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We describe a unique patient-derived xenograft (PDX) and cell culture model of succinate dehydrogenase-deficient gastrointestinal stromal tumor (SDH-deficient GIST), a rare mesenchymal tumor that can occur in association with paragangliomas in hereditary and non-hereditary syndromes. This model is potentially important for what it might reveal specifically pertinent to this rare tumor type and, more broadly, to other types of SDH-deficient tumors. The primary tumor and xenografts show a very high proliferative fraction, and distinctive morphology characterized by tiny cells with marked autophagic activity. It is likely that these characteristics resulted from the combination of the germline SDHB mutation and a somatic KRAS G12D mutation. The most broadly relevant findings to date concern oxygen and oxidative stress. In paragangliomas harboring SDHx mutations, both hypoxic signaling and oxidative stress are putative drivers of tumor growth. However, there are no models for SDH-deficient paragangliomas. This related model is the first from a SDHB-mutated human tumor that can be experimentally manipulated to study mechanisms of oxygen effects and novel treatment strategies. Our data suggest that tumor growth and survival require a balance between protective effects of hypoxic signaling vs deleterious effects of oxidative stress. While reduced oxygen concentration promotes tumor cell survival, a further survival benefit is achieved with antioxidants. This suggests potential use of drugs that increase oxidative stress as novel therapies. In addition, autophagy, which has not been reported as a major finding in any type of SDH-deficient tumor, is a potential target of agents that might trigger autophagic cell death.
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Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
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Tumors caused by loss-of-function mutations in genes encoding TCA cycle enzymes have been recently discovered and are now of great interest. Mutations in succinate dehydrogenase (SDH) subunits cause pheochromocytoma/paraganglioma (PCPG) and syndromically associated tumors, which differ phenotypically and clinically from more common SDH-intact tumors of the same types. Consequences of SDH deficiency include rewired metabolism, pseudohypoxic signaling and altered redox balance. PCPG with SDHB mutations are particularly aggressive, and development of treatments has been hampered by lack of valid experimental models. Attempts to develop mouse models have been unsuccessful. Using a new strategy, we developed a xenograft and cell line model of SDH-deficient pheochromocytoma from rats with a heterozygous germline Sdhb mutation. The genome, transcriptome and metabolome of this model, called RS0, closely resemble those of SDHB-mutated human PCPGs, making it the most valid model now available. Strategies employed to develop RS0 may be broadly applicable to other SDH-deficient tumors.
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Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia
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