Abstract A085: First-in-class humanized antibody targeting alternatively spliced tissue factor augments anti-metastatic efficacy of chemotherapy in a preclinical model of pancreatic ductal adenocarcinoma

Abstract

Abstract Introduction. Alternatively spliced tissue factor (asTF) promotes progression of pancreatic ductal adenocarcinoma (PDAC) via activating b1-integrins on PDAC cell surfaces. hRabMab1, a humanized inhibitory anti-asTF antibody we recently developed, can suppress PDAC primary tumor growth as a single agent. Whether hRabMab1 has the potential to suppress metastases in PDAC is unknown. Aim. To test hRabMab1’s ability to suppress metastatic spread in combination with chemotherapy. Methods. asTF-proficient, KRAS G12V-mutant human PDAC cell line PaCa44 yields aggressive primary orthotopic tumors that spread spontaneously to the relevant anatomical sites, accompanied by severe leukocytosis. 5 × 105 PaCa44 cells were implanted into the pancreata of NOD-SCID mice (n=40). 10 days post-implantation, mice were randomized into 4 cohorts: vehicle; hRabMab1 administered IV at 18 mg/kg; gemcitabine/paclitaxel (gem/paclitaxel, 50 mg/kg/3 mg/kg); and hRabMab1+gem/paclitaxel. Results. Post-mortem analysis of tumor tissue and luciferase imaging of the abdominal cavity showed that gem/paclitaxel alone reduced primary tumor volume, but not metastatic spread; only the combination of hRabMab1 and gem/paclitaxel significantly reduced metastatic spread (p=0.0114 vs vehicle, 1-way ANOVA). RNAseq analysis of primary tumor tissue followed by gene set enrichment of differentially expressed genes showed that the addition of hRabMab1 to gem/paclitaxel downregulated tubulin binding and microtubule motor activity. Genes involved in extracellular matrix/collagen production and neovascularization were upregulated in response to gem/paclitaxel; addition of hRabMab1 to gem/paclitaxel tentatively reduced this compensatory effect. In the liver, hRabMab1 reduced liver metastasis as a single agent (p=0.031 vs vehicle) and in combination with gem/paclitaxel (p=0.0054 vs vehicle, 1-way ANOVA). In the surgical incision site, metastatic penetrance was as follows: vehicle, 100%; hRabMab1, 100%; gem/paclitaxel, 44% (4/9); hRabMab1+gem/paclitaxel, 0% (p=0.037715, gem/paclitaxel vs hRabMab1+gem/paclitaxel, Chi square test). Only the combination of hRabMab1 and gem/paclitaxel eliminated leukocytosis; levels of neutrophils, monocytes, eosinophils, and basophils were significantly lower in the hRabMab1+gem/paclitaxel cohort vs gem/paclitaxel cohort (p=0.035, p=0.051, p=0.032, and p=0.026, respectively). Leukocytes recruited from the circulation fuel tumor progression in PDAC. To address the potential significance of white blood cell (WBC) count normalization in our model, we performed correlation analysis between WBC counts and tumor volumes across all cohorts; there was a highly significant positive correlation between these two parameters (R=0.682, p=0.00002). Conclusions. This is the first study demonstrating that hRabMab1 can suppress metastasis in PDAC. hRabMab1’s ability to improve anti-metastatic efficacy of chemotherapy is potentially significant and warrants further investigation. Citation Format: Clayton S. Lewis, Charles Backman, Sabahat Ahsan, Ashley Cliff, Arthi Hariharan, Jen Jen Yeh, Davendra P. S. Sohal, Vladimir Y. Bogdanov. First-in-class humanized antibody targeting alternatively spliced tissue factor augments anti-metastatic efficacy of chemotherapy in a preclinical model of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A085.