ARWRArrowhead Pharmaceuticals Inc (NASDAQ:ARWR) investors are having a rough day following the news that deaths observed in non-human primate toxicology studies put the company’s ARC-520 program, a 12-patient trial, on hold in the U.S. The carrier molecule, EX1, which directs the drug to the liver appears to be the culprit.

Arrowhead shares reacted to the news, falling 26% in Wednesday’s trading session.

The FDA did not indicate the clinical hold was based on any human findings. To date, EX1 has been administered over 800 times in more than 300 human study subjects and patients. Across this substantial clinical experience, only 3 serious adverse events (SAE) have been observed. Two of these were fevers, treated with acetaminophen, after which the patients continued on the study with no further complications. The other SAE was an instance of hepatic carcinoma in a patient with chronic HBV and cirrhosis, judged by the treating physician to be unrelated to the drug. A small minority (6%) of infusions in ARC-520 studies have been associated with infusion reactions, with 4 patients discontinuing ARC-520 treatment. In addition, across the ARC-520, ARC-521, and ARC-AAT clinical programs, laboratory values have not been deemed indicative of any drug-induced organ toxicity.

Arrowhead has not yet received written notice of the clinical hold from the FDA; however, based on verbal communications the clinical hold was prompted by deaths at the highest dose of an ongoing non-human primate toxicology study. This study involves higher doses of EX1 than those used clinically in humans and higher than those used in the company’s previous animal toxicology studies. The cause of these animal deaths is unknown and under investigation. The EX1 delivery vehicle is used in the company’s ARC-520, ARC-521, and ARC-AAT programs.

Arrowhead remains committed to working collaboratively with regulatory authorities worldwide. The company has disseminated data from the same animal study to agencies across our development programs and is providing updates as appropriate. The company believes the findings in animal toxicology studies are related to dose level, and that the safety profile seen in human clinical studies across the three programs involving EX1 supports continuing all ongoing clinical studies. (Original Source)

On the ratings front, Arrowhead has been the subject of a number of recent research reports. In a report issued on October 5, Jefferies analyst Eun Yang reiterated a Hold rating on ARWR, with a price target of $6.50, which represents a potential upside of 35% from where the stock is currently trading. Separately, on September 29, Chardan’s Madhu Kumar reiterated a Buy rating on the stock and has a price target of $10.00.

According to TipRanks.com, which ranks over 7,500 financial analysts and bloggers to gauge the performance of their past recommendations, Eun Yang and Madhu Kumar have a yearly average loss of 3.0% and 14.2% respectively. Yang has a success rate of 45% and is ranked #3661 out of 4186 analysts, while Kumar has a success rate of 39% and is ranked #3860.

Arrowhead Pharmaceuticals, Inc. engages as a biopharmaceutical company developing targeted RNAi therapeutics. Its pipeline includes clinical programs in chronic hepatitis B virus and partner based programs in obesity and oncology.