AstraZeneca leukemia drug bags priority review status, setting up third-quarter approval

FDA
Almost two-thirds of participants in AstraZeneca's phase 1 experienced complete responses. (FDA)

The FDA has granted priority review status to AstraZeneca’s treatment for hairy cell leukemia (HCL). Snagging the accelerated review sets AstraZeneca up to win approval of the antibody-drug conjugate in the third quarter. 

AstraZeneca is seeking approval of moxetumomab pasudotox in HCL patients who have undergone at least two prior lines of treatment. 

The 2% of leukemia patients with the hairy cell form of the disease typically respond well to purine analogs cladribine and pentostatin, resulting in decade-long remissions.

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The treatment is not a cure, however. Many patients have residual disease following treatment and HCL can recur years later. Purine analogs are used treat recurrences but efficacy wanes with each course.

AstraZeneca thinks moxetumomab pasudotox is a better option for some patients with relapsed or refractory forms of HCL. The treatment consists of an anti-CD22 antibody fragment fused to a fragment of Pseudomonas exotoxin-A. The combination enables the asset to deliver a toxic payload to cells that express the CD22 surface receptor, such as malignant B cells.

Late last year, AstraZeneca quietly disclosed that the drug had triggered durable complete responses in third-line and beyond HCL patients, resulting in the pivotal study hitting its primary endpoint. AstraZeneca has yet to share a look at the data but whatever it saw was compelling enough for the FDA put the filing on its fast track.

The designation pulls forward the finish line for a drug that has been through a fairly lean clinical trial program. Cambridge Antibody Technology moved the drug into phase 1 early in 2007. AstraZeneca, which bought CAT in 2006, took the trial over and posted dose-escalation data in 2012. The pivotal, 80-person phase 3 started the following year.

Subsequent analyses of the 33-patient phase 1 showed almost two-thirds of participants experienced complete responses. No evidence of minimal residual disease was found in more than half of the responders. Almost all of those patients were in complete remission at the end of the trial.

The findings, if replicated in phase 3, suggest moxetumomab pasudotox will significantly extend the lives of some patients. But the orphan nature of HCL means the business opportunity is relatively small for AstraZeneca.