Pfizer’s investigational antibody-drug conjugate inotuzumab ozogamicin has been awarded ‘breakthrough’ status in the US for the treatment of acute lymphoblastic leukaemia, potentially putting the drug on a faster development and review pathway.

Inotuzumab is comprised of a monoclonal antibody targeting CD22, a cell surface antigen expressed on around 90% of B-cell malignancies, linked to a cytotoxic agent. When the drug binds to CD22 on malignant B-cells it is taken into the cell, where the cytotoxic agent calicheamicin is released to destroy it.

ALL is an aggressive type of leukaemia with high unmet need and a poor prognosis. The current standard treatment is intensive, long-term chemotherapy, but advancing therapies “is crucial as only 10% of adults with ALL who relapse after first-line therapy survive five years or more with current treatment options,” noted Mace Rothenberg, chief medical officer for Pfizer Oncology.

The breakthrough designation comes on the back of data from the Phase III INO-VATE trial, which compared the drug to standard of care chemotherapy in 326 adult patients with relapsed or refractory CD22-positive ALL, and showed that inotuzumab more than doubled complete remission rates.

The co-primary endpoint of complete remission with incomplete haematologic recovery was achieved by 80.7% of patients treated with Pfizer’s drug and 33.3% of those given the standard of care, according to preliminary results presented at the European Haematology Association meeting in June this year.

The news will be especially sweet to Pfizer given that the drug previously failed to improve overall survival in paients with an aggressive form of non-Hodgkin's lymphoma.