Synthetic activation of caspases: Artificial death switches

Abstract

The development of safe vectors for gene therapy requires fail-safe mechanisms to terminate therapy or remove genetically altered cells. The ideal ''suicide switch'' would be nonimmunogenic and nontoxic when uninduced and able to trigger cell death independent of tissue type or cell cycle stage. By using chemically induced dimerization, we have developed powerful death switches based on the cysteine proteases, caspase-1 ICE (interleukin-1␤ converting enzyme) and caspase-3 YAMA. In both cases, aggregation of the target protein is achieved by a nontoxic lipid-permeable dimeric FK506 analog that binds to the attached FK506-binding proteins, FKBPs. We find that intracellular cross-linking of caspase-1 or caspase-3 is sufficient to trigger rapid apoptosis in a Bcl-x L -independent manner, suggesting that these conditional proapoptotic molecules can bypass intracellular checkpoint genes, such as Bcl-x L , that limit apoptosis. Because these chimeric molecules are derived from autologous proteins, they should be nonimmunogenic and thus ideal for long-lived gene therapy vectors. These properties should also make chemically induced apoptosis useful for developmental studies, for treating hyperproliferative disorders, and for developing animal models to a wide variety of diseases.

Ablation of microvessels in vivo upon dimerization of iCaspase-9

“…28,29 In contrast, approaches that directly target the cell death machinery might be more effective in inducing endothelial cell apoptosis and disrupting microvessels in vivo. Because the caspase-9 allele used in the present studies acts as a cellular artificial death switch (ADS) which is activated with dimerizer drugs, the construct used here or related caspase-based suicide switches 18,21 could be activated in a controlled manner in tumors.…”

“…Because apoptotic stimuli often engage multiple intracellular pathways, it is unknown whether activation of apical caspases is sufficient to induce endothelial cell apoptosis and disruption of microvessels in vivo. In this report, we expressed iCaspase-9, a conditional caspase-9 molecule that is activated upon drug-induced dimerization, [18][19][20][21] in primary endothelial cells and evaluated the effect of active iCaspase-9 in functional human microvessels engineered in immunodeficient mice.…”

Protein‐protein interactions as a target for drugs in proteomics

“…Linkers consist of 5-16 atoms [121,122]. The concentrations required for induction of dimerization by such compounds vary in a relatively narrow range of 1-10 nM [121,123]. The effectiveness of dimerizers depends on the anchors affinity [122] and the length of the linkers [121,122].…”

Antiangiogenic gene therapy: disruption of neovascular networks mediated by inducible caspase-9 delivered with a transcriptionally targeted adenoviral vector

“…13,17,23,24 In this approach, a protein can be fused to a CID-binding domain that will mediate noncovalent crosslinking by high-affinity interactions with a dimerizer compound. 15 When the catalytic domain of caspase-9 is fused to one or more CID-binding domains, the resulting fusion protein (inducible caspase-9, named iCaspase-9) can be activated with a dimerizer compound (eg AP20187) and initiate an irreversible signaling pathway that results in cell death.…”