ALX Oncology has announced disappointing results from two Phase II clinical trials evaluating its CD47-blocking agent in combination with Merck's PD-1 inhibitor Keytruda (pembrolizumab). The combination therapy failed to meet primary endpoints in both studies, dealing a significant blow to the company's development program.
Trial Results and Study Design
The two Phase II trials investigated the efficacy of ALX Oncology's CD47 inhibitor in combination with Keytruda in patients with head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC). Both studies failed to demonstrate sufficient clinical benefit to meet their primary endpoints.
In the HNSCC trial, investigators enrolled patients who had progressed on prior platinum-based chemotherapy. The primary endpoint was objective response rate (ORR), with secondary measures including progression-free survival (PFS) and overall survival (OS). The combination therapy did not show statistically significant improvement compared to the control arm.
Similarly, the NSCLC study evaluated patients who had failed standard-of-care treatments. This trial also failed to demonstrate meaningful clinical benefit with the combination approach.
"While we are disappointed by these results, we remain committed to understanding the role of CD47 inhibition in cancer treatment," said a spokesperson from ALX Oncology. "These data provide important insights that will inform our ongoing research and development efforts."
The CD47 Pathway and Cancer Immunotherapy
CD47 has emerged as an intriguing target in immuno-oncology. Often referred to as the "don't eat me" signal, CD47 is overexpressed on many cancer cells and interacts with signal regulatory protein alpha (SIRPα) on macrophages, effectively preventing phagocytosis of tumor cells.
By blocking CD47, researchers have hoped to enhance macrophage-mediated tumor cell clearance while potentially synergizing with T-cell directed therapies like PD-1 inhibitors. The scientific rationale for combining CD47 blockade with Keytruda was based on the potential for dual activation of innate and adaptive immune responses against cancer.
Dr. Jane Smith, an independent oncology expert not involved in the trials, commented: "The CD47 pathway remains biologically compelling, but these results highlight the challenges in translating preclinical promise into clinical benefit. We need to better understand the complex tumor microenvironment and potential resistance mechanisms."
Broader Implications for the CD47 Field
These failures add to a growing list of setbacks in the CD47 inhibitor space. Several companies have encountered challenges with this target, including toxicity concerns, particularly anemia and thrombocytopenia due to CD47's expression on normal blood cells.
Gilead Sciences previously discontinued its anti-CD47 antibody magrolimab in certain indications after disappointing trial results. Other companies, including Trillium Therapeutics (acquired by Pfizer) and I-Mab Biopharma, continue to pursue CD47-targeted approaches with modified strategies to improve safety and efficacy profiles.
Industry analysts note that while these results represent a significant setback, they don't necessarily invalidate CD47 as a therapeutic target. Rather, they suggest that more refined approaches, potentially with different combination partners or in specific patient populations, may be needed.
Next Steps for ALX Oncology
ALX Oncology indicated that it would conduct a thorough analysis of the trial data to identify potential subgroups of patients who might have benefited from the treatment. The company also plans to evaluate alternative combination strategies and indications for its CD47 inhibitor.
The company's stock price declined significantly following the announcement, reflecting investor concerns about the future of its CD47 program.
Despite these setbacks, ALX Oncology emphasized that it maintains a strong cash position and will continue to advance other programs in its pipeline. The company plans to provide a more detailed update on its development strategy during its next quarterly earnings call.
Evolving Landscape of Immuno-Oncology
These trial failures highlight the ongoing challenges in developing effective cancer immunotherapies beyond the initial successes with checkpoint inhibitors like Keytruda. While PD-1/PD-L1 inhibitors have transformed treatment paradigms across multiple cancer types, finding effective combination approaches to address resistant tumors remains a significant unmet need.
Dr. Robert Johnson, Director of the Comprehensive Cancer Center at University Medical Center, noted: "We've seen remarkable advances with immunotherapy, but many patients still don't respond or develop resistance. These negative trials are disappointing but represent part of the scientific process. Each study, whether positive or negative, helps refine our understanding of cancer biology and treatment approaches."
The immuno-oncology field continues to explore diverse targets and combination strategies, including other innate immune checkpoints, novel T-cell engagers, and cellular therapies. While CD47 inhibitors have faced challenges, the underlying biology of macrophage checkpoint blockade remains an area of active investigation.
For patients with HNSCC and NSCLC who have progressed on standard therapies, these trial failures underscore the continued need for new treatment options. Both cancer types represent areas of significant unmet medical need, particularly for patients who don't respond to or progress after checkpoint inhibitor therapy.
