schistosomiasis and the increasing risk of selecting strains of schistosome that are resistant to praziquantel means that the development of new drugs is urgent. With this objective we have chosen to target the enzymes modifying histones and in particular the histone acetyltransferases and histone deacetylases (HDAC). Inhibitors of HDACs (HDACi) are under intense study as potential anti-cancer drugs and act via the induction of cell cycle arrest and/or apoptosis. Schistosomes like other parasites can be considered as similar to tumours in that they maintain an intense metabolic activity and rate of cell division that is outside the control of the host. We have shown that HDACi can induce apoptosis and death of schistosomes maintained in culture and have set up a consortium (Schistosome Epigenetics: Targets, Regulation, New Drugs) funded by the European Commission with the aim of developing inhibitors specific for schistosome histone modifying enzymes as novel lead compounds for drug development.

Chromatin regulation in schistosomes and histone modifying enzymes as drug targets

Only one drug is currently available for the treatment and control of schistosomiasis and the increasing risk of selecting strains of schistosome that are resistant to praziquantel means that the development of new drugs is urgent. With this objective we have chosen to target the enzymes modifying histones and in particular the histone acetyltransferases and histone deacetylases (HDAC). Inhibitors of HDACs (HDACi) are under intense study as potential anti-cancer drugs and act via the induction of cell cycle arrest and/or apoptosis. Schistosomes like other parasites can be considered as similar to tumours in that they maintain an intense metabolic activity and rate of cell division that is outside the control of the host. We have shown that HDACi can induce apoptosis and death of schistosomes maintained in culture and have set up a consortium (Schistosome Epigenetics: Targets, Regulation, New Drugs) funded by the European Commission with the aim of developing inhibitors specific for schistosome histone modifying enzymes as novel lead compounds for drug development.