Super-resolution microscopy of the B-cell receptor (BCR) on the surface of diffuse large B-cell lymphoma cells. On the left, the lymphoma cell is untreated and displays BCRs that form microclusters, which provide oncogenic, pro-survival signals for the lymphoma cells. On the right, the lymphoma cells have been treated with an inhibitor of the enzyme OST, which is responsible for N-linked glycosylation of membrane proteins. Note that the de-glycosylated BCRs are now dispersed and are much less active in providing survival signals.
Attaching sugar molecules to proteins can affect protein activities in the cell — and this behavior can be exploited to treat diffuse large B-cell lymphomas (DLBCL), according to a recent study led by CCR researchers. The finding, published May 4, 2023, in Cancer Discovery, sets up an unexpected approach to targeted therapy for this aggressive disease.
Only about 65% of people with DLBCL survive for at least five years after diagnosis, and currently many endure serious side effects from standard chemotherapy treatments, explains Louis M. Staudt, M.D., Ph.D., Chief of the Lymphoid Malignancies Branch and senior author on the study. His research has focused on finding targeted therapies that are better tolerated by patients. In this study, he looked at blocking the B-cell receptor signaling pathway, which is known to help lymphoma cells live longer.
When Staudt’s team screened the genome for important regulators of the pathway, they were surprised to find that B-cell receptor signaling relies heavily on an enzyme called OST-B, which attaches sugar molecules to proteins. The importance of this in the survival of lymphoma cells was completely unanticipated by the team.
“We like to be surprised and gravitate toward the unexpected,” said Staudt, who credits Sebastian Scheich, Ph.D., a postdoctoral fellow in the laboratory, with designing the experiments to understand why sugar modifications are so important to B-cell receptor signaling.
Scheich teamed up with JiJi Chen, Ph.D., Staff Scientist with the NIH Advanced Imaging and Microscopy Resource, to look at the B-cell receptors on the cancer cell surface. Using super-resolution microscopy, they were able to visualize clustered B-cell receptors that dispersed when exposed to a drug that blocks the sugar-modification activities of OST enzymes. The team then discovered that the dispersed receptors, when not clustered together by sugar modifications, more easily interacted with a protein called CD22, which turns off B-cell receptor signaling.
“It’s really an unexpected mechanism,” Staudt emphasized. In a final test, the team again used the drug in two lymphoma cell lines and in an animal model of the disease. In all three cases, the OST enzyme-blocking drug reduced tumor formation without any signs of toxicity. This effect was enhanced even more when the drug was combined with known inhibitors of other important survival pathways in B cells.
The team’s next step is to work with their colleagues in the Chemical Biology Laboratory to identify a drug inhibitor that blocks the OST-B enzyme specifically to limit off-target effects. “Modification of proteins and sugar molecules looks to be an under-studied but rich area of investigation in cancer research,” said Staudt. “We are looking forward to the potential for combinations of targeted therapies that are much better tolerated by the patient.”
