Short interfering RNA (siRNA) is an effective and highly specific strategy for 'knocking down' gene expression in animal models. This method of molecular control might now become more clinically relevant, as Tim Devling and colleagues report that siRNA against KEAP1 could represent a unique class of cancer chemopreventive agent.

Reducing neoplastic disease through chemoprevention is a highly desirable goal and several strategies have been considered. Chemopreventive blocking agents, for example, increase the expression of cytoprotective genes in human cells. These include drug-metabolizing enzymes such as NAD(P)H:quinone oxidoreductase 1 ( NQO1 ) and glutathione (GSH) transferases, as well as antioxidant genes such as glutamate cysteine ligase catalytic ( GCLC ) and modifier ( GCLM ) subunits, which help synthesize GSH. However, to be chemoprotective, such chemicals must induce reduction–oxidation (redox) stress in the cells, which can be potentially damaging.

Genes that are regulated in this manner contain antioxidant response elements (AREs) in their promoters, and their transcription is stimulated in response to the ARE-mediated recruitment of a complex that contains nuclear factor erythroid 2 p45-related factor 2 (NRF2). NRF2 accumulates in the nucleus in response to redox stress and after treatment with chemopreventive blocking agents.

The redox-sensitive kelch-like ECH-associated protein 1 (KEAP1) is an NRF2-specific adaptor protein for the CULLIN3–ROC1 ubiquitin ligase. Under homeostatic conditions it promotes the proteasome-mediated degradation of NRF2 and thereby keeps ARE-containing genes switched off. Under conditions of natural redox stress, or after treatment with chemopreventive blocking agents, KEAP1 no longer fulfills this role, NRF2 is stabilized and the ARE-containing genes are switched on. The authors therefore wanted to test whether specifically reducing KEAP1 levels using siRNA would activate transcription of the ARE-containing genes in the absence of stress.

A duplex 21-nucleotide siRNA was designed that successfully knocked down KEAP1 mRNA to <30% of normal levels after transfection into human keratinocytes. This upregulated NRF2 and increased the levels of NQO1, GCLC and GCLM as well as aldo-keto reductase 1C1/2 and GSH in the cells.

Therefore, the authors suggest that siRNA against KEAP1 is a potentially valuable method for inducing the pre-adaptation of human cells to oxidative stress. This could be useful for treating degenerative disease without exposing cells to potentially harmful chemicals.