Pfizer Discontinues Phase II Trial for CD47 Blood Cancer Drug Amid Recruitment Challenges

Pharmaceutical giant Pfizer has announced the termination of a Phase II clinical trial evaluating maplirpacept, its investigational CD47-targeting fusion protein, in patients with diffuse large B-cell lymphoma (DLBCL). The decision comes as a result of significant recruitment difficulties, highlighting the ongoing challenges faced by the pharmaceutical industry in clinical trial execution.

Trial Discontinuation and Recruitment Issues

According to an update on a federal clinical trials database, Pfizer cited the "inability to recruit the planned number of subjects" as the primary reason for discontinuing the study. Since its initiation in August 2023, the trial had only managed to enroll six participants, falling far short of the intended recruitment goals. A Pfizer spokesperson confirmed to Endpoints News that the decision was based solely on "recruiting challenges" and not on any safety or efficacy concerns related to maplirpacept.

The terminated study was designed to assess maplirpacept, an intravenously delivered recombinant fusion protein targeting CD47, in DLBCL patients. CD47, a cell surface ligand overexpressed in blood cancer cells, plays a crucial role in helping these malignant cells evade immune system detection. By blocking CD47, maplirpacept aims to enhance both innate and adaptive immune responses against cancer cells.

Ongoing Development and Future Prospects

Despite this setback, Pfizer remains committed to the development of maplirpacept in other blood cancer indications. The company spokesperson stated that studies of the drug candidate are ongoing in multiple myeloma and other hematological malignancies. Additionally, a Phase I/II trial combining maplirpacept with Roche's Columvi in relapsed or refractory DLBCL patients is currently recruiting, with a primary completion date set for September 2026.

Pfizer acquired maplirpacept through its $2.26 billion purchase of Trillium Therapeutics in August 2021, demonstrating the company's significant investment in the CD47 space. However, the recent trial discontinuation adds to a series of challenges faced by CD47-targeting therapies across the pharmaceutical industry.

Broader Implications for CD47-Targeted Therapies

The setback for maplirpacept is not an isolated incident in the CD47 therapeutic landscape. Earlier this year, ALX Oncology reported that its CD47 blocker evorpacept, in combination with Merck's Keytruda, failed to meet primary endpoints in two mid-stage studies focusing on metastatic or unresectable recurrent head and neck cancer.

Perhaps the most notable disappointment in the CD47 field has been Gilead's magrolimab. After facing partial clinical holds imposed by the FDA in early 2022 due to safety concerns, Gilead ultimately discontinued the development of magrolimab in July 2023. The termination of a late-stage study in myelodysplastic syndromes, citing futility, marked the end of magrolimab's troubled development journey.

These collective setbacks underscore the complexities and challenges inherent in developing effective CD47-targeted therapies, prompting a reevaluation of strategies within this promising but difficult area of cancer research.