Small interfering RNA molecules (siRNAs) are designed to intervene in the pathway of RNA interference (RNAi), a naturally operating mechanism, wherein they bind to a complex within the cell termed the RNA-induced silencing complex (RISC); after binding, the RISC structure in the siRNA-RISC complex is altered, allowing it to cleave specific messenger RNA molecules (mRNAs). The siRNA-RISC complex is catalytic, and thus can cleave multiple copies of the mRNA that it targets; cleaved mRNAs are not translated into proteins, and thus the concentration of the protein targeted by the siRNA design is decreased.The proprotein convertase, PCSK9, is a liver-produced and -secreted serine protease whose binding and action on LDL receptors results in their increased lysosomal degradation in hepatocytes, a consequence of which is an increase in the level of circulating LDL cholesterol (and inhibition of which, the decrease in this level). Studies of PCSK9 genetics supported the conclusion that decreases in circulating LDL cholesterol accomplished in this way would result in "diminished cardiovascular risk... with no apparent negative health consequences", and long term administration of antibodies with short in vivo half-lives, 1-2 times a month, reduced circulating PCSK9 and LDL cholesterol levels, with the result of a "lower incidence of cardiovascular events than placebo".
At day 510, the inclisiran group had an average LDL-C decrease of 51% whereas the placebo group had an average LDL-C increase of 1%. Study 2 enrolled 1,414 adults with ASCVD. At day 510, the inclisiran group had an average LDL-C decrease of 46% whereas the placebo group had an average LDL-C increase of 4%. Study 3 enrolled 482 adults with HeFH. At day 510, the inclisiran group had an average LDL-C decrease of 40% whereas the placebo group had an average LDL-C increase of 8%.The effect of inclisiran on cardiovascular morbidity (suffering from a disease) and mortality (death) has not been determined. References
Further reading
Ray KK, Landmesser U, Leiter LA,  et al. (April 2017). "Inclisiran in Patients at High Cardiovascular Risk with Elevated LDL Cholesterol" (PDF). N. Engl. J. Med. 376 (15): 1430–1440. doi:10.1056/NEJMoa1615758. hdl:10044/1/45416. PMID 28306389. S2CID 205101529. Ray KK, Wright RS, Kallend D,  et al. (March 2020). "Two Phase 3 Trials of Inclisiran in Patients with Elevated LDL Cholesterol". N. Engl. J. Med. 382 (16): 1507–1519. doi:10.1056/NEJMoa1912387. PMID 32187462. External links
"Inclisiran". Drug Information Portal. U.S. National Library of Medicine. Clinical trial number NCT03399370 for "Inclisiran for Participants With Atherosclerotic Cardiovascular Disease and Elevated Low-density Lipoprotein Cholesterol (ORION-10)" at ClinicalTrials.gov
Clinical trial number NCT03400800 for "Inclisiran for Subjects With ACSVD or ACSVD-Risk Equivalents and Elevated Low-density Lipoprotein Cholesterol (ORION-11)" at ClinicalTrials.gov
Clinical trial number NCT03397121 for "Trial to Evaluate the Effect of Inclisiran Treatment on Low Density Lipoprotein Cholesterol (LDL-C) in Subjects With Heterozygous Familial Hypercholesterolemia (HeFH) (ORION-9)" at ClinicalTrials.gov