Time-dependent human tumor cell-to-plasma partitioning of 6 and DON (1) release. 6 was incubated in P493B lymphoma cells suspended in human plasma, and at 0.25, 0.5, 1, and 2 h, aliquots were removed and evaluated for 6 and DON released from 6 using liquid chromatography (LC)–mass spectrometry (MS). (A) In human plasma, 6 was stable over the 2 h incubation period with minimal DON released. (B) In contrast, 6 partitioned into P493B tumor cells and was biotransformed to DON. These results confirm selective uptake and bioactivation of 6 to DON in tumor cells over 2 h.