Sangamo Therapeutics Presents Advances in Zinc Finger Nucleases for Gene-Editing Use

Margarida Azevedo, MSc avatar

by Margarida Azevedo, MSc |

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Sangamo Therapeutics recently presented what it characterized as key improvements to its technology platform for engineering highly specific zinc finger nucleases (ZFNs), which are used for targeted editing of the human genome. This technique has broad applicability, namely for the treatment of hemophilia B and other disorders.

The company’s SB-FIX is the first in vivo genome-editing product to enter the clinic, and is being evaluated in a Phase 1/2 clinical trial (NCT02695160), which is currently recruiting patients, to treat severe hemophilia B. The U.S. Food and Drug Administration (FDA) recently granted SB-FIX with orphan drug designation.

The company also is conducting a Phase 1/2 trial to evaluate SB-525, another gene therapy approach, to treat hemophilia A. The FDA recently cleared SB-525’s Investigational New Drug (IND) application.

Sangamo is developing a ZFN-mediated gene editing approach for use in a patient’s own hematopoietic stem cells (HSCs) as a potential single-administration long-acting therapeutic avenue for blood disorders.

In HSCs, this technology can be used to precisely disrupt the erythroid-specific “enhancer” of BCL11A expression, a regulatory DNA sequence that is essential for expression of BCL11A, a key transcriptional regulator of human fetal hemoglobin. Reducing or eliminating the expression of BCL11A, by knocking out the enhancer, enables the continued production of therapeutic fetal globin.

In a presentation during the Keystone Symposium on Precision Genome Engineering,  Sangamo’s vice president Edward Rebar, PhD, made an overview of data of genome editing of therapeutic gene targets in clinical cell types, such as high levels of targeted gene modification (80%) of the BCL11A enhancer in hematopoietic stem and progenitor cells with no significant off-target activity.

Genomes are huge and offer a lot of possible binding sites for a nuclease with an intrinsic potential to bind DNA, so there is a certain risk of off-target activity. In the data presented during the meeting, the experiments assessed off-target activity.

“Based on a human DNA-binding motif, we believe ZFNs are the most advanced, flexible and precise genome editing technology available, and, as our scientists have demonstrated, they can be further engineered to refine their specificity and potency for therapeutic use,” Sandy Macrae, Sangamo’s CEO, said in a press release.

“The new architectures and strategies that we describe represent a substantial improvement in our capabilities while retaining full compatibility with our existing genome editing platform. The modifications enable us to target any investigator chosen site in the genome with enhanced precision and a reduction in off-target cleavage to levels that are at or below the limit of detection even under conditions of very high on-target activity. Importantly, these results are achievable at clinical scale, using clinical delivery conditions, and in clinically relevant cell types,” Macrae said.

Zinc finger nucleases (ZFNs), a prominent tool in the field of genome editing, are molecular scissors that replace specific DNA sequences by cutting through the double helix, after which the cell’s repair machinery fixes the break. Specifically, they are artificial restriction enzymes generated by fusing a zinc finger DNA-binding domain to a DNA-cleavage domain. Zinc-finger domains can be engineered to target specific desired DNA sequences enabling ZFNs to target unique sequences within complex genomes.

In his presentation, Rebar described various progressions in the field, and also demonstrated that modifications of key framework residues in the zinc fingers can specifically suppress off-target cleavage activity.

“These engineering advances are exciting because they enable development of extremely specific nucleases for therapeutic applications that are not limited by the targeting constraints inherent to other cleavage platforms,” Rebar, said. “These new architectures will also accelerate development of highly active and specific ZFNs, resulting in much faster identification of therapeutic leads.”

Sangamo CEO Sandy Macrae also recently presented an overview of the company’s plans, research and clinical development programs at the JP Morgan Healthcare Conference in San Francisco.