Pathogenesis and imaging of neuroblastoma metastases
Final Report Abstract
During the initial steps of the project we were able to optimize the novel orthotopic mouse neuroblastoma model yielding adrenal tumors not macroscopically invading the surrounding tissues. Experimental tumors were shown to be suitable for the analysis using modern imaging modalities. To induce adrenal tumors, an orthotopic injection of luciferaseexpressing IMR5/75 and IMR-32 neuroblastoma cell lines established as MYCN high/low model sensitive to the treatment with doxycycline was used. However, persistent knockdown of MYCN could not be observed in the tumor material. In line with this, we observed no statistically significant difference between doxycycline treated and control animals with respect to the tumor burden after the injection of IMR5/75 cells using magnetic resonance imaging, optical (bioluminescence) imaging, nuclear medicine methods (PET and SPECT) and histology. For IMR-32 tumor-bearing animals we were unable to determine the extent of the tumor burden due to significantly decreased tumor take rate after the doxycycline treatment. Using above mentioned methods we could not observe the presence of distant metastases in this preclinical model. We have found 68Ga-DOTATOC PET to be very well suitable for the assessment of neuroblastoma in this mouse model. Contrary to that, we did not observe accurate signal from adrenal tumors by using 123Iod-mIBG SPECT. Therefore, when comparing the suitability of diagnostic modalities commonly used for neuroblastoma disease, we found that in this particular MYCN high/low model 68Ga-DOTATOC PET has a clear preference over 123Iod-mIBG SPECT and should be considered as a first line method. With respect to the establishment of a reliable model for micro- or macrometastases, further efforts will be necessary. With our metabolic analysis, we demonstrated that oncogenic MYCN sensitizes neuroblastoma cells to ferroptosis when intracellular cysteine availability for glutathione synthesis and the cystine/cysteine redox cycle is limited. A high-MYCN state in neuroblastoma cells sensitizes them to lipid peroxidation, which in combination with acute intracellular cysteine reduction triggers massive ferroptotic cell death. Taken together, with cystine uptake and transsulfuration, we identified two metabolic processes as novel vulnerabilities of MYCN-amplified neuroblastomas that could be therapeutically exploited. We have furthermore generated model systems suitable for analysing the role of key pathway enzymes in metastasis formation (AHCY, MAT2A). The orthotopic NB model system is now used to validate targets in the cysteine metabolism for NB tumor growth in vitro.
