Hybrid Molecules From Benzylguanidine and Cytotoxic Drugs (Busulfan, Melphalan, Thiotepa) for Specific Therapy of Neuroblastoma

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Around the world, iodine-123 labeled meta-iodobenzylguanidine ([123I]-mIBG) is used for the scintigraphic diagnosis of neuroblastoma. The isotopologe [131I]-mIBG is a routine therapeutical for the same disease. These are culmination points of developments in the sequel of the first respective clinical successes with neuroblastoma in Heidelberg and Tübingen (independent and simultaneous in 1984). Interestingly, non-radioactive [127I]-mIBG reveals anti-neuroblastoma activity, too (and the MYC-associated tumor-specific glucose metabolism plays an important role). The same activity would be exhibited by the para isomer [127I]-pIBG, but its rapid deiodination in the body prevents its clinical application. This joint project of a clinical and a synthetic research plans to endow analogs of mIBG und pIBG, which shall be iodine-free for the first time, with a therapeutic potential for neuroblastoma.We design these analogs as hybrid structures of the iodine-deprived IBG scaffold and of the alkylating moieties of pertinent cytostatics. The structural motive benzylguanidine (BG) shall allow our analogs (BG-drug candidates) to enter neuroblastoma cells via the noradrenalin transporter. The alkylating moieties are inspired by busulfan, mel¬phalanx, and thiotepa. Busulfan and melphalan were selected specifically because they are superior to other cytostatic drugs in conditioning before stem-cell transplantation in neuroblastoma. Accordingly, it may be expected that their incorporation assures an appropriate cytotoxicity. The goal of our 3-year collaborative research plan is to use this design for pairing cell selectivity with cell toxicity in such putative anti-neuroblastoma compounds. Freiburg will synthesize 42 BG-drug candidates and 6 [14C]-labeled isotopologs thereof. This volume of work is realistic due to our unprecedented concept of abolishing iodine from whatever target molecule: this reduces the step requirement by 50%. Tübingen will test all BG-drug candidates. A basic screening will include proliferation/vitality studies and comparisons with busulfan, melphalan, thiotepa, and unlabeled mIBG. Moreover, cell culture assays shall reveal, by which mechanism and to which extent these compounds are taken up by neuroblastoma cells and whether they cause an accumulation in mitochondria. The impact of BG-drug candidates on the metabolism of neuroblastoma cells shall be analyzed at the beginning of an advanced screening. One focus will be on the tumor (neuroblastoma) specific glucose metabolism (Warburg effect) including BG effects on N-myc expression. Another focus will be on DNA damage by the alkylating moieties. The most promising BG-drug candidates at this point of our study shall be analyzed using a neuroblastoma spheroid model. A still more restricted selection of compounds shall be tested on a neuroblastoma-bearing mouse model for identifying the most suitable BG-drug candidate(s) for a potential application in human patients.