  Intracellular transport of DNA carriers is a fundamental step of gene
delivery. We present here a theoretical approach to study generically a single
virus or DNA particle trafficking in a cell cytoplasm. Cellular trafficking has
been studied experimentally mostly at the macroscopic level, but very little
has been done so far at the microscopic level. We present here a physical model
to account for certain aspects of cellular organization, starting with the
observation that a viral particle trajectory consists of epochs of pure
diffusion and epochs of active transport along microtubules. We define a
general degradation rate to describe the limitations of the delivery of plasmid
or viral particles to the nucleus imposed by various types of direct and
indirect hydrolysis activity inside the cytoplasm. Following a homogenization
procedure, which consists of replacing the switching dynamics by a single
steady state stochastic description, not only can we study the spatio-temporal
dynamics of moving objects in the cytosol, but also estimate the probability
and the mean time to go from the cell membrane to a nuclear pore. Computational
simulations confirm that our model can be used to analyze and interpret viral
trajectories and estimate quantitatively the success of nuclear delivery.
