K-ras mutation and p53 loss are the most prevalent genetic alterations in pancreatic cancer. In addition to these two alterations, pancreatic tumors frequently contain a third genetic defect. Mutations in the WNT/ß-catenin signaling molecules occur in 15-20% of pancreatic cancer patients and co-exist with K-ras mutation and p53 loss. However, the contribution of the WNT/ß-catenin pathway in pancreatic tumorigenesis is still unclear. Methods: We generated Pdx1-CreKras G12D p53 L/+ APC L/+ (KPA) mice and compared their phenotypes with Pdx1-CreKras G12D p53 L/+ (KPC) mice. The signaling pathways specifically activated in the KPA mice were investigated and the therapeutic effect by targeting the activated pathways was evaluated. We finally validated our findings in human blood and tumor samples. Results : Survival of the KPA mice was shorter than that of the KPC mice. The KPA cancer cells are highly invasive and exhibit distorted morphology in organoid culture with extensive invadopodia formation and elevated matrix metalloproteinase (MMP) activity. The platelet-derived growth factor (PDGF) pathway is upregulated in the KPA cancer cells, and PDGF production induced by ß-catenin triggers constitutive activation of the Src kinase via the PDGF receptor in the cells. Serum PDGF concentration of the KPA mice is much higher than that of the normal and KPC mice. The Src inhibitor dasatinib effectively inhibits tumor growth and metastasis of the KPA cancer cells. Patient's serum PDGF level is significantly correlated with the expression of PDGF and phosphor-Src in tumors and elevated PDGF/phosphor-Src level in tumors predicts increased recurrence and poor survival. Moreover, mutations of the WNT/ß-catenin signaling molecules are higher in patients with elevated PDGF/phosphor-Src level. Conclusion: ß-catenin activation, coupled with K-ras mutation and p53 loss, activates an autocrine PDGF/Src signaling in pancreatic cancer and defines a subset of patients who might be sensitive to Src inhibition. In addition, serum PDGF level could be a reliable biomarker for patient selection in clinic.

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4122 Background: The VEGF pathway is the predominant mediator of angiogenesis in pancreatic cancer. Vatalanib (PTK787/ZK 222584) is a small molecule tyrosine kinase inhibitor of all known VEGF receptors. We initiated a phase I study of vatalanib and gemcitabine for advanced pancreatic cancer. Methods: Patients with newly diagnosed unresectable or metastatic pancreatic adenocarcinoma were enrolled. Previous adjuvant chemoradiotherapy with fluorouracil was allowed. Gemcitabine was given by fixed-dose rate infusion weekly x 3 in a 28-day cycle, and vatalanib was given orally daily. Dose-limiting toxicities (DLT) are defined as any grade 3/4 toxicity during the first cycle. The dose levels are as follows: Results: To date, 11 patients are evaluable for toxicity (5M/6F; median age 62 years, range 40–82 years; median KPS 90%). Thus far, 42 cycles have been given, with a median of four cycles per patient. Two patients have experienced DLT. The first patient (cohort 1) experienced grade 3 diarrhea and hypokalemia and grade 4 neutropenia occurring simultaneously and treated without sequelae. The second patient (cohort 3) developed grade 3 deep vein thrombosis. Beyond the first cycle, grade 3 toxicities included neutropenia (1), anemia (3), thrombocytopenia (1), hypertension (2), diarrhea (1), hypokalemia (1), thrombosis (1), and proteinuria (1). Three of eleven patients (27%) did not complete treatment to the first evaluation timepoint (2 cycles); two discontinued due to toxicity and one discontinued due to disease progression. Two of eleven patients (18%) had a partial response by RECIST. Six of eleven patients (55%) had stable disease as the best response ranging from 2–6 months. Conclusions: The combination of gemcitabine and vatalanib is generally well-tolerated with most grade 3/4 toxicities occurring late in the treatment course. Antitumor responses have been observed at initial dose levels and accrual to the final cohort with BID dosing of vatalanib continues. [Table: see text] No significant financial relationships to disclose.