DNA alkyation and mutagenicity of related hydroxypropylating and methylating agents in V79 cells

N‐Nitrosobis (2‐hydroxypropyl) amine (BHP) and N‐nitrosobis (2‐oxopropyl) amine (BOP) require metabolism to be carcinogenic and mutagenic. This metabolism produces hydroxypropylating and methylating alkylating species. To measure the effects of these species, we compared the action of direct‐acting model compounds that are hydroxypropylating or methylating agents with those of BHP and BOP. Mutagenicity in V79 cells and the alkylation of V79 cell DNA were measured. The model compounds were ethyl‐N‐nitroso (2‐oxopropyl) carbamate (NOPC), a methylating agent, and its 2‐hydroxypropyl congener (NHPC), a hydroxypropylating agent. BHP and BOP were metabolized by hepatocytes from male Syrian hamsters. At the highest dose (2 mM) BOP produced 12 times more mutants than BHP but only 2.5 times more O⁶methylguanine (O⁶MeG) than BHP. When a pancreas duct homogenate was used, 87 (BOP) and six (BHP) mutants/10⁶ survivors were measured. When hepatocytes (not a homogenate) were used to metabolize BOP, 351 μmol O⁶MeG/mol guanine (G) and 39 μmol O⁶ (2‐hydroxypropyl) G (O⁶HpG)/mole G were found in V79 DNA. When a pancreas duct homogenate was used BHP produced O⁶HpG (65 μmol/mol G) and BOP O⁶MeG (20 μmol/mol G). NOPC produced five times more mutants than NHPC, over the range of doses. At the highest dose (10 μM) it produced less (70%) O⁶alkylG than NHPC. These data show that methylation was a more mutagenic lesion than hydroxypropylation. There was no evidence of a correlation between mutagenicity and the formation of O⁶alkylG. ©1993 Wiley‐Liss, Inc.