Relationship between the exposure to cisplatin, DNA-adduct formation in leucocytes and tumour response in patients with solid tumours

The study was designed to investigate possible relationships between tumour response and exposure to cisplatin (area under the curve of unbound cisplatin in plasma, AUC) and DNA-adduct formation in leucocytes (WBC) in patients with solid tumours. Patients were treated with six weekly courses of cisplatin at a dose of 70 or 80 mg m^-2. The AUC was determined during the first course and DNA-adduct levels in WBC during all courses at baseline, 1 h (A(max) and 15 h after a 3 h infusion of cisplatin. The area under the DNA-adduct-time curve (AUA) was calculated. The tumour response was determined after six courses. Forty-five evaluable patients received 237 courses of cisplatin. Sixteen patients with head and neck cancer received a dose of 80 mg m^-2 and 29 with various other tumour types received 70 mg m^-2 plus daily 50 mg oral etoposide. There were 20 responders (partial and complete) and 25 non-responders (stable and progressive disease). The AUC was highly variable (mean ± s.d. = 2.48 ± 0.51 μg h^-1 ml^-1; range 1.10-3.82) and was closely correlated with the AUA (r = 0.78, P < 0.0001) and A(max) (r = 0.73, P < 0.0001). The AUC, AUA and A(max) were significantly higher in responders than in non-responders in the total population (P < 0.0001) and in the two subgroups treated at 70 or 80 mg m^-2. In logistic regression analysis AUC, AUA and A(max) were important predictors of response. The magnitude of exposure to cisplatin is, through DNA-adduct formation, the major determinant of the response rate in this population. Hence, individualised dosing of cisplatin using AUC or DNA-adducts should lead to increased response rates.