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Delta-like ligand-3 (DLL3) is a single-pass, type I transmembrane protein that plays a role in inhibiting the Notch signaling pathway. The Notch signaling pathway is a highly conserved intercellular signaling pathway that regulates embryonic development. Conventionally, the Notch signaling pathway is driven through the DSL family of Notch ligands. However, DLL3 is a divergent, otherwise termed ‘mutated’, member of the DSL family expressed due to a mutation in the Notch gene. This mutation drives the overexpression of DLL3, which in turn, inhibits the subsequent Notch signaling pathway within the DLL3-expressing cell and does not initiate the Notch pathway on adjacent cells.

Spotlight Summary
Protein Name	DLL3, Delta-like canonical Notch ligand 3
Molecular Weight*	50.4 kDa
AA Length	619
Accession #	Q9NYJ7-1

Biological Significance

This dysregulation of the Notch pathway by DLL3 contributes to cell proliferation and reduced apoptosis, thus driving tumorigenesis. Below are a few key effects of DLL3 on the Notch signaling pathway:

1. DLL3 – Notch 1 Binding: This resulting binding leads to the inhibition of the Notch signaling pathway, downregulation HES1 and HEY1, both of which contribute to regulation of tumor cell.

2. DLL3 – Notch 2 Binding: Upregulation of expression levels of cell cycle proteins to increase cell cycle protein expression.

3. DLL3-Notch2-Notch4 Binding: Mediates cell proliferation and differentiation in ovarian cancer.

In general, DLL3 can bind to different Notch receptors and play multiple functions in cell proliferation, differentiation, and apoptosis. However, in different disease types, Notch receptor expression regulated by DLL3 can vary with the same resulting effect of driving tumor growth. As such, clarifying the interplay between DLL3 and Notch receptors in different tumorigenesis applications remains a key milestone in biological research.

Figure 1. Potential Modalities to Target DLL3-expressing Cells

Clinical Significance & Applications

Despite the unclarity of DLL3’s biological function and role within Notch signaling, clinically, DLL3 is a clear biomarker for SCLC with its overexpression in over 75% in SCLC clinical trial populations. Furthermore, Notch mutations that drive DLL3 expression are exclusive to the lung, further emphasizing DLL3’s role as a biomarker for SCLC. As such, various therapies have been developed or are under development, including bispecific T-cell engagers (BiTEs), antibody-drug conjugates, and cell therapies, as seen in Table 1.

Table 1. DLL3 drug clinical information

Currently, the most promising DLL3 therapeutics are ADCs, BiTEs, and CAR cell therapies summarized in Figure 2. Each of these methods target DLL3, but rather than directly inhibiting DLL3 and its biological function, these therapeutics use DLL3 as a homing target to identify SCLC and other cancerous cells. Due to the specificity of DLL3 expression on SCLC cells, these therapies can accurately and precisely identify cancerous cells without affecting healthy, non-cancerous cells.

Biological Significance

Clinically, the use of DLL3 is an up-and-coming biomarker that is finally entering the clinical stage. Further emphasis of these biologics should be focused more on manufacturing, finding methodologies to scale-up antibody production and optimize targeting, payload delivery, or improving ADCC interactions. Currently, there are numerous drugs from different companies that are entering the clinical stage, with a significant increase in DLL3-targeting drug pipelines, thus proving DLL3 is a significant direction for treatment of SCLC. Another aspect is cell therapy; beyond the conventionally approved FDA cell therapies targeting CD19 and BCMA, DLL3 could prove to be the first CAR target that enables cell therapy to combat solid tumors, presenting a significant milestone to cell therapies.

However, beyond its clinical use, biologically, that lack of understanding between DLL3 and Notch hinders its clinical application beyond SCLC. This is especially evident when differentiating between SCLC and non-SCLC, where seemingly opposing effects are evident between DLL3-expressing cells, yet still drive tumorigenesis.

To promote DLL3 and Notch signaling research, both in biologics manufacturing and in basic research, ACROBiosystems offers a wide array of DLL3 and Notch 1/2/3/4 protein products that are expressed using our HEK293 expression platform. Various labels are available, with validated applications including immunization, biopanning, and biofunctional verification assays.