Use of [8-3H]guanine-labeled deoxyribonucleic acid to study alkylating agent reaction kinetics and stability

Preclinical safety assessment of pathogen reduced red blood cells treated with amustaline and glutathione

BACKGROUND

The nucleic acid targeted pathogen reduction (PR) system utilizing amustaline (S-303) and glutathione (GSH) is designed to inactivate blood-borne pathogens and leukocytes in red blood cell concentrates (PR-RBCC). Inactivation is attained after amustaline intercalates and forms covalent nucleic acid adducts preventing replication, transcription, and translation. After pathogen inactivation, amustaline spontaneously hydrolyzes to S-300, the primary negatively charged reaction product; amustaline is below quantifiable levels in PR-RBCC. GSH quenches free unreacted amustaline.

STUDY DESIGN AND METHODS

The genotoxic and carcinogenic potential of PR-RBCC, the reaction by-products, and S-300 were assessed in accordance with the International Conference on Harmonization (ICH) guidelines and performed in compliance with the Food and Drug Administration (FDA) good laboratory practice standards, 21 CFR Part 58. in vitro bacterial reverse mutagenicity and chromosomal aberration assays were performed with and without exogenous S9 metabolic activation, and in in vivo clastogenicity and carcinogenic assays using validated murine models.

RESULTS

PR-RBCCs were not genotoxic in vitro and in vivo and were non-carcinogenic in p53+/- transgenic mice transfused over 26 weeks. Estimated safety margins for human exposure ranged from >90 to >36 fold for 2 to 5 PR-RBCCs per day, respectively. PR-RBCCs and S-300 did not induce chromosome aberration in the in vivo murine bone marrow micronucleus assay at systemically toxic doses.

CONCLUSIONS

PR-RBCCs did not demonstrate genotoxicity in vitro or in vivo and were not carcinogenic in vivo. These studies support the safety of PR-RBCCs and suggest that there is no measurable genotoxic hazard associated with transfusion of PR-RBCCs.

Interspecies dose extrapolation for inhaled dimethyl sulfate: a PBPK model-based analysis using nasal cavity N7-methylguanine adducts

Dimethyl sulfate (DMS) is a volatile sulfuric acid ester used principally as a methylating agent in a wide variety of industrial applications. DMS reacts with organic macromolecules by a SN2 mechanism. The weight of experimental evidence suggests that DMS possesses genotoxic and carcinogenic potential. Inhalation studies have shown that repeated exposure to DMS leads to tumors in the nasal cavity and lower respiratory tract in both rats and mice. Here we present a quantitative assessment for cross-species dose extrapolation for inhaled DMS using a physiologically based pharmacokinetic (PBPK) model. The model is designed to simulate N7-methylguanine (N7 mG) DNA adduct levels in the nasal mucosa following DMS exposure in rats and humans. This model was parameterized and predictions were tested by comparison against experimentally measured N7 mG DNA adduct levels in rat nasal mucosa following inhalation exposure to DMS. The model-based interspecies dose comparison, using N7 mG adduct levels in the nasal respiratory tissue as the appropriate dose metrics, predicts a dose rate seven times higher in rats compared to humans.

Mechlorethamine-induced enhancement of radiation sensitivity of guanine

This study describes and characterizes the interactions of nitrogen mustard mechlorethamine (HN2) with guanine and the radiation sensitivity of guanine in the presence of HN2. Briefly, in an equimolar solution (0.5 mmol dm-3) the pH-dependence (pH 3.0-12.0) and time-dependence (0-36 h) of alkylation of guanine at room temperature were determined using a reverse-phase high-performance liquid chromatography (hplc) column. Based on the hplc peak areas of the product and intact guanine, the optimal pH for alkylation was determined to be 8.0. Similarly, the optimal time required for alkylation was 10 h. Two products, i.e. alkylated guanines, were detected (10:1, peak areas measured at 260 nm) and purified. Structural studies of the products were performed by direct insertion probe-electron impact mass spectrometry. These products were identified as N-(2-chloroethyl)-N-[2-(7-guanyl)ethyl]-methylamine (product 2). At optimal conditions, samples of either guanine or an equimolar solution of guanine and HN2 were 60Co irradiated (gamma-ray) at 25 Gy min-1 at doses up to 400 Gy. Both sets of samples were analysed by hplc. In each case, the sole radiation product observed and characterized was 8-hydroxy-guanine. Dose-yield plots were linear and showed that HN2 enhanced the radiation sensitivity of guanine. This increase in radiation sensitivity is attributed to the differences in electrophilic properties between nitrogen mustard and guanine.

Quantum molecular modeling of the interaction between guanine and alkylating agents--2--nitrogen mustard

The alkylation mechanism of guanine by nitrogen mustard (HN2) was studied by using a supermolecular modeling at the ab initio 6-31G level. Our computations show that interaction of guanine with the aziridinium form of HN2 necessitates a transition state for the N7 alkylation route. The pathway of N7-guanine alkylation by nitrogen and sulfur mustards is discussed on the basis of the Molecular Electrostatic Potential and HOMO-LUMO properties of these molecules.