Related Experiment Videos
In vitro reactions of isopropyl methanesulfonate with DNA and with 2'-deoxyribonucleosides
1Department of Environmental Medicine, New York University School of Medicine, New York 10016.
Abstract:
Isopropyl methanesulfonate (IPMS), an SN1 alkylating agent, is a direct-acting mutagen in bacteria. We recently reported that s.c. and topical administration of IPMS to mice resulted in the rapid induction of thymic lymphomas. Thymic lymphoma induction was not observed following administration of the SN2 alkylating agents methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS). We have studied the reactions of IPMS with dAdo, dCyd, dGuo and dThd at pH 6.5 to 7.5 and 37 degrees C for 3 h. IPMS formed the following isopropyl (IP) adducts: 7-IP-Gua (4% yield), O6-IP-Gua (8%), O2-IP-Cyt (1%), O2-IP-dThd (2%), 3-IP-dThd (1%), and O4-IP-dThd (0.4%). Adducts were characterized from UV and mass spectra. IPMS was reacted in vitro with calf thymus DNA (pH 6.5 to 7.5, 37 degrees C, 3 h) and yielded (nmol/mg DNA): 7-IP-Gua (22) O6-IP-dGuo (11), O2-IP-Cyt (9), O2-IP-dThd (2), O4-IP-dThd (2), 3-IP-Ade (0.2) and 3-IP-dThd (0.2). The relatively greater alkylation of exocyclic oxygen atoms in DNA by IPMS compared to values for MMS and EMS reported by others, may play a role in the induction of thymic lymphomas in mice by IPMS and the lack of such activity by MMS and EMS.
Insights
Isopropyl methanesulfonate (IPMS) rapidly induces thymic lymphomas in mice, unlike SN2 agents. This study details IPMS
Area of Science:
- Chemical mutagenesis and carcinogenesis
- DNA adduct formation and toxicology
Background:
- Isopropyl methanesulfonate (IPMS) is a direct-acting mutagen.
- IPMS induces thymic lymphomas in mice, while SN2 alkylating agents like MMS and EMS do not.
- Understanding the mechanism of IPMS-induced lymphomagenesis is crucial.
Purpose of the Study:
- To investigate the in vitro reactions of IPMS with DNA nucleosides and calf thymus DNA.
- To characterize the specific DNA adducts formed by IPMS.
- To compare the DNA alkylation profile of IPMS with that of MMS and EMS.
Main Methods:
- Incubation of IPMS with deoxyadenosine, deoxycytidine, deoxyguanosine, and deoxythymidine at physiological conditions (pH 6.5-7.5, 37°C, 3h).
- Reaction of IPMS with calf thymus DNA under identical conditions.
- Characterization of formed isopropyl (IP) adducts using UV and mass spectrometry.
Main Results:
- IPMS formed several isopropyl adducts with DNA nucleosides, including 7-IP-Gua (4%), O6-IP-Gua (8%), and O2-IP-Cyt (1%).
- IPMS alkylation of calf thymus DNA yielded significant levels of 7-IP-Gua (22 nmol/mg DNA) and O6-IP-dGuo (11 nmol/mg DNA).
- IPMS showed a relatively greater alkylation of exocyclic oxygen atoms in DNA compared to reported values for MMS and EMS.
Conclusions:
- The distinct DNA adduct formation profile of IPMS, particularly increased exocyclic oxygen alkylation, may explain its potent lymphomagenic activity.
- This selective DNA damage mechanism differentiates IPMS from less carcinogenic SN2 alkylating agents.
- Further research into DNA repair pathways for these specific adducts is warranted.