The Saga of PI3K Inhibitors: Part 2 – The shifting role of overall survival

In Part 1 of our blog series on the saga of PI3K inhibitors, we reviewed the FDA’s recent Oncologic Drugs Advisory Committee (ODAC) meeting on April 21, 2022, to discuss the agency’s concerns about PI3K inhibitors (PI3Kis). The panel voted resoundingly (16 yes votes; 1 abstention) that future approvals of PI3Kis should be supported by randomized data that would allow an assessment of overall survival (OS)—an action that makes accelerated approvals less likely and more difficult to obtain in slow-growing cancers with a long median survival.

At the heart of the FDA’s concerns with the PI3Ki class is an apparent excess of deaths in clinical trials of PI3Kis, indicating a potential detriment to long-term survival in patients who were treated with PI3Kis. However, assessing OS in patients with indolent blood cancers, who have very long lifespans, can be exceedingly difficult—and the results are not always interpretable.

In this second installment of this blog series, we will focus on the OS data for PI3Kis presented by the FDA, the complexities of evaluating OS in blood cancers with long lifespans, and the broader regulatory implications of an increased focus on OS as a safety endpoint in patients with indolent diseases.

Regulatory pressure to withdraw PI3Kis continues…

The Class 1 phosphatidylinositol-3-kinases (PI3Ks) are master regulators of cell proliferation, growth, survival, motility, and immune cell function that are highly dysregulated in blood cancers. Four PI3Kis (idelalisib, duvelisib, copanlisib, and umbralisib) have been approved by the FDA for B-cell malignancies such as chronic lymphocytic leukemia (CLL), and indolent non-Hodgkin’s lymphomas (iNHL), including marginal zone lymphoma (MZL) or follicular lymphoma (FL). Please see Part 1 for additional background on PI3Kis.

As of writing this post, all accelerated approvals for PI3Kis in iNHL have been withdrawn, mostly due to a failure to complete a confirmatory trial. These withdrawals also likely reflect the ODAC decision in favor of a requirement for randomized data to support future approvals for PI3Kis (rather than single-arm trial data, which are often used to support accelerated approvals in oncology).

Currently, there are 2 PI3Kis (idelalisib and duvelisib) with full approval in later-line treatment of CLL that remain on the market.

Since the April ODAC, however, the FDA has increased pressure on sponsors to withdraw even fully approved indications for PI3Kis on the basis of a potential detriment to overall survival. The most recent development came on June 30 with a warning issued by the FDA that Secura Bio’s PI3Ki, duvelisib, may increase the risk of death when used as a third-line treatment for patients with CLL. Duvelisib received full approval for CLL in 2018 on the basis of the phase 3 DUO trial. The FDA warning stated that the agency plans to hold a future public meeting to discuss the updated overall survival data of duvelisib, and whether duvelisib should continue to stay on the market – hinting that another potential ODAC meeting may be on the horizon.

Since the April ODAC, however, the FDA has increased pressure on sponsors to withdraw even fully approved indications for PI3Kis on the basis of a potential detriment to overall survival.

“The ultimate safety endpoint”: Do PI3Kis lead to a detriment in OS?

The FDA views OS as “the ultimate safety endpoint” because it encompasses deaths directly caused by adverse events related to the drug, and deaths that might be related to long-term side effects of the drug, which can be difficult to identify. Importantly, the FDA specifies that OS “does not require [the] same statistical considerations when used as a primary safety endpoint.” The FDA’s viewpoint is straightforward: The ultimate goal with any drug therapy should be to prolong life without inflicting long-term harm. From this viewpoint, OS has a dual purpose of providing information about the effectiveness of a drug, while also informing safety.

The FDA presented data at the April ODAC showing that in six phase 3 randomized trials for the approved PI3Kis, most had OS hazard ratios (HR) >1 (Figure 1) . An HR >1, based on Kaplan-Meier estimates, suggests that more patients died on the experimental arm (in this case the PI3Ki) than on the comparator arm. In 3 trials with idelalisib (the first approved PI3Ki drug), there was a much higher risk of death in the idelalisib arm, with a nearly 5× greater risk of dying in the 313-0124 trial in iNHL, and a more than 3× greater risk of dying in the 312-0123 trial in CLL.

The FDA views OS as “the ultimate safety endpoint” because it encompasses deaths directly caused by adverse events related to the drug, and deaths that might be related to long-term side effects of the drug, which can be difficult to identify.1

The OS results in trials with other PI3Kis across various patient populations and treatment regimens (DUO, CHRONOS-3, and UNITY CLL) did not show a survival imbalance as extreme as that observed in the idelalisib trials. Although most of these trials exhibited OS HRs >1, the 95% confidence interval was very wide and included 1. The CHRONOS-3 trial of copanlisib in iNHL was an exception, with an HR of 0.87 (95% CI: 0.57, 1.35) (Figure 1).

Figure 1: Summary of overall survival data and toxicity risk in FDA-approved PI3Kis. Slide 45 of the FDA presentation at the April 21 ODAC meeting.   

The FDA interprets these data to indicate an overall pattern of potential detriment to survival in patients treated with PI3Ki as a class, possibly linked to an increased risk of infection or immune-mediated adverse events, or unidentified long-term effects of PI3Kis that may negatively impact the efficacy of subsequent therapies.3

Imbalances in OS are not unheard of in blood cancer clinical trials…

The FDA repeatedly describes a pattern of detriment in survival with PI3Kis as “unprecedented” in oncology, but are unfavorable imbalances in OS in blood cancer trials really unprecedented? A quick review of the literature disproves this notion.

The Bruton’s tyrosine kinase inhibitor (BTKi) ibrutinib was approved for previously untreated CLL in January 2019 on the basis of the iLLUMINATE trial. At the final analysis from iLLUMINATE, there was an OS HR of 1.08 in favor of the comparator arm. Similarly, venetoclax, a B-cell lymphoma 2-targeted inhibitor (BCL2i), was approved for first-line CLL treatment in May 2019 on the basis of the CLL14 trial with an initial OS HR of 1.24 at the time of approval, although with 4 years of follow-up the OS HR improved to 0.85, albeit with results that were still not significant. Importantly, both ibrutinib and venetoclax are approved in multiple indications and are considered successful and paradigm-shifting drugs, despite never having shown a significant improvement in OS in blood cancers (nor have they definitively ruled out potential detriment).

