Growth factor and cytokine signaling cascades have been implicated in pancreatic cancer growth and angiogenesis, which in part occurs through activation of transcription factors such as hypoxia-inducible factor-1α (HIF-1α) and signal transducer and activator of transcription-3 (STAT3). Since heat-shock protein 90 (Hsp90) has been identified to be crucial for stability and functionality of signaling intermediates, including the transcription factors HIF-1α and STAT3, we hypothesized that Hsp90 blockade would disrupt growth factor and cytokine induced signaling and consequently reduce tumor growth and angiogenesis in vivo. Human pancreatic cancer cells (L3.6pl, H-PAF-II) were used to test the effects of Hsp90 inhibitors (17-AAG, 17-DMAG) in vitro and in vivo. Effects of Hsp90 blockade on IGF-I and IL-6 induced activation of signaling pathways were investigated by Western blotting. Expression of VEGF in the presence or absence of 17-AAG was assessed by RT-PCR and ELISA. Impact of 17-AAG on tumor cell migration was evaluated in modified Boyden chambers. For in vivo experiments, the water-soluble compound 17-DMAG was used. Effects of Hsp90 inhibition on tumor growth and angiogenesis were investigated in an orthotopic pancreatic cancer model. Mice received 17-DMAG (10 mg/kg/day) and/or oxaliplatin (5 mg/kg/bi-weekly) by intraperitoneal injections. In vitro, 17-AAG inhibited constitutive and growth factor, or cytokine induced, phosphorylation of MAPK/Erk and Akt. In addition, activation of HIF-1α and STAT3 was diminished. Levels of VEGF-A mRNA and protein were significantly reduced by 17-AAG treatment (P<0.05). Furthermore, 17-AAG led to marked inhibition of tumor cell migration in vitro (P<0.05). In vivo, 17-DMAG treatment significantly reduced tumor growth and angiogenesis, as determined by measuring final tumor weights on day 28 and staining of tumor sections for CD31 (P<0.05, for both). However, combination of 17-DMAG with oxaliplatin elicited only a trend towards improved efficacy in terms of growth inhibition, but mice treated with this combination therapy had developed substantially fewer lymph node metastases (0/9) than did mice of the control group (6/10). In conclusion, inhibition of Hsp90 disrupted multiple growth factor and cytokine induced signaling cascades in pancreatic cancer cells and led to significant reduction of tumor growth and angiogenesis in vivo. Thus, inhibitors to Hsp90 may be a valuable addition to antineoplastic therapy regimens for treatment of pancreatic cancer.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA