With a recent flurry of new drug approvals, the treatment landscape for acute myeloid leukemia has expanded, raising new questions about how to incorporate those drugs into patient care.
Until about a decade ago, advances in AML therapy centered mainly around iterations of daunorubicin and cytarabine. Now, novel and targeted agents, many specifically going after mutational byproducts, are yielding some great results and raising hopes for better survival outcomes, Jeffrey Lancet, MD, said in an interview.
“When I go to sleep at night, I often dream about … 10-year survival rates in the 80% range. And then I wake up … and I realize this is actually [the survival curve for chronic myeloid leukemia]. This is where we’d like to be [with AML].” Those outcomes are a long way off, but appreciable incremental gains may lie ahead with the recent advances in AML therapy, said Dr. Lancet, chair of the department of malignant hematology at Moffitt Cancer Center in Tampa.
In addition to the new approvals, 16 drugs are in late stage clinical development and will likely contribute to an AML market that is expected to surpass $1.5 billion by 2026, according to projections by the market intelligence company GlobalData.
The liposome-encapsulated combination of daunorubicin and cytarabine (Vyxeos) was approved in August by the Food and Drug Administration for the treatment of therapy-related AML and AML with myelodysplasia-related changes.
In a phase 3 randomized trial , the fixed-dose combination product was associated with median overall survival of 9.6 months, compared with 5.9 months with a standard combination of cytarabine and daunorubicin (7+3).
“I would envision that Vyxeos will hold and become the primary standard of care for fit chemotherapy-suitable older patients, or any patients for that matter, who are dealing with secondary-like AML or high-risk AML, based on the phase 3 results that we demonstrated,” Dr. Lancet, the principal investigator for the trial, said in an interview.
Asked whether the improved survival with Vyxeos is primarily related to more patients becoming transplant eligible or to significant reductions in disease burden, Dr. Lancet remarked that it’s likely a mixture of both.
The high remission rate with Vyxeos vs. standard 7+3 therapy means Vyxeos has the ability to stand on its own, and “the potential to send more patients to transplant and to get better results.”
“Transplant is part of the continuum of care of AML, including in older patients, and Vyxeos is going to become a standard part of that care,” he remarked. But transplant outcomes were not a predesignated component of the phase 3 trial, and further study will be needed to determine Vyxeos’ role as a bridge to transplant. “At this stage I can reasonably state that it has a role in the upfront therapy of secondary and high-risk AML, regardless of whether the patient is being considered for transplant.”
The early stages of working Vyxeos into the therapeutic mix come with some challenges, however, according to Donna Capozzi, PharmD.
The combined use of two agents in this fashion is relatively uncommon in intravenous chemotherapy, so there is a learning curve, Dr. Capozzi, associate director of ambulatory services in the department of pharmacy at the University of Pennsylvania, Philadelphia, said in an interview.
Vyxeos is a fixed-dose combination that comes in vials containing 44 mg daunorubicin and 100 mg cytarabine encapsulated in liposomes. Patient dosing is based on the daunorubicin component and calculated based on body surface area (mg/m2), meaning the cytarabine dose does not need to be calculated. There are both pros and cons to this approach, she explained.
Benefits include a longer half-life with Vyxeos vs. standard 7+3, and the fact that during induction the drug is delivered on days 1, 3, and 5 for 90 minutes rather than continuously for 7 days as with 7+3, Dr. Capozzi said.
The main concern relates to ensuring that the dosing is calculated based on the proper component, she said.
“We had our first patient last week. It was very time consuming, with double and triple checking to make sure everything was correct,” she said. Preparing the drug is also time-consuming, as it involves multiple steps, such as warming, which is not required with standard 7+3; the additional labor factors will have to be built into workflow, she noted.
“The other piece not fully in place right now is building [the use of Vyxeos] into electronic health records,” she said, adding that safeguards put into place through EHRs will also help to streamline the administration process.
For example, cardiac toxicity is a known effect of daunorubicin; the EHR will help track lifetime cumulative dosing of that component, which is otherwise challenging, especially when using a combination product, she said.
The process will get easier over time, as use of Vyxeos becomes more prevalent in practice, she added. “None of these are insurmountable issues.”
Cost is another matter. Based on average wholesale prices, the cost per cycle is approximately $40,000 with Vyxeos vs. about $4,300 for conventional 7+3 therapy, Dr. Capozzi said. Given the differential, there will be a great deal of debate as to which patients will derive the most benefit from Vyxeos, she said.
Also, it will take time to figure out the extent of adverse events. “For liposomal products in general, rash-type side effects can be really significant. Hand-foot syndrome was not reported in the initial trials, but we’ll keep our eyes open to see how that plays out,” she said noting that the one patient treated so far at the University of Pennsylvania is doing very well. “We will learn more with real world experience.”
Oral targeted therapies
Enasidenib (Idhifa) was approved under priority review in August in conjunction with a companion diagnostic IDH2 assay for patients with relapsed or refractory disease and specific mutations in the IDH2 gene. Midostaurin (Rydapt) was approved in April for use in conjunction with standard daunorubicin and cytarabine induction and cytarabine consolidation in adults with FLT3 mutation-positive AML.
