Establishment of a melphalan-resistant rhabdomyosarcoma xenograft with cross-resistance to vincristine and enhanced sensitivity following buthionine sulfoximine-mediated glutathione depletion.
A melphalan-resistant human rhabdomyosarcoma xenograft, TE-671 MR, was established in athymic mice by serial melphalan treatment of the parent xenograft, TE-671, at the 10% lethal dosage (LD10); significant resistance was evident after ten passages of the tumor. TE-671 MR demonstrated a doubling time of 3.5 days and a latency period to 1000-mm3 tumors of 27.5 days. The glutathione level of TE-671 MR was 2.36 mumol/g tumor, wet weight, 2-fold higher than the parent line. The glutathione S-transferase activity of TE-671 MR was 117.8 mumol/min/mg protein, essentially unchanged from the parent line. Although TE-671 MR demonstrated cross-resistance to vincristine, dot blot analysis did not reveal an elevated expression of mdr1 mRNA in the resistant line. TE-671 MR demonstrated a 9.7-day growth delay following treatment with melphalan at the LD10 (compared to 20.9 days for the parent line). Treatment with L-buthionine-SR-sulfoximine (BSO) resulted in increased sensitivity to melphalan subsequently administered at 50% of the LD10 (melphalan alone, growth delays of 3.7 and 4.6 days in duplicate trials; melphalan plus BSO, growth delays of 7.2 and 9.8 days). Sensitivity to melphalan equal to that of the parent line TE-671 was not achieved, however. Treatment with BSO did not result in significantly enhanced sensitivity to subsequently administered vincristine (50% of the LD10) (vincristine alone, growth delays of 6.8 and 6.9 days in duplicate trials; vincristine plus BSO, growth delays of 10.9 and 7.5 days). These results suggest that generation of melphalan resistance may be associated with development of cross-resistance to vincristine; this resistance may be associated with (although not necessarily mediated by) glutathione elevation; this resistance may be partially overcome by BSO-mediated depletion of glutathione.
Rosenberg
M C
MC
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710.
Colvin
O M
OM
Griffith
O W
OW
Bigner
S H
SH
Elion
G B
GB
Horton
J K
JK
Lilley
E
E
Bigner
D D
DD
Friedman
H S
HS
D000818:Animals; D019328:Buthionine Sulfoximine; D004347:Drug Interactions; D004351:Drug Resistance; D005260:Female; D005978:Glutathione / Q000037:antagonists & inhibitors*; D005982:Glutathione Transferase / Q000032:analysis; D006801:Humans; D008297:Male; D008558:Melphalan / Q000627:therapeutic use*; D008717:Methionine Sulfoximine / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D012208:Rhabdomyosarcoma / Q000188:drug therapy*; D014183:Transplantation, Heterologous; D014750:Vincristine / Q000627:therapeutic use*
D008717:Methionine Sulfoximine; D019328:Buthionine Sulfoximine; D014750:Vincristine; D005982:Glutathione Transferase; D005978:Glutathione; D008558:Melphalan