These examples cast doubt on a narrative that PI3Kis are somehow uniquely detrimental to survival in indolent blood cancers. Rather, the problem with evaluating OS in blood cancer trials may be a reflection of the disease itself, rather than any particular class of drugs.

These examples cast doubt on a narrative that PI3Kis are somehow uniquely detrimental to survival in indolent blood cancers. Rather, the problem with evaluating OS in blood cancer trials may be a reflection of the disease itself, rather than any particular class of drugs.

The complexities of evaluating OS in blood cancers with long lifespans

There are several considerations that make OS data difficult to interpret in blood cancers with very long life expectancies. Most importantly, because there are few deaths, it is not feasible to appropriately power these trials to assess OS with statistical confidence. As a result, OS analyses tend to have wide confidence intervals that are highly unstable over time. For these reasons, OS is not used as a primary endpoint in indolent blood cancers. Instead, studies are typically powered for the primary endpoint of progression free-survival (PFS), which provides more clearly interpretable results. OS is often included as a secondary or exploratory endpoint, but is not usually considered conclusive.  

The interpretation of OS is further challenged by trial design realities in indolent diseases; for example, patients may go on to receive several different lines of therapy before their death and trials often include a crossover arm (wherein patients on the control arm may choose to receive the experimental treatment after disease progression). Consequently, analyses of OS may be confounded and rendered uninterpretable. Finally, identifying the cause of death is fraught with difficulty when a large number of deaths may occur years after patients have discontinued study drug.

It is also worth mentioning that COVID-19 deaths present a unique challenge to interpreting OS in indolent blood cancers (and, to some extent, all clinical trials affected by the pandemic) not only because of the timing of COVID-19 infection waves and deaths, but also because of shifts in standard of care that can no longer be controlled for by randomization. Given these circumstances, it is possible, or even likely, that a pattern of OS detriment seen with the newer PI3Kis in recent clinical trials is a chance finding, rather than a real reflection of risk.

How should sponsors use OS to support benefit-risk assessments?

If it is not possible to adequately power a trial for OS or to interpret the results, how exactly should an “assessment” of OS be performed to support benefit-risk evaluation of PI3Kis? When asked this question directly by a panelist, the FDA fell back on its stance that the burden is on sponsors to prove that PI3Kis are not producing a detriment to survival – a difficult situation for drug developers. However, the FDA provided few clues as to what it is looking for (see slide 75 of the FDA presentation).  

Sponsors developing new PI3Kis should be prepared to incorporate detailed analyses of the causes of death on each arm into study protocols, with the goal of providing assurance that the experimental arm is not causing excess deaths related to immune-mediated toxicity or an increased risk of infection due to PI3K inhibition. This type of analysis would require a much more in-depth investigation than is typically done, given the problems discussed above with tracking deaths that occur long after a patient has left the study. Sponsors should also attempt to design future studies so that the OS data are better able to withstand an increased level of scrutiny. For example, trial designs that include an option to cross over to the experimental arm after progression may not be advisable.

Ultimately, even following the FDA’s suggested changes to clinical trial design, there is no guarantee that OS can be evaluated with sufficient statistical clarity to definitively show that PI3Kis are not causing a detriment to survival.

What do the experts think?

Notably, not all physicians agreed with the FDA’s conclusion of a pattern of detriment to OS with PI3Kis. In a public docket comment in response to the April ODAC meeting, Jennifer Brown, MD, PhD, “urge[d] caution in the interpretation of trials in different clinical settings,” “as well as the interpretation of long term follow-up data which may be confounded by subsequent therapy choice and crossover study design.” Dr. Brown went on to note that PI3Kis have provided “transformative and life-saving” benefits, and “in patients who are heavily pretreated, as is the case with all the existing approvals and the drugs in development, the toxicity is readily managed.”  

In the context of excellent benefits in progression-free survival with PI3Kis and high unmet need for alternative therapies in heavily pre-treated patients, many physicians still view the benefit-risk profile for PI3Kis as favorable. On July 1, the CLL Society sent a letter to the FDA that received signatures of support from 40 of the top CLL/SLL physicians in the country, which urged the FDA to maintain approved PI3Kis as an option for patients with CLL:

“Going forward and looking more widely at the CLL therapeutic landscape, safety must never be compromised. But drug innovation should continue to be encouraged. We believe the FDA can leverage the power of electronic medical records and real-world data to further assess the safety of PI3K inhibitors. Delays associated with the wait for overall survival data have already started to dampen research efforts in CLL and have slowed patient access to potentially life-saving therapies. CLL is a chronic cancer, and patients are often exposed to multiple therapies over the span of their disease. Survival data will come too slowly for many patients and will never be ‘statistically pure.’ CLL Society and many others have pushed for crossover in clinical trials to ensure equipoise, which while further confounding the survival data, saves lives. In the opinion of CLL Society, clinical trial design focused on overall survival endpoints will ultimately delay or deny the best possible care to patients with CLL.”

Coming Next: Part 3 – How should dose optimization be conducted in drug classes with known immune-mediated toxicity risks?

The FDA has raised concerns that for the approved PI3Kis, dose modifications or treatment interruptions due to AEs are too common in clinical trials, indicating that the dose may be too high. The dosing regimen for all approved PI3Ki was selected based on standard, phase 1, single-arm dose escalation studies in small cohorts of patients. However, in the FDA’s view, this standard approach may lead sponsors to default to selecting the maximum tolerated dose, rather than the optimal (likely lower) dose that might achieve similar efficacy with less toxicity.

InIn Part 3 of this series, ProEd will review the panel discussion of how best to optimize drug dosing for PI3Kis, the broader FDA regulatory initiatives (ie, “Project Optimus”) surrounding dose optimization, and how these considerations may impact clinical trial design and dose-finding studies for targeted oncology drugs that modulate the immune system.

Angela W. Corona, PhD
Scientific Director, ProEd RegulatoryAngela is a Scientific Director for ProEd Regulatory. She is responsible for helping sponsors navigate complex regulatory communications such as FDA advisory committee meetings. She develops clinical and regulatory strategy along with high-quality scientific and medical content across a wide range of therapeutic and drug development areas. Angela received her PhD in Neuroscience from The Ohio State University and completed her postdoctoral training at Case Western Reserve University in Cleveland, Ohio.

