Physiologically based pharmacokinetic modeling to predict human pharmacokinetics of a novel mithramycin analog for Ewing sarcoma

PURPOSE: To develop and qualify a physiologically based pharmacokinetic (PBPK) modeling strategy for mithramycin (MTM) and its analog, MTMSA-Trp, with the aim of projecting first-in-human plasma pharmacokinetics and supporting the translational development of MTMSA-Trp for Ewing sarcoma treatment. METHODS: using a middle-out approach, incorporating preclinical pharmacokinetic data from mice, rats, and cynomolgus monkeys. Human clearance was estimated through three methods: an additional clearance approach, allometric scaling, and single-species scaling from monkeys. The model was evaluated using clinical MTM plasma PK data and then employed to project human MTMSA-Trp plasma PK, with tissue predictions considered exploratory to contextualize hepatotoxicity risk. RESULTS: The additional clearance approach provided the most accurate prediction of human MTM plasma PK. Across all clearance prediction methods, MTMSA-Trp was predicted to achieve 8- to 15-fold higher human plasma exposure than MTM at the same dose. Model-derived liver exposures were 2- to 4-fold higher, with a lower predicted liver partition for MTMSA-Trp; however, these tissue predictions remained sensitive to distribution assumptions. Parameter sensitivity analysis identified the blood-to-plasma ratio as the most influential parameter among those examined. CONCLUSION: PBPK modeling supports the projection that MTMSA-Trp will achieve substantially higher plasma exposure than MTM in humans. This empirically developed workflow may inform translational efforts for the first-in-human development of MTMSA-Trp.