Abstract 513: Stromal desmoplasia is induced by a hypoxia and HIF-1α mediated increase in sonic hedgehog formation in pancreatic cancer

Abstract

Abstract Pancreatic tumors are notoriously hypoxic and characterized by a dense fibro-inflammatory stromal reaction (desmoplasia). Hedgehog (Hh) signaling is a major contributor to tumor desmoplasia in pancreatic and other cancers, resulting in decreased tumor blood flow, decreased drug delivery and resistance to therapy. We hypothesized that the hypoxia inducible factor-1α (HIF-1α) transcription factor, a major component of the cell's response to hypoxia is an important mediator of the mechanism inducing desmoplasia in pancreatic cancer. We observed that a hypoxic environment (1% O2 for 24 hr) increased the expression of sonic Hh (SHH) mRNA and secreted SHH protein, in both MiaPaCa-2 and Panc-1 pancreatic cancer cells, and that this was blocked by siRNA targeting HIF-1α. NIH-3T3 fibroblasts transfected with a GLi1-firefly luciferase reporter exposed to conditioned media from hypoxic MiaPaCa-2 and Panc-1, or co-cultures of the Panc-1 and the fibroblasts showed an increase in GLi activity. siRNA to sHH transfected into Panc-1 tumor cells blocked the fibroblast GLi1 response. NIH-3T3 fibroblasts alone did not show an increase in Hh components or Hh signaling upon exposure to hypoxia. MiaPaCa-2 cells transfected with a GLi1-firefly luciferase reporter showed no increase in GLi1 activity upon exposure to hypoxia suggesting there is no autocrine stimulation of the cancer cells by the SHH they secrete. Fibroblasts co-cultured with the pancreatic cancer cells showed increased expression of two markers of desmoplasia, collagen-1 and fibronectin under hypoxic conditions that was blocked by siRNA to HIF-1α. Thus, increased pancreatic cancer cell SHH formation in response to hypoxia and mediated by HIF-1α, stimulates Hh signaling which increases fibroblast GLi1 transcriptional activity without activating Hh signaling in the cancer cell itself. We also compared levels of nuclear HIF-1α and SHH by immunohistochemistry in patient pancreatic cancer samples and found a significant correlation between tumor HIF-1α and stromal SHH (p< 0.01). Furthermore, both tumor HIF-1α and stromal SHH correlated with decreased patient survival. The findings suggest that tumor hypoxia and increased HIF-1α in pancreatic cancer which is likely a consequence of the desmoplasia, is also a cause of the desmoplasia. Breaking the cycle of hypoxia, HIF-1α, and desmoplasia, could offer a new therapy for pancreatic cancer. Supported by CA109552-05 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 513. doi:10.1158/1538-7445.AM2011-513