Assessment of the inhibitory effects of different radiation qualities or chemotherapeutic agents on a human melanoma cell line

The correlation between time dependent viabilities, after applying two radiation qualities and two alkylating agents on HTB140 melanoma cells, has been studied. Irradiations were performed with γ-rays and 62 MeV protons, close to the Bragg peak maximum, delivering doses of 8–24 Gy. Treatments with fotemustine (FM) and dacarbazine (DTIC) were carried out with concentrations of 0.05–2 mM. High radio-resistance of HTB140 cells revealed by a clonogenic assay was confirmed by microtetrasolium and sulforhodamine B, through the surviving fraction at 2 Gy (SF2), being 0.961–0.956 for γ-rays and 0.931–0.887 for protons. A better efficiency of protons was illustrated by relative biological effectiveness at 2 Gy (RBE), ranging from 1.69 to 1.89. A kinetic study of concentration dependent cytotoxicity indicated that the best effect of the drugs, estimated as the concentration that produces 50% of growth inhibition (IC50), was obtained at 48 h, having values of 76 μM for DTIC and 145 μM for FM. The cytostatic ability of the drugs pointed out that the presence of DTIC at 24 h, compared to FM, was insufficient to produce an effect. Protons and FM demonstrated their pro apoptotic capacity. Cross-resistance between treatments applied to the HTB140 cells was observed, protons being the most efficient, while DTIC, FM and γ-rays demonstrated a lower level of cell inactivation.