Abstract 1657: HSP90 inhibition down regulates EGFR and its effector signaling proteins in pancreatic cancer cell lines

Abstract

Abstract Rationale: Currently approved therapies, including EGFR inhibitors, have minimal effect on survival in pancreatic cancer (PC). HSP90 is a molecular chaperone that specifically enables activity of numerous protein kinases, including EGFR and other signaling proteins. We have reported that simultaneous inhibition of EGFR and HSP90 may be additive in inhibiting cell viability in PC cell lines. Here we report possible molecular mechanisms underlying HSP90 and EGFR inhibition. Methods: MiaPaCa-2 and PANC-1 were treated with EGFR inhibitor, compound 56 (CMP56) (5 − 35 μmol), and HSP90 inhibitor geldanamycin (250 nmol − 1μmol). Growth inhibition was evaluated using the MTT assay, and apoptosis was evaluated by caspase-3 and PARP cleavage. The effect on relevant cell signaling proteins was assessed by immunoblotting with specific antibodies directed against EGFR and effectors such as AKT, STAT-3 and JNK. Results: Growth inhibition was significantly (p < 0.05) higher in both MiaPaCa-2 and PANC1 cells treated with CMP56 and geldanamycin than in cells treated with either agent at various concentrations. The molecular effects are shown in table 1. There was a decrease in phosphorylation of EGFR in bothe cell lines after treatment with CMP56. Concomitant inhibition of EGFR and HSP90 was associated with decreased phosphorylation of ERK, JNK and AKT and with an increase in caspase-3, PARP cleavage in MiaPaCa-2 cells, but not in PANC-1 cells. Conclusions: These results suggest that HSP90 inhibition in MiaPaCa-2 cells induces down regulation of EGFR, STAT-3 and AKT, but not in PANC-1 cells. Higher concentrations of geldanamycin may be required in PANC-1cells. Combined inhibition of EGFR and HSP90 induced apoptosis additively. We are studying further to understand the other potential molecular pathways involved in this strategy.Table.Molecular effects of EGFR and HSP90 inhibition in PC Cell lines ↘ - Decrease, - No change, GEL - Geldanamycin (500 nmol), CMP-56 - Compound 56 (10 μmol)Protein of interest MiaPaCa-2 PANC-1 GELCMP56GEL + CMP56 GELCMP56GEL + CMP56EGFR↘-↘↘ --↘AKT↘-↘↘ --↘STAT-3↘-↘↘ --↘ Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1657.