References

  1. Pazdur R. The saga of PI3K inhibitors in haematological malignancies: survival is the ultimate safety endpoint. Lancet. 2022 April 14 [Online ahead of print]. https://doi.org/10.1016/S1470-2045(22)00200-5
  2. FDA Presentation, Introductory Comments; Presented by Nicole Gormley. Oncologic Drugs Advisory Committee Meeting. Phosphatidylinositol 3-Kinase (PI3K) Inhibitors in Hematologic Malignancies. April 21, 2022. https://www.fda.gov/media/157837/download
  3. FDA Briefing Document. Oncologic Drugs Advisory Committee Meeting. Phosphatidylinositol 3-Kinase (PI3K) Inhibitors in Hematologic Malignancies. April 21, 2022. https://www.fda.gov/media/157762/download
  4. Moreno C, et al. First-line treatment of chronic lymphocytic leukemia with ibrutinib plus obinutuzumab versus chlorambucil plus obinutuzumab: final analysis of the randomized, phase 3 iLLUMINATE trial. Haematologica. 2022 Jan 13 [Online ahead of print]. https://doi.org/10.3324/haematol.2021.279012.
  5. Fischer K, et al. Venetoclax and obinutuzumab in patients with CLL and coexisting conditions. N Engl J Med. 2019;380(23):2225-2236. https://pubmed.ncbi.nlm.nih.gov/31166681/
  6. Al-Sawaf O, et al. Minimal residual disease dynamics after venetoclax-obinutuzumab treatment: extended off-treatment follow-up from the randomized CLL14 study. J Clin Oncol. 2021;39(26):4049-4060. https://pubmed.ncbi.nlm.nih.gov/34709929/

The Saga of PI3K Inhibitors: Part 1 — The ODAC Decision

The FDA’s Oncology Division has recently taken a hard stance on PI3K inhibitors, a novel class of drugs that inhibit various isoforms of phosphatidylinositol 3-kinase (PI3K) and are approved for treating blood cancers. Recent actions by the FDA, including withdrawing some approved indications, indicate that they will likely be seeking a higher bar for new approvals of PI3K inhibitors for certain blood cancers. So, why is this promising class of drugs suddenly in the hot seat? At the heart of the issue is an excess of deaths in clinical trials of PI3K inhibitors and the FDA’s concern about their safety profile.

On April 21 of this year, the FDA convened a public Oncologic Drugs Advisory Committee (ODAC) meeting to discuss the agency’s concerns about PI3K inhibitors. The panel voted resoundingly (16 yes votes; 1 abstention) that future approvals of PI3K inhibitors should be supported by randomized data, which would allow for an assessment of overall survival (OS)—an action that makes accelerated approvals less likely and more difficult to obtain in cancers with a long life expectancy.

The panel voted resoundingly (16 yes votes; 1 abstention) that future approvals of PI3K inhibitors should be supported by randomized data, which would allow for an assessment of overall survival (OS)—an action that makes accelerated approvals less likely and more difficult to obtain in cancers with a long life expectancy.

We’ll take you inside this evolving saga. This first installment describes the drug class and what happened at a recent ODAC meeting, with top-line takeaways for drug developers in this field. Subsequent installments will analyze the implications of the panel discussion and the broader regulatory implications of that ODAC meeting and the FDA’s recent actions.

“Not a Typical ODAC Meeting”

The FDA used the April 21 ODAC meeting to zero-in on safety concerns with the class as a whole and to reevaluate the appropriate regulatory approach for future approvals. Nicole Gormley, MD, Director the Division of Hematologic Malignancies, opened up the FDA presentation by first explaining that “this committee meeting is not a typical ODAC where we would discuss the risk-benefit profile of a specific product. But instead, we will discuss the class of PI3K inhibitors as a whole, the unique toxicities that they present, and the best development approach for future drugs in this class.”

This is actually quite unusual—typically, FDA does not ask ODAC panels to provide forward-looking advice for hypothetical future new drug approvals.

Some panelists questioned if it was appropriate to make determinations for an entire drug class on the basis of collective data rather than the individual merits of each drug. Indeed, the one panel member who abstained from voting, Anthony Sung, MD, from Duke, cited this fact as the reason for his abstaining, “I still feel uncomfortable labelling an entire class and requiring that future drugs in that class be supported by randomized data. If the phase 1 data [are] not concerning, then I don’t know if randomized studies should be needed in that case.” While Dr. Gormley assured the panel that flexibility would be applied in specific cases, saying “nobody has a ‘crystal ball’,” the nature of the ODAC and recent agency actions suggests that the FDA plans to apply this advice broadly.

I still feel uncomfortable labelling an entire class and requiring that future drugs in that class be supported by randomized data.

Approved PI3K Inhibitors: Promising efficacy, paired with lingering safety concerns

The Class 1 PI3Ks are master regulators of cell proliferation, growth, survival, motility, and immune cell function. They have long been recognized as one of the most frequently aberrantly activated pathways in cancer, making this a “holy grail” drug target. Certain PI3K isoforms are implicated more strongly in different cancers. PI3Kδ and γ, for example, are preferentially expressed in B lymphocytes and are often constitutively activated in B-cell malignancies.1 Consequently small-molecule PI3K inhibitors with varying levels of selectivity for several PI3K isoforms have been developed, mainly for B-cell malignancies like chronic lymphocytic leukemia (CLL), and indolent non-Hodgkin’s lymphomas (iNHL), including marginal zone lymphoma (MZL) or follicular lymphoma (FL).

Table 1 summarizes the FDA-approved PI3K inhibitors that were the subject of the April 21 ODAC, and the history of FDA approvals for each. As of writing this article, most accelerated approval indications in Table 1, and several new marketing applications for PI3K inhibitors in blood cancer, have been withdrawn (including applications for accelerated approval in MZL/FL for MEI Pharma’s zandelisib (ME-401) and Incyte’s parsaclisib, and most recently, TG Therapeutics’ umbralisib).

