NEW YORK (TheStreet) -- Shares of Alnylam Pharmaceuticals  (ALNY)  were plunging 46.43% to $37.67 on heavy trading volume late Thursday morning after the company said it was ending the development of revusiran, one of its two gene-silencing drugs. 

A late-stage trial of the treatment showed that more patients died after receiving the drug than those who took a placebo, the Cambridge, MA-based company said in a statement. 

The drug was being developed to treat patients suffering from a fatal disease that can cause heart failure. 

TheStreet's Adam Feuerstein said experimental drug failures are common in biotech, but Alnylam's decision to end revusiran development is a "bigger deal" because it raises fears that a highly sought after drug could be a "total bust."

JPMorgan subsequently downgraded the stock to "neutral" from "overweight" and cut its price target to $51 from $83, according to TheFly.

The firm said revusiran was a "key asset" to the biopharmaceutical company's pipeline.

Barclays also reduced Alnylam's stock rating to "equal weight" from "overweight" this morning. The firm slashed its price target to $50 from $85.

Alnylam has faced a set of recent pipeline setbacks, but the firm said it still feels "very comfortable" with the company's patisiran gene-silencing drug that's currently in development. 

About 9 million of Alnylam's shares have changed hands so far today vs. its average volume of 591,340 shares per day.

Separately, 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 articles's author.

The team rates Alnylam as a Sell with a ratings score of D. The company's weaknesses can be seen in multiple areas, such as its deteriorating net income, disappointing return on equity, weak operating cash flow, generally disappointing historical performance in the stock itself and feeble growth in its earnings per share.

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

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