Proteon’s Blood Vessel Drug Flunks Main Phase 3 Test, Shares Plummet

Xconomy Boston — 

A Proteon Therapeutics drug developed for chronic kidney disease patients has failed the key test in its late-stage clinical trial, putting the company’s shares into a tailspin.

Proteon (NASDAQ: PRTO) was studying its drug vonapanitase in patients who need kidney dialysis. The Waltham, MA-based company said that compared against a placebo, its experimental drug failed the study’s main goal of keeping a blood vessel open in patients being prepared for kidney dialysis. Proteon’s stock price was hovering around $2.96 Tuesday morning, down more than 70 percent from Monday’s closing price.

The Proteon drug was developed to improve the chances of success for a surgical procedure called arteriovenous fistula (AVF), in which a connection is created between an artery and a vein in the patient’s arm. This connection boosts blood flow, helping to thicken the wall of the blood vessel, which makes it better able to withstand the needle pricks from kidney dialysis.

But AVF procedures often fail within the first year because cells accumulate in the healing blood vessel, clogging it up and cutting off blood flow. Proteon’s experimental drug was an engineered form of the human enzyme elastate, which was developed to prevent that from happening. The drug is topically applied to blood vessels during the AVF surgery.

Proteon formed in 2006 based on research from Johns Hopkins University. Early work on the Proteon drug caught the interest of Novartis (NYSE: NVS); in 2009 the drug giant inked a $550 million deal with Proteon that included an option to buy the company or license its drug following a Phase 2 trial. Those options never materialized and Proteon instead forged ahead on its own, raising money from private investors before filing for an initial public stock offering in 2014. Proceeds from the IPO supported late-stage clinical trials on the Proteon drug.

Despite vonapanitase’s failure to hit the clinical trial’s main goal, Proteon says it is encouraged by the drug’s performance in a secondary measure. The second endpoint of the trial was the length of time from surgically creating the opening in the blood vessel to the final failure of this opening. Proteon said that the risk of this failure decreased 34 percent over one year in patients treated with its drug compared to patients treated with a placebo. Steven Burke, Proteon’s chief medical officer, said in a prepared statement that the secondary outcome is “clinically relevant.” He added that Proteon will evaluate those findings as the Phase 3 trial continues.

Through the end of November, Proteon reported having $43.3 million in cash. The company says that’s enough money to carry the company into the third quarter of 2018.