title: Cytocidal activities of topoisomerase 1 inhibitors and 5-azacytidine against pheochromocytoma/paraganglioma cells in primary human tumor cultures and mouse cell lines.
abstract: There is currently no effective treatment for metastatic pheochromocytomas and paragangliomas. A deficiency in current chemotherapy regimens is that the metastases usually grow very slowly. Drugs that target dividing tumor cells have therefore had limited success. To improve treatment, new strategies and valid experimental models are required for pre-clinical testing. However, development of models has itself been hampered by the absence of human pheochromocytoma/paraganglioma cell lines for cultures or xenografts. Topoisomerase 1 (TOP1) inhibitors are drugs that interfere with mechanisms that maintain DNA integrity during transcription in both quiescent and dividing cells. We used primary cultures of representative human tumors to establish the cytotoxicity of camptothecin, a prototypical TOP1 inhibitor, against non-dividing pheochromocytoma/paraganglioma cells, and then employed a mouse pheochromocytoma model (MPC) to show that efficacy of low concentrations of camptothecin and other TOP1 inhibitors is increased by intermittent coadministration of sub-toxic concentrations of 5-azacytidine, a DNA methylation inhibitor that modulates transcription. We then tested the same drugs against a clonal MPC derivative that expresses CMV reporter-driven luciferase and GFP, intended for in vivo drug testing. Unexpectedly, luciferase expression, bioluminescence and GFP expression were paradoxically increased by both camptothecin and SN38, the active metabolite of irinotecan, thereby masking cell death. Expression of chromogranin A, a marker for neuroendocrine secretory granules, was not increased, indicating that the drug effects on levels of luciferase and GFP are specific to the GFP-luciferase construct rather than generalized cellular responses. Our findings provide proof of principle for use of TOP1 inhibitors against pheochromocytoma/paraganglioma and suggest novel strategies for enhancing efficacy and reducing toxicity by optimizing the combination and timing of their use in conjunction with other drugs. The paradoxical effects of TOP1 inhibitors on luciferase and GFP dictate a need for caution in the use of CMV promoter-regulated constructs for cancer-related imaging studies.
authors: Department of Pathology, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors: James F
authors: JF
authors: Powers
authors: Small Animal Imaging/Preclinical Testing Facility, Tufts University School of Medicine, Boston, Massachusetts, United States of America.
authors: Parimal G
authors: PG
authors: Korgaonkar
authors: Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America ; 1st Department of Medicine, University Medical Center Schleswig-Holstein Lübeck, Lübeck, Germany.
authors: Stephanie
authors: S
authors: Fliedner
authors: Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America.
authors: Alessio
authors: A
authors: Giubellino
authors: Department of Pathology, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors: Karel
authors: K
authors: Pacak
authors: G Gary
authors: GG
authors: Sahagian
authors: Department of Pathology, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors: Arthur S
authors: AS
authors: Tischler
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000188:drug therapy* / Q000473:pathology; D000818:Animals; D001374:Azacitidine / Q000494:pharmacology / Q000627:therapeutic use*; D016923:Cell Death / Q000187:drug effects*; D045744:Cell Line, Tumor; D006801:Humans; D051379:Mice; D010235:Paraganglioma / Q000188:drug therapy* / Q000473:pathology; D010673:Pheochromocytoma / Q000188:drug therapy* / Q000473:pathology; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D059004:Topoisomerase I Inhibitors; D001374:Azacitidine