MON-199 Targeting Pheochromocytoma/Paraganglioma with Polyamine Inhibitors

Background: Pheochromocytomas (PCCs) and paragangliomas (PGLs) are neuroendocrine tumors that are mostly benign. Metastatic disease occurs in about 10% of cases, and for these patients no effective therapies are available. Patients with mutations in the succinate dehydrogenase subunit B (SDHB) gene tend to have metastatic disease with very little treatment options. To find a new treatment strategy, we utilized a metabolomics approach to identify unique metabolic pathways. A metabolomic analysis was performed on human hPheo1 cells and shRNA SDHB knockdown hPheo1 (hPheo1 SDHB KD) cells. Additional analysis of 50 human fresh frozen PCC/PGL samples was conducted. Since the polyamine pathway surfaced in the metabolomics analysis, we hypothesized that treatment with polyamine inhibitors would be an effective option for aggressive PCC/PGL tumors. In vitro studies using N1,N11-diethylnorspermine (DENSPM) and N1,N12- diethylspermine (DESPM) treatments were carried out. DENSPM efficacy was assessed in xenograft models. Results: Components of the polyamine pathway were elevated in hPheo1 SDHB KD cells compared to wild-type cells. A similar observation was noted in SDHx PCC/PGLs tumor tissues compared to their SDHB wild-type counterparts. Specifically, spermidine, and spermine were significantly elevated in SDHx-mutated PCC/PGLs, with a similar trend in hPheo1 SDHB KD cells. Polyamine pathway inhibitors DENSPM and DESPM effectively inhibited growth of hPheo1 cells in vitro as well in mouse xenografts. Conclusions: This study demonstrates overactive polyamine pathway in PCC/PGL with SDHB mutations. Treatment with polyamine inhibitors significantly inhibited hPheo1 cell growth and led to growth inhibition in xenograft mouse models treated with DENSPM. These studies strongly implicate the polyamine pathway in PCC/PGL pathophysiology and provide new foundation for exploring the role for polyamine analogue inhibitors in treating metastatic PCC/PGL.

Parkinson's disease-associated human P5B-ATPase ATP13A2 increases spermidine uptake

P-type ion pumps are membrane transporters that have been classified into five subfamilies termed P1–P5. The ion transported by the P5-ATPases is not known. Five genes, ATP13A (ATPase type 13A) 1–ATP13A5, that belong to the P5-ATPase group have been identified in humans. Mutations of the human gene ATP13A2 underlie a form of PD (Parkinson's disease). Previous studies have suggested a relation between polyamines and P5B-ATPases. We have recently shown that the cytotoxicity induced by the polyamine analogue paraquat (1,1′-dimethyl-4,4′-bipyridinium), which is an environmental agent related to PD development, was increased in ATP13A2-expressing CHO (Chinese-hamster ovary) cells. In the present study we showed that ATP13A2-expressing CHO cells exhibit a 2-fold higher accumulation of spermidine. Increasing concentrations of spermidine reduced the viability of CHO cells stably expressing ATP13A2. The higher levels of spermidine attained by the ATP13A2-expressing CHO cells were correlated with an increase in the ATP-dependent spermidine uptake in an isolated subcellular fraction containing lysosomes and late endosomes. The results of the present study support the idea that the human P5B-ATPase ATP13A2 is involved in polyamine uptake.