An FDA review raises a number of potentially significant safety concerns about the cholesterol-lowering drug mipomersen. The review appears ahead of a Thursday meeting of the Endocrinologic and Metabolic Drugs Advisory Committee to evaluate Genzyme’s new drug application (NDA) for use of the drug as an adjunct to maximally tolerated lipid-lowering medications and diet to reduce LDL, apolipoprotein B, total cholesterol, non-high density lipoprotein-cholesterol and lipoprotein (a) in patients with homozygous familial hypercholesterolemia (FH). Mipomersen is an antisense oligonucleotide inhibitor which targets apoB-100. (On Wednesday the same committee will meet to discuss a similar indication for lomitapide capsules, manufactured by Aegerion.)
FDA reviewers said that mipomersen was generally effective in lowering LDL cholesterol. More than half of patients in clinical trials had more than a 20% decrease in LDL levels. In the pivotal trial with homozygous FH patients mipomersen reduced LDL by 24.7%. As expected, mipomersen also resulted in significant reductions in app B, total cholesterol, and non-HDL cholesterol.
Because of their small size the mipomersen trials were not powered to assess cardiovascular outcomes, though cardiovascular benefit is of course the ultimate intended effect of the drug. However, the numbers in the phase 3 studies ran in the wrong direction. Serious adverse events of cardiac disorders occurred in 3.8% (10/261) of patients in the mipomersen group compared with 3.1% (4/129) in the placebo group. The reviewers concluded that “the possibility that mipomersen therapy increases the risk for cardiovascular events cannot be excluded.”
More troubling is the FDA safety review, mostly centering on liver-related problems. Mipomersen was associated with increases in serum transaminases and hepatic fat. In phase 3 trials, hepatic steatosis occurred in 7.3% (19/261) of mipomersen-treated patients compared with 1.6% (2/129)of placebo-treated patients. ALT increased in 9.6% of mipomersen treated patients compared with 0.8% of placebo-treated patients. In a long-term extension trial one-quarter of mipomersen-treated patients had an average liver fat fraction greater than 20%. The FDA reviewers said they did not know whether long-term use of mipomersen could cause irreversible liver damage, but warned that patients could be at risk for cirrhosis and liver-related death if the observed liver changes progressed.
Other safety issues in the trials included injection site reactions and flu-like symptoms. The committee will also likely spend time discussing the cancer findings. According to the review, during clinical testing neoplasms, both benign and malignant, were detected in 3.1% (23/749) of patients who received mipomersen compared with 0.9% (2/221) of patients who received placebo. However, the FDA clinical reviewer noted that there was a diversity of malignant neoplasms and that two out of nine mipomersen patients who developed a malignancy had been on mipomersen for less than a month, “making it highly unlikely that mipomersen played a role.” The review concluded that ”there are several confounding factors that make it difficult to conclude that mipomersen is playing a dominant role in this cancer imbalance.”
The FDA will also ask the panel to evaluate a proposed Risk Evaluation and Mitigation Strategies (REMS) if the drug gains approval. The program, similar to the one proposed by the FDA for lomitapide, would ”educate prescribers about the approved indication for use of mipomersen, the potential risk of hepatotoxicity associated with the use of mipomersen, and the need to monitor patients during treatment with mipomersen as per product labeling.” The REMS would require special certification for health care professionals and pharmacies that prescribe and dispense the drug.
Given the severity and rarity of homozygous FH it is difficult to predict how the committee will vote, but the safety concerns raised by the FDA make it extremely unlikely the drug could receive an expanded indication for heterozygous FH anytime in the near future.