Rocket Pharmaceuticals in orbit after gene therapy read-out

Shares in Rocket Pharmaceuticals have been living up to their name, shooting up following encouraging early-stage clinical trial results from a gene therapy for a serious inherited rare heart disease.

Results came from a phase 1 trial of RP-A501 for treatment of Danon Disease and sent shares up 75% on the Nasdaq to more than $56, a five-year high.

The surging stock price indicates the market's confidence in gene therapy products after the successful launch of products such as Roche/Spark Therapeutics' Luxturna, a gene therapy for a rare inherited eye disease.

Danon Disease is a rare X-linked disorder caused by genetic mutations in the LAMP2 gene and the therapy works by instructing the body to express a healthy copy of the LAMP2B protein in order to correct the condition.

The disease that affects boys and men more severely causes accumulation of autophagosomes – tiny structures that cause cells’ internal structures to break down – in the heart muscle and other tissues.

Together with a build-up of glycogen this can lead to severe and frequently fatal degradation of the heart muscle.

RP-A501 could be the first gene therapy for the disease and the early data showed a positive increase in cardiac protein expression.

As of November, three patients have been treated with a low dose of the therapy and two have been treated with a high dose.

An early trial readout showed two patients with LAMP2B expression that was 50% more than normal, measured nine and 12 months after treatment.

A 15%-20% increase could lead to clinically meaningful improvements in cardiac function and the trial reported a 50% decrease in a key biomarker of heart failure.

There was also a reduction in myocardial cell disarray and a visible reduction in autophagic vacuoles, a hallmark of the disease.

The company also noted stabilisation of three other measures – a heart failure biomarker known as BNP,  plus levels of transaminases and creatine kinase that also indicate skeletal and heart muscle damage.

However one patient who received the highest dose and had a degree of immunity to the adeno-associated virus used in the therapy had an immune reaction classified as a serious adverse event.

Rocket said the event was likely due to complement activation, resulting in reversible thrombocytopenia and acute kidney injury requiring a short round of haemodialysis.

The patient returned to baseline within three weeks and regained normal kidney function.

Dr Barry Greenberg, director of the Advanced Heart Failure Treatment Program at UC San Diego Health, Professor of Medicine at UC San Diego School of Medicine, and the principal investigator said: “Children with Danon Disease live with a heavy disease burden. Young boys are often severely afflicted.

“They show evidence of early onset skeletal muscle weakness and heart disease that can progress rapidly to end-stage with death occurring on the average before age 20. A heart transplant can be performed but is not curative and is associated with its own significant problems.

“The results-to-date for this first investigational gene therapy for monogenic heart failure show the potential for direct clinical benefit without emergence of unanticipated side effects of therapy.”

The company has also begun a stock offering of $175 million in shares to fund further development following the results.