PKPD Modeling of VEGF, sVEGFR-2, sVEGFR-3, and sKIT as Predictors of Tumor Dynamics and Overall Survival Following Sunitinib Treatment in GIST.

The predictive value of longitudinal biomarker data (vascular endothelial growth factor (VEGF), soluble VEGF receptor (sVEGFR)-2, sVEGFR-3, and soluble stem cell factor receptor (sKIT)) for tumor response and survival was assessed based on data from 303 patients with imatinib-resistant gastrointestinal stromal tumors (GIST) receiving sunitinib and/or placebo treatment. The longitudinal tumor size data were well characterized by a tumor growth inhibition model, which included, as significant descriptors of tumor size change, the model-predicted relative changes from baseline over time for sKIT (most significant) and sVEGFR-3, in addition to sunitinib exposure. Survival time was best described by a parametric time-to-event model with baseline tumor size and relative change in sVEGFR-3 over time as predictive factors. Based on the proposed modeling framework to link longitudinal biomarker data with overall survival using pharmacokinetic-pharmacodynamic models, sVEGFR-3 demonstrated the greatest predictive potential for overall survival following sunitinib treatment in GIST.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e84; doi:10.1038/psp.2013.61; advance online publication 20 November 2013.

Genetic background regulates semaphorin gene expression and epileptogenesis in mouse brain after kainic acid status epilepticus.

The host response to neural injury, which can include axonal sprouting and synaptic reorganization is likely to be under tight genetic regulatory control at the level of the genome and may be implicated in epileptogenesis. Despite its importance, however, the molecular basis of synaptic reorganization is unclear. We have studied the development of synaptic reorganization, semaphorin gene expression, and epileptogenesis in hippocampus of epileptogenic sensitive (FVB/NJ) and epileptogenic resistant (C57BL/6J) mice (i.e. distinct genetic backgrounds) after kainic acid-induced status epilepticus. Our results support the hypothesis that disruption of transcriptional regulation of axon guidance genes leads to a differential loss of tonic neuropilin-2 dependent activation of semaphorin 3F receptors on hippocampal neurons on distinct genetic backgrounds. This results in rearranged synaptic circuitry and thus promotes epileptogenesis. These findings may define biologic principles underlying the role of semaphorin signaling which may broadly apply to other systems undergoing neural regeneration.

Pharmacokinetics of plasmid DNA in the rat.

PURPOSE: The pharmacokinetics of plasmid DNA after IV bolus administration in the rat by following supercoiled (SC), open circular (OC), and linear (L) pDNA forms of the plasmid. METHODS: SC, OC, and L pDNA were injected at 2,500, 500, 333, and 250 microg doses. The concentrations in the bloodstream of OC and L pDNA were monitored. RESULTS: SC pDNA was detectable in the bloodstream only after a 2,500 microg dose, and had a clearance of 390(+/-50) ml/min and Vd of 81(+/-8) ml. The pharmacokinetics of OC pDNA exhibited non-linear characteristics with clearance ranging from 8.3(+/-0.8) to 1.3(+/-0.2) ml/min and a Vd of 39(+/-19) ml. L pDNA was cleared at 7.6(+/-2.3) ml/min and had a Vd of 37(+/-17) ml. AUC analysis revealed that 60(+/-10) % of the SC was converted to the OC form, and nearly complete conversion of the OC pDNA to L pDNA. Clearance of SC pDNA was decreased after liposome complexation to 87(+/-30) ml/min. However the clearance of OC and L pDNA was increased relative to naked pDNA at an equivalent dose to 37(+/-9) ml/min and 95(+/-37) ml/min respectively. CONCLUSIONS: SC pDNA is rapidly metabolized and cleared from the circulation. OC pDNA displays non-linear pharmacokinetics. Linear pDNA exhibits first order kinetics. Liposome complexation protects the SC topoform, but the complexes are more rapidly cleared than the naked pDNA.

Kinetic modeling of plasmid DNA degradation in rat plasma.

A major obstacle in gene delivery is the transport of intact plasmid DNA (pDNA) to target sites. We sought to investigate the kinetic processes underlying the degradation of pDNA in a rat plasma model, as this is one of the main components responsible for the clearance of pDNA after intravenous administration. We further sought to construct a complete kinetic model to describe the degradation of all three topoforms (supercoiled, open circular, and linear) of pDNA in a rat plasma model. Supercoiled pDNA was incubated in isolated rat plasma at 37 degrees C in vitro. At various time points, the plasma was assayed by electrophoresis for the amounts of supercoiled, open circular, and full-length linear pDNA remaining. The calculated amounts remaining were fit to linear differential equations describing this process. In this model, pDNA degradation is considered to be a unidirectional process, with supercoiled degrading to open circular and then to the linear topoform. The calculated kinetic parameters suggested that supercoiled pDNA degrades in rat plasma with a half-life of 1.2 minutes, open circular pDNA degrades with a half-life of 21 minutes, and linear pDNA degrades with a half-life of 11 minutes. Complexation of pDNA with liposomes resulted in a portion of the supercoiled plasmid remaining detectable through 5.5 hours.