Journal of Pathology J Pathol 2013; 230: 410–419 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/path.4199 ORIGINAL PAPER Clinical response to chemotherapy in oesophageal adenocarcinoma patients is linked to defects in mitochondria Michaela Aichler, 1,# Mareike Elsner, 1,# Natalie Ludyga, 2 Annette Feuchtinger, 1 Verena Zangen, 3 Stefan K Maier, 1,4 Benjamin Balluff, 1 C´ edrik Sch ¨ one, 1 Ludwig Hierber, 3 Herbert Braselmann, 3 Stephan Meding, 1 Sandra Rauser, 1 Hans Zischka, 5 Michaela Aubele, 2 Manfred Schmitt, 6 Marcus Feith, 7 Stefanie M Hauck, 8 Marius Ueffing, 8 Rupert Langer, 9 Bernhard Kuster, 4 Horst Zitzelsberger, 3 Heinz H ¨ ofler 1,2,9 and Axel K Walch 1 * 1 Research Unit of Analytical Pathology, Institute of Pathology, Helmholtz Zentrum M¨ unchen–German Research Centre for Environmental Health, Neuherberg, Germany 2 Institute of Pathology, Helmholtz Zentrum M¨ unchen–German Research Centre for Environmental Health, Neuherberg, Germany 3 Research Unit of Radiation Cytogenetics, Helmholtz Zentrum M¨ unchen–German Research Centre for Environmental Health, Neuherberg, Germany 4 Department of Proteomics and Bioanalytics, Technische Universit¨ at M¨ unchen, Germany 5 Institute of Toxicology, Helmholtz Zentrum M¨ unchen–German Research Centre for Environmental Health, Neuherberg, Germany 6 Frauenklinik der Technischen Universit¨ at M¨ unchen, Klinikum Rechts der Isar, Munich, Germany 7 Department of Surgery, Klinikum Rechts der Isar, Technische Universit¨ at M¨ unchen, Germany 8 Research Unit of Protein Science, Helmholtz Zentrum M¨ unchen–German Research Centre for Environmental Health, Neuherberg, Germany 9 Institute of Pathology, Technische Universit¨ at M¨ unchen, Germany *Correspondence to: A Walch, Research Unit Analytical Pathology, Institute of Pathology, Helmholtz Zentrum M¨ unchen – German Research Centre for Environmental Health, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany. E-mail: axel.walch@helmholtz-muenchen.de # These authors contributed equally to this study. Abstract Chemotherapeutic drugs kill cancer cells, but it is unclear why this happens in responding patients but not in non- responders. Proteomic profiles of patients with oesophageal adenocarcinoma may be helpful in predicting response and selecting more effective treatment strategies. In this study, pretherapeutic oesophageal adenocarcinoma biopsies were analysed for proteomic changes associated with response to chemotherapy by MALDI imaging mass spectrometry. Resulting candidate proteins were identified by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and investigated for functional relevance in vitro. Clinical impact was validated in pretherapeutic biopsies from an independent patient cohort. Studies on the incidence of these defects in other solid tumours were included. We discovered that clinical response to cisplatin correlated with pre-existing defects in the mitochondrial respiratory chain complexes of cancer cells, caused by loss of specific cytochrome c oxidase (COX) subunits. Knockdown of a COX protein altered chemosensitivity in vitro, increasing the propensity of cancer cells to undergo cell death following cisplatin treatment. In an independent validation, patients with reduced COX protein expression prior to treatment exhibited favourable clinical outcomes to chemotherapy, whereas tumours with unchanged COX expression were chemoresistant. In conclusion, previously undiscovered pre-existing defects in mitochondrial respiratory complexes cause cancer cells to become chemosensitive: mitochondrial defects lower the cells’ threshold for undergoing cell death in response to cisplatin. By contrast, cancer cells with intact mitochondrial respiratory complexes are chemoresistant and have a high threshold for cisplatin-induced cell death. This connection between mitochondrial respiration and chemosensitivity is relevant to anticancer therapeutics that target the mitochondrial electron transport chain. Copyright  2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. Keywords: COX7A2; MALDI imaging mass spectrometry; chemotherapy; oesophageal adenocarcinoma; tumour response Received 21 December 2012; Revised 25 February 2013; Accepted 28 March 2013 No conflicts of interest were declared. Introduction The incidence of oesophageal adenocarcinoma, Barrett’s cancer, is rising more rapidly than that of any other tumour in North America and Europe and most of the patients present with already advanced tumour stages [1]. The most common therapeutic approach for these tumours is a multimodal treat- ment that includes pre-operative application of cis -diamminedichloroplatinum II (cisplatin) and 5-flurouracil (5-FU) chemotherapy, followed by resection [2–8]. Patients who respond to neoadjuvant Copyright  2013 Pathological Society of Great Britain and Ireland. J Pathol 2013; 230: 410–419 Published by John Wiley & Sons, Ltd. www.pathsoc.org.uk www.thejournalofpathology.com