Heat shock protein 90 promotes
tumor progression and survival and has emerged as a vital therapeutic target. Previously we reported that the combinatorial treatment of
17AAG/sihsp90α significantly downregulated Hsp90α
mRNA and
protein levels in
Glioblastoma Multiforme (GBM). Here we investigated the ability of
cell penetrating peptide (Tat48-60 CPP)-mediated
siRNA-induced hsp90α knockdown as a single agent and in combination with
17-allylamino-17-demethoxygeldanamycin (17-AAG) to induce
tumor growth inhibition in GBM and whether it possessed therapeutic implications. GBM and non-tumorigenic cells exposed to
siRNA and/or
17-AAG were subsequently assessed by qRT-PCR, immunofluorescence, FACS analysis, quantitative Akt, LDH leakage and cell viability assays. PAGE was performed for serum stