Metabolism of the anticancer agent 1-(4-acetylphenyl)-3,3-dimethyltriazene

Pharmacokinetics of dacarbazine (DTIC) in pregnancy

PURPOSE

The purpose of this report is to describe, for the first time, the pharmacokinetics of dacarbazine (DTIC) and its metabolites [5-[3-methyl-triazen-1-yl]-imidazole-4-carboxamide (MTIC), 5-[3-hydroxymethyl-3-methyl-triazen-1-yl]-imidazole-4-carboxamide (HMMTIC) and 5-aminoimidazole-4-carboxamide (AIC)] during pregnancy (n = 2) and postpartum (n = 1).

METHODS

Non-compartmental DTIC, MTIC, HMMTIC, and AIC pharmacokinetics (PK) were estimated in one case at 29 week gestation and 18 day postpartum and a second case at 32 week gestation, in women receiving DTIC in combination with doxorubicin, bleomycin, and vinblastine for treatment of Hodgkin's lymphoma. Drug concentrations were measured by HPLC.

RESULTS

In the subject who completed both pregnancy and postpartum study days, DTIC area under the concentration-time curve (AUC) was 27% higher and metabolite AUCs were lower by 27% for HMMTIC, 38% for MTIC, and 83% of AIC during pregnancy compared to postpartum. At 7 and 9 year follow-up, both subjects were in remission of their Hodgkin's lymphoma.

CONCLUSIONS

Based on these two case reports, pregnancy appears to decrease the metabolism of the pro-drug dacarbazine, likely through inhibition of CYP1A2 activity. Lower concentrations of active metabolites and decreased efficacy may result, although both these subjects experienced long-term remission of their Hodgkin's lymphoma.

Comparison of metabolism and activity of an aryldimethyltriazene and an aryldiethyltriazene

The antitumoral activity and metabolism of 1-(4-acetylphenyl)-3,3-dimethyltriazene [pAc-(CH3)2] and 1-(4-acetylphenyl)-3,3-diethyltriazene [pAc-(C2H5)2] were studied in mice. pAc-(CH3)2 showed significant antitumoral activity against M5076 ovarian reticular cell sarcoma, L1210 leukemia, EL 4 lymphoma in mice, but not against Lewis lung carcinoma. pAc-(C2H5)2 was inactive in all these murine tumors and was much more toxic than pAc-(CH3)2. pAc-(CH3)2 and pAc-(C2H5)2 were rapidly metabolized in vitro and in vivo to their respective monoalkyltriazenes and to 4-aminoacetophenone (pAc-NH2). In vitro, 79% of the dimethyltriazene was metabolized to its monomethyl analogue, but only 27% of the diethyltriazene was metabolized to the monoethyltriazene. The monoalkytriazenes were almost completely biotransformed to pAc-NH2 by a 9000 g liver fraction. The metabolic pattern in the in vitro study was comparable to that found in vivo.