Evaluation of the alkaline comet assay and urinary 3-methyladenine excretion for monitoring DNA damage in melanoma patients treated with dacarbazine and tamoxifen.
OBJECTIVE
To develop, using dacarbazine as a model, reliable techniques for measuring DNA damage and repair as pharmacodynamic endpoints for patients receiving chemotherapy.


METHODS
A group of 39 patients with malignant melanoma were treated with dacarbazine 1 g/m(2) i.v. every 21 days. Tamoxifen 20 mg daily was commenced 24 h after the first infusion and continued until 3 weeks after the last cycle of chemotherapy. DNA strand breaks formed during dacarbazine-induced DNA damage and repair were measured in individual cells by the alkaline comet assay. DNA methyl adducts were quantified by measuring urinary 3-methyladenine (3-MeA) excretion using immunoaffinity ELISA. Venous blood was taken on cycles 1 and 2 for separation of peripheral blood lymphocytes (PBLs) for measurement of DNA strand breaks.


RESULTS
Wide interpatient variation in PBL DNA strand breaks occurred following chemotherapy, with a peak at 4 h (median 26.6 h, interquartile range 14.75-40.5 h) and incomplete repair by 24 h. Similarly, there was a range of 3-MeA excretion with peak levels 4-10 h after chemotherapy (median 33 nmol/h, interquartile range 20.4-48.65 nmol/h). Peak 3-MeA excretion was positively correlated with DNA strand breaks at 4 h (Spearman's correlation coefficient, r=0.39, P=0.036) and 24 h (r=0.46, P=0.01). Drug-induced emesis correlated with PBL DNA strand breaks (Mann Whitney U-test, P=0.03) but not with peak 3-MeA excretion.


CONCLUSIONS
DNA damage and repair following cytotoxic chemotherapy can be measured in vivo by the alkaline comet assay and by urinary 3-MeA excretion in patients receiving chemotherapy.
Braybrooke
J P
JP
Imperial Cancer Research Fund Medical Oncology Unit, Churchill Hospital, Oxford OX3 7LJ, UK.
Houlbrook
S
S
Crawley
J E
JE
Propper
D J
DJ
O'Byrne
K J
KJ
Stratford
I J
IJ
Harris
A L
AL
Shuker
D E
DE
Talbot
D C
DC
D000225:Adenine / Q000031:analogs & derivatives* / Q000652:urine; D000328:Adult; D000368:Aged; D018906:Antineoplastic Agents, Alkylating / Q000009:adverse effects* / Q000627:therapeutic use; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects*; D003606:Dacarbazine / Q000009:adverse effects* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008214:Lymphocytes; D008297:Male; D008545:Melanoma / Q000188:drug therapy* / Q000235:genetics; D008875:Middle Aged; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000235:genetics
D018906:Antineoplastic Agents, Alkylating; C025946:3-methyladenine; D003606:Dacarbazine; D000225:Adenine