The proto-oncogene c-kit and its ligand stem-cell factor (SCF) may play an important role in the development of normal and malignant testicular tissue. This study investigates the presence of SCF and c-kit protein in 32 orchiectomy specimens of patients with testicular cancer, in 5 specimens of normal testicular tissue and in three established non-seminomatous germ-cell cancer cell lines (H12.1, H32, 577ML) by an immunohistochemical approach. Out of 9 testicular cancer specimens classified as pure seminomas, 7 (78%) showed a strong immunohistochemical reaction for both SCF and c-kit protein on the surface of the tumour cells. Fourteen non-seminomatous germ-cell tumours composed of embryonal carcinoma were completely negative for both SCF and c-kit proteins and only faint positivity was found in 6 tumours (26%). Differentiated teratomatous structures within the specimens on non-seminomatous tumours showed a strong immunohistochemical reaction for SCF and c-kit protein in 8 of 11 (73%) cases. All three testicular cancer cell lines showed only faint staining reactions for c-kit protein and none for SCF. No secretion of SCF by the three lines in vitro was detected. The addition of high concentrations of SCF (100 ng/ml) to the testicular cancer cell lines in culture conditions without fetal calf serum resulted in a 1.4 to 3-fold growth stimulation compared to cell growth in serum-free medium alone. This effect was not detectable when the cells were cultured in serum-containing media. In the normal testicular tissue the germ-cells displayed a strong immunohistochemical reaction for c-kit protein while SCF positivity was found at the tubular membrane and on the surface of Sertoli cells. The SCF/c-kit system may possess a regulatory function in normal testicular tissue by possibly providing the microenvironment necessary for spermatogenesis. With the development of testicular cancer, this regulatory system seems to be lost, particularly in non-seminomatous germ-cell tumours. A growth-stimulatory effect of high concentrations of SCF on non-seminomatous testicular cancer cell lines can be detected only in culture conditions with serum-free media. The effects achievable by the combination of SCF with other growth factors need to be further studied, as well as the role of the c-kit/SCF regulatory system for normal spermatogenesis and its possible implications for the understanding and treatment of male infertility.

Naturally occurring chromosomal fusion of the Ewings Sarcoma Oncogene (EWS) to distinct cellular transcription factors, produces aberrant transcriptional activators that function as dominant oncogenes. In Malignant Melanoma of Soft Parts the N-terminal region of EWS is fused to C-terminal region of the cAMP-inducible transcription factor ATF1. The EWS/ATF1 fusion protein binds to ATF sites present in cAMP-responsive promoters via the ATF1 bZIP domain and activates transcription constitutively in a manner that is dependent on an activation domain (EAD) present in EWS. To further define the requirements for trans-activation we have performed mutational analysis of EWS/ATF1 in mammalian cells and report several new findings. First, trans-activation by EWS/ATF1 does not require dimerisation with other ATF family members present in mammalian cells. Second, in contrast to the earlier suggestion of an allosteric role, the EAD can act directly. Third, determinants of trans-activation are dispersed throughout the EAD and cooperate synergistically to produce potent trans-activation. We also report that the region of EWS containing the EAD can activate transcription in Yeast. This latter finding might enable a genetic approach to understanding the mechanism of transcriptional activation by EWS and development of high-throughput screens for EWS inhibitors.

S 9788 is a novel triazinoaminopiperidine derivative which does not belong to any of the classes of compounds known to reverse multidrug resistance (MDR). S 9788 was far more potent than verapamil (VRP) in reversing resistance to adriamycin (ADR) in the ADR-selected murine leukaemia cell lines P388/ADR-1 and P388/ADR-10, and the human chronic myelogenous leukaemia K562/R. Fold reversion with S 9788 (5 microM) was, respectively, 3.5, 5.4 and 11.3 times greater than that with VRP (5 microM). S 9788 was also a more potent reversant of ADR resistance in the intrinsically resistant human colon adenocarcinoma COLO 320DM (2.3 fold), and of vincristine (VCR) resistance in the human MDR1 gene-transfected squamous lung carcinoma line S1/tMDR1 (5.6 fold). The activity of S 9788 depended on both the MDR cell line and the cytotoxic agent. S 9788 (50-100 mg/kg/d) administered IP once a day on days 1-4 resulted in a dose-dependent increase in the chemotherapeutic effect of VCR (0.25 mg/kg/d) in P388/VCR - bearing mice and ADR (4 mg/kg/d) in P388/ADR - bearing mice. Increases in antitumor activity were (% T/C) of +20-34% in the P388/ADR model and + 50-78% in the P388/VCR model with respect to cytotoxic agent treatment alone. S 9788 appeared to be devoid of toxicity at its effective doses. The mechanism of action of S 9788 is unknown but S 9788 (0.5-10 microM) induced a dose-dependent increase in ADR accumulation in KB-Al cells and compared to verapamil its effect was twice as active and approximately seven times more potent. We conclude that S 9788 is a novel agent capable of reversing MDR in vitro and in vivo, and whose pharmacological profile warrants its selection as a candidate drug for eventual assessment in the clinic.

