Abstract
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. Clin Cancer Res; 24(15); 3755-66. ©2018 AACR.
Highlights
Testicular germ cell tumors (TGCT) of adolescent and young adults are the most common malignancy in young men [1,2,3]
Establisment of orthoxenografts of TGCT NSE tumors To study cisplatin resistance in TGCTs, our laboratory has compiled a valuable collection (n 1⁄4 14) of both cisplatin-sensitive and -refractory TGCT NSE orthoxenografts (Supplementary Table S1). These orthoxenografts grew on mouse testicles as a big solid mass, displaying a strong correlation with their corresponding primary tumors in terms of histological appearance and expression of cellular markers (Fig. 1A and B). These tumors were kept stable throughout serial passages and, as occurring in patients, the secreted beta subunit of human chorionic gonadotropin (b-hCG) and/or alpha-fetoprotein (AFP) were detected in mouse serum as surrogate markers of tumor growth (Supplementary Table S1; refs. 27, 28)
Orthoxenografts reproduce in mice some of the patterns of dissemination observed in humans with the presence of retroperitoneal lymph nodes, lungs, and liver metastasis
Summary
Testicular germ cell tumors (TGCT) of adolescent and young adults are the most common malignancy in young men [1,2,3]. They can be classified as seminomas (SE; originated in epithelium of the seminiferous tubules), which represent around 40% of cases, and nonseminomas (NSE; 60%). 10%–15% of patients die due to cisplatin refractoriness and the absence of alternative effective resensitizing therapies [5,6,7] Such high success in treating advanced testicular cancer has limited the number of studies addressing the treatment failure in refractory patients [8, 9]
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