Drug Name, (Company) PI3Ki Isoform Selectivity Indication(s) Monotherapy/ Combination Approval History
idelalisib/Zydelig
(Gilead)
PI3Kδ inhibitor R/R CLL Combination with rituximab 2014, Regular approval
FL/SLL after ≥2 prior systemic therapies Monotherapy 2014, Accelerated approval
2022, Voluntary withdrawal
copanlisib/Aliqopa
(Bayer)
Pan-PI3K inhibitor FL after ≥2 prior systemic therapies Monotherapy 2017, Accelerated approval
Relapsed iNHL Combination with rituximab 2022, Voluntary withdrawal of marketing application
duvelisib/Copiktra
(Secura Bio)
Dual PI3Kγ/δ inhibitor CLL/SLL after ≥2 prior systemic therapies Monotherapy 2018, Regular approval
FL after ≥2 prior systemic therapies Monotherapy 2018, Accelerated approval
2021, Voluntary withdrawal
alpelisib/Piqray*
(Novartis)
PI3Kα inhibitor Advanced breast cancer (PIK3CA-mutated, HR+, HER2–) Combination with fulvestrant 2019, Regular approval
umbralisib/Ukoniq
(TG Therapeutics)
PI3Kδ inhibitor (also inhibits CK1ε) CLL/SLL, treatment-naive or relapsed Combination with ublituximab 2022, Voluntary withdrawal of marketing application
R/R MZL/FL Monotherapy 2021, Accelerated approval
2022, Voluntary withdrawal

Table 1: Summary of FDA-approved PI3K inhibitors and current status of approvals and new marketing applications for additional indications.

CLL=chronic lymphocytic leukemia; FL=follicular lymphoma; HER2, human epidermal growth factor receptor-2–negative; HR+, hormone receptor-positive; iNHL=indolent non-Hodgkin’s lymphoma; MZL=marginal zone lymphoma; PI3K=phosphatidylinositol 3-kinase; PIK3CA, phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha; R/R= relapsed/refractory; SLL, small lymphocytic leukemia. *Because of the FDA’s focus on PI3K inhibitors in blood cancer, the PI3Kα inhibitor, alpelisib, approved for advanced breast cancer in 2019, was not included in recent ODAC discussions and is not discussed in this post.

These approvals validated the promising clinical activity of PI3K inhibitors in blood cancers based on improvements in progression-free survival (PFS) and overall response rates (ORR); nevertheless, the class has been associated with safety issues. Because PI3K regulates the immune response, inhibition of this pathway leads to immune-related adverse events such as transaminitis, pneumonitis, diarrhea/colitis, and rash that are sometimes severe.2 These agents are also associated with an increased risk of infection. This means that adverse events and infectious complications need to be carefully managed by the treating physician.2

The core of FDA’s concern was a pattern suggesting a potential detriment in overall survival (OS) in patients treated with PI3K inhibitors. The FDA presented data at the ODAC showing that in 6, randomized, phase 3 trials for the approved PI3K inhibitors, most demonstrated an OS hazard ratio (HR) >1. A HR >1 means that there were more patients who died on the experimental PI3K inhibitor arm than on the comparator arm. The FDA hypothesized that this pattern could be caused by an increased risk of infection or immune-mediated adverse events or by unidentified long-term effects of PI3K inhibitors, which may negatively affect the efficacy of subsequent therapies.4

The core of FDA’s concern was a pattern suggesting a potential detriment in overall survival (OS) in patients treated with PI3K inhibitors.

Not all PI3K inhibitors have identical safety profiles. To minimize risks, drug companies have developed next-generation PI3K inhibitors, such as umbralisib and duvelisib, with greater selectivity for specific PI3K isoforms. These developments have led to hope in the scientific community that next-generation PI3K inhibitors are “finally coming of age.”5 However, infections and immune-mediated adverse events are still important recognized risks related to the class.

Topline Takeaway: Randomized trial data with an evaluation of OS to support new approvals of PI3K inhibitors

The primary outcome of the April 21 ODAC was the panel’s unanimous vote that randomized trials should be necessary to support future approvals of PI3K inhibitors. Sponsors should anticipate that the ODAC vote will likely translate into regulatory policy. While this does not necessarily affect the regulatory threshold for full approvals (where randomized data has always been required), this decision would make accelerated approvals based on single-arm trials less likely for PI3K inhibitors. Sponsors seeking new approvals for PI3K inhibitors should plan to base their New Drug Applications on randomized clinical trial data and should design clinical trials to include an evaluation of OS. Sponsors should be aware, however, that FDA appears to be looking for an OS hazard ratio of <1.

Sponsors seeking new approvals for PI3K inhibitors should plan to base their New Drug Applications on randomized clinical trial data and should design clinical trials to include an evaluation of OS. Sponsors should be aware, however, that FDA appears to be looking for an OS hazard ratio of <1.

Coming Next: Part 2 — How Should Overall Survival Data Be Evaluated in Blood Cancers?

The rationale for requiring randomized trials specifically for PI3Kis was to allow for an assessment of OS as a safety endpoint. However, assessing OS in patients with indolent blood cancers, who have very long lifespans, can be exceedingly difficult—and the results are not always interpretable. Many panelists questioned the feasibility of assessing OS and how this information should be used in regulatory decision making moving forward.

In Part 2 of this series, ProEd will review in detail the OS data for PI3K inhibitors presented at the April 21 ODAC and the broader regulatory implications of an increased focus on OS as a safety endpoint in patients with indolent blood cancers.

Angela W. Corona, PhD
Scientific Director, ProEd Regulatory

Angela is a Scientific Director for ProEd Regulatory. She is responsible for helping sponsors navigate complex regulatory communications such as FDA advisory committee meetings. She develops clinical and regulatory strategy along with high-quality scientific and medical content across a wide range of therapeutic and drug development areas. Angela received her PhD in Neuroscience from The Ohio State University and completed her postdoctoral training at Case Western Reserve University in Cleveland, Ohio.

