Could DLK1 Be an Immunotherapeutic Target to Treat Neuroblastoma?

By Kate Knab

The Findings

Proteogenomic analyses of tumor and normal tissues revealed 60 high-confidence candidate cell surface proteins to serve as immunotherapeutic targets for neuroblastoma, including Delta-like canonical notch ligand 1 (DLK1).

Researchers found a direct correlation between high expression of DLK1 and a super-enhancer, which is a unique transcriptional regulation that promotes cancer growth. Decreased expression of DLK1 resulted in increased cellular differentiation, indicating cells began to resemble healthy tissue. The investigators went on to show that the antibody-drug conjugate (ADC) ADCT-701 — a DLK1-targeting antibody linked to a toxic payload that specifically binds to and kills cells expressing DLK1 on the surface, as in neuroblastoma— demonstrated potent and specific anti-tumor activity.

Why it Matters

Previous immunotherapy studies in childhood cancer have focused largely on known “targets” such as CD19 in leukemia and GD2 in neuroblastoma. For childhood solid cancers, the known targets each have liabilities that limit their effectiveness and/or cause significant toxicities. This work represents an agnostic and comprehensive search for new optimal immunotherapy targets and discovered several that are being pursued. Because an ADC targeting DLK1 had already been developed for liver cancers, the investigators quickly worked with animal models to show the potential of this approach in treating aggressive neuroblastoma tumors and translating this work to an ongoing clinical trial.

The investigators also showed that DLK1 is highly expressed in many other malignancies in addition to neuroblastoma, including endocrine, gastrointestinal, and liver tumors. The development of ADCs and CAR T cells that target DLK1 could potentially provide safe and effective new treatment for several cancers with no known effective immunotherapies available.

Who Conducted the Study

Researchers from the United States, Canada, and the United Kingdom conducted this study, including senior author Sharon Diskin, PhD, a tenured Associate Professor at the University of Pennsylvania and Children’s Hospital of Philadelphia in the Division of Oncology and the Center for Childhood Cancer Research. First author Amber Hamilton, PhD, is a postdoctoral fellow at CHOP and led the study with Dr. Diskin, along with John Maris, MD, the Giulio D'Angio Endowed Professor, and Yael Mossé, MD, the Patricia Brophy Endowed Professor, both at CHOP and Penn.

How They Did It

Researchers used proteogenomic analyses and RNA sequencing to map cell surface proteins on neuroblastoma tumors and identify which were optimal for immunotherapy development. They also assessed mechanisms of over-expression by evaluating epigenetic processes, such as a protein’s acquisition of a super-enhancer, which differentiates DLK1 from previously identified immunotherapeutic targets. 

To determine whether DLK1 could be a target, researchers validated its expression on the surface of neuroblastoma cells using immunofluorescence and flow cytometry. Testing the efficacy of ADCT-701 in targeting DLK1, researchers performed immunohistochemistry staining on tumor models with high, moderate, and low-DLK1 expression and observed subsequent tumor growth responses.

Quick Thoughts

“The proteogenomic approach designed here enables the identification of high-confidence proteins for immunotherapy development,” Dr. Diskin said. “The data from this study supported the development and implementation of an ongoing Phase 1 first-in-human DLK1-directed immunotherapy clinical trial using ADCT-701 to treat neuroendocrine neoplasms, including neuroblastoma, in adult patients.”

What’s Next

The goal is to open a clinical trial of ADCT-701 immunotherapy for children with cancer once a safe dose is established in adults. The team also has applied their integrative, multi-omic approach to other high-risk childhood malignancies and are actively validating additional surface proteins for immunotherapy development. 

Where the Study was Published

The study appears in Cancer Cell.