Conditional constitutive expression system of a drug protein in vivo by positive feedback loop using an inducer-independent artificial transcription factor

Bacterial-mediated drug delivery is a potential and promising strategy for the specific treatment of cancer with therapeutic molecules, especially with genetically encoded proteins. These proteins must be tightly regulated due to cytotoxicity and thus are usually expressed under the control of the PBAD and TetA/TetR promoters in vivo. Since protein expression from these systems is triggered by exogenous inducer, periodic intravenous injection of inducer is necessary. However, these treatments can result in non-homogenous and/or inefficient expression of therapeutic proteins in vivo due to impeded diffusion and dilution of the inducer further from the injection site. To overcome these hurdles, we designed a conditional constitutive expression system equipped with the artificial transcription factor, AraCC, which has two operator-binding domains and simultaneously binds to the I1 and I2 operators of the PBAD promoter for gene expression in an arabinose-independent manner. Using this construct and the wild type protein AraC under the control of the PBAD promoter, we constructed a self-positive feedback system to constitutively express the therapeutic protein when the induction of AraC was triggered once using arabinose. This expression system could be useful in various cancer treatment strategies using bacteria to deliver genetically encoded drugs in vivo.