 

References

  1. Phillips TJ, Michot JM, Ribrag V. Can next-generation PI3K inhibitors unlock the full potential of the class in patients with B-cell lymphoma? Clin Lymphoma Myeloma Leuk. 2021;21(1):8-20.e3.
  2. Hanlon A, Brander DM. Managing toxicities of phosphatidylinositol-3-kinase (PI3K) inhibitors. Hematology Am Soc Hematol Educ Program. 2020;2020(1):346-356. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7727518/
  3. FDA Presentation, Introductory Comments; Presented by Nicole Gormley. Oncologic Drugs Advisory Committee Meeting. Phosphatidylinositol 3-Kinase (PI3K) Inhibitors in Hematologic Malignancies. April 21, 2022. https://www.fda.gov/media/157837/download
  4. FDA Briefing Document. Oncologic Drugs Advisory Committee Meeting. Phosphatidylinositol 3-Kinase (PI3K) Inhibitors in Hematologic Malignancies. April 21, 2022. https://www.fda.gov/media/157762/download
  5. Vanhaesebroeck B, Perry MWD, Brown JR, André F, Okkenhaug K. PI3K inhibitors are finally coming of age. Nat Rev Drug Discov. 2021;20(10):741-769.

Regulatory Policy Watch: Proposed Reforms to the Accelerated Approval Pathway

By Jackie Orabone, PhD and Angela Corona, PhD

The accelerated approval (AA) pathway was introduced in 1992 (in response to the AIDS epidemic) to shorten the FDA approval process for drugs to treat serious or life-threatening diseases or rare diseases where there is a high unmet medical need. AA allows for drugs to be approved on the basis of surrogate endpoints that are “reasonably likely to predict clinical benefit.”1 Part 1 of this blog series provided an introduction to the accelerated approval pathway, and Part 2 explained how surrogate endpoints for accelerated approval are identified and validated. In Part 3 of this series, we explored what happens when confirmatory trials are not completed or fail to confirm clinical benefit.

Here in Part 4 of this series, we will review recently proposed reforms to the AA pathway. Each proposed reform has slightly different provisions, but all strive to modify and update policies and procedures, better define surrogate endpoints, and implement mechanisms to ensure that confirmatory trials are completed in a timely manner.

Why are calls for reform of the AA increasing?

Most criticism of the AA pathway stems from the perception that there are insufficient guardrails, a lack of transparency in decision making, and/or a lack of sufficient incentives for sponsors to complete confirmatory trials once a drug has been granted AA. For example, there is currently no defined requirement for FDA or sponsors to withdraw an AA indication when confirmatory trials fail to confirm clinical benefit, nor is there a defined time limit for AAs. In addition, there are no strict rules defining surrogate endpoints. Therefore, calls for reform of the AA pathway have grown louder, and investigations and legislation that seek to amend the current AA process are now making their way through Congress.

US Department of Health and Human Services (HHS) Review

In August of 2021, the US HHS Office of the Inspector General announced its intent to conduct a Review of the FDA’s AA Pathway.2 This was spurred by the controversial approval of Aduhelm (aducanumab) based on an unvalidated surrogate endpoint despite the FDA advisory committee’s nearly unanimous vote against approval. HHS will review how the FDA makes decisions about when AA is appropriate. In particular, they will scrutinize how regulators apply AA in cases where a surrogate endpoint is not accepted by the scientific community to be “reasonably likely to predict clinical benefit”—as is often the case in neurology indications. Completion of the report is expected in 2023; however, legislators are not waiting for the results of this report to propose reforms.

Accelerated Approval Integrity Act of 2022 (HR 6963)

The Accelerated Approval Integrity Act of 2022,3 proposed on March 7, 2022, takes aim at a highly criticized issue with the AA pathway—the fact that there is no mechanism in place to ensure that confirmatory trials are completed in a timely manner.4 The bill proposes several reforms to the AA pathway intended to expedite the completion of confirmatory trials, and importantly, the speedy withdrawal of AAs that fail to demonstrate clinical benefit. Key proposed revisions are listed below:4

  • Codifying requirements for manufacturers to conduct post-approval studies. Provisions include
    1. Allowing the FDA to require that studies be underway at the time of AA,
    2. Requiring an agreement on how the studies will be conducted before FDA can grant AA, and
    3. Requiring more frequent updates on the status of post-approval studies.
  • Outlining expedited procedures for the FDA to withdraw approval, which would include due notice and an opportunity for a written appeal to FDA, which may result in the FDA consulting an advisory committee more frequently on these topics.
  • Requiring that AA status be reflected in the product label.
  • Proposing, most controversially, a 5-year deadline for completing confirmatory trials, and automatic expiration dates for AA status 1 year after post-approval studies are scheduled to be complete. Automatic expiration of AA would eliminate any flexibility on the part of FDA to consider the unmet medical need when making decisions about withdrawal of AA, which has advocates of AA and the medical community concerned.
  • Including, importantly, provisions to make certain actions by the sponsor, such as failure to submit reports, prohibited and subject to penalties and fines.

Accelerating Access for Patients Act of 2022 (HR 6996)

The Accelerating Access for Patients Act of 20225 is the competing bill to the AA Integrity Act. It is similar in that it requires the FDA to establish requirements for confirmatory studies following AA and expedited procedures to withdraw AA if post-marketing requirements are not met or confirmatory studies are not conducted with due diligence. A key difference, however, is that this bill does not include a provision for automatic expiration of AA status or penalties for sponsors (a measure that is perceived to be more favorable to industry).6 In addition, 2 provisions seek to “modernize” the definition of surrogate endpoints and the design of confirmatory clinical trials:5

  • The bill clarifies the type of evidence that can be used to justify a surrogate endpoint and appears to be directed towards identifying surrogate endpoints suitable for supporting AA in neurodegenerative and rare diseases, where AA has previously been controversial.
  • The bill requires that the FDA issue guidance on the “use of novel clinical trial designs that may be used to conduct appropriate post-approval studies,” which may allude to the potential use of real-world evidence in confirmatory trials.

The Promising Pathway Act (S 1644)

Some legislators have opted to propose an entirely new regulatory framework for AA, rather than incrementally reforming the existing pathway.7 The Promising Pathway Act,8 reintroduced to the Senate in May 2021, would allow for time-limited, “provisional” approvals on the basis of substantial evidence of safety, along with relevant early evidence of efficacy—such as data that could be provided by a phase 1/2 study. Under the act, a provisional approval would be limited to a 2-year period and would include strict requirements for patients receiving provisionally approved drugs to join a patient registry. The act relies heavily on real-world evidence (RWE), which would be collected from patient registry data and submitted in regular reports to the agency. Importantly, the act would require the FDA to accept real-world data and surrogate endpoints as evidence to demonstrate efficacy and convert a provisional approval to a full approval.

