Orthoxenografts of testicular germ cell tumors demonstrate genomic changes associated with cisplatin resistance and identify PDMP as a resensitizing agent

[Purpose] To investigate the genetic basis of cisplatin resistance as efficacy of cisplatin-based chemotherapy in the treatment of distinct malignancies is often hampered by intrinsic or acquired drug resistance of tumor cells.[Experimental Design] We produced 14 orthoxenograft transplanting human nonseminomatous testicular germ cell tumors (TGCT) in mice, keeping the primary tumor features in terms of genotype, phenotype, and sensitivity to cisplatin. Chromosomal and genetic alterations were evaluated in matched cisplatin-sensitive and their counterpart orthoxenografts that developed resistance to cisplatin in nude mice.[Results] Comparative genomic hybridization analyses of four matched orthoxenografts identified recurrent chromosomal rearrangements across cisplatin-resistant tumors in three of them, showing gains at 9q32-q33.1 region. We found a clinical correlation between the presence of 9q32-q33.1 gains in cisplatin-refractory patients and poorer overall survival (OS) in metastatic germ cell tumors. We studied the expression profile of the 60 genes located at that genomic region. POLE3 and AKNA were the only two genes deregulated in resistant tumors harboring the 9q32-q33.1 gain. Moreover, other four genes (GCS, ZNF883, CTR1, and FLJ31713) were deregulated in all five resistant tumors independently of the 9q32-q33.1 amplification. RT-PCRs in tumors and functional analyses in Caenorhabditis elegans (C. elegans) indicate that the influence of 9q32-q33.1 genes in cisplatin resistance can be driven by either up- or downregulation. We focused on glucosylceramide synthase (GCS) to demonstrate that the GCS inhibitor DL-threo-PDMP resensitizes cisplatin-resistant germline-derived orthoxenografts to cisplatin[Conclusions] Orthoxenografts can be used preclinically not only to test the efficiency of drugs but also to identify prognosis markers and gene alterations acting as drivers of the acquired cisplatin resistance.Several authors are grateful recipients of predoctoral fellowships: J.M. Piulats from the AECC and F.J. García-Rodríguez from the Instituto de Salud Carlos III (ISCIII). This study was supported by grants from the Spanish Ministry of Economy and Competitiveness (SAF2002-02265 and FIS: BFU2007-67123; PI10-0222, PI13-01339, and PI16/01898, to A. Villanueva; PI15-00895, to J. Ceron; SAF2013-46063R, to F. Vi nals; PI030264, to ~ X. García-del-Muro), Fundacio La Marat o TV3 (051430, to F. Vi nals and X. ~ García-del-Muro), Generalitat de Catalunya (2014SGR364, to A. Villanueva and F. Vinals; FIS09/0059, to A. Morales), cofunded by FEDER funds/ ~ European Regional Development Fund (ERDF) — a way to Build Europe. A. Villanueva received a BAE11/00073 grant. We thank the staff of the Animal Core Facility of IDIBELL for mouse care and maintenance.Peer reviewe