Next-Generation Targeted Therapies Show Promise in AML Treatment Landscape

Jay Yang, MD

Jay Yang, MD

In the past 1.5 years, there have been 5 FDA approvals as treatment options for acute myeloid leukemia (AML). However, the treatment paradigm could be strengthened by novel second-generation FLT3 inhibitors and BCL-2 inhibitors, according to Jay Yang, MD.

“It has been really exciting and refreshing as a leukemia physician,” said Yang. “It's always good to have new and better therapies that give us more options for our patients.”

After seeing approvals by the FDA approval for midostaurin (Rydapt), enasidenib (Idhifa), CPX-351 (Vyxeos), gemtuzumab ozogamicin (Mylotarg), and ivosidenib (Tibsovo), a supplemental new drug application (sNDA) has been received by the FDA for venetoclax (Venclexta) in combination with a hypomethylating agent or low-dose cytarabine.

The sNDA was submitted for the frontline treatment of patients with AML who are ineligible for intensive chemotherapy based on 2 phase Ib/II trials that demonstrated complete remissions (CRs) in more than 60% of patients.¹

Though venetoclax may be nearing regulatory approval, Yang noted that quizartinib has also made an impact in clinical studies. In August, the FDA granted a breakthrough therapy designation to the FLT3 inhibitor for adult patients with relapsed/refractoryFLT3-ITD—positive AML. The designation was announced following the results of the phase III QuANTUM-R study, in which there was a 24% reduction in the risk of disease progression or death compared with salvage chemotherapy following frontline treatment.²

In an interview withTargeted Oncology, Yang, oncologist at the Barbara Ann Karmanos Cancer Institute, discussed the evolution of the treatment landscape for AML and the future outlook for these treatments.

TARGETED ONCOLOGY:How would you describe the evolution of AML treatment?

Yang:AML is an aggressive hematopoietic malignancy. It is one that has been notoriously difficult to treat. For many decades now, we've been struggling to find better and novel therapies for patients with this disease. Over the past 5 to 15 years, there has been a lot of development in understanding the genetic mutations that are seen in this disease. The discovery of these mutations means that sometimes we can find targeted therapies. We have targeted FDA-approved therapies for some of these mutations, and that can be extremely relevant for our patient population.

TARGETED ONCOLOGY:What are some of these molecular targets?

Yang:There are a large number of mutations that are found in AML. There are currently more than 70 mutated genes in the AML genome. All of these could potentially be targets for drug therapies. However, only a few of them have been successful so far. The main ones are FLT3, which comes in 2 forms—–TKDandITDmutations—– andIDH1/2mutations. As of now, all 3 of those are targetable.

TARGETED ONCOLOGY:What has it been like to see the wave of progress in the past year?

Yang:For many years, we have been looking at our colleagues who treat multiple myeloma, Hodgkin lymphoma, B-cell lymphoma, and also chronic myeloid leukemia and chronic lymphocytic leukemia. [All those malignancies have] new drugs for patients. In the past 18 months, there have been 5 drug approvals in AML.

TARGETED ONCOLOGY:What can we expect in the next year or so?

Yang:There are a couple of drugs that could be nearing regulatory approval. One of them is venetoclax, which is an antiapoptotic protein. It's a BCL-2 inhibitor that has shown some activity in relapsed/refractory AML as a single agent. We've been most impressed by venetoclax in newly diagnosed, treatment-naïve patients who are not fit for intensive chemotherapy. The combination of venetoclax with either low-dose cytarabine or hypomethylating agents has been very impressive, perhaps more than anyone would have expected. It's probably one of the biggest developments in the past year or so. For this reason, there is a lot of interest in it. It very well could become available in the clinic in the near future.

The other potential drug that I could see reaching the clinic might be quizartinib. Of course, we have midostaurin, but it's a first-generation multikinase FLT3 inhibitor. It doesn’t have much activity for relapsed/refractory patients, but for newly diagnosed patients it is approved in combination with standard chemotherapy.

Quizartinib is a second-generation FLT3 inhibitor. It is much more potent againstFLT3-ITD— mutated AML. In the relapsed/refractory setting, data have recently been presented showing that it is better, to some degree, than standard chemotherapy. Statistically speaking, it showed an improvement in overall survival. Some would say the results are a little bit modest, but there is a fairly good chance that it will be approved based on those results.

TARGETED ONCOLOGY:What about glasdegib?

Yang:That is an interesting drug. It is completely different than anything else that's in the pipeline. It's a hedgehog pathway inhibitor. As a single agent, it has not shown much activity in AML. However, in combination with chemotherapy and in combination with hypomethylating drugs, it has shown some additional activity. In randomized phase II trials, very promising results were presented. There is a randomized phase III trial looking at chemotherapy with or without this hedgehog inhibitor. Time will tell whether this will be fruitful or not

TARGETED ONCOLOGY:What are the biggest challenges that lie ahead?

Yang:Despite all the drug approvals, there are still a lot of challenges. Targeting molecular mutations like FLT3 and IDH1/2 you might consider [to be] the lowest hanging fruit. These are common mutations, and they were able to rapidly develop drugs that specifically target those mutations. Going forward, it's going to be a little bit tougher. There are a lot of mutations out there, but AML is a very tricky and difficult disease to treat. Just because you have a drug that can target a mutation, doesn't mean that it's going to be effective.

TARGETED ONCOLOGY:Are there other mutations beside FLT3 andIDH1/2that are showing promise as potential targets?

Yang:The one that is interesting to me is the spliceosome modulator; there is a class of mutations called spliceosome mutations. There are 4 of them—–SF3B1, SRSF2,andZRSR2,andU2AF1. They are fairly common, especially in myelodysplastic syndrome (MDS). More than 50% of patients with MDS will carry one of these mutations, and perhaps 20% to 30% of patients with AML will also carry this mutation. H3B-8800 is a spliceosome modulator and is currently being evaluated in a phase I/II study in the clinic. We're participating in that clinical trial as well.

TARGETED ONCOLOGY:Is there anything else you would like to emphasize?

Yang:One important topic is minimal residual disease (MRD). We've known about this for a long time. We know that patients, even if they're in morphologic or cytogenetic remission (CR), many times we can still measure MRD by more specific techniques—whether it be flow cytometry or polymerase chain reaction-based techniques. Patients who are in remission but who are MRD-positive have a much higher relapse rate than those who are MRD-negative. If a patient is MRD-positive, despite reaching a complete response, they might benefit from having an allogeneic stem cell transplant. That's important. The problem is, there's no standardized testing for MRD. That really should be a priority moving forward for investigators.

References:

1. Genentech announces submission of supplemental new drug application for Venclexta for people with previously untreated acute myeloid leukemia who are ineligible for intensive chemotherapy. Published July 12, 2018. Accessed July 12, 2018. https://bit.ly/2mdU4VQ.
2. Cortes J, Khaled S, Martinelli G, et al. Quizartinib significantly prolongs overall survival in patients with FLT3-internal tandem duplication—mutated (MUT) relapsed/refractory AML in the phase 3, randomized, controlled QuANTUM-R trial. In: Proceedings from the 2018 EHA Congress; June 14-17, 2018; Stockholm, Sweden. Abstract LB2600.