TRAP-1 Is a New Surrogate Marker for SDH Mutation in Pheochromocytoma/Paraganglioma and a Potential Target for Chemotherapy.
James F Powers, Stephanie M Fliedner, Irwin Leav, Dario C Altieri, Karel Pacak, Arthur S Tischler. Tufts Medical Center, Boston, MA; NIH/NICHD, Bethesda, MD; University of Massachusetts Medical Center, Worcester; Wistar Institute, Philadelphia, PA
Background: TNF receptor-associated protein 1 (TRAP-1) is an anti-apoptotic protein related to HSP-90 that accumulates in mitochondria of a variety of tumor cells but not of normal cells. Gamitrinibs are a new class of drugs that target TRAP-1 and induce tumor cell death (Kang et al, J Clin Invest 119:454-64, 2009). The mitochondrial enzyme succinate dehydrogenase (SDH) is the critical link between the Krebs cycle and the mitochondrial electron transport chain. Germline mutations of the SDHA, B, C and D genes are causes of hereditary pheochromocytoma/paraganglioma (PCC/PGL) syndromes. PCC/PGL associated with SDHB mutations are particularly likely to metastasize, and there are currently no effective treatments after metastases have occurred. It is therefore important to distinguish patients harboring SDH mutations from those with sproradic tumors.
Design: We hypothesized that PCC/PGL harboring SDH mutations might be particularly prone to accumulate TRAP-1 because of their intrinsic mitochondrial defect. Eighteen genetically characterized PCC/PGL (10 SDHB or SDHD, 5 sporadic, 3 VHL) were analysed for TRAP-1 protein expression by immunohistochemistry (IHC). Staining was scored 0-3 based on percentage of stained cells and staining intensity. Immunoblots (IB) were also performed on 9 of the tumors. Gamitrinib cytotoxicity was tested using Gamitrinib-triphenylphosphonium in cell cultures of a mouse pheochromocytoma (MPC) cell line expressing high levels of TRAP-1 and in primary cultures of a separate set of 5 human PCC/PGL that showed variable TRAP-1 expression in IBs.
Results: TRAP-1 immunostaining was positive in all but one SDH-mutated tumor and was completely negative in all sporadic tumors. One VHL tumor also showed positive staining. IB confirmed the association of TRAP-1 with SDH mutation. In the mouse cell culture model gamitrinib (10uM) caused 60-65% cell death at 1 week of treatment and 90-95% cell death at 2 weeks. Responses of the human tumors ranged from no effect to ∼ 60% cell death at 2 weeks.
Conclusions: IHC for TRAP-1 is promising as a new tool to triage patients who present with apparently sporadic PCC/PGL to be genetically tested for SDH mutations. In addition, some PCC/PGL expressing high levels of TRAP-1 might respond to treatment with gamitrinibs. The latter possibility requires further pre-clinical testing. This research was supported in part by a grant from the PheoPara Alliance (to AST).
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 47, Tuesday Afternoon