Evaluation of Chemotherapeutic Drugs for Treatment of (Cisplatin-Resistant) Germ Cell Cancer Cell Lines

The New Tumour Biomarker miRNA-371-3p Influences Cisplatin Sensitivity of Testicular Germ Cell Tumour Cell Lines

Cisplatin is used to treat a variety of malignancies, including testicular germ cell tumours (TGCTs). Although cisplatin-based chemotherapy yields high response rates, a subset of patients develop cisplatin resistance, limiting treatment options and worsening prognosis. Therefore, there is a high clinical need for new therapeutic strategies targeting cisplatin-resistant TGCTs. MicroRNA-371a-3p (miR-371), the new serum biomarker for TGCTs, shows significantly increased expression in cisplatin-resistant TGCT cell lines compared to sensitive parental cell lines. However, the functional impact of miR-371 on cisplatin sensitivity has not been investigated yet. To evaluate the impact of miR-371 on cisplatin sensitivity, antagomirs were used to inhibit miR-371 expression, resulting in a > 98% decrease in miR-371 expression. Cisplatin sensitivity was significantly increased after miR-371 inhibition in cisplatin-resistant and corresponding parental TGCT cell lines, indicating a strongly reduced viability and increased apoptosis after cisplatin treatment in miR-371-inhibited cells. Our results suggest that miR-371 may contribute to the development of cisplatin resistance in TGCTs. Interfering with miR-371 expression can increase the cisplatin sensitivity of tumour cells, which may represent a promising approach to improve future therapeutic outcomes in patients with TGCTs, especially those with cisplatin-resistant disease.

The signal transducer CD24 suppresses the germ cell program and promotes an ectodermal rather than mesodermal cell fate in embryonal carcinomas

Testicular germ cell tumors (GCTs) are stratified into seminomas and nonseminomas. Seminomas share many histological and molecular features with primordial germ cells, whereas the nonseminoma stem cell population-embryonal carcinoma (EC)-is pluripotent and thus able to differentiate into cells of all three germ layers (teratomas). Furthermore, ECs are capable of differentiating into extra-embryonic lineages (yolk sac tumors, choriocarcinomas). In this study, we deciphered the molecular and (epi)genetic mechanisms regulating expression of CD24, a highly glycosylated signaling molecule upregulated in many cancers. CD24 is overexpressed in ECs compared with other GCT entities and can be associated with an undifferentiated pluripotent cell fate. We demonstrate that CD24 can be transactivated by the pluripotency factor SOX2, which binds in proximity to the CD24 promoter. In GCTs, CD24 expression is controlled by epigenetic mechanisms, that is, histone acetylation, since CD24 can be induced by the application histone deacetylase inhibitors. Vice versa, CD24 expression is downregulated upon inhibition of histone methyltransferases, E3 ubiquitin ligases, or bromodomain (BRD) proteins. Additionally, three-dimensional (3D) co-cultivation of EC cells with microenvironmental cells, such as fibroblasts, and endothelial or immune cells, reduced CD24 expression, suggesting that crosstalk with the somatic microenvironment influences CD24 expression. In a CRISPR/Cas9 deficiency model, we demonstrate that CD24 fulfills a bivalent role in differentiation via regulation of homeobox, and phospho- and glycoproteins; that is, it is involved in suppressing the germ cell/spermatogenesis program and mesodermal/endodermal differentiation, while poising the cells for ectodermal differentiation. Finally, blocking CD24 by a monoclonal antibody enhanced sensitivity toward cisplatin in EC cells, including cisplatin-resistant subclones, highlighting CD24 as a putative target in combination with cisplatin.