Regulatory Challenges of Gene Therapy and Cancer Drugs: Industry Trends Behind the Withdrawal of Zydelig and FDA's Response

In 2022, Gilead announced that it would voluntarily withdraw Zydelig from the U.S. market for two lymphoma treatments, a full six years after it suspended the trial due to patient deaths. A Gilead spokesperson clarified that the withdrawal was not due to safety concerns, but rather because of insurmountable obstacles to recruiting subjects for additional research trials required by the FDA. Nevertheless, Zydelig retains its eligibility for the treatment of chronic lymphocytic leukemia and remains on the market for patients.

Notably, the withdrawal of Zydelig coincides with the withdrawal of several other PI3K inhibitors used to treat follicular lymphoma: Secura Bio's duvelisib (trade name Copiktra) withdrawn in December 2021, TG's umbralisib (trade name Ukoniq) withdrawn in 2022 (here may be a clerical error, read "February" or adjusted to another month), Bayer's copanlisib (trade name Aliqopa) also withdrew from the market in November 2023. Together, these events outline an industry trend.

A study published in JAMA Internal Medicine reveals an interesting data point: Before Gilead decided to withdraw some uses of Zydelig from the U.S. market, its global sales had reached a staggering $842 million. This reflects the wide application and high recognition of the drug in the market, although it ultimately failed to fully meet all expectations for various reasons.

Interestingly, the pharmaceutical industry sometimes employs a series of ingenious strategies to speed up the process of bringing a product to market. Eli Lilly, for example, successfully used all four avenues of acceleration to bring oncology product Lartruvo to market in 2016. The key clinical data for the product is based only on the results of a trial involving 133 patients, and while the results showed a possible positive impact on survival outcomes for sarcoma, a cancer that affects muscles and other soft tissues, the specific effect on slowing cancer growth is unclear. However, just over two years later, a larger study revealed that Lartruvo had no significant impact on patient survival, and Eli Lilly had to withdraw it from the market. Despite this, Lartruvo still managed to achieve a whopping $500 million in sales during its short market life.

Among the many drugs approved for accelerated marketing, oncology products have become the hardest hit by ineffective drugs. However, as the development of therapies continues to deepen and progress, new questions continue to emerge and are presented to the FDA. In particular, advanced therapies represented by cell and gene therapies, when they meet with the accelerated approval system, have brought unprecedented challenges to this "old revolution". Given the complexity of cell and gene therapies and the relative lack of understanding of their safety, once ineffective advanced therapies are released to the market, the consequences and impacts will be far beyond the scope of small molecule ineffective drugs. For example, the tragic death of a three-year-old boy in a clinical trial of Pfizer's fordadistrogene movaparvovec, a gene therapy for Duchenne muscular dystrophy, highlights the shortcomings and limitations of researchers in predicting the potential for serious adverse events.

As vectors of ssRNA (single stranded RNA), viruses (such as AAV) play a critical role in gene therapy, but can also cause a series of serious adverse events including cardiopulmonary failure, myocarditis, thrombotic microangiopathy, and acute liver failure. These potential risks have forced the FDA to be more cautious and rigorous in approving gene therapies. Speaking at the annual meeting of the American Society for Gene and Cell Therapy, CBER director Peter Marks said speeding up the withdrawal of approved gene therapies could be easier and faster than for small-molecule therapies. At the same time, he stressed that "accelerated approval of gene therapy is not a get-out-of-jail-free ticket." The FDA will not hesitate to withdraw accelerated approval of rare disease gene therapies if they fail subsequent confirmatory trials."

Marks further points out that the "one-size-fits-all" nature of gene therapy makes confirmatory studies easier to follow and monitor patients over time. It also makes for greater clarity and clarity on the question of whether to withdraw gene therapy. In contrast, there may be more controversy and disagreement in the decision process of withdrawing cancer therapy. Marks, however, said the FDA would only withdraw gene therapy if it was clear that the patient benefit was likely to be "minimal" but the side effects were significant. He cited a case in which Bluebird Bio's sickle cell gene therapy Lyfgenia (lovotibeglogene autotemcel) caused patients to develop myelodysplastic syndrome and leukemia during treatment. The product was approved by the FDA in December 2023 with a boxed warning about hematologic malignancies. Marks said it is unclear whether these malignancies are related to the preconditioning regimen associated with Lyfgenia treatment, the underlying disease, or the gene therapy itself.

In addition, the case of drug manufacturers refusing to voluntarily withdraw the market is not unique in the history of FDA accelerated approval. Everything from the withdrawal of Makena, a drug that reduced the risk of preterm birth, after 12 years on the market, to the legal battle between Pepaxto and the FDA highlights the complexity and seriousness of the issue. In the face of these challenges, FDA has to seek the support of legislation to strengthen its regulatory power and capability. Fortunately, the introduction of the FDORA (Comprehensive Food and Drug Reform Act) bill provides the FDA with greater flexibility and autonomy to act without public hearings.