Inhibition of neuroblastoma xenograft growth by Hsp90 inhibitors

Abstract

Background: Advanced-stage neuroblastomas are often resistant to chemotherapy. Heat shock protein (Hsp) 90 is a molecular chaperone that maintains the stability of important signal transduction proteins. We have previously reported that geldanamycin (GA), an Hsp90 inhibitor, decreases Raf-1 and Akt protein expressions and induces apoptosis in neuroblastoma cells. We sought to determine the in vivo effects of Hsp90 inhibitor compounds on human neuroblastomas.

Materials and methods: Human neuroblastoma (LAN-1 and SK-N-SH) xenografts (4-mm3 tumor implants) were placed in the flanks of athymic nude mice. The mice received either Hsp90 inhibitors (17-AAG or EC5) or vehicle (control). The tumor dimensions were measured twice weekly. Proteins were extracted for Western immunoblotting.

Results: Hsp90 inhibitor compounds significantly blocked both LAN-1 and SK-N-SH neuroblastoma growth in vivo. Drug-treated tumors showed decreases in Raf-1 and cleaved PARP expressions.

Conclusion: Hsp90 inhibitors may prove to be important novel therapeutic agents for patients with advanced-stage neuroblastoma who fail to respond to current treatment regimens.

Figure 1

(A) Tumor volumes in nude mice bearing SK-N-SH human neuroblastoma during treatment with 17-AAG. (*=p<0.05 vs. control). (B) Western immunoblots demonstrate depletion in Raf-1 and Akt expression in 17-AAG treated group. β-actin shows relative equal protein loading. Three representative tumors from each group are shown. (C) Percentage of protein measurement of Raf-1 and Akt are presented. Values were normalized with the expression of β-actin. (*=p<0.05 vs. control).

Figure 2

(A) Treatment with 17-AAG resulted in inhibition of LAN-1 neuroblastoma growth (*=p<0.05 vs. control). (B) Western immunoblots show reduction in Raf-1 and Akt protein levels in 17-AAG treated group. β-actin shows relative equal protein loading.(C) Percentages of Raf-1 and Akt protein measurements as in B (*=p<0.05 vs. control).

Figure 3

(A) Growth inhibition of LAN-1 neuroblastoma xenografts with 17-AAG and EC5 treatment (*=p<0.05 vs. control). (B) Effect of treatment with 17-AAG and EC5 on tumor weight of LAN-1 human neuroblastoma xenografts. (*=p<0.05 vs. control). (C) Western blots show induction in cleaved PARP expression with 17-AAG or EC5 treatment. β-actin shows relative equal protein loading. (D) Percentage of cleaved PARP protein measurements as in C (*=p<0.05 vs. control).