Inducible control of gene expression: prospects for gene therapy.

A number of drug-related gene expression systems are available for controlling target gene transcription through the use of small-molecule inducing compounds. While the utility of such systems has been demonstrated in vitro and in transgenic mice, recent improvements are likely to make these systems more amenable for use in a therapeutic context, such as gene therapy. These improvements include further optimization of the antiprogestin-regulated gene switch, rendering it more sensitive to RU486, and the synthesis of nonimmunosuppressive rapamycin analogs for use in dimerization-based strategies of gene regulation.