Semi-mechanistic pharmacodynamic modelling of gene expression and silencing processes

BackgroundSuppressed expression of transgene is a major obstacle in gene therapy. Understanding of the mechanisms involved in expression and silencing of exogenous genes is required to overcome gene therapy hurdles.PurposeTo develop a semi-mechanistic model describing the effects of transgenes over the activity of an expression cassette.MethodsTwelve Balb/c mice received 40 μg of plasmid DNA. Animals were assigned to one of the following treatments: (I) 20 μg of the plasmid expressing luciferase (pEF-Luc) and 20 μg of “empty” plasmid; (II) pEF-Luc (20 μg) and 20 μg of plasmid expressing murine interferon alpha (IFNα); and (III) pEF-Luc (20 μg), and 20 μg of plasmid expressing β-galactosidase (pCMVβ). The expression of luciferase over time, quantified by a noninvasive method, was used as a measured of pEF-Luc activity and modelled using NONMEM.ResultsThe selected model suggests the co-existence of two forms of active DNA differing in their transcription efficiencies. The core model was expanded to describe reversible and irreversible silencing processes, induced by the coexpression of IFNα or β-galactosidase, respectively.ConclusionCoupling noninvasive in vivo imaging and mathematical modelling allows quantitative description of gene transfer, providing a tool to select the best regulatory elements to construct a therapeutic expression cassette.