Infants with rare cases of SMA get stronger, live longer on Isis drug

Isis CEO Stan Crooke

The infants and young children who suffer from rare cases of spinal muscular atrophy, or SMA, don't live long. Defects in the survival motor neuron 1 gene, a key player in promoting neuromuscular growth, cause them to grow progressively weaker and suffer from a series of harsh events ending in a very early death.

But Isis Pharmaceuticals ($ISIS) says that the latest update on the infants enrolled in their mid-stage program for ISIS-SMNrx shows that toddlers with the most severe form of the disease have been getting progressively stronger and living longer while taking this drug.

Nineteen infants with Type 1 SMA who were evaluable in the single-arm study were given either a 6-mg or 12-mg dose of the therapy, says Isis CEO Stan Crooke. The median event-free age of four patients in the 6-mg arm jumped from 16.3 months to 19.9 months and from 11.6 months to 16.7 months in the 12-mg arm. Seven infants in the original group of patients saw their median event-free age increase from 9.6 months on April 7, 2014 to 21.4 months on April 17, 2015. And executives for the company say that there have been no events over the last two months to report as well.

"Based on the historical control we would expect infants to have an event by 6 to 10 months old, 10 on the outside," says Crooke. "What we've seen is extraordinarily more than we expected."

Not only are the children living longer without suffering from setbacks, they're also getting stronger, says the CEO. Instead of seeing their strength scores decline steadily, he added, slightly more than half of the kids taking this drug have seen their scores reach back up into a low normal range.

"They are living longer, achieving milestones that are simply unheard of," says Crooke. Five of the Type 1 patients are now able to able to sit unassisted. "What we hoped to see (in this study) were good safety data. We never dreamt we'd see this."

Another update on a group of children recruited for a separate Phase II trial is due out in a few weeks, says Crooke, and that looks good as well. The focus at Isis has shifted to the ongoing, placebo-controlled Phase III program, which will be used for a new drug application.

This drug is among a half dozen late-stage programs in Isis' pipeline, and Crooke considers it one of the most significant, both from its ability to help patients as well as its future commercial prospects. Biogen ($BIIB) is partnered on the drug and Isis stands to earn additional milestones as well as a double digit royalty on sales.

"Obviously this is an important commercial asset," says Crooke. "We think it could be a substantial commercial success."

Asked how he expects the data to end up, Crooke said: "No one knows. These babies have never lived this long. We're in completely uncharted waters."

- here's the release