Engineering an anti-granulocyte colony stimulating factor receptor nanobody for improved affinity

AIMS

Granulocyte colony-stimulating factor (G-CSF) is a cytokine that induces proliferation and differentiation of hematopoietic precursor cells and activation of mature neutrophils. G-CSF is overexpressed in several malignant tumors and blocking its binding to the receptor can lead to significant decrease in tumor growth, vascularization and metastasis. Furthermore, targeting G-CSF receptor has shown therapeutic benefit in other diseases such as rheumatoid arthritis, progressive neurodegenerative disorder and uveitis. Camelid single-chain antibodies (nanobodies) have exceptional properties making them appropriate for tumor imaging and therapeutic application. In this study we aim to use the rational design approach to engineer a previously described G-CSF-R targeting nanobody (VHH1), to improve its affinity toward G-CSF-R.

MAIN METHODS

We redesigned the complementary determining region 3 (CDR3) domain of the VHH1 nanobody to mimic G-CSF interaction to its receptor and developed five new engineered nanobodies. Binding affinity of the engineered nanobodies was evaluated by ELISA (Enzyme-linked immunosorbent assay) on NFS60 cells.

KEY FINDINGS

Enzyme-linked immunosorbent assay (ELISA) confirmed the specificity of the engineered nanobodies and ELISA-based determination of affinity revealed that two of the engineered nanobodies (1c and 5a) bind to G-CSF-R on the surface of NFS60 cells in a dose-dependent manner and with a higher potency compared to the parental nanobody.

SIGNIFICANCE

Additional studies are required to better characterize these nanobodies and assess their interaction with G-CSF-R in vitro and in vivo. These newly developed nanobodies could be beneficial in tumor imaging and therapy and make a basis for development of additional engineered nanobodies.

Expression of recombinant G-CSF receptor domains and their inhibitory role on G-CSF function

Background and purpose:

Granulocyte colony-stimulating factor (G-CSF) is routinely used in combination with chemotherapy to battle neutropenia. However, studies suggest that this chemokine may increase the risk of metastasis and malignancy in many cancers. To counteract the adverse effects of G-CSF in cancer, antibodies have been used to block its action. However, antibodies are large and complex molecules which makes their production expensive. Thus in this study, we aim to construct different structure variants of the G-CSF receptor containing different domains and select the best variant that prevents the adverse actions of this chemokine. These novel structures are smaller than antibodies and easier to produce.

Experimental approach:

Different domains of the G-CSF receptor were designed and cloned into the pET28a expression vector. These recombinant receptor subunits were then expressed in Escherichia coli and purified using standard affinity chromatography techniques. Interaction of recombinant receptor subunits with G-CSF was assessed using enzyme-linked immunosorbent assay and NFS60 cells.

Findings / Results:

Two recombinant receptor subunits containing D1 + D2 + D3 domains and D2 domain showed the strongest inhibitory activity to G-CSF.

Conclusion and implications:

These novel recombinant receptor variants could be candidates for further studies in the development of novel therapeutics.