The inhibition of glutamine synthetase sensitizes human sarcoma cells to L-asparaginase.
OBJECTIVE
To evaluate the activity of the antitumor enzyme L: -asparaginase (ASNase) on tumor cells of mesenchymal origin and the contribution of glutamine synthetase (GS) to the adaptation to the metabolic stress caused by the anti-tumor enzyme.


METHODS
We studied the effects of ASNase in six human sarcoma cell lines: HT1080 (fibrosarcoma); RD (rhabdomyosarcoma); SW872 (liposarcoma); HOS, SAOS-2, and U2OS (osteosarcoma) in the absence or in the presence of the GS inhibitor methionine L: -sulfoximine (MSO).


RESULTS
HT1080 and SW872 cells were highly sensitive to ASNase-dependent cytotoxicity. In contrast, RD, SAOS-2, HOS, and U2OS cells exhibited only a partial growth suppression upon treatment with the anti-tumor enzyme. In these cell lines ASNase treatment was associated with increased levels of GS. When ASNase was used together with MSO, the proliferation of the poorly sensitive cell lines was completely blocked and a significant decrease in the IC(50) for ASNase was observed. Moreover, when ASNase treatment was carried on in the presence of MSO, HOS and U2OS osteosarcoma cells exhibited a marked cytotoxicity, with increased apoptosis.


CONCLUSIONS
In human sarcoma cells (1) GS markedly contributes to the metabolic adaptation of tumor cells to ASNase and (2) the inhibition of GS activity enhances the antiproliferative and cytotoxic effects of ASNase. The two-step interference with glutamine metabolism, obtained through the combined treatment with ASNase and MSO, may provide a novel therapeutic approach that should be further investigated in human tumors of mesenchymal origin.
Tardito
S
S
Unit of General and Clinical Pathology, Department of Experimental Medicine, University of Parma, Italy.
Uggeri
J
J
Bozzetti
C
C
Bianchi
M G
MG
Rotoli
B M
BM
Franchi-Gazzola
R
R
Gazzola
G C
GC
Gatti
R
R
Bussolati
O
O
D000970:Antineoplastic Agents / Q000494:pharmacology; D001215:Asparaginase / Q000494:pharmacology*; D020169:Caspases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D008717:Methionine Sulfoximine / Q000494:pharmacology; D012509:Sarcoma / Q000188:drug therapy* / Q000201:enzymology*; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D008717:Methionine Sulfoximine; D020169:Caspases; D001215:Asparaginase; D005974:Glutamate-Ammonia Ligase