Summary Cisplatin is one of the most active cytotoxic agents in the treatment of testicular cancer, but its clinical use is associated with side-effects such as ototoxicity, neurotoxicity and nephrotoxicity. Long-term kidney damage from cisplatin particularly affects the proximal tubular apparatus and can be detected by increased urinary excretion of brush-border enzymes, such as L-alanine-aminopeptidase (AAP), and magnesium. In the current study, the flavonoid silibinin was used as a nephroprotectant for cisplatin-induced nephropathy in a rat animal model. Infusion of silibinin before cisplatin results in a significant decrease in glomerular (indicated by creatinine clearance and serum urea level) and tubular kidney toxicity (excretion of brush-border enzymes and magnesium). Silibinin given alone had no effect on renal function. In order to exclude an inhibition of the anti-tumour activity of cisplatin and 4-hydroperoxy-ifosfamide by coadministration of silibinin, in vitro studies were performed in three established human testicular cancer cell lines. Dose-response curves for cisplatin (3-30 000 nmol) combined with non-toxic silibinin doses (7.25 x 10-6 or 7.25 x 10-5 mol 1-1) did not deviate significantly from those of cisplatin alone as measured by relative cell survival during a 5 day assay using the sulphorhodamine-B staining technique. Also silibinin did not influence the cytotoxic activity of 4-hydroperoxy-ifosfamide (30-10 000 nmol) in vitro. In summary, these in vitro data rule out a significant inhibition of the anti-tumour activity of the major nephrotoxic components, cisplatin and 4-hydroperoxy-ifosfamide, by co-administration of silibinin in a human germ cell tumour cell line model. Together with these demonstrated cytoprotection effects in the rat animal model, these data form the basis for a randomised clinical trial of silibinin for the protection of cisplatin-associated nephrotoxicity in patients with testicular cancer.

The expression of the major histocompatibility complex (MHC) class I antigens is suppressed in early postimplantation embryonic cells as well as in embryonal carcinoma (EC) cells, but could be upregulated by treatment with interferon (IFN)-g or retinoic acid. In a number of human and murine tumours, defects in the expression of the different components of the MHC class I antigen processing machinery, such as the proteasomal subunits LMP-2 and LMP-7 and the peptide transporters TAP-1 and TAP-2, account for impaired MHC class I surface expression. Here, we analysed the constitutive and IFN-g regulated mRNA and protein expression of the LMP, TAP and MHC class I molecules in the human EC line 577LM. In comparison to lymphoblastoid control cells, poor constitutive mRNA and protein expression of LMP-7, TAP-1, HLA class I, and b 2 -microglobulin, but not of TAP-2 and LMP-2, was detected in 577LM cells. The lack of MHC class I surface expression on 577LM cells could not be enhanced either by culturing cells at low temperature or by their incubation with exogenous MHC class I specific binding peptides: thus, the defective MHC class I surface expression was not only caused by impaired generation and processing of antigenic peptides. IFN-g treatment of 577LM resulted in a significant increase of MHC class I surface expression which was preceded by an upregulation of TAP, LMP and MHC class I transcripts as well as of TAP-1 and TAP-2, but not of LMP-2 and LMP-7, protein expression. These data suggest that human EC cell lines show a stable expression of a MHC class I low/deficient phenotype. The deficiencies associated with this phenotype involve different levels of the MHC class I restricted antigen presentation machinery and could be modified by treatment with IFN-g.

Approximately 70-80% of patients with metastatic testicular cancer will become disease free with cisplatin-based chemotherapy and most of these patients will be long-term survivors. Despite these impressive results, the two limitations of cisplatin are its severe and potentially long-term side-effects, and the emergence of drug resistance which prevents a small proportion of these patients from achieving long-term remission. Oxaliplatin has an improved toxicity profile compared to cisplatin and contains the diaminocyclohexane (DACH) substituent known to be correlated with a lack of cross-resistance with cisplatin. A phase II study has shown interesting activity when used in combination with cisplatin in cisplatin-refractory testicular cancer patients. Here we report the results of the first in vitro study investigating whether oxaliplatin as a single agent exhibits cross-resistance to cisplatin in a panel of non-seminomatous germ cell tumor (NSGCT) cell lines using short and long-term drug exposures in a five-day sulfhodamine B in vitro cytotoxicity assay. Oxaliplatin cytotoxicity was significantly superior to cisplatin in cell lines with both acquired (H12DDP) and intrinsic (1777NRp Cl-A) intermediate level resistance to cisplatin. Following 24 h or 96 h drug exposure the fold resistance in H12DDP and 1777NRp Cl-A was 1.7-2.2 with oxaliplatin compared to 3.9-6.1 with cisplatin. The cytotoxic activity of oxaliplatin was not significantly different from that of cisplatin in cisplatin-sensitive cell lines or in cell lines with a high level (10-20 fold) of cisplatin resistance. The results of this study suggest that further preclinical studies in NSGCT are of interest, particularly in combination with cisplatin, ifosfamide and etoposide. Furthermore, the in vitro results support the use of an oxaliplatin administration schedule giving prolonged drug exposure, such as the flat or circadian rhythm-modulated schedule already under investigation for oxaliplatin.

S 9788, a new triazinoaminopiperidine derivative, was found to be a potent reversant of vincristine resistance in the in vivo murine leukemic P388/VCR model. In two treatment regimens (Q4D days 1, 5 and 9 and QD days 1-9), S 9788 enhanced the antitumor activity of vincristine in a dose-dependent manner, resulting in a complete circumvention of drug resistance for well-tolerated doses of S 9788. S 9788 was also effective in enhancing therapeutic effects of vincristine in the treatment of sensitive P388-bearing mice. These results strongly suggest that S 9788 may be a potential candidate for circumvention of multidrug resistance (MDR) in clinical practice.

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