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

Purpose: To investigate the genetic basis of cisplatin resistance. Efficacy of cisplatin chemotherapy in the treatment of distinct malignancies is often hampered by intrinsic/ acquired drug resistance of tumors. Experimental design: We produced 14 orthoxenograft transplanting human nonseminomatous (NSE) testicular germ cell tumors (TGCTs) to mice, keeping the primary tumor features (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 vivo. 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 in metastatic TGCTs. We study the expression profile of the sixty genes located at that genomic region. POLE3 and AKNA were the only two genes deregulated in resistant tumors harboring the 9q32-q33.1 gain. 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 C. elegans indicate that the influence of 9q32-q33.1 genes in cisplatin resistance can be driven by either up- or down-regulation. We focused on glucosylceramide synthase (GCS) to demonstrate that the GCS inhibitor DL-threo-PDMP re-sensitizes cisplatin-resistant germline-derived orthoxenografts to cisplatin. Conclusions: Orthoxenografts can be used preclinically to test the efficiency of drugs and also to identify prognosis markers and gene alterations acting as drivers of the acquired cisplatin resistance.

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