Needless to say, regulators have raised some concerns regarding this proposal. The reliance on RWE has been identified as particularly problematic, given that studies have cast doubt on the feasibility of replicating high-quality clinical trial data using RWE.10 It’s unclear if the required patient registries under the act would be sufficient to make rigorous RWE studies feasible. However, this proposal has received vocal support from patient advocacy groups, especially in the ALS community,9 where surrogate endpoints have not been identified and few to no treatment options are available.

Accelerated approval reforms tacked onto “must pass” FDA user fee (PDUFA) renewal legislation

We now know that some of these proposed reforms are likely to become law, albeit in slightly watered-down form, as part of the PDUFA reauthorization bill. In draft legislation released on May 4, 2022, provisions were included to speed the withdrawal process for AAs and strengthen requirements for speedy confirmatory trials. Other provisions grant FDA the authority to require that confirmatory studies be underway at the time of AA and that product labels note AA status along with details on the surrogate endpoint used and any uncertainties about anticipated clinical benefit. Missing from the legislation was the controversial 5-year deadline for confirmatory trials proposed in HR 6963.

With bipartisan support, the PDUFA reauthorization bill is expected to pass and be ready for President Biden’s signature before August. Sponsors should prepare for increased scrutiny and tightened regulations around accelerated approvals.

Jackie Orabone, PhD
Scientific Director, Scientific Services

Jackie combines her scientific expertise in immunology and research knowledge with more than 2 years of medical communications agency experience to help clients define their strategy and develop their core content in preparation for FDA Advisory Committee meetings and other scientific communications. She has experience in a variety of therapeutic areas such as oncology, dermatology, and HIV, and in products such as vaccines and targeted biologics. Jackie earned her PhD in Pathology from Case Western Reserve University, Cleveland, Ohio, where she went on to complete a post-doctoral fellowship in genomics and bioinformatic techniques. Connect with Jackie on LinkedIn.

 

Angela W. Corona, PhD
Scientific Director, ProEd Regulatory

Angela is a Scientific Director for ProEd Regulatory. She is responsible for helping sponsors navigate complex regulatory communications, such as FDA advisory committee meetings. She develops clinical and regulatory strategy along with high-quality scientific and medical content across a wide range of therapeutic and drug development areas. Angela received her PhD in Neuroscience from The Ohio State University and completed her postdoctoral training at Case Western Reserve University.

 

References:

  1. US Food and Drug Administration. Expedited programs for serious conditions – drugs and biologics. May 2014. Updated June 25, 2020. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/expedited-programs-serious-conditions-drugs-and-biologics
  2. US Department of Health and Human Services, Office of Inspector General. Review of the FDA’s Accelerated Approval Pathway. August 2021. https://oig.hhs.gov/reports-and-publications/workplan/summary/wp-summary-0000608.asp
  3. Congress.gov. H.R.6963 – 117th Congress (2021-2022): Accelerated Approval Integrity Act of 2022. March 7, 2022. https://www.congress.gov/bill/117th-congress/house-bill/6963
  4. House Committee on Energy & Commerce. Pallone Introduces Bill to Improve FDA’s Accelerated Approval Program [press release]. March 7, 2022. https://energycommerce.house.gov/newsroom/press-releases/pallone-introduces-bill-to-improve-fda-s-accelerated-approval-program
  5. Congress.gov. H.R.6996 – 117th Congress (2021-2022): Accelerating Access for Patients Act of 2022. March 8, 2022. https://www.congress.gov/bill/117th-congress/house-bill/6996/text#:~:text=Introduced%20in%20House%20(03%2F08%2F2022)&text=To%20amend%20the%20Federal%20Food,condition%2C%20and%20for%20other%20purposes
  6. Cafero B and Reuter T. Competing bills propose amendments to FDA’s accelerated approval program. Health Industry Washington Watch. March 18, 2022. https://www.healthindustrywashingtonwatch.com/2022/03/articles/legislative-developments/competing-bills-propose-amendments-to-fdas-accelerated-approval-program/
  7. Pitts PJ. Creating a promising pathway for faster access to new drugs — and a Califf confirmation. STAT. February 14, 2022. https://www.statnews.com/2022/02/14/creating-promising-pathway-to-new-drugs-califf-confirmation/
  8. Congress.gov. S.1644 – 117th Congress (2021-2022): Promising Pathway Act. May 13, 2021. https://www.congress.gov/bill/117th-congress/senate-bill/1644.
  9. I Am ALS. Senator Mike Braun reintroduces Promising Pathway Act (PPA) & The Accelerated Drug Approval for Prescription Therapies (ADAPT) Act. May 14, 2021. https://iamals.org/updates/senator-mike-braun-reintroduces-promising-pathway-act-ppa-the-accelerated-drug-approval-for-prescription-therapies-adapt-act/
  10. Wallach JD, Zhang AD, Skydel JJ, et al. Feasibility of using real-world data to emulate postapproval confirmatory clinical trials of therapeutic agents granted US Food and Drug Administration accelerated approval. JAMA Netw Open. 2021;4(11):e2133667. doi: 10.1001/jamanetworkopen.2021.33667.

Surrogate Endpoints for Accelerated Approval

Surrogate endpoints have been used for accelerated approval (AA) since the early 1990s, playing a vital role in getting therapies for serious conditions to patients sooner. The AA pathway was first created in 1992 to accelerate the approval of drugs intended to treat “serious conditions that fill an unmet medical need.” In the intervening 30+ years, surrogate endpoints have played a major role in oncology and rare disease clinical trials, but their appropriate use is still being debated in the literature. Most often that debate centers around whether an endpoint is a true surrogate that predicts clinical benefit in the clinical context in which it is being used.

What is a “surrogate”endpoint? How is it different from “clinical outcome”endpoint?

A “surrogate” endpoint is a biomarker, lab measurement, radiographic image, physical sign, or other measure that is “reasonably likely to predict clinical benefit” whereas a “clinical outcome” endpoint is one that “directly measures clinical benefit.” Importantly, the FDA definition of clinical benefit is how a patient feels, functions, or survives.

