Updated with new information from the conference call
Arrowhead Research ( ARWR) just released interim results from a mid-stage study of its experimental RNA interference therapy for hepatitis B. The announcement is short on specific details but the Arrowhead drug, ARC-520, appears to have passed through its first clinical hurdle in hepatitis B patients relatively well.
Arrowhead shares closed Tuesday at $13 ahead of the ARC-520 data announcement. The stock is down 5% to $12.25 in the after-market session, reflecting some uncertainty about the results, perhaps confusion or frustration over why the company chose not to be more forthcoming with actual numbers.
I wrote a preview of the ARC-520 data recently. Here's how Arrowhead describes the ARC-520 results today:
-- Initial blinded data suggest that the magnitude of HBsAg knockdown is similar to non-human primate studies, including the chronically infected chimpanzee reported on previousl
-- Duration of knockdown appears to be substantially more sustained than in non-human primates, with patients in the 2 mg/kg group still demonstrating substantial knockdown after 8 weeks, which is the most recent time point available.
-- HBsAg levels appear to continue to decline in a number of patients at the 8 week time point in the 2 mg/kg group
First thing you should notice is the lack of specific numbers. Arrowhead executives, on a conference call, said the study is still blinded. If the study is blinded, how can Arrowhead report results differentiated between patients dosed with ARC-520 and those on a placebo? Arrowhead says educated guesses are being made based on the blinded responses. Yes, it's a bit unusual, even weird, although I assume Arrowhead assumes hepatitis B patients treated with a placebo would show little or no response at all, making it easy to identify responses to the drug.
In a previous study of ARC-520 involving a chimp infected with hepatitis B, treatment with ARC-520 caused a 0.8 log reduction in HBsAG, which is a measure of the presence of hepatitis B virus in the body. Arrowhead says ARC-520 response in human hepatitis B patients was "similar" to the chimp results but the duration of the knockdown was longer.