A Proteomics-Based Translational Approach Reveals an Antifolate Resistance Inherent in Human Plasma Derived from Blood Donation

The inhibition of dihydrofolate reductase (DHFR) by antifolates is a common practice both in cell culture and in chemotherapy. Surprisingly, antifolate resistance was also observed in cultured murine myeloma cells (SP2/0) in the presence of human plasma (HP); thus, we used a proteomic approach to identify novel plasma biomarker(s) for this condition. In contrast to the in vitro antifolate response, metabolic enzymes and translation machinery proteins were found to be up-regulated in the presence of HP. The antifolate resistance inherent in HP may be explained by a simultaneous promotion of cell proliferation and the maintenance of DNA integrity. Furthermore, the factor(s) was found to be extrinsic, heat stable and very small in size. Adenine, a supplemented additive in erythrocyte preservation, was subsequently identified as the contributing factor and exogenous addition in cultures reversed the cytotoxicity induced by antifolates. Importantly, adenine-containing blood components, which may provide enhanc...