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Key for effective application of a new revolutionary cholesterol lowering drug resides in a 30 year old Leiden Patent

‘’ And then the world changed forever ,welcome to the future’’. These are the words that Kausik Ray (President of the European Atherosclerosis Society) spoke when the worldwide first dose of inclisiran, a novel SiRNA based cholesterol lowering agent, was administered at the Cardiology lipid clinic at the University of Vienna. The SiRNA , provided with a GalNAc anchor for targeting to the liver, lowers PCSK9, a protein that normally degrades the LDL-receptor. This leads to upregulation of the LDL-receptor in the liver and consequently to a 50% lowering of LDL cholesterol in the blood. Due to the novel mechanism of action two injections/year are sufficient. Such an administration frequency mimics the protocol for vaccination, only 2 shots a year for control of cholesterol! This first SiRNA drug was developed by Alnylam, a company based in Boston and founded in 2002. The Medicines Company financed the clinical studies and due to its effectivity and potential market, last year the Medicines Company and thus the drug inclisiran was acquired by Novartis for 9.7 billion dollar.

The basis for this medicine however lies in the 2006 Nobel Prize in Physiology or Medicine. The winners Drs Mello and Fire discovered the system of RNA interference by small RNA ( SiRNA). Only a single SiRNA is needed to cleave a large number of target RNA, so the actions of an SiRNA are catalytic . It is also possible to design SiRNA for the mRNA of any desired gene, so the possibilities to influence the expression of any gene are within reach. The Nobel laureate Craig Mello and Phil Sharp founded Alnylam to commercialise this unique way of influencing gene expression.

A major obstacle was however the delivery of the SiRNA to its intracellulair site of action and the company faced a dark period in which major investors and large pharmaceutical companies lost their interest.

Galactose targeting:

Already in 1984 our group ,in collaboration with Herman-Jan Kempen and Jacques Van Boom , started to work on a synthetic high affinity substrate for the asialoglycoprotein receptor, which is only expressed on liver parenchymal cells. The aim was to use such a high affinity ligand for the specific targeting of various therapeutics to the liver.

The department of organic synthesis of Leiden University , headed by Jacques Van Boom and Gijs van der Maarel, succeeded in synthesizing a triantennary galactose structure which could be coupled to cholesterol. This triantennary galactose structure induced very rapid removal of the therapeutic from the blood circulation and rapid uptake in the liver parenchymal cells. We published a paper in the J. Med.Chem and 2 papers in the J.Biol.Chem. Eric Biessen , then a postdoc within the Division Of Biopharmaceutics of the LACDR, optimized subsequently the cluster glycosides and in 1992 the Patent “ Triantennary cluster glycosides, their preparation and use “ was worldwide granted with the inventors Biessen, Van Berkel and Van Boom. The applicants were the Leiden University and the Dutch Heart Foundation. 

A start-up company Called GendoMed was raised and commercial application was aimed by approaching all the major pharmaceutical companies. Although the system of drug delivery was considered elegant and efficient , no concrete steps were taken by the pharmaceutical industry and thus the patent was no longer sustained.

In the meantime Patrick Rensen and Eric Biessen further optimized the antennary system by replacing the Galactose group by N-acetylgalactosamine ( GalNAc) , leading to a 50-fold increase in affinity and we published the synthesis in the J.Med.Chem.( 1999 and 2004) and its application in J.Biol.Chem.(2001) and Circulation (1995) and Arteriosclerosis,Thrombosis and Vascular Biology (2006).

In 2007 Manoharan working as organic chemist with Alnylam, wrote me an e-mail and suggested to start a collaboration on the specific delivery of Si-RNA. As mentioned Alnylam was in a dark age as major collaborating pharmaceutical companies lost their believe in the application of SiRNA .The major obstacle was to bring the very effective molecule to its desired site of action. 

I visited Alnylam in March 2008 for the first time and presented a seminar entitled’’ Therapeutic Opportunities in Atherosclerosis’’ including our data on targeting the asialoglycoprotein receptor by cluster galactosides. Since then I visited Alnylam numerous times and we started a very nice and pleasant collaboration on utilizing the asialoglycoprotein receptor for the selective delivery of Si-RNA to the liver, leading not only to 2 nice highly cited publications in the J Am. Chem Soc (2014) and Mol.Ther. (2018) , but also to the widespread use of Gal-NAc as delivery agent for Si-RNA and antisense oligonucleotides to the liver.

I once stated at Alnylam on a question on the physiological function of the asialoglycoprotein receptor that”it was made for efficient drug delivery”, but now realise that this bold statement is becoming a Reality.

The GalNAc-SiRNA for PCSK9 , called inclisiran, is 9 december 2020 approved by the EMA and waiting for Registration in the Netherlands. Alnylam is working on 8 more applications for liver related diseases with GalNAc as delivery agent. Clinical trials using the GalNAc conjugates are now also performed by Arrowhead Pharmaceuticals and Dicerna Pharmaceuticals and thus the GalNAc platform can form a spectacular milestone for clinical application in multiple disease fields.

I am proud that we at Leiden University have contributed to the basic work to achieve this goal, while the Manoharan/Fitzgerald group at Alnylam believed in the system and brought it to the clinic. The inclisiran ( now called Leqvio by Novartis) story does teach that valorisation of a challenging concept can take 30 years .


Prof. Dr. Theo J C Van Berkel emeritus 

Leiden University, 

The Netherlands


Below the comments on the first clinical application outside of the development phase of inclisiran by Kevin Fitzgerald, senior Vice President and Chief Scientific Officer at Alnylam Pharmaceuticals .

First author of the first clinical study on inclisiran:A highly durable RNAi Therapeutic Inhibitor of PCSK9 . N.Engl.J.Med.376(2017) 41-51

Kausik Ray President of the European Atherosclerosis Society from the Imperial College in London.

First author of additional clinical studies on inclisiran: N.Engl.J.Med. 376(2017)1430-1440; 382(2020)1507-1519 and 382(2020)1520-1530

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