Many of the drugs we use to fight cancer or ward off pain aim to inhibit the activity of proteins that the body naturally produces. Instead of inhibiting the activity of a protein, what if you could just instruct your body to stop making it altogether? Or instead of getting injected with a lab-produced protein that your body isn’t making enough of, wouldn’t it be more convenient to just tell your body to use the instructions in its own DNA to make more? Sangamo Biosciences is pursuing these exact approaches to gene regulation using an engineered class of proteins called transcription factors. These so-called “designer” proteins promise to change the way medicine is practiced, and that’s why Sangamo is one of Biotech Mashup’s top 15 picks for companies that have the potential to change medicine.

The instructions for making proteins reside in DNA. For a protein to be produced, the DNA must be copied into an intermediate molecule, RNA, and then translated into protein. The first step of copying DNA to RNA relies on a large class of proteins termed transcription factors. Transcription factors can recognize and bind to a specific DNA sequence. Whence bound, they can either repress or stimulate the copying of DNA into the RNA that is required for protein production. Sangamo’s technology is based upon a class of transcription factors termed zinc finger transcription factors, or ZF-TFs. ZF-TFs are especially useful because their DNA binding domains and functional domains can be assembled as modules. It is thus possible to attach a transcriptional repressor or activator to the same DNA binding sequence. In this manner, it is possible to increase or decrease the expression of any gene depending upon the choice of functional domain. Transcriptional activators and repressors are not the only functional domains that can be attached to ZF proteins. It is also possible to attach nucleases, proteins that cut DNA, to a ZF protein. Nucleases can be used for targeted repair of a defective gene, or gene disruption to completely knock-out the gene.

The technology gets even better. The DNA binding domain of ZF-TFs is also modular. So it is possible to pick individual protein fragments that are known to bind to 3-base stretches of DNA and string the protein pieces together so that they collectively recognize larger stretches. Stringing just six such protein fragments together permits the unique targeting of almost any 18-base pair DNA sequence. Sequences as short as 18 bases have so many possible combinations that they are almost guaranteed to be unique within the entire human genome.

According to Sangamo, an advantage of activating an endogenous gene, rather than supplying the lab-generated protein product, is that activation of the endogenous gene results “In the production of all of the normal splice variants and thus the natural protein isoforms in the ratios normally observed in nature.” For VEGF-A, a vascular endothelial growth factor, this is especially important. “VEGF A, in its natural state, has multiple splice variants that are involved in the normal physiologic response and appear to be required for the generation of normal, functional vasculature,” according to Sangamo.

Sangamo, located in Richmond, California,  has a large pipeline of therapeutic ZF-TFs aimed at diseases including diabetic neuropathy, HIV, congestive heart failure, cancer, and cardiovascular disease. The technology has its technical limitations, however. For instance, delivering protein therapeutics to the nucleus of a cell, where this class of compounds must function, is not straightforward. Viruses carrying DNA that encodes the ZF-TFs are one approach, but they carry their own set of risks. As with most technologies, when there is a will, there is a way. We believe that ZF-TFs hold such promise as therapeutics that delivery obstacles will be overcome.