Abstract B32: JAK2 inhibition blocks STAT3 signaling and enhances drug delivery and therapeutic response in pancreatic cancer.

Introduction: The failure of conventional and molecularly targeted chemotherapeutic regimes to produce meaningful impact on survival in patients with pancreatic cancer (PDAC) highlights a desperate need for novel treatment strategies. A hallmark in PDAC is the presence of a dense desmoplastic reaction (stroma) within the tumor microenvironment (TME) which is characterized by proliferation of fibrotic tissue in which the vasculature functions poorly and impedes the delivery of chemotherapeutic drugs to the tumor cells. STAT3 modulates the transcription of responsive genes involved in the regulation of a variety of critical functions, including cell differentiation, proliferation, apoptosis, angiogenesis, metastasis, and immune responses. We have previously established a mechanistic rationale for activated STAT3 as a biomarker of resistance to cytotoxic and molecularly targeted therapy in PDAC. The purpose of this study was to test whether the delivery and efficacy of gemcitabine could be improved by co-administration of AZD1480, a drug inhibits JAK2/STAT3 signaling. Experimental Procedures: Total and activated STAT3 protein expression was determined in human pancreatic tissues (n=106) and human and genetic mouse pancreatic cell lines generated from PanIn, primary PDAC and liver metastasis. IC50 values for AZD1480, a JAK2/STAT3 inhibitor, was determined against nine human PDAC cell lines and sensitive and resistant cell lines to this agent were identified. Cell lines MiaPACA2, PANC1, CEPAC, Capan1, BxPC3, HPAC and SW1990 were assayed for cell proliferation and apoptosis. The in vitro and in vivo effects of AZD1480 on multiple signaling pathways, downstream effectors and tumorigenicity in PDAC were investigated. Knockdown and over expressed STAT3 cells were developed and assayed for tumorigenicity and multiple downstream effectors with or without gemcitabine. In vivo effects of AZD1480, gemcitabine or the combination was determined on xenografts of BxPC3 and PANC1 cells. In vivo expression of pSTAT3, cleaved caspase3 and Ki67 were studied by immunohistochemistry and drug delivery was analyzed by imaging MALDI-mass-spectometry. Results: STAT3 activation is necessary for the malignant phenotype and affects survival in PDAC. The combination of AZD1480 and gemcitabine resulted in cooperative inhibition of cell migration and invasion of both sensitive and resistant PDAC cells at concentrations that were ineffective as individual agents. Treatment with AZD1480 resulted in inhibition of VEGF and stromal markers SPARC and fibronectin. The combined treatment of AZD1480 and gemcitabine enhanced inhibition of growth of resistant tumor xenografts in vivo. Furthermore, combined treatment of AZD1480 and gemcitabine increased drug delivery to the resistant pancreas tumor tissues in vivo. Conclusions: These results provide evidence that targeted JAK2/STAT3 inhibition with AZD1480, in addition to cytotoxic gemcitabine chemotherapy, inhibits the tumor stroma and enhances in vivo drug delivery to the tumor resulting in improved therapeutic response of PDAC. Citation Format: Nagaraj Nagathihalli, Yugandhar Beesetty, Michelle Reyzer, Chanjuan Shi, Richard Caprioli, Nipun Merchant. JAK2 inhibition blocks STAT3 signaling and enhances drug delivery and therapeutic response in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr B32.