Natural Products to Drugs: New Sonic Hedgehog Pathway Inhibitors in Meduloblastoma

The medulloblastoma is the most frequent malignant brain tumor of childhood, it belongs to the group of embryonal neuroepithelial tumors. Medulloblastoma is thought to arise from stem cells or early progenitor cells in the cerebellum. The Hedgehog (Hh) pathway is critical for the maintenance and self-renewal of neural stem cells and for tumorigenesis. Aberrant Hh signalling occurs in medulloblastoma as a consequence of genetic or epigenetic changes affecting several components of the pathway1-2. The most promising targets of the pathway are the G-protein coupled receptor smoothened (SMO), which transduces the Hh signal inside the cell, and the effector protein Gli1 which acts downstream of the SMO and promotes the transcription of Hh target genes. Several small-molecule antagonists of SMO have been discovered3, some of which are currently under clinical investigation, whereas no records on the discovery of Gli1 antagonists are available. The aim of this project is to discover and develop small organic molecules and/or natural compounds capable of inhibiting the Hh signaling pathway by antagonizing the SMO receptor and/or the Gli1 protein, thereby providing anticancer activity. Virtual screening was used for prioritizing possible Hh antagonists among a unique library of more than 800 natural compounds,the most promising compounds were selected and tested in vitroon various cell-based assays as, for example, in Hh-responsive cell lines and in stem/progenitor cells. The binding properties on the SMO receptor were investigated by competition assays with Bodipy-cyclopamine, whereas the direct interaction with Gli1 was studied by biophysical methods. Biological activity data were used for refining computational models, while the most interesting active hits were optimized through the rational design and synthesis. The most potent and less toxic compounds are considered as leads for further and in depth studies such as pre-clinical trials.