Characterization of intact hemoglobin and oxaliplatin interaction by nanoelectrospray ionization tandem mass spectrometry.

BACKGROUND Mass spectrometric (MS) detection of intact hemoglobin (Hb) adducts presents considerable analytical challenges because of the noncovalent association of the 4 subunits of Hb, and MS characterization of the interaction of intact Hb with platinum drugs has not been reported. We developed a technique for detecting intact Hb and its drug adduct and studied the interactions between intact Hb and oxaliplatin. METHODS We incubated a series of mixtures of Hb and oxaliplatin at 37 degrees C for 24 h or 5 days to investigate adduct formation. Blood samples from colorectal cancer patients undergoing oxaliplatin treatment were analyzed for novel adducts of intact Hb-oxaliplatin, which were characterized with nanoelectrospray ionization quadrupole time-of-flight MS. RESULTS Two intact Hb adducts, one with the whole oxaliplatin molecule and the other with oxaliplatin losing the oxalate ligand, were identified. Analysis of erythrocytes from the cancer patients provided direct evidence that oxaliplatin accumulated as Hb adducts in erythrocytes. A higher fraction (approximately 70%) of Hb was bound to oxaliplatin in erythrocytes from a patient who could not tolerate oxaliplatin treatment than in erythrocytes from another patient who benefited from this treatment. CONCLUSIONS The nanoelectrospray tandem MS technique enabled determination of the intact Hb tetramer and its association with oxaliplatin. Hb-oxaliplatin adducts in erythrocytes may serve as a clinical biomarker for toxic response and treatment efficacy.