Alnylam Pharmaceuticals announced this week that it has added its preclinical hypercholesterolemia program targeting proprotein convertase subtilisn/kexin type 9, or PCSK9, to its formal development pipeline.
The company also said it expects that one of the two investigational new drug applications it intends to file next year will be for a PCSK9-targeting therapeutic, which would be Alnylam’s first systemically delivered RNAi drug candidate.
By tapping the PCSK9 program for further development, Alnylam has for now shelved its other hypercholesterolemia effort, which targets the cholesterol-metabolizing protein apolipoprotein B.
PCSK9, a protease that degrades the cell-surface receptor for low-density lipoprotein, “is a compelling target for … hypercholesterolemia and complications of acute coronary syndromes,” Alnylam President and CEO John Maraganore said in a statement.
"Based on its novel mechanism of action and pre-clinical data to date, we believe an RNAi therapeutic targeting PCSK9 has the potential to lower LDL cholesterol while functioning synergistically with statins in the treatment of hypercholesterolemia,” Jay Horton, associate professor at the University of Texas Southwestern Medical Center and Alnylam collaborator, added.
Speaking at Alnylam’s annual R&D day this week in New York City, company officials said that the significant body of data suggesting that PCSK9 suppression can safely lower cholesterol levels played a key role in the decision to move the program forward despite the success the drug developer has had with its apoB research.
“We’ve used apoB very successfully as a model proving efficacy of RNAi therapeutics,” Kevin Fitzgerald, associate director of research at Alnylam, noted during a presentation at the R&D day.
For example, in November 2004 the company published data in Nature showing that cholesterol-conjugated siRNAs targeting apoB delivered intravenously into mice could cut apoB mRNA levels in the liver and jejunum, decrease plasma levels of apoB protein, and reduce total cholesterol (see RNAi News, 11/11/2004).
Earlier this year, Alnylam published additional data in Nature showing that lipid-encapsulated siRNAs targeting apoB could be used with clinical efficacy after systemic administration in non-human primates (see RNAi News, 3/30/2006).
According to Fitzgerald, this year’s Nature paper “was the first time anyone was able to show an RNAi therapeutic delivered in a non-human primate … model was able to not only … lower the transcript and the protein level of apoB, but do it in a therapeutically meaningful way by lowering LDL cholesterol.”
However, after conducting this work and honing its ability to systemically deliver RNAi agents into the liver, Alnylam “went through … a bunch of different liver targets and categorized them to focus on the ones that had the best validation and [that] we felt were the best,” Fitzgerald said. “Very quickly, we came upon PCSK9.”
Among the research motivating Alnylam to select PCSK9 as a drug target were data, published in the Proceedings of the National Academy of Sciences last year by the company’s collaborators at UTSMC, showing decreased plasma cholesterol and hypersensitivity to statins in knockout mice lacking the PCSK9 gene.
Even more compelling evidence supporting PCSK9’s promise appeared earlier this year in the New England Journal of Medicine when the UTSMC researchers published the results of a study examining the effect of nonsense mutations in PCSK9 on the incidence of coronary heart disease in 3,363 black subjects and 9,524 white subjects over a 15-year period. when the UTSMC researchers published the results of a study examining the effect of nonsense mutations in PCSK9 on the incidence of coronary heart disease in 3,363 black subjects and 9,524 white subjects over a 15-year period.
"Based on its novel mechanism of action and pre-clinical data to date, we believe an RNAi therapeutic targeting PCSK9 has the potential to lower LDL cholesterol while functioning synergistically with statins in the treatment of hypercholesterolemia.”
According to that paper, 2.6 percent of the black subjects had nonsense mutations in PCSK9, which were associated with a 28-percent reduction in mean LDL cholesterol and an 88-percent reduction in the risk of coronary heart disease.
By comparison, 3.2 percent of the white subjects had a sequence variation in PCSK9 that was associated with a 15-percent reduction in LDL cholesterol and a 47-percent reduction in the risk of CHD, the paper’s authors wrote, adding that the data “indicate that moderate lifelong reduction in the plasma level of LDL cholesterol is associated with a substantial reduction in the incidence of coronary events, even in populations with a high prevalence of non-lipid-related cardiovascular risk factors.”
With these findings in hand, Alnylam began in vivo experiments evaluating different siRNAs targeting PCSK9, and in October the company presented some of its preclinical data at the annual Oligonucleotide Therapeutics Society meeting.
As reported by RNAi News, two of the siRNAs Alnylam created silenced about 60 percent of PCSK9 in normal mice, which translated into about a 30-percent reduction in total cholesterol levels (see RNAi News, 10/26/2006).
At Alnylam’s R&D day, Fitzgerald presented new PCSK9 in vivo data from experiments in a UT Southwestern-developed transgenic mouse that expresses the human PCSK9 transcript in its liver and circulates the PCSK9 protein in its bloodstream.
He said that one siRNA active against human PCSK9 was able to lower levels of the PCSK9 transcript over 80 percent 72 hours after intravenous administration. Additionally, treatment with the siRNA led to “a drop in PCSK9 plasma protein levels 500- to 1,000-fold at two days after injection.”
”Our next steps are to move forward into non-human primates … looking at both efficacy and safety,” Fitzgerald said. “We then will proceed into IND-enabling toxicity [studies] and our goal is to file an IND in 2007.”
Also next year Alnylam expects to publish data on the so-called lipidoid nanoparticle technology it used to deliver the siRNAs and developed in the lab of Massachusetts Institute of Technology researcher Robert Langer, he added.