Decreased cisplatin/DNA adduct formation is associated with cisplatin resistance in human head and neck cancer cell lines.
OBJECTIVE
To evaluate the correlation between cisplatin sensitivity, intracellular glutathione, and platinum/DNA adduct formation (measured by atomic absorption spectroscopy) in a series of seven head and neck cancer cell lines, and to evaluate the effect of biochemical modulation of glutathione on platinum/DNA adduct formation and repair.


METHODS
Cisplatin/DNA adducts were measured by atomic absorption spectroscopy. Glutathione content was measured by enzymatic assay and was modulated with buthionine sulfoximine. Apoptosis was measured by double-labeled flow cytometry.


RESULTS
Intracellular glutathione concentration was strongly correlated with cisplatin resistance (P = 0.002, R2 = 0.7). There was also a statistically significant inverse correlation between cisplatin/DNA adduct formation and the IC50 for cisplatin in these cell lines. (P = 0.0004, R2 = 0.67). In addition, resistant cells were able to repair approximately 70% of cisplatin/DNA adducts at 24 h, while sensitive cells repaired less than 28% of adducts in the same period. However, despite the positive correlation between cellular glutathione and cisplatin resistance, there was no direct correlation between intracellular glutathione concentration and platinum/DNA adduct formation. Further, depletion of intracellular glutathione by buthionine sulfoximine did not dramatically alter formation of cisplatin/DNA adducts even though it resulted in marked increase in cisplatin cytotoxicity and was associated with increased apoptosis.


CONCLUSIONS
These results suggest that glutathione has multiple effects not directly related to formation of cisplatin/DNA adducts, but may also be an important determinant of the cell's ability to repair cisplatin-induced DNA damage and resist apoptosis.
Yang
Z
Z
Lombardi Cancer Center, Georgetown University, Washington, DC 20007, USA.
Faustino
P J
PJ
Andrews
P A
PA
Monastra
R
R
Rasmussen
A A
AA
Ellison
C D
CD
Cullen
K J
KJ
D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D002945:Cisplatin / Q000633:toxicity*; D018736:DNA Adducts / Q000187:drug effects* / Q000235:genetics; D004260:DNA Repair / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005978:Glutathione / Q000378:metabolism; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D018307:Neoplasms, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D010984:Platinum / Q000737:chemistry; D013054:Spectrophotometry, Atomic; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D018736:DNA Adducts; D010984:Platinum; D005978:Glutathione; D002945:Cisplatin