The role of the interactions between N domain and Linker 2 of DKK1 in modulating the immunosuppressive tumor microenvironment mediated by DKK1 C domain

Project: Research project

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Description

Immunosuppressive tumor microenvironment (TME) is the critical barrier in immunotherapy, which may result in immune checkpoint inhibitors being ineffective. Myeloid-derived suppressor cells (MDSCs) could suppress T cell responses in TME and promote tumor proliferation. Downregulation of β-catenin is critical for MDSC accumulation in immunosuppressive TME. Dickkopf-1 (DKK1) could downregulate β-catenin in MDSCs and exert immunosuppressive TME. DKK1 expression levels showed significant positive correlation with MDSC numbers and negative correlation with infiltrating levels of CD8+ T cells in various cancers. The high expression of DKK1 was also associated with poor progression and short disease-free survival in multiple cancers. Consequently, DKK1 has become a promising target for immunotherapy. DKK1 inhibition by therapeutic antibody against DKK1 C domain has additive activity in combination therapy with immune checkpoint inhibitor (PD-1 antibody) in clinical trials, but demonstrated limited inhibitory effect in monotherapy. Therefore, understanding the mechanism of DKK1 in modulating the immunosuppressive TME could facilitate the development of the next generation DKK1 inhibitors to achieve optimizing effects in immunotherapy. There are five domains in DKK1. It was reported that C domain of DKK1 could bind to LRP6, downregulate β-catenin in MDSCs and modulate immunosuppressive TME. To further validate the role of C domain, we have developed a DNA aptamer against DKK1 C domain (AptDKK1-C) as a pharmacological tool for studying the role of DKK1 C domain. We found that the AptDKK1-C could decrease MDSCs accumulation and decrease the tumor growth in vivo, but the efficacy could be further improved. It was reported that N domain of DKK1 could compete the binding between C domain and LRP6. We found that Linker 2 could interact with N domain to hinder the interaction between N domain and C domain, by molecular modeling approach. Based on the above data, we hypothesized that the interactions between N domain and Linker 2 could facilitate the binding of C domain to LRP6 to enhance the immunosuppressive TME mediated by DKK1 C domain. In our preliminary study by genetic approach, it was found that Linker 2 depletion by genetic mutations could enhance the effect of AptDKK1-C on inhibiting the binding of DKK1 to LRP6 and rescuing β-catenin expression in the MDSCs in vitro. To further study the role of interaction between Linker 2 and N domain by pharmacologic approach, we identified a DNA aptamer against Linker 2 (AptDKK1-L2) as a pharmacologic tool. We found the combination of AptDKK1-L2 and AptDKK1-C could synergistically inhibit the binding of DKK1 to LRP6 and rescue β-catenin expression in MDSCs in vitro. More importantly, AptDKK1-L2 could decrease MDSC accumulation and decrease the tumor growth in melanoma (B16) tumor mice model in vivo. To further test the above hypothesis in vivo, we have the following specific aims in this proposal by using AptDKK1-L2 as a pharmacologic tool to block the interaction between N domain and Linker 2 of DKK1 and using AptDKK1-C to inhibit the binding of C domain to LRP6:

Aim 1: To determine the tumor growth in melanoma (B16) syngeneic mice and melanoma (B16) NSG immunodeficient mice, respectively, after treatment with AptDKK1-C monotherapy, AptDKK1-L2 monotherapy, and their combination therapy, respectively.

Aim 2: To evaluate the immune response and tumor growth in mice with gastric carcinoma after treatment with AptDKK1-C monotherapy, AptDKK1-L2 monotherapy, and their combination therapy, respectively.

Aim 3: To evaluate the immune response and tumor growth in TNBC mice after treatment with AptDKK1-C+AptDKK1-L2, PD-1 antibody, and AptDKK1-C+AptDKK1-L2+PD-1 antibody, respectively.

If the hypothesis could be supported, it could facilitate the development of the next generation DKK1 inhibitors to achieve optimizing inhibition effects on immune suppressive TME.
StatusActive
Effective start/end date1/01/2330/06/25

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