In a phase 1 dose escalation study reported at the annual meeting of the European Hematology Association, enasidenib was associated with an overall response rate of 37% in patients with relapsed/refractory AML, including 20.1% complete responses and 7.9% complete responses with incomplete recovery of platelets or incomplete hematologic recovery, 3.7% with partial responses, and 5.1% with a morphologic leukemia-free state. Patients who had a CR had a median overall survival of 22.9 months. For patients with responses other than CR, the median OS was 15.1 months. For patients with no response to the drug, the median OS was 5.6 months, Dr. Eytan M. Stein, of Memorial Sloan Kettering Cancer Center in New York, reported.
Additionally, need for transfusions was reduced in 34% of 157 patients who required transfusions at study entry.
“In a relapsed or refractory group of patients where there’s no true standard of care, this drug definitely represents a major breakthrough and has a lot of utility as a single agent, as a potential bridge to a transplant, and in combination with new or even old drugs – including regular old induction chemotherapy as a way to improve responses and outcomes in the future,” Dr. Lancet said, adding that as an oral agent it has potential for development as a maintenance strategy.
This agent could have a large impact, he said, adding: “I think this sets the paradigm for novel targeted therapies.”
Midostaurin has also emerged as a new standard of care, particularly for younger patients, Dr. Lancet said.
The approval of the multitargeted kinase inhibitor was based on the results of the randomized, placebo-controlled phase 3 RATIFY trial , which demonstrated significantly longer overall and event-free survival vs. placebo and standard chemotherapy in newly diagnosed AML patients with FLT3 gene mutations.
“I think this will be the new comparator for future studies, whatever they may be, for this patient population,” he said.
Dr. Capozzi noted that she has had some difficulty obtaining prior authorization for enasidenib due to its high cost (about $1,000/day).
The drug is taken orally on days 8-21 of a 28-day treatment cycle. In RATIFY, patients who achieved complete remission after induction therapy received four 28-day cycles of consolidation therapy.
Dr. Capozzi noted that the dosing regimen can be confusing, as it changes depending on whether it is used for induction or consolidation. It remains to be seen how these agents will fit into the treatment setting, she said.
Targeted therapies in development
Other targeted therapies in development for AML include an IDH1 inhibitor, the BCL2 inhibitor venetoclax, and several second-generation FLT3 inhibitors such as gilteritinib , Dr. Lancet said.
Venetoclax, which is currently approved for chronic lymphocytic leukemia, has shown single agent activity, but is even more promising in combination with low-dose cytarabine or aza-nucleosides, he noted.
For example, in one recent study reported at the annual congress of the European Hematology Association, response rates in older, newly diagnosed AML patients were as high as 72% for azacitidine plus venetoclax, and 76% for decitabine plus venetoclax.
“So there’s a lot of interest and promise,” Dr. Lancet said, adding that venetoclax may have broad application in AML. “We’ll be seeing a lot more data in the next year or two.”
An unusual aspect of venetoclax, which is used often for CLL, is the need for observation during dose escalation, Dr. Capozzi noted. Patients tend to question the need for admission for observation with the use of an oral agent, thus efforts are underway to develop criteria for outpatient observation.
Otherwise, venetoclax is fairly easy to access and use, and is well tolerated, she said.
“I expect as we learn more about where (venetoclax) fits in, it will be a much more commonplace agent” as part of AML therapy, she said.
Gilteritinib, as well as the second generation FLT3 inhibitors quizartinib and crenolanib, are also of interest in AML. With midostaurin already on the market, however, different strategies are being pursued, Dr. Lancet said.
“I believe gilteritinib is entering the fray in relapsed/refractory disease, and crenolanib is being looked at in the upfront FLT3 AML-positive setting and ultimately will be compared to midostaurin in combination with chemotherapy in that setting,” he added, noting that these drugs have the advantage of being more potent and selective inhibitors of FLT3, and some appear to have the ability to target resistance-conferring mutations.
“It still remains to be determined what the ultimate role will be, especially now that midostaurin is approved as frontline therapy and, in my opinion, will likely be entrenched there for awhile,” he said. “It’s a fairly competitive field right now, but certainly one where there’s a lot of excitement. The encouraging part is the second generation inhibitors, especially crenolanib and gilteritinib, are able to rescue some patients who may have failed primary therapy with an FLT3 inhibitor.”
Future direction and outcomes
So how should one go about selecting therapies, in the absence of data on combining therapies, for patients with multiple mutations?
Ideally, that means teasing out which of the AML patient’s mutations is clonal and the driver of their disease, and which one is subclonal. There are no guarantees, but that seems like a rational way to begin and move the field forward to studies of combination therapies, Dr. Lancet said.
“I think with the right combinations that target leukemias that are mutationally driven, there is potential to treat subsets of patient with very targeted therapies that will lead to prolonged survival. Right now, for the most part, we don’t have drugs for many of the targets that are very important in AML, and we don’t always know which target is driving the disease … these are considerations that remain to be discovered,” he said. “But I do think that in 10 years we will have the ability with novel drugs and increased understanding of the clinical relevance of these targets to really personalize the approach more so than we are today, and to increase response rates significantly and improve survival as a result.”
Dr. Lancet is a consultant for Jazz Pharmaceuticals, Daiichi Sankyo, and Celgene. Dr. Capozzi reported having no disclosures.