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A staggering 600,000 people will die from heart disease in the U.S. alone this year, but if a promising new therapy under development by Alnylam Pharmaceuticals (NASDAQ:ALNY) succeeds, then that number could fall significantly. That's because Alnylam's ALN-PCSsc, which is being co-developed by The Medicines Company (NASDAQ:MDCO), works in an entirely new way that may lower bad cholesterol levels better than current approaches.

Major changes in treatment
For decades, doctors have relied on statins that lower cholesterol production in the liver to reduce bad cholesterol levels and help prevent heart disease, yet despite the use of statins in tens of millions of Americans every day, heart disease continues to take the lives of one in four people in the U.S. each year.

In a bid to improve upon those figures, drugmakers developed a new strategy that may help prevent cholesterol from building up as artery-clogging plaque that is responsible for heart attacks and stroke.

This strategy is the inhibition of PCSK9, a protein that destroys bad cholesterol receptors in the liver. By limiting PCSK9 activity, the number of bad cholesterol receptors in the liver increases, allowing more bad cholesterol to be cleared from the bloodstream.

This past summer, The FDA approved the first two PCSK9-inhibiting therapies: Regeneron (NASDAQ:REGN) and Sanofi's (NYSE:SNY) Praluent, and Amgen's (NASDAQ:AMGN) Repatha.

Praluent is dosed every two weeks, and Repatha is dosed either every two weeks or once monthly, and in trials, both of these drugs reduced bad cholesterol levels by about 60% versus placebo when used alongside statins.

Initially, the use of Praluent and Repatha is limited to patients that have suffered a cardiac event or who suffer from high cholesterol that is caused by genetic mutations, but PCSK9 drugs could eventually be used as part of a standard of care in many of the more than 76 million Americans with elevated bad cholesterol.

Improving upon this advance in treatment
Although Praluent and Repatha are incredibly effective, they're not perfect drugs. In trials, roughly 5% of patients discontinued Praluent treatment because of adverse effects, including allergic reactions or elevated liver enzymes.

Additionally, Praluent and Repatha's dosing schedule could lead to patients failing to take their medicine as prescribed, particularly given that these are injection-based therapies rather than pills.

Because of these drawbacks, Alnylam and The Medicines Company's ALN-PCSsc may have a big advantage over Praluent and Repatha.

Although ALN-PCSsc is a PCSK9-targeting therapy like these other two drugs, early-stage data suggests ALN-PCSsc may have a dosing schedule that's as convenient as once every six months, and that it may cause fewer adverse events that lead to patients discontinuing treatment. 

Rather than targeting PCSK9's ability to bind to bad cholesterol receptors in the liver like Praluent and Repatha, ALN-PCSsc uses Alnylam's RNAi expertise to turn off PCSK9 production, thereby halting the ability of PCSK9 to destroy bad cholesterol receptors at the source.

In phase 1 trials, a single dose of ALN-PCSsc effectively lowered bad cholesterol similarly to Praluent and Repatha and importantly, none of the patients taking ALN-PCSsc discontinued treatment because of an adverse event. If those results hold up in later-stage, larger trials, then ALN-PCSsc could prove to be the best-in-class PCSK9 therapy. 

Looking ahead
Following the phase 1 success, a phase 2 trial of ALN-PCSsc will begin by the end of this year that will enroll 480 patients with high cholesterol levels that are already receiving the maximum dose of statins.

These patients will be randomized to receive either one dose of ALN-PCSsc on day zero of the trial, or one dose on day zero and a second dose on day 90. The primary endpoint of this trial will be ALN-PCSsc's ability to lower bad cholesterol at the six-month mark, and this study is expected to wrap up late next year, allowing for data to become available in 2017.

If phase 2 results are positive, then Alnylam and The Medicines Company will kick off a phase 3 study shortly thereafter. The companies are also planning to study ALN-PCSsc head to head against Regeneron and Amgen's PCSK9 inhibitors, which, if successful, could help cement ALN-PCSsc's best-in-class standing.

Overall, ALN-PCSsc could be a major advance in heart disease prevention, but doctors, patients, and investors will need to be patient, because it will still be years before we know for certain if ALN-PCSsc is really as good of a drug as it seems to be exiting phase 1.

Todd Campbell has no position in any stocks mentioned. Todd owns E.B. Capital Markets, LLC. E.B. Capital's clients may have positions in the companies mentioned. The Motley Fool owns shares of and recommends Alnylam Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.