A complex adenovirus vector that delivers FASL-GFP with combined prostate-specific and tetracycline-regulated expression

Cell-type-restricted transgene expression delivered by adenovirus vectors i s highly desirable for gene therapy of cancer, as it can limit cytotoxic ge ne expression to tumor cells. However, many tumor- and tissue-specific prom oters are weaker than the constitutively active promoters and are thus less effective. To combine cell-type specificity with high-level regulated tran sgene expression, we have developed a complex adenoviral vector. We have pl aced the tetracycline transactivator gene under the control of a prostate-s pecific ARR2PB promoter, and a mouse Tnfsf6 (encoding FASL)-GFP fusion gene under the control of the tetracycline responsive promoter. We have incorpo rated both expression cassettes into a single construct. We show that FASL- GFP expression from this vector is essentially restricted to prostate cance r cells, in which it can be regulated by doxycycline. Higher levels of pros tate-specific FASL-GFP expression were generated by this approach than by d riving the FASL-GFP expression directly with ARR2PB. More FASL-GFP expressi on correlated with greater induction of apoptosis in prostate cancer LNCaP cells. Mouse studies confirmed that systemic delivery of both the prostate- specific and the prostate-specific/tet-regulated vectors was well tolerated at doses that were lethal for FASL-GFP vector with CMV promoter. This stra tegy should be able to improve the safety and efficacy of cancer gene thera py using other cytotoxic genes as well.