Predictions of effect for intracellular antisense oligodeoxyribonucleotides from a kinetic model

We have analyzed the implications of a simple two-compartment mathematical model (Hargrove and Schmidt, 1989) to anticipate the limits of antisense oligodeoxyribonucleotide action within single cells. The steady-state equations are derived for four special cases representing the following mechanisms: (i) ribosome blockage, (ii) mRNA cleavage by RNase H, (iii) concurrent ribosome exclusion and RNase H action, and (iv) decreased delivery of mature mRNA to the cytoplasm due to transcriptional blockage, interference with nucleocytoplasmic transport, or splicing. Dose-response relationships have been derived for these mechanisms under ideal conditions. Our results indicate that frequently translated mRNAs producing stable proteins are the most attractive antisense targets because these protein levels are sensitive to the changes in the mRNA levels that can be effected using antisense oligodeoxyribonucleotides. The nonsteady-state solutions show that both mRNA and protein half-life can determine the kinetics of antisense oligonucleotide action. A rapid onset of effect will be observed when the mRNA is rapidly degraded and slowly translated and when the translated protein is rapidly degraded. When the protein is slowly degraded, the kinetics of effect are limited by protein half-life. When the translational rate constant is large compared to the absolute difference between the mRNA and protein degradation rate constants, the kinetics of antisense action are determined by both degradation rate constants but are limited by the slower of the two degradative processes. We also show that the steady-state and nonsteady-state solutions may be used to design experiments that discriminate among mechanisms of antisense action.