Sangamo Fails To Impress Investors With Genome Editing Studies

Sangamo Therapeutics Inc SGMO shares have come under pressure following an announcement concerning interim results from two genome editing studies presented at the WORLDSymposium 2019 in Orlando, Florida.

What Happened

Sangamo said SB-318 zinc finger nuclease, or ZFN, which is being evaluated in a Phase 1/2 study dubbed EMPOWERS in patients with mild mucopolysaccharides Type 1, or MPS 1, receiving weekly enzyme replacement therapy, or ERT, suggested a dose-dependent increase in leukocyte alpha-L-iduronidase, or IDUA, enzyme activity.

Plasma IDUA activity was unchanged from the baseline in all three patients studied, while baseline urine GAG measurements were at or slightly above normal.

MPS 1, aka Hurler syndrome, is a genetic disorder resulting from a deficiency of IDUA, a lysosomal enzyme essential for the breakdown of large sugar molecules called glycosaminoglycans, or GAGs.

Accumulation of GAGs leads to tissue and organ damage.

SB-318 is studied for treating MPS 1 using ZFNs, which are designed to insert a normal copy of the IDUA gene into a precise location in the DNA of the liver cells, enabling the liver to produce a continuous supply of functional IDUA enzymes. 

The current standard of care for MPS 1 is ERT given as weekly intravenous infusions; severely affected patients are treated with bone marrow transplant.

"Leukocytes are an easily accessible target tissue for IDUA and therefore provide an estimate of tissue enzyme activity for patients with MPS I. Whether these observed increases will translate into clinical benefit from SB-318 is yet to be determined," Dr. Paul Harmatz, the lead investigator of the study, said in a statement. 

Presenting interim results from another Phase 1/2 study dubbed CHAMPIONS — which is evaluating the SB-913 ZFN genome editing product candidate in patients with MPA II, or Hunter syndrome — the company said the genome-edited liver cells were able to generate active IDS enzyme in patients with MPS II.

"More data are needed to understand whether the small increases in IDS enzyme activity observed can translate into improved outcomes in MPS II patients treated with this first generation of SB-913," said Dr. Joseph Muenzer, a lead study investigator.

What's Next

Sangamo said additional data will be critical in assessing the safety profile and potential therapeutic benefit of SB-318.

ERT withdrawal is to be done in patients later in 2019, after which the clinical data and patient outcomes will be analyzed.

The company expects to report analyses of liver biopsies later this year.

Additional data from the five patients who received the high-dose of SB-913 in the CHAMPIONS study is due later this year.

Sangamo also said it will integrate a second-generation, potentially more potent ZFN construct designed to increase editing efficiency after assessing additional data from its in vivo gene editing programs.

Sangamo shares were falling 31.81 percent to $8.20 at the time of publication Thursday. 

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