Abstract 2446: The effects of dacomitinib (PF-299) on pancreatic ductal adenocarcinoma (PDAC) and cancer-associated fibroblasts (CAFs).

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background: PF-299 is an oral irreversible small molecule that is an effective inhibitor of the ErbB pathway, which has been shown to play a critical role in pancreatic ductal adenocarcinoma (PDAC) pathogenesis. Indirect activation of Epidermal Growth Factor Receptor (EGFR) signaling through ErbB3 heterodimerization and stromal ligand production has been shown to act as an escape mechanism for EGFR directed therapies. This phenomenon may explain the modest clinical benefit of anti-EGFR drugs in PDAC. We have previously shown that CAFs are responsible for the secretion of ErbB pathway ligands. The addition of CAFs to PDAC xenografts improves the tumor modeling and adds testing stringency to novel targeted therapies. We hypothesize that PF-299 inhibition of multiple ErbB receptors results in effective inhibition of PDAC tumor progression. Materials: AsPC-1, BxPC-3, C3, Panc-1 and Panc-1+ErbB3 (stable ErbB3 transfected cell line) PDAC cells were treated with different concentrations of PF-299. PDAC cell proliferation and ErbB signaling was analyzed in vitro. Subcutaneous xenografts were developed using the AsPC-1 and BxPC-3 cell lines alone and in combination with CAFs. CAFs were obtained from surgically resected PDAC tissue. Xenografts were analyzed for tumor growth and tumor-associated ErbB signaling after treatment with PF-299. Results: In vitro, PF-299 effectively inhibited AsPC-1, BxPC-3, C3, Panc-1 and Panc-1+ErbB3 cell proliferation in a dose-dependent manner (1-10 μM). PF-299 decreased migration of AsPC-1 cells by 54%, while the addition of CAFs (in co-culture) increased cell migration by 13% in the PF-299 treated group compared to an increase of 273% in the control group. In vivo, tumor proliferation of AsPC-1 and BxPC-3 xenografts was significantly inhibited by PF-299 treatment (p=0.04 and p=0.002, respectively). Combination of AsPC-1/BxPC-3+CAFs xenografts increased initial tumor size by 22.5% (p=0.17) for the AsPC-1 cell line and by 11.6% (p=0.46) for the BxPC-3 cell line compared to cells without CAFs. The AsPC-1+CAFs PF-299 treated tumors were 4.1% smaller than placebo treated tumors (p=0.99), while BxPC-3+CAFs PF-299 treated tumor were 26% smaller than the placebo treated group (p=0.05). Immunoblot analysis of AsPC-1/BxPC-3+CAFs xenografts confirmed PF-299 mediated inhibition of both EGFR and ErbB3 mediated signaling. Conclusion: We demonstrated that PF-299 targets multiple ErbB receptors, including ErbB3. PF-299 significantly inhibited PDAC cell proliferation, migration and tumor progression by targeting EGFR and ErbB3 signaling. CAFs may provide a novel addition to current models by increasing tumor virulence while pan-ErbB receptor targeting may improve therapeutic approaches to PDAC. Citation Format: Brett L. Broussard, Alevtina Mikhaylina, Juan P. Arnoletti, Martin J. Heslin, Andrey Frolov. The effects of dacomitinib (PF-299) on pancreatic ductal adenocarcinoma (PDAC) and cancer-associated fibroblasts (CAFs). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2446. doi:10.1158/1538-7445.AM2013-2446