Synergy Pharmaceuticals Inc., of New York, will boost its development of plecanatide, a candidate for gastrointestinal disorders, with an offering of $90 million of common stock. Plecanatide has the potential to treat disorders like chronic idiopathic constipation (CIC) and constipation-predominant irritable bowel syndrome (IBS-C).

If underwriters exercise an overallotment option in full, the size of the offering would be $103.5 million in aggregate value. Credit Suisse, Citigroup and Canaccord Genuity are book-running managers for the offering.

Plecanatide is a guanylate cyclase C receptor agonist and an analogue of uroguanylin, which regulates ion and fluid transport in the intestine. Synergy has completed a Phase I trial of the drug in healthy volunteers and a Phase IIa trial in patients with CIC, and has begun a Phase IIb trial in patients with IBS-C.

The Phase IIa trial, completed in September 2010, enrolled 78 patients at 14 sites in the U.S. to receive a 14-day course of of placebo or plecanatide at oral doses of 0.3 mg, 1 mg, or 9 mg. The drug showed a favorable safety profile with no severe adverse events, and particularly, no diarrhea. The rate of adverse events was 10 percent for plecanatide and 8.6 percent for placebo.

All plecanatide groups except the 0.3-mg group had significant decreases in time to first bowl movement after dosing compared to placebo.

A large, multicenter trial showed similarly positive results. That trial enrolled 951 patients who received 0.3 mg, 1 mg or 3 mg plecanatide or placebo for 12 weeks. The 0.3-mg group had a response rate of 19 percent, and a mean increase in complete spontaneous bowel movements (CSBMs) over the 12-week period of 2.13 compared to 1.03 for placebo. That trial met a number of secondary endpoints, as well, including frequency of CSBMs and SBMs, stool consistency, straining and treatment satisfaction.

The ongoing Phase IIb trial of plecanatide in IBS-C will enroll 350 patients who will receive 0.3 mg, 1 mg, 3 mg or 9 mg plecanatide or placebo once daily for 12 weeks. The primary objective is selection of doses for Phase III studies. Results are due in the first quarter of 2014.

Synergy's second-generation GC-C receptor analogue, SP-333, is in development for inflammatory bowel diseases. SP-333 is a synthetic analogue of uroguanylin, and according to Synergy, deficiency of uroguanylin has been linked to formation of polyps leading to colon cancer and other disorders such as ulcerative colitis and Crohn's disease.

Synergy submitted an investigational new drug application to the FDA in September 2012. It completed a Phase I trial of the drug in 70 healthy volunteers in December and began a multiple-ascending oral dosing study in healthy volunteers in January.

The company is also developing FV-100, which it acquired from Bristol-Myers Squibb Co., for shingles.

Synergy's last public offering of 1.88 million units priced at $8 apiece, closed for gross proceeds of $15 million. Each unit contained two common shares and a five-year warrant to purchase an additional share at $5.50.

In other financings news:

• VistaGen Therapeutics Inc., of South San Francisco, will receive a $36 million investment from Bergamo Acquisition Corp. in consideration for 72 million shares of restricted VistaGen common stock at 50 cents per share. The transaction will close on or before April 30, 2013. The shares issued represent a majority of issued and outstanding VistaGen common stock.