NEW YORK (TheStreet) -- XenoPort (XNPT)  shares are surging 56.48% to $6.89 in Monday afternoon trading on heavy trading volume as Arbor Pharmaceuticals agreed to acquire the company in a deal valued at about $467 million. 

Under the terms of the deal, Arbor will buy all of XenoPort's outstanding shares for $7.03 a share. The transaction is expected to be completed in the third quarter of 2016.

"We evaluated many potential options to maximize the value for stockholders and believe this transaction represents a great outcome for XenoPort stockholders," XenoPort CEO Vincent J. Angotti stated. 

Also commenting on the deal, Arbor CEO Ed Schutter said, "We are pleased to be adding Horizant and the XenoPort pipeline to the growing portfolio of Arbor products."

Horizon offers patients a treatment option for moderate-to-severe primary restless legs syndrome and postherpetic neuralgia.

As of 3:40 p.m., more than 50.7 million shares of XenoPort were changing hands, significantly higher than the company's average trading volume of about 475,500 shares. 

Separately, TheStreet Ratings currently has a "Sell" rating on the stock with a letter grade of D-.

This is driven by multiple weaknesses, which we believe should have a greater impact than any strengths, and could make it more difficult for investors to achieve positive results compared to most of the stocks we cover. The company's weaknesses can be seen in multiple areas, such as its disappointing return on equity, generally disappointing historical performance in the stock itself and generally high debt management risk.

Recently, TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this article's author.

You can view the full analysis from the report here: XNPT