Influence of therapy on the antioxidant status in patients with melanoma

Some anticancer drugs can result in increased production of reactive oxygen species (ROS). Alkylating agents are the most frequently used drugs in chemotherapeutic regimens for the treatment of malignant melanoma. It is known that triazenes exhibit in vivo activity by alkylation of nucleic acids and proteins, but there is no data about ROS formation during oxidative metabolism. Single agents of most interest for treatment of malignant melanomas include 5-(3,3-dimethyltriazene-1-yl)-imidazole-4-carboxamide (DTIC) and nitrosoureas such as 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), but complete response to these drugs is rare. The present study aimed to determine whether an oxidative stress occurs during the clinical course of melanoma and the influence of therapy on the antioxidant status of patients with melanoma. For this purpose, we investigated plasma concentrations of MDA as indices of the levels of lipid peroxidation products. In addition, we studied the activities of the antioxidant enzymes superoxide dismutases (SOD) and catalase (CAT) in patients with melanoma before any treatment, after surgical removal of melanoma, and after chemotherapy with DTIC or in combination with CCNU of the operated patients.

Twenty one patients with melanoma were studied. Patients were operated prior to chemotherapy. After recovery for 10-20 days postoperatively, they were studied again for MDA, SOD and CAT activity. The patients were divided into two groups according to the chemotherapy (3-7 treatment cycles): with DTIC-given orally daily for 5 days, every 3 weeks as a single 2200 mg/kg dose and with the combination-DTIC (the same dose) + CCNU-administered orally at a dosage of 120 mg/m(2) once every 40 days in accordance with protocols, approved by the Bulgarian Ministry of Health. The total amount of lipid peroxidation products in plasma was assayed.

Plasma levels of MDA and CAT activity were significantly higher, and erythrocyte SOD activity significantly lower, in patients with melanoma, than in control healthy volunteers (P < 0.0001). Ten to twenty days after surgery, oxidative stress decreased but levels of MDA increased as a result of therapy. Important sources of increased ROS production may be the monocytes, phagocytosis of tumour cells and the cancer tissues. Plasma MDA in patients treated with DTIC + CCNU were significantly higher (P < 0.001), but erythrocyte SOD statistically lower (P < 0.00001), compared with patients treated with DTIC only. However, a combination of DTIC + CCNU did not attenuate oxidative stress, or reduced antioxidant status. Patients treated with this combination are at bigger risk of oxidative injury. Therefore, this disturbance might be due to augmented generation of toxic ROS, possibly from the metabolism of CCNU.

Increased oxidative stress follows an imbalance in antioxidant defence in non-treated patients with melanoma. The impaired antioxidant system favours accumulation of ROS, which may promote the cancer process. After complete removal of melanoma tissues, oxidative stress decreased. The antioxidant status of melanoma patients operated on was influenced by the different chemotherapeutic regimens used and may play an important role in the response. Patients on DTIC + CCNU are at higher risk of oxidative injury. This drug combination probably exerts its toxic activity by ROS, which could be products of the metabolism of CCNU.