To illustrate the difference between surrogate and clinical endpoints, below are some oncology-specific examples:

Surrogate Endpoints Clinical Outcome Endpoint
Progression-Free Survival (PFS) Overall Survival (OS)
Objective Response Rate (ORR)
Duration of Response (DoR)

The FDA publishes a Surrogate Endpoint Table updated every 6 months and listing surrogate endpoints that can support approval of a drug or a biological product under both accelerated and traditional approval pathways.1 The FDA encourages development of “novel” surrogate endpoints; a novel endpoint can become established as a surrogate based on persuasive evidence that it predicts clinical benefit in the context of a specific disease and patient population. The FDA determines the acceptability of a surrogate endpoint on a case-by-case basis, dependent on context and influenced by the disease, patient population, therapeutic mechanism of action, and currently available treatments (ie, unmet need for new treatments). If a surrogate endpoint was previously used to support AA, but subsequent confirmatory trials consistently fail to demonstrate the expected clinical benefit, that surrogate endpoint should no longer be accepted for that use.

When is it appropriate to use a surrogate endpoint?

The main purpose for using a surrogate endpoint is to shorten clinical development timelines or improve the feasibility of clinical studies in rare diseases where the number of patients is limited and large, controlled studies are challenging. In many cases, a surrogate endpoint can be reached much sooner and with fewer patients than a clinical outcome endpoint such as overall survival (OS), which is a direct measure of clinical benefit. Sponsors must think about this in the context of the specific disease and indication for which they are developing the drug.

For example, in cancer patients with a long life expectancy, a surrogate endpoint such as progression-free survival (PFS) can provide a much earlier readout than a clinical outcome endpoint such as overall survival (OS). If PFS has been shown to correlate with OS in that specific disease and indication, there is a good chance that the confirmatory trial would be able to show an OS benefit. However, in some cases this can be challenging.

In the context of rare genetic diseases, for example, the surrogate endpoint is often a biomarker that can be easily measured with precision and that is reasonably likely to predict how patients feel or function. Because clinical measures of how patients function over time can be difficult to assess with precision, they often require much larger studies to demonstrate a clinically meaningful effect. For example, in Duchenne muscular dystrophy, rather than measuring functional outcomes such as ability to walk, which can vary from one day to the next, researchers will often use a surrogate endpoint such as quantitative measurements of dystrophin protein expression.

In severe respiratory diseases, measures of lung function are often used as a surrogate to predict how well the patient can perform activities of daily living, which can often be difficult to measure with precision. These few examples illustrate how surrogate endpoints can be used to facilitate clinical research.

How much time is saved by using these endpoints?

The amount of time saved by using a surrogate endpoint is disease dependent. For example, use of PFS rather than OS in breast cancer can save almost a full year, whereas the use of response rate (RR) versus OS can save 19 months.2 It all depends on the natural history of the disease and the nature of the endpoint being studied. So, while the use of surrogate endpoints can save time on the front end, and while patients will benefit sooner, the tradeoff is that the sponsor must invest in the development of an additional post-approval confirmatory trial—and there is no guarantee that a direct clinical benefit will be confirmed. Thus, there is a chance that the patient might be taking a drug that turns out not to help them in the long run.

What are “validated” surrogate endpoints?

A “validated” surrogate endpoint meets a higher standard and can be used to support full approval. This requires that the endpoint be “supported by a clear mechanistic rationale and clinical data providing strong evidence that an effect on the surrogate endpoint predicts a specific clinical benefit.”3

Two examples include:

  • HbA1c predicting improvements in long-term complications of type 2 diabetes mellitus
  • Virologic suppression of HIV as a proxy for preventing progression to AIDS

More than 75% of approvals that used a surrogate endpoint came through the traditional pathway using a validated surrogate endpoint.3 The AA pathway does not require the use of validated surrogate endpoints.

Aaron Csicseri, PharmD, Aaron has 10+ years’ experience as a Senior Scientific Director, Medical Director, or Clinical Strategist within the medical communication field. He is responsible for overseeing and developing high-quality scientific and medical content that incorporates key communication objectives and accurate representation of data. Aaron is experienced in the development of strategic scientific communication platforms, strategic publication planning and implementation, medical expert outreach and engagement, guiding and executing medical education programs, and support for medical affairs. He received his PharmD from the University of Buffalo.

 

Sources:

  1. US FDA. Table of Surrogate Endpoints That Were the Basis of Drug Approval or Licensure. Updated February 28, 2022. Accessed March 8, 2022. https://www.fda.gov/drugs/development-resources/table-surrogate-endpoints-were-basis-drug-approval-or-licensure
  2. Chen EY, Joshi SK, Tan A, Prasad V. Estimation of study time reduction using surrogate end points rather than overall survival in oncology clinical trials. JAMA Intern Med. 2019;179(5):642-647.
  3. US FDA. Surrogate Endpoint Resources for Drug and Biologic Development. Updated July 24, 2018. Accessed March 8, 2022. https://www.fda.gov/drugs/development-resources/surrogate-endpoint-resources-drug-and-biologic-development

Introduction to the Accelerated Approval Pathway

The FDA has developed several mechanisms to speed drugs to market when a compelling medical need exists including Accelerated Approval (AA), Priority Review, Fast Track, and Breakthrough Therapy Designation. Accelerated Approval is an important regulatory pathway that provides patients with earlier access to treatments for serious medical conditions when there is an unmet medical need. This is the first post in a 3‑part series on the AA Pathway. Herein, I’ll focus on how this pathway is used to bring drugs to market and highlight some of the key issues surrounding it.

The AA Pathway was created in 1992 in response to the AIDS crisis and was codified in 2012 under the Food and Drug Administration Safety Innovations Act (FDASIA) in an effort to bring potentially life-saving drugs to market more quickly. The majority of drugs granted AA have been for AIDS, rare diseases, and cancer. Over the past 10 years, there has been a steady increase in the number of New Drug Applications (NDAs) seeking AA (Figure1,2); this increase has been driven largely by immune checkpoint inhibitors, which have transformed the treatment of many types of cancer.

Figure: Novel Drugs Approved Using the Accelerated Approval Pathway.

