The Discovery of SSTR2

The Expression of SSTR2

SSTR2 mRNA and protein are widely expressed in normal tissues, but have low expression consistency. The protein form of SSTR2 has the highest expression in the brain and kidneys. At the same time, SSTR2 is widely expressed in solid tumors. Since it is highly expressed in neuroendocrine tumors (NETs), SSTR2 is the key target for the treatment of NETs at present.

Recent studies have shown that SSTR2 is significantly methylated in colorectal cancer and has also been implicated in tumorigenesis in gastric and breast cancers. Furthermore, the researchers found that SST binding to SSTR2 inhibited the release of cytokines from immune cells and impacted on the tumor microenvironment (TME).

The Expression of SSTR2 in 20 cancers from the Human Protein Atlas

To study the expression of SSTR2 in different cancers, the team from Xinqiao Hospital of Third Military Medical University integrated IHC data from the Human Protein Atlas. The results showed that the IHC positive rate of SSTR2 in 13 cancers was higher than 50%; 5 cancers slightly expressed SSTR2 (positive rate 25% ~ 50%); 2 cancers slightly expressed SSTR2 (positive rate 0% ~ 24%). It can be seen that the expression of SSTR2 is differential and widely distributed in various cancer types. Furthermore, cell-mediated immunity may be better activated and maintained in patients with high SSTR2 expression.

The Structure and Function of SSTR2

SSTR2 is a member of the G protein-coupled receptor (GPCR) family and is a seven-pass transmembrane protein with the N-terminal extracellular and the C-terminal intracellular. Studies have shown that some SSTRs can heterodimerize with other members of the SST family and unrelated GPCRs, including DRD2, β-adrenergic receptors. The co-expression of such interacting receptors in cells can affect SSTRs transport, signal transduction, or biological activity. Therefore, the role of these heterodimers in physiological or pathological conditions will be an interesting area for future research.

The Structure of SSTR2

SSTR2 inhibits the release of many hormones and other secreted proteins by binding to the SST, inhibiting cell proliferation and angiogenesis. The antitumor activity of SST occurs through direct and indirect mechanisms:

(a) Binding to SSTR on the tumor surface activates downstream cell cycle arrest or related apoptotic factors.

(b) SSTR induces tumor angiogenesis and the production of tumor growth inhibitors. SSTR2 gene expression is absent in 90% of human pancreatic cancers. The construction of human pancreatic cells expressing SSTR2 (without expressing endogenous SSTR2) induces the expression of its ligand (SST), thereby inhibiting cell proliferation, tumorigenicity, and metastasis.

SSTR2 as a prognostic marker in kidney cancer (unfavorable) and pancreatic cancer (favorable)

Representative clinical therapeutic drugs targeting SSTR2

Tidutamab (XmAb-18087) is a representative drug targeting SSTR2 which is developed by Xencor. As a bispecific antibody (IgG1), XmAb-18087 can bind to CD3 to activate T cells for the efficient and targeted killing of SSTR2-expressing tumor cells. XmAb-18087 is currently in Phase I/II, and its main indications are neuroendocrine tumors and lung cancer.

ACROBiosystems has successfully developed HEK293 expressed full-length SSTR2-VLP protein (Met 1-Ile 369) via "FLAG" to support drugs and therapies R&D targeting SSTR2.

SSTR2：Verification Data

Full-length SSTR2 6-VLP Protein (Cat. No. SS2-H5216)

High bioactivity verified by ELISA

Immobilized Human SSTR2 Full Length Protein-VLP (Cat. No. SS2-H5216) at 10 μg/mL (100 μL/well) can bind Anti SSTR2 Monoclonal Antibody, Mouse IgG with a linear range of 0.005-0.625 μg/mL (QC tested).

Protocol

>>> Learn more about “FLAG”: full-length multi-pass transmembrane proteins and technology platforms

References:

1．Marily Theodoropoulou, Günter K. Stalla. Somatostatin receptors: From signaling to clinical practice. Frontiers in Neuroendocrinology (2013). http://dx.doi.org/10.1016/j.yfrne.2013.07.005

2．Aoyun Wang, Yixiao Yuan, Han Chu, et al. Somatostatin Receptor 2: A Potential Predictive Biomarker for Immune Checkpoint Inhibitor Treatment. Pathol. Oncol. (2022) https://doi.org/10.3389/pore.2022.1610196