Kinetics and characterization of oxaliplatin-DNA adduct formation in naked DNA and cancer cells using accelerator mass spectrometry

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Sang Soo Hah, hah2@llnl.gov1, Rhoda A. Sumbad1, Kenneth W Turteltaub, turteltaub2@llnl.gov2, and Paul T. Henderson, Henderson48@llnl.gov3. (1) Biology and Biotechnology Research Program, Lawrence Livermoe National Laboratory, Mail Code L-441, 7000 East Avenue, Livermore, CA 94550-9698, (2) Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, Livermore, CA 94550, (3) Chemistry, Materials and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, L-441, Livermore, CA 94551
(trans-R,R)1,2-Diaminocyclohexaneoxalatoplatinum(II) (oxaliplatin) is a recently approved platinum analogue for use in chemotherapy of metastatic colorectal cancer. Like many cytotoxic drugs, oxaliplatin exerts its anti-tumor effects by covalent modification of DNA. We report the use of an accelerator mass spectrometry (AMS) assay to measure the kinetics of oxaliplatin-induced DNA damage and repair. We measured the rate of oxaliplatin adduction to salmon sperm DNA, which allowed refinement of the kinetics of hydration of the parent compound and subsequent covalent binding to DNA. Oxaliplatin-DNA adduct distribution was further investigated at the nucleoside level by HPLC-AMS following enzymatic digestion. The data indicate that a higher fraction of the DNA adducts formed by oxaliplatin are toxic compared to those reported for other analogs such as cisplatin and carboplatin. Rates of cellular drug influx, efflux, DNA damage and DNA repair were quantitated by AMS. Cultured platinum-sensitive testicular (833K) and platinum-resistant breast and bladder (MDA-MB-231 and T24, respectively) cancer cells were incubated with a sub-pharmacological dose of oxaliplatin (0.2 uM). The lowest concentration of radiocarbon measured was approximately 1 amol/ug of DNA, when assaying 1 ug of DNA. This sensitivity for measuring oxaliplatin-DNA adducts is the highest reported to date. The sensitivity offered by this method may be applicable to other DNA-damaging drugs and useful for directly determining the rates of drug metabolism in humans, development of diagnostics for prediction of drug efficacy. Work performed at the Research Resource for Biomedical AMS, operated at LLNL under the auspices of the U.S. DOE contract #W-7405-ENG-48 and partially supported by NIH/NCRR, Biomedical Technology Program (RR1346) and DOE/LDRD (06-LW-023).
 

Poster Session and Awards
6:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- 204 A/B, Poster

Division of Chemical Toxicology

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007