Rare-disease specialist Alexion hails progress on Sanfilippo B drug

Alexion's Martin MacKay

Alexion Pharmaceuticals ($ALXN) is making positive progress with an early-stage orphan drug snapped up in its $8.4 billion buyout of Synageva.

The enzyme replacement therapy SBC-103--targeting Sanfilippo B syndrome--was cited as a top prospect for Alexion when the biotech completed the buyout last spring, which was primarily focused on the recently approved Kanuma.

In an ongoing Phase I/II study of SBC-103, researchers said that they were tracking a 26.2% mean reduction in heparan sulfate (HS) levels in cerebrospinal fluid after 24 weeks of therapy in the highest dose cohort. And with a fairly clean safety profile to date, the biotech says there's room for further dose escalation as investigators look for the best approach to nailing down pivotal data.

Sanfilippo B syndrome, or mucopolysaccharidosis IIIB (MPS IIIB), is triggered by genetic mutations that shutter N-acetyl-α-D-glucosaminidase (NAGLU) enzyme activity. That in turn causes levels of heparan sulfate to rise in the brain and other organs.

SBC-103 is designed to replace the missing enzyme and correct a condition that leads to severe cognitive impairment as well as early death. The study recruited 11 children for its first-in-human study.

Aside from the cerebrospinal data, which are used to track how the drug flushes HS in the brain, researchers tracked "mean reductions in total serum HS at 24 weeks of 39.6 percent, 53.9 percent, and 40.5 percent at 0.3, 1.0 and 3.0 mg/kg, respectively."

The progress with SBC-103 comes the week that Alexion is moving into its new headquarters building in New Haven, CT. That was paid for by Soliris, Alexion's pioneering orphan drug that went on to become one of the most expensive therapies on the planet. After adding Kanuma and Strensiq to its list of marketed drugs last year, the focus now is on gaining a slate of new product and indication approvals.

The primary focus of the new study is safety and tolerability, but Alexion also wants to see what kind of impact the drug has on cognition and other symptoms of the disease.

"SBC-103 is manufactured with our proprietary protein expression platform, and we are encouraged by its potential to be administered intravenously and cross the blood-brain barrier to provide both systemic and CNS clinical benefits for patients suffering from MPS IIIB," said Martin Mackay, executive vice president and global head of R&D at Alexion. "These 24-week results, coupled with the increased dose response observed in animal models, support dose escalation for all patients in the study."

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