Animal study: Direct to brain is best route of administration for Upstaza

Approved mode for AADC deficiency therapy better than other routes

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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An illustration of a scientist holding a flashlight to a giant image of a brain while another examines it with a magnifying glass.

The route of administration now used for the gene therapy Upstaza (eladocagene exuparvovec) — directly into the brain region, called the putamen, that’s affected by aromatic L-amino acid decarboxylase (AADC) deficiency — is better than other modes of delivery, an animal study showed.

The other tested routes included intracerebroventricular (ICV) injection into fluid-filled cavities in the brain, called the cerebral ventricles, and intrathecal (IT) injection into the spinal canal.

Putamen-targeted administration achieved the highest therapeutic distribution and activity in the targeted areas while minimizing the risk of side effects, the researchers noted.

The study, “AAV2-hAADC (Eladocagene Exuparvovec) Biodistribution and Expression: Superiority of Intraputaminal versus Intracerebroventricular and Intrathecal (Lumbar) Routes of Administration,” was published in the International Journal of Toxicology.

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AADC deficiency is caused by mutations in the DDC gene, which provides the instructions to make AADC, an enzyme involved in the production of several vital neurotransmitters. Those are the molecules used by nerve cells to communicate.

Disease-causing DDC mutations result in the production of too little enzyme and/or a faulty enzyme, which ultimately leads to a defective production of neurotransmitters. That, in turn, results in the disease’s neurologic symptoms, which include physical and mental developmental delays and movement disorders.

Upstaza (formerly called PTC-AADC) is a gene therapy that uses a modified and harmless virus to deliver a working copy of the DDC gene to cells. It is administered directly into the putamen — a delivery mode called intraputaminal injection — a brain region that plays a role in motor function and shows the highest AADC enzymatic activity under normal circumstances.

As such, the single-dose therapy is expected to restore the production of the AADC enzyme and thus halt or slow disease progression.

The therapy was approved last year in the U.K. and in the European Union member states, as well as in Iceland, Liechtenstein, and Norway. The therapy’s developer, PTC Therapeutics, has announced it intention to ask regulators for approval in the U.S. later this year.

The regulatory approvals to date were based on clinical trial data showing Upstaza safely led to significant improvements in motor and cognitive function and body weight in children with AADC deficiency for more than five years following treatment. It also led to reductions in symptom severity over the same timeframe.

Now, scientists at PTC sought to investigate the biodistribution and activity of two less invasive routes of Upstaza administration: intracerebroventricular, or ICV, and intrathecal, or IT. The team used non-human primates to compare these delivery methods to the itraputaminal route of administration.

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Contrary to intraputaminal administration, ICV and IT routes do not target specific brain regions, but deliver the therapy into the cerebrospinal fluid (CSF), the liquid surrounding the brain and spinal cord.

The goal was to determine “whether ICV and/or IT administration might serve as a viable alternative to intraputaminal administration,” the researchers wrote.

Twelve cynomolgus monkeys — six males and six females, all ages 1-2 years — received a full dose of Upstaza either by intraputaminal, ICV, or IT administration. Four monkeys were used to test each delivery method.

Upstaza’s human intraputaminal dose was scaled to a monkey dose based on total brain weight, and ICV and IT doses were increased by 10 times in an attempt to achieve comparable brain biodistribution.

Results showed that one month after dosing, the intraputaminal route yielded the highest levels of human DDC gene DNA in most of the targeted brain regions, including the putamen and the caudate — the second-highest site of normal AADC enzyme activity.

However, levels in the spinal cord were undetectable, as were those in the dorsal root ganglia (DRG), a cluster of nerves extending from the spinal cord and whose targeting by virus-based therapies may cause toxicity.

By comparison, with either ICV or IT administration, the highest levels of human DDC gene DNA was detected in the spinal cord and the DRG, and the lowest in the putamen or caudate.

Similar findings were obtained for human DDC gene activity, with intraputaminal administration resulting in the highest activity levels in the putamen and caudate.

In turn, ICV delivery was associated with minimal DDC gene activity levels in the caudate and none in the putamen. The IT route failed to promote such activity beyond the spinal cord and DRG.

The intraputaminal dose group also showed no signs of human DDC gene DNA in their blood by day two or one month, “suggesting a lower likelihood of off-target toxicities,” the researchers wrote.

In contrast, animals from both ICV and IT groups showed detectable blood levels of the treatment DNA by day two but not after one month. All routes produced comparable CSF gene levels.

These data demonstrate the superiority of [direct-to-brain] administration over [other] routes in achieving [human DDC gene distribution and activity] in target therapeutic areas while minimizing risk of toxicity.

Regardless of the route of administration, the gene therapy was generally tolerated well and did not affect animal weights, as all of the monkeys either maintained or gained weight. Also, there were no signs of tissue damage or major changes in lab tests for any of the monkeys.

Morerover, intraputaminal administration resulted in the lowest level of antibodies against the therapy’s viral carrier compared with ICV and IT routes. This type of antibodies can reduce treatment efficacy.

“Together, these data demonstrate the superiority of intraputaminal administration over ICV/IT routes in achieving [human DDC gene distribution and activity] in target therapeutic areas while minimizing risk of toxicity,” the researchers wrote.