title: Pharmacokinetic-pharmacodynamic analysis of vismodegib in preclinical models of mutational and ligand-dependent Hedgehog pathway activation.
abstract: OBJECTIVE
  Vismodegib (GDC-0449) is a potent and selective inhibitor of the Hedgehog (Hh) pathway that shows antitumor activity in preclinical models driven by mutational or ligand-dependent activation of the Hh pathway. We wished to characterize the pharmacokinetic-pharmacodynamic (PK/PD) relationship of vismodegib in both model systems to guide optimal dose and schedule for vismodegib in the clinic.
  
  
  METHODS
  Preclinical efficacy and PK/PD studies were carried out with vismodegib in a Ptch(+/-) allograft model of medulloblastoma exhibiting mutational activation of the Hh pathway and patient-derived colorectal cancer (CRC) xenograft models exhibiting ligand-dependent pathway activation. Inhibition of the hedgehog pathway was related to vismodegib levels in plasma and to antitumor efficacy using an integrated population-based PK/PD model.
  
  
  RESULTS
  Oral dosing of vismodegib caused tumor regressions in the Ptch(+/-) allograft model of medulloblastoma at doses ≥25 mg/kg and tumor growth inhibition at doses up to 92 mg/kg dosed twice daily in two ligand-dependent CRC models, D5123, and 1040830. Analysis of Hh pathway activity and PK/PD modeling reveals that vismodegib inhibits Gli1 with a similar IC(50) in both the medulloblastoma and D5123 models (0.165 μmol/L ±11.5% and 0.267 μmol/L ±4.83%, respectively). Pathway modulation was linked to efficacy using an integrated PK/PD model revealing a steep relationship where > 50% of the activity of vismodegib is associated with >80% repression of the Hh pathway.
  
  
  CONCLUSIONS
  These results suggest that even small reductions in vismodegib exposure can lead to large changes in antitumor activity and will help guide proper dose selection for vismodegib in the clinic.
authors: Department of Translational Oncology, Genentech Inc, 1 DNA Way, South San Francisco, California 94080, USA.
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