UPDATE 1-ARCA: FDA denies approval for heart drug, seeks data

* Says FDA denies approval for heart drug in present form

* Says FDA asks co to conduct additional studies

* Shares sink almost 58 pct

June 1 (Reuters) - ARCA biopharma Inc (ABIO.O) said U.S. health regulators denied approval for its experimental drug to treat chronic heart failure in the present form and asked the company to conduct additional clinical studies, knocking its shares down almost 58 percent.

In its complete response letter, the U.S. Food and Drug Administration said the late-stage trial of the drug Gencaro does not adequately demonstrate its efficacy in reducing all-cause mortality in patients with heart failure, the company said.

FDA also raised concerns about the integrity of the trial data based on the audit of certain clinical sites.

An independent audit of additional clinical sites and other actions may be required to verify the integrity of the data, ARCA quoted the letter as saying.

The FDA, in the letter, said ARCA would need to conduct additional studies -- including a clinical efficacy trial in patients with heart failure and clinical pharmacology studies to address pharmacokinetic issues -- in order to get approval.

However, the FDA acknowledged that several substantial amendments to the new drug application submitted by the company in May 2009 were not reviewed by it in issuing the complete response letter, ARCA said.

Shares of the company plunged almost 58 percent to $3.91 before paring some losses to trade down 43 percent at $5.30, making them the highest percentage loser on Nasdaq.

For the alerts double-click [ID:nWNAB5042] . (Reporting by Anand Basu in Bangalore; Editing by Himani Sarkar)