Statins, molecular mining in neuroblastoma

Neuroblastoma is one of the most common solid tumours of early childhood. The disease originates typically in the adrenal medulla or less frequently at other sites of the sympathetic nervous system. The genetic background of this disease has been studied extensively, including family history and changes in gene expression. However, these insights did not translate into the development of a successful therapeutic approach in advanced stages of the tumor. Statins lower plasma cholesterol and also its intermediates which play important roles in membrane integrity, cell signalling, protein synthesis and cell cycle progression. This pharmacological profile displays adjuvant chemotherapeutic potential and is currently a matter of debate and investigations. The overall success of stains in preventing cardiovascular events is only in part attributable to inhibition of the HMG-(3-hydroxy-3- methylglutaryl) CoA reductase, thus pleiotropic targets have to exist. Preliminary data of our laboratory show that human SH-SY5Y neuroblastoma cells are susceptible to simvastatin induced apoptosis, which is not the case for differentiated SH-SY5Y cells. Moreover, statins are capable to inhibit ABC transporters which participate in multidrug resistance. Based on these observations the working hypothesis is elaborated, that statins may have adjuvant chemotherapeutic potential in neuroblastoma. Throughout the project the following issues should be clarified: (i) Identification of the molecular mechanisms of statin induced apoptosis in various human neuroblastoma cells and in dependency of the differentiation status of the cells. (ii) Evaluation of the direct and indirect functional regulation and expression of ABC transporters, especially P- glycoprotein (ABCB1) in the presence of statins. In vitro elucidation of synergistic actions of statins with chemotherapeutics. (iii) Verification of the underlying hypothesis of the project, that statins posses an adjuvant chemotherapeutic potential in neuroblastoma in an in vivo xenograft mouse model. This project will provide new insights in the molecular mechanisms of action of statins and thereby contribute to improved drug safety. Moreover, experiments outlined in this proposal may define new therapeutic targets and thus devise statins as a novel approach in adjuvant cancer treatment.

Statins are widely used cholesterol lowering drugs which are well tolerated. Long-term exposure elucidated beneficial effects of statins which are summarized as pleiotropic effects. Among these, anti-cancer effects have been described but couldnt be explained on molecular level. Throughout this project we could successfully identify mechanistic insights, which support the idea to apply statins in anti-cancer regimens of distinct cancer entities. Neuroblastomas are early childhood tumours of the sympathetic nervous system which represent the leading cancer types in this age group. Depending on the histological classification and the grade of metastasis these children have a poor prognosis. The development of multidrug resistance during chemotherapy further reduces the therapeutic effect, which makes it necessary to develop new therapeutic concepts to escape these resistance mechanisms. In particular, protein pumps like P-glycoprotein (ABCB1) extrude chemotherapeutic drugs and are often found to be up-regulated in human cancers when exposed to chemotherapeutics. Throughout this project we could show that statins directly inhibit the transporter, ABCB1, reduce the expression in the tumour cells and thereby enhance susceptibility to anti-cancer drugs. This principle of action is not limited to cells of neuroblastoma but also observed in the aggressive childhood tumours, rhabdomyosarcoma. This breakthrough in chemoresistance was confirmed also in animal models. In addition, statins are capable to initiate a suicide program in tumour cells, the so called apoptosis. Beside neuroblastoma and rhabdomyosarcoma cells we could also identify a statin induced pro-apoptotic suicide factor in human metastatic melanoma cells. Application of this prostaglandin induced apoptosis only in transformed tumour cells and is therefore a hot candidate for therapeutic usage. Throughout this project we also collaborated with the St. Anna Childrens Cancer Research Institute and developed a new therapeutic concept which is already successfully confirmed to work in an in vivo model. The results of this project have been published in international journals, were presented at national and international conferences and have led to the initiation of new collaborations, which aim to translate the findings into a clinical context. The delineation of the signal transduction of the statin induced prostaglandin is currently under investigation for therapeutic usage and represents the starting point of a new FWF-grant application.