Synthetic expressions

How synthetic biology could lead to a new generation of gene therapies

Bringing synthetic biology to transcriptional regulation could catalyze a new generation of gene therapies that are more tunable, disease-specific and easy to deliver than the products dominating the field.

The new constructs include synthetic promoters that can optimize expression of vector-encoded genes, and synthetic transcription factors that can activate silent regions of a patient’s own genome.

Gene therapies typically employ promoters that are either constitutively active or tissue-specific to drive the expression of genes encoded in delivery vectors. The trade-off is that constitutively active promoters induce higher gene expression, but are more prone to off-target effects.

Synthetic promoters offer the chance to bridge the gap by combining optimized sequences from different natural promoters to concentrate potent expression in disease-relevant cell types or tissues. The technology, which first took off in agricultural engineering, is now gaining traction for biomedical applications (see “Synthetic Synthesis”).

Figure: Synthetic synthesis

Synthetic promoters and transcription factors could advance gene therapies by enabling controlled expression of exogenous or endogenous genes. Design strategies include combining natural cell-specific promoter sequences to create new promoters, and co-opting CRISPR machinery or pharmacological DNA binders to generate transcription factors.

Synthetic promoters. Synpromics Ltd.’s PromPT platform uses bioinformatics to find promoters (green) that are activated in a cell type of interest. The platform generates combinations of the natural promoter sequences, clones them into constructs containing DNA barcodes (striped bars), and transfects the barcoded library into the relevant cell type. The strongest promoter combinations are identified by finding the barcodes that are most abundantly transcribed. Top hits are used to drive cell type-specific expression of a therapeutic gene.

Cas9-based synthetic transcription factors. A group from the Salk Institute for Biological Studies

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