Biomedical applications of accelerator mass spectrometry: kinetics of oxaliplatin-DNA binding in genomic DNA and human cancer cells

AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA 3205 Oxaliplatin is a relatively new platinum analogue that is currently used in chemotherapy of metastatic colorectal cancer. Oxaliplatin exerts its anti-tumor effects by covalent modification of DNA to form monoadducts, and intra- and interstrand diadducts, like other platinum-based anticancer drugs such as cisplatin and carboplatin. Very recently, we reported the use of accelerator mass spectrometry (AMS), an extremely sensitive detection method, to measure both in vitro and cell-based kinetics of carboplatin-DNA monoadduct formation. We report an application of our approach to measurement of both the kinetics of [14C]oxaliplatin-DNA adduct formation with genomic DNA and drug uptake and DNA binding in 833K human testicular cancer cells, T24 human bladder cancer cells and MDA-MB-231 multi-drug resistant human breast cancer cells. A strength of this approach is that because radiocarbon is located in the carrier group, not only the total amount of oxaliplatin-DNA adducts can be measured, but a series of adducts can also be discriminated following DNA digestion and HPLC separation. The in vitro binding study of [14C]oxaliplatin to salmon sperm DNA, and digestion of the resulting platinated DNA followed by HPLC-AMS measurement, allowed for straightforward kinetic calculations that revealed the mechanism of action for oxaliplatin, and for differential oxaliplatin-DNA adduct formation as a function of time. In addition, 833K cells, T24 cells and MDA-MB-231 cells were incubated with a sub-pharmacological dose of [14C]oxaliplatin, resulting in the both drug uptake and oxaliplatin-DNA adduct quantitation. Interestingly, HPLC-AMS data of the digested DNA resulting from the incubation of [14C]oxaliplatin with T24 cells for 24 h shows a similar compositional pattern, but a significantly different mass distribution of oxaliplatin-DNA adducts, compared with that from the in vitro experiments. Of importance, the lowest concentration of radiocarbon measured was approximately 1 amol/1 μg of DNA. This sensitivity may allow the method to be useful for clinical applications. Work was performed at the Research Resource for Biomedical AMS, operated at UC LLNL under the auspices of the U.S. DOE contract #W-7405-ENG-48 and partially supported by NIH/NCRR, Biomedical Technology Program grant #P41 RR13461 and DOE/LDRD grant 06-LW-023.