On Tuesday evening, Arrowhead Research (ARWR) released the first human results for its experimental therapeutic ARC-520 in hepatitis B along with its second quarter financial results. Though not exactly what Wall Street wanted to see, the initial results suggest that higher doses of ARC-520, which the company is now testing, have a good shot at achieving the desired/expected knockdown of HBsAG (hepatitis B surface antigen). Whether that translates to a functional cure for HBV won’t be known until 2015.
ARWR’s phase 2a study tests ARC_520 at 1 mg/kg and 2 mg/kg doses in HBV patients. Initial data suggest that the magnitude of HBsAg knockdown is similar to results seen in a single non-human primate tested with -520 (a 0.8 log reduction). Arrowhead did not give exact numbers because the company remains blinded, and the analysis comes from best guesses as to which patients received placebo and which received active therapy.
Arrowhead also indicated that duration of knockdown appears to be substantially more sustained than expected based on non-human primates, with patients in the 2 mg/kg group still demonstrating knockdown after 8 weeks. This contributed to the company’s inability to assess the entirety of knockdown data.
Sell-side analysts were looking for ≥.5log reduction in HBsAG from ARC-520, while investors on Wall Street had a higher threshold for success, at ≥1.0 log. ARWR sold off hard in afterhours trading with the ambiguity of the company’s press release, but climbed almost back to its closing price as investors got comfortable with the new scenario. Arrowhead is now enrolling a higher dose (3mg/kg) in the phase 2a study and expects to have more data (and likely more precise HBsAG numbers) around AASLD’s Liver Meeting in early November (7-11). Though the can has been kicked down the road, AASLD sets up the next big event for ARWR. Investors will pin hopes on the 3mk/kg dose – and possibly 2mg/kg as HBsAG knockdown was ongoing at 8 weeks – achieving HBsAG knockdown of close to 1log.
