Arrowhead Research (NASDAQ: ARWR) released data Thursday showing humans and chimpanzees treated with the company’s hepatitis B virus (HBV) candidate during Phase IIa clinical trials had significantly lower levels of antigens.
Shares in the company opened at $9.01, up 33 percent from the previous day’s $6.74 closing price. (The company sent out a press release announcing the results about two hours before the opening bell rang.) However, shares fell throughout the day and finished at $7.19 for a 6.7 percent gain on the day.
The drug candidate, known as ARC-520, attacks the virus using ribonucleic acid interference (RNAi), which destroys messenger RNA from viruses before the infected cell turns those RNA into proteins that propagate the infection. This interference is also known as “gene silencing.”
According to the World Health Organization, more than 360 million people globally are chronically infected with HBV and about 620,000 die from the virus each year.
HBV can cause diseases like cirrhosis and hepatocellular carcinoma, the most common type of liver cancer.
CEO Chris Anzalone says Arrowhead is further along in clinical trials than any other company developing a RNAi-based treatment for HBV. Arbutus Biopharma (NASDAQ: ABUS) has started a Phase I clinical trial for its competing candidate and Alnylam (NASDAQ: ALNY) has its own nascent RNAi HBV program, according to a RBC Capital Markets report.
Arrowhead says ARC-520 was able to significantly reduce amounts of particular proteins found in the blood of patients with HBV.
HBeAg, also known as the E-antigen, is a protein that runs through infected blood when HBV is actively replicating. One group of HBV patients who tested positive for the E-antigen received a background treatment, followed by a single dose of ARC-520. They experienced a 98 percent peak reduction in circulating HBeAg and an average reduction of 92 percent.
The S-antigen, short for “surface,” is another HBV protein indicating someone is infectious and can spread the virus to others. A cohort of “treatment-naive” patients—meaning they hadn’t had any background therapy—saw S-antigen, or HBsAg, decrease by as much as 99 percent.
“This is the highest knockdown ever reported in a human using RNAi,” says Anzalone.
Arrowhead did not share the average percentage by which ARC-520 lowered HBsAg. However, Anzalone points out that researchers captured the data 15 days after the drug was administered and S-antigen levels generally bottom out around 20 or 25 days post-treatment. The company will provide a comprehensive dataset to the public when the 85-day trial concludes, he says.
None of the 84 humans who have received ARC-520 to date have experienced serious or severe adverse events (AEs), according to the release. Nor have there been any discontinuations due to an AE or signs of end organ toxicity in lab results.
The chimp study, in which nine animals were given monthly doses of ARC-520 for six to 11 months, found levels of S-antigen reduction between 81 percent and 99 percent.
Arrowhead will reveal more data from the chimp study in November at a conference organized by the American Association for the Study of Liver Disease, says Anzalone.
He says the company kicked off multi-dose, Phase IIb trials on ARC-520 earlier this year. It figures to be the most important stage yet because the company has said the drug will be a multi-dose therapy and all trials through Phase IIa have been single-dose.
It’s likely the company won’t have more data on the candidate to share with the public for at least a year, Anzalone says.