Antisense oligonucleotide (ASO) drugs are a relatively new way to very specifically target genes on the mRNA level and are used in different medical fields. Mipomersen, the first ASO used in hypercholesterolaemia, interferes with the encoding mRNA for ApoB100. The production of ApoB100 is reduced via inhibition of translation to the protein. Consequently less very low density lipoprotein (VLDL) is assembled in the liver resulting in lower levels of circulating LDL-c. As a side effect, less triglycerides are excreted from the liver and accumulate often leading to fatty liver disease and elevated transaminases [
43,
44]. By what mechanism levels of Lp(a) are lowered is not entirely clear. In four phase 3 trials mipomersen given subcutaneously versus placebo levels of Lp(a) were significantly reduced by 21–39% [
45]. Thus mipomersen might reduce the necessity for lipoprotein apheresis in high-risk patients [
46,
47]. The most common side effects were severe injection site reactions and liver steatosis is also of concern. Because of the side effects mipomersen was not widely approved and is available in the USA only.
Apo(a) antisense oligonucleotide
IONIS-APO(a)
Rx, an antisense oligonucleotide molecule, is the first measure developed to specifically address the mRNA of Apo(a). Trials in transgenic mice [
48] and phase 1 results showed relevant decreases of Lp(a). In a phase 1 trial in healthy volunteers (Lp(a) levels ≥25 nmol/l) IONIS-APO(a)
Rx significantly lowered Lp(a) in a dose-dependent manner. The highest dose of 300 mg reduced Lp(a) by 77.8%. In one individual the maximal reduction was 88.8% after 36 days. Impressively Lp(a) did not increase immediately but was still low 84 days after the last application [
49]. The use was safe and the most common side effects were injection site reactions. As a ligand-conjugated variant of IONIS-APO(a)
Rx the hepatocyte specific IONIS-APO(a)-L
Rx was developed. The triantennary N‑acetylgalactosamine complex (GalNAc
3) facilitates the fast and specific uptake by hepatocytes [
50]. This modification enhanced the potency of the Apo(a)-ASO by >30 times [
51]. Since Apo(a) is targeted VLDL is produced and there is no fat accumulation in the liver.
The IONIS-APO(a)
Rx phase 2 trial confirmed the positive results regarding effectivity and safety [
51]. In 64 participants IONIS-APO(a)
Rx was applied subcutaneously in an escalating-dose manner for 12 weeks (100 mg, 200 mg, and 300 mg, each once a week for 4 weeks) versus placebo. Two cohorts were formed according to Lp(a) baseline levels: cohort A: Lp(a) 125–437 nmol/l (placebo group: mean 251.6 nmol/l and median 216.3 nmol/l, verum group: mean 254 nmol/l, median 261.4 nmol/l) and cohort B: Lp(a) ≥438 nmol/l (placebo group: mean 488.3 nmol/l and median 498.3 nmol/l, verum group: mean 444.9 nmol/l, median 457.6 nmol/l). The primary efficacy endpoint was reduction of Lp(a) at day 85 or 99. Secondary endpoints were effects on other lipoproteins and risk factors.
In both cohorts Lp(a) was reduced significantly: cohort A—66.8%, cohort B—71.6% at day 85/99. Additionally, levels of LDL-c, ApoB, and oxidised phospholipids (OxPL) were reduced significantly in both cohorts. LDL-c was lowered by 13.0% in cohort A and by 23.9% in cohort B, ApoB by 11.3 and 18.5%, respectively, OxPL-ApoB by 35.2 and 42.5%, respectively, and OxLP-Apo(a) 26.6 and 36.7%, respectively. Baseline statin therapy had no significant effect on these results. The treatment was safe and well tolerated. Two myocardial infarctions and one episode of angina pectoris in high-risk patients were not assessed as treatment related. Injection site reactions occurred in 10% in cohort A and in 19% in cohort B (one participant stopped treatment).
Another phase 1/2a first-in-man trial [
51] was done with the GalNAc
3 modified IONIS-APO(a)-L
Rx′ in healthy volunteers with levels of Lp(a) ≥75 nmol/l. In the single-dose phase participants (
n = 28) received one subcutaneous injection of 10, 40, 80, or 120 mg versus placebo. In the multiple-dose phase (
n = 30) IONIS-APO(a)L
Rx 10 mg, 20 mg, or 40 mg were administered at days 1, 3, 5, 8, 15, and 22 versus placebo. The primary efficacy endpoint was reduction of Lp(a) at day 30 (single-dose phase) and day 36 (multiple-dose phase). Baseline levels of Lp(a) were 147.8 nmol/l (mean) and 128.6 nmol/l (median) in the single-dose phase and 153.8 nmol/l (mean) and 145.6 nmol/l (median) in the multiple-dose phase.
In the single ascending dose phase Lp(a) was reduced significantly in a dose-dependent manner at day 30. The mean treatment differences versus placebo (+2.8%) were 24.8% (10 mg group), 35.1% (20 mg group), 48.2% (40 mg group), 82.5% (80 mg group), and 84.5% (120 mg group). The reduction was still significant after 90 days (46% in the 80 mg group and 44% in the 120 mg group). Also in the multiple ascending dose phase Lp(a) was reduced significantly. The treatment differences versus placebo were 59.4% (10 mg group), 72.3 (20 mg group), and 82.4% (40 mg group). At day 113 after the last application the lowering effect was still significant with 39% (10 mg group), 53% (20 mg group), and 58% (40 mg group).
The results of the biggest conducted IONIS-APO(a)-L
Rx (AKCEA-APO(a)-L
Rx) phase 2 trial were presented at the AHA Scientific Sessions, Late-Breaking Clinical Trial Presentation, on 10 November 2018 [
52]. The trial was a randomized, double-blind, placebo-controlled, and dose-ranging trial in 286 patients with established CVD and high levels of Lp(a) (baseline mean of approximately 100 mg/dl [250 nmol/l]). Five cohorts were compared: 20 mg were administered every 4 weeks, 40 mg every 4 weeks, 20 mg every 2 weeks, 60 mg every 4 weeks, and 20 mg every week, each for 6–12 months. The primary efficacy endpoint was percent change in Lp(a) from baseline at 6 months.
AKCEA-APO(a)-LRx decreased Lp(a) in all groups (20 mg every 4 weeks: −35%, 40 mg every 4 weeks −56%, 20 mg every 2 weeks: −58%). The effect was even greater in the highest doses (60 mg every 4 weeks: −72%, 20 mg weekly: −80%) and in about 81% and 98%, respectively, Lp(a) levels <50 mg/dl were achieved. The completion rate was high (90%) and comparable in both groups (verum 12.1%, placebo 14.9%). There were no severe safety concerns and few adverse events. Injection site reactions were the most common (26%) with one patient discontinuing.