Biocryst Pharmaceuticals Inc.'s licensing deal with CSL Ltd. for the FDA-approved influenza treatment Rapivab (peramivir) brings $33.7 million aboard, with as much as $12 million more possible if regulatory milestones are hit, while letting the firm keep rights to U.S. pandemic stockpile orders – "the greatest potential source of income," according to Piper Jaffray analyst Charles Duncan, who viewed the CSL agreement as a bonus.

Indicated for acute uncomplicated flu in adults 18 years and older, the neuraminidase inhibitor Rapivab is also licensed for use in Japan and Korea. CSL's subsidiary Biocsl gets rights to commercialize the products in territories excluding those two along with Taiwan and Israel, and will take on the stockpiling responsibility outside the U.S. Tiered royalties are part of the deal, too.

Cash from the pact with Melbourne, Australia-based CSL provides Biocryst, of Research Triangle Park, N.C., with padded coffers ahead of the widely anticipated data from Opus-2, the phase IIb trial of kallikrein inhibitor BCX-4161 for hereditary angioedema (HAE), expected to yield results around the end of the year. Enrollment began last December – by coincidence, also when the flu therapy won the FDA's nod, one year after the new drug application filing – in the 12-week, three-arm, parallel-cohort experiment to evaluate the efficacy and safety in HAE of two different dose regimens of BCX4161 administered three-times daily, 300 mg and 500 mg, compared with placebo. The trial is being conducted in the U.S. and selected European countries, testing 100 HAE patients with a history of moderately frequent to very frequent attacks. The primary efficacy endpoint for the trial is the mean attack rate for each BCX4161 dose group compared to placebo. (See BioWorld Today, Dec. 23, 2103.)

As for Rapivab, Duncan wrote in a research report that his firm had kept it "in the 'show me' category, primarily because of low visibility on governmental stocking orders. This deal is good because it realizes what we viewed as a 'free' [in the sense of largely sunk costs, and those mainly paid by governmental grants] call option for Biocryst. And [in] what could be the largest upside option, U.S. stocking orders remain available." What's more, he pointed out, Rapivab was largely funded by federal grants "and thus was not shouldered by investors. This [CSL] transaction points to a core capability, in our view, for savvy business development by the Biocryst team, and we anticipate this may again be shown if the HAE program continues to emerge."

During Biocryst's conference call on earnings last month, Duncan asked if any blinded information from the Opus-2 study might be disclosed by the company, but chief medical officer William Sheridan held back, saying he was "sort of allergic to blinded combined analyses because they can be very misleading – I've had that experience before. I think what we can say, to give you some reassurance, is we're recruiting into the study, we got sites up and running in the U.S. and Europe. There is always competition for patients in clinical studies." The company was able to say that it has gained "an insight into adherence with filling out the electronic diary" and with taking the drug, which amounts to "operational tracking, if you like," he said. "We use an electronic diary to try to facilitate that. That's going quite well. That's a good sign in terms of getting what we need to have an interpretable study."

In November 2013, the Opus-1 phase IIa proof-of-concept began enrolling and signed up 24 patients with a history of HAE attack frequency of one per week. In May 2014, the company disclosed that Opus-1 met the primary efficacy endpoint, several secondary endpoints, and all other objectives established for the trial. Treatment with BCX4161 turned up a statistically significant mean attack rate reduction of 0.45 attacks per week vs. placebo (p<0.001). The mean attack rate per week was 0.82 on BCX4161 treatment, compared to 1.27 on placebo.

Biocryst "did liberalize the inclusion criteria in terms of attack rate required for the [Opus-2] study," Sheridan noted, though "in other respects, it's quite similar to the criteria for Opus-1. But I think it would be pretty much impossible to get 100 patients like the [24] Opus-1 patients in any reasonable time frame. My expectation is that the placebo attack rate will be somewhat less."

Biocryst's stock (NASDAQ:BCRX) closed Wednesday at $13.18, up 53 cents.