DNA Alkylation Products Formed by 1-(2-chloroethyl)-1-nitrosourea As Molecular Dosimeters of Therapeutic Response

This study has investigated if individual DNA adducts formed in human glioma cells treated with (3)H-1-(2-chloroethyl)-1-nitrosourea ((3)H-CNU) could be used as molecular dosimeters of response after CENU treatment. The levels of individual DNA alkylation products were compared with the induction of cytotoxicity in six human glioma cell lines after treatment with (3)H-CNU. The levels of seven DNA adducts N7-(2-hydroxyethyl)guanine, (N7-HOEtG); N7-(2-chloroethyl)guanine, (N7-ClEtG); 1,2-[diguan-7-yl]-ethane, (N7-bis-G); N1-(2-hydroxyethyl)-2-deoxyguanosine, N1-HOEtdG; 1-[N1-2-deoxyguanosinyl], 2-[N3-2-deoxycytidyl]-ethane, dG-dC; O(6)-(2-hydroxyethyl)-2-deoxyguanosine, O(6)-HOEtdG and phosphotriesters (PTE), were quantified in each of the cell lines following treatment with (3)H-CNU. The levels of N7-HOEtG, N7-ClEtG; O(6)-HOEtdG and PTE were not significantly different in the glioma lines and their levels were not associated with the induction of cytotoxicity by CNU treatment. The levels of N7-bis-G, N1-HOEtdG and dG-dC crosslink were significantly lower in both SF-188 and SF-763 cell lines compared to their levels in U87MG, U251MG and SF-126. There was a significant correlation between CNU LD(10) values and with the levels of levels of N7-bis-G and N1-HOEtdG (R = -0.91, P = 0.01) and dG-dC crosslink (R = -0.94, P = 0.005) in the glioma cell lines. Pretreatment of SF-188 cells with varying concentrations of MNU prior to CNU treatment resulted in no change in the levels of N7-HOEtG, N7-ClEtG; O(6)-HOEtdG and PTE and a dose dependent increase in the levels of N7-bis-G, N1-HOEtdG and dG-dC crosslink. Taken together, these results suggest that the levels of the N7-bis-G, N1-HOEtdG and dG-dC crosslink could be used as molecular dosimeters of therapeutic response following treatment with BCNU or related CENU.