Abstract B041: DCLK1 isoforms 2 and 4 c-terminal extracellular binding domain mediates PDAC tumorigenesis through protein-protein interactions

Abstract Doublecortin-like kinase 1 (DCLK1) plays a major role in tumor initiation, progression, and metastasis of solid tumors including pancreatic ductal adenocarcinoma (PDAC). Elevated expression of DCLK1 in patient tumors leads to poor overall survival, however, the precise mechanisms that regulate the pro-tumorigenic functions of DCLK1 continue to be explored. We have reported that the proprietary monoclonal antibody, CBT-15, binds to the C-terminal extracellular domain of DCLK1 isoforms 2/4 in PDAC and treatment with CBT-15 resulted in tumor xenograft growth arrest in PDAC and reduced tumor growth in the KPC mouse model of PDAC. To determine the functional activity of the DCLK1 isoform 2/4 extracellular domain and CBT-15 action, we screened a peptide library against DCLK1 isoform 4 and identified eight peptides that bound to the C-terminal extracellular domain. In this study, we evaluated the biological impact of these peptides on colony and spheroid formation using AsPC-1 and Capan-1 pancreatic cancer cell lines. We found a greater than 90% reduction in spheroid formation compared to vehicle control for Capan-1 cells treated with peptide #1 (1 μM). Furthermore, peptide #1 treatment of AsPC-1 cells derived mouse xenografts resulted in a greater than 65% reduction in xenograft growth (P-value < 0.01, 10 mg/kg, i.p.). This highly active peptide binds the extracellular domain with 60% inhibition at 50 nM determined by SPR and has a Kd of 30±10 nM. To identify potential DCLK1 extracellular domain binding partners, we developed an algorithm that identified five proteins that are key regulators of tumorigenesis and exhibit structural characteristics that would allow for binding to the DCLK1 extracellular domain. Further work is focused on confirming the interactions between DCLK1 extracellular domain and candidate targets as well as whether peptide #1 blockade of protein-protein interactions disrupts pro-tumorigenic functions of DCLK1. Citation Format: Parthasarathy Chandrakesan, Landon Moore, Randal May, Kamille Pitts, Edwin Bannerman-Menson, Milton Brown, Courtney Houchen. DCLK1 isoforms 2 and 4 c-terminal extracellular binding domain mediates PDAC tumorigenesis through protein-protein interactions [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B041.