Ta. Dunn et al., PRECLINICAL ACTIVITY OF TAXOL IN NONSEMINOMATOUS GERM-CELL TUMOR-CELLLINES AND NUDE-MOUSE XENOGRAFTS, Investigational new drugs, 15(2), 1997, pp. 91-98
Taxol (Paclitaxel) is a novel anti-cancer drug which has shown excelle
nt clinical activity in a variety of solid tumors, particularly in met
astatic breast and ovarian cancer. 70-80% of patients with metastatic
non-seminomatous germ cell tumor (NSGCT) attain disease-free status wi
th standard cisplatin-based combination chemotherapy but the emergence
of drug resistance still prevents a small proportion of these patient
s from achieving long-term remission. Here we report the results of pr
e-clinical studies investigating whether taxol exhibits cross-resistan
ce to cisplatin or ifosfamide in human NSGCT cell lines and in a cispl
atin refractory xenograft model of human NSGCT. Following 96-h drug ex
posure in a 5-day sulphohodamine B (SRB) in vitro assay, taxol demonst
rated potent cytotoxicity in cell lines which were cisplatin sensitive
(577 LM, H32, H12.1; mean IC5Os 1.5-3.0 nM) or those with acquired or
intrinsic cisplatin resistance (H12DDP, H23.1; mean IC5Os 2.5 nM). Co
mpared to the drug-sensitive cell line, H12.1, the IC50 values of taxo
l were increased in cell line 1777NRp Cl-A with intermediate level res
istance to cisplatin and ifosfamide (4.7 nM; p > 0.05) and significant
ly elevated in cell line 1411HP, with a high level of cisplatin resist
ance (6.9 nM; p < 0.01). The latter 2 cell lines may represent models
corresponding to patients relapsing after high-dose platinum-based che
motherapy who seem to be resistant to taxol therapy. The IC5Os of taxo
l in H32 and H12DDP were approximately 100-fold lower following drug e
xposure times exceeding 24 hours compared with short exposure times (1
-6 h). Dose-dependent anti-tumor activity was observed with taxol in a
cisplatin-refractory xenograft model of NSGCT (H23.1), with significa
nt anti-tumor activity observed at a dose of 15mg/kg/d injected intrav
enously on days 1 through 5. The results of this study are in accordan
ce with the most recent clinical data which showed that taxol is a use
ful drug in relapsed cisplatin-refractory testicular germ cell cancer,
with significant anti-tumor activity being observed in 25% of patient
s, but poor activity in patients previously treated with high-dose the
rapy. Further pre-clinical research, especially using models such as 1
411HP and 1777NRp Cl-A, on the combinations of taxol with other regime
ns are required to enable successful treatment of the most drug-resist
ant relapsed germ cell tumors.