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Targeting Heat Shock Protein 90 in Pancreatic Cancer Impairs Insulin-like Growth Factor-I Receptor Signaling, Disrupts an Interleukin-6/Signal-Transducer and Activator of Transcription 3/Hypoxia-Inducible Factor-1 Autocrine Loop, and Reduces Orthotopic Tumor Growth

Authors' Affiliations: ¹ Departments of Surgery and Surgical Oncology, and ² Institute of Pathology, University of Regensburg Medical Center, Regensburg, Germany

Requests for reprints: Oliver Stoeltzing, Departments of Surgery and Surgical Oncology, University of Regensburg Medical Center, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany. Phone: 49-941-944-6801; Fax: 49-941-944-6802; E-mail: oliver.stoeltzing{at}klinik.uni-regensburg.de.

Purpose: Inhibitors of heat-shock protein 90 (Hsp90) may interfere with oncogenic signaling pathways, including Erk, Akt, and hypoxia-inducible factor-1 (HIF-1). Because insulin-like growth factor-I receptor (IGF-IR) and signal transducer and activator of transcription 3 (STAT3) signaling pathways are implicated in the progression of pancreatic cancer, we hypothesized that blocking Hsp90 with geldanamycin derivates [17-allylamino-geldanamycin (17-AAG), 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG)] would impair IGF-I– and interleukin-6–mediated signaling and thus reduce pancreatic tumor growth and angiogenesis in vivo.

Experimental Design: Human pancreatic cancer cells (HPAF-II, L3.6pl) were used for experiments. Changes in signaling pathway activation upon Hsp90 blockade were investigated by Western blotting. Effects of Hsp90 inhibition (17-AAG) on vascular endothelial growth factor were determined by ELISA and real-time PCR. Effects of 17-DMAG (25 mg/kg; thrice a week; i.p.) on tumor growth and vascularization were investigated in a s.c. xenograft model and in an orthotopic model of pancreatic cancer.

Results: 17-AAG inhibited IGF-IR signaling by down-regulating IGF-IRß and directly impairing IGF-IR phosphorylation. Hypoxia- and IL-6–mediated activation of HIF-1 or STAT3/STAT5 were substantially inhibited by 17-AAG. Moreover, a novel IL-6/STAT3/HIF-1 autocrine loop was effectively disrupted by Hsp90 blockade. In vivo, 17-DMAG significantly reduced s.c. tumor growth and diminished STAT3 phosphorylation and IGF-IRß expression in tumor tissues. In an orthotopic model, pancreatic tumor growth and vascularization were both significantly reduced upon Hsp90 inhibition, as reflected by final tumor weights and CD31 staining, respectively.

Conclusions: Blocking Hsp90 disrupts IGF-I and IL-6–induced proangiogenic signaling cascades by targeting IGF-IR and STAT3 in pancreatic cancer, leading to significant growth-inhibitory effects. Therefore, we suggest that Hsp90 inhibitors could prove to be valuable in the treatment of pancreatic cancer.