Data sources: Darrow JJ, et al. JAMA. 2020 (through 2017);1 FDA CDER reports 2017-20212

How does Accelerated Approval work?

Under normal or traditional FDA approval pathways, a drug must show evidence of clinical benefit based on endpoints that measure how a patient feels, functions, or survives. In contrast, AA allows FDA to grant a drug a “conditional” approval based on its effect on a surrogate or an intermediate clinical endpoint that is reasonably likely to predict clinical benefit.3 (We’ll share more on this in part 2 of this series.) In some cases, AA can shave years off the clinical development timeline. Under the same law, the FDA requires sponsors to conduct a confirmatory clinical trial in the postmarketing setting to confirm that the drug does provide meaningful clinical benefit, and FDA can withdraw approval if further trials fail to verify the predicted clinical benefit.

Pros of the Accelerated Approval Pathway

The majority of drugs granted AA are for rare diseases, where the unmet need is great (90% of rare diseases have no approved therapy),4 and for oncologic indications where the disease is often life-threatening. In the case of rare diseases where patients are few and far between, it can be extremely challenging to conduct controlled clinical trials of sufficient size to demonstrate clinical benefit using traditional endpoints. The use of surrogate endpoints under an AA may be the only feasible path to approval; however, it can often be difficult subsequently to confirm clinical benefit in the postmarketing setting. In the case of oncology drugs, clinicians want to have access to promising new therapies for patients who have limited time to wait for the latest, potentially life-saving innovation, so speed to market becomes paramount.

Cons of the Accelerated Approval Pathway

The nature of the AA Pathway allows drugs to be marketed for a given indication before clinical benefit has actually been demonstrated using validated clinical endpoints. Although a surrogate endpoint must be reasonably likely to predict clinical benefit, this anticipated benefit must be verified in a confirmatory trial.

FDA prefers that a well-designed confirmatory trial be planned or underway at the time of AA, but there is no action enforceable by the FDA to require completion of confirmatory trials. According to a recent investigation in the British Medical Journal, nearly half of the drugs granted AA have not confirmed clinical benefit,5 and only 16 AAs have been withdrawn. This calls into question whether some of the drugs approved through the AA pathway are actually providing the promised clinical benefit to patients. That being said, there are many situations, particularly in rare diseases, where it can be difficult to complete confirmatory trials.

Finally, even more problematic, is what to do when confirmatory trials fail. In some cases, FDA will convene an advisory committee meeting to discuss whether the unmet need still exists and whether additional ongoing trials may confirm clinical benefit. (We’ll share more on this in part 3 of this series.)

Conclusion

While confirmatory trials can be difficult to complete, the AA pathway has been used to approve an increasing number of novel drugs in the past 10 years and remains an important regulatory pathway that provides patients with earlier access to treatments for serious medical conditions. Stay tuned for our next installment, which will explore the use of surrogate endpoints in Accelerated Approvals.

Jackie Orabone, PhD, helps clients prepare for FDA Advisory Committee meetings by combining her scientific expertise and research knowledge in immunology with over 2 years of medical communications agency experience. Connect with Jackie on LinkedIn.

 

References:

  1. Darrow JJ, Avorn J, Kesselheim, AS. FDA approval and regulation of pharmaceuticals, 1983-2018. JAMA. 2020;323(2):164-176.
  2. US FDA. New Drugs at FDA: CDER’s New Molecular Entities and New Therapeutic Biological Products. Current as of January 27, 2022. Accessed March 3, 2022. https://www.fda.gov/drugs/development-approval-process-drugs/new-drugs-fda-cders-new-molecular-entities-and-new-therapeutic-biological-products
  3. US FDA. Accelerated Approval. Current as of January 4, 2018. Accessed March 3, 2022. https://www.fda.gov/patients/fast-track-breakthrough-therapy-accelerated-approval-priority-review/accelerated-approval
  4. Huron J. New report finds medical treatments for rare diseases account for only 11% of US drug spending; nearly 80% of orphan products treat rare diseases exclusively. March 4, 2021; National Organization for Rare Disorders. Accessed March 3, 2022. https://rarediseases.org/new-report-finds-medical-treatments-for-rare-diseases-account-for-only-11-of-us-drug-spending-nearly-80-of-orphan-products-treat-rare-diseases-exclusively/#:~:text=Approximately%207%2C000%20known%20rare%20diseases,rare%20diseases%20have%20no%20treatment
  5. Mahase E. FDA allows drugs without proven clinical benefit to languish for years on accelerated pathway. BMJ. 2021;374:n1898.

Common Protocol Template—Streamlining Protocol Implementation

Study protocols are required for every clinical trial. Approximately 20,000 are submitted and posted to www.clinicaltrials.gov every year1—each one different. The format and core content can vary from sponsor to sponsor, costing the US Food and Drug Administration (FDA) time and resources to interpret, review, and ultimately, approve each uniquely complex protocol. This process, as it stands, slows down progress for new drug development. Clearly, there is a need to accelerate the pace at which protocols are approved so that new clinical studies can be initiated. In a world where technology continues to offer a platform for efficiency and accuracy, the development of the Common Protocol Template (CPT) is a welcome addition to the medical field. Common Protocol Templates can lead to faster review time, simplified trial startup, and prompt execution of clinical trials. Although the use of a CPT is not required for all new clinical trials, it is only a matter of time before its use becomes commonplace in drug development. Continue reading

Making Sense of FDA’s Expedited Drug Approval Pathways and Designations – for the Non-Regulatory Professional

blog header linkedin - FDA Approval v6 blog sizeOne of the fundamental responsibilities of the US Food and Drug Administration (FDA) is to approve effective medicines for people who need them, while upholding high standards for safety. That mission also demands that the FDA work efficiently and not delay approval of life-saving medical advances. Today, the FDA is reviewing applications for approval of new medicines faster than ever, and that’s a welcome change from the status quo 25 years ago. In the era from 1962 (immediately following the thalidomide recall) to the early 1990s, FDA review times for a New Drug Application (NDA) or Biologic License Agreement (BLA) were often measured in years rather than months. In 1993, the standard review time (from NDA or BLA submission to decision) for a new molecular or biologic entity (parlance for a drug not previously approved for any other use) was about 28 months,1 and in some cases, approvals were delayed for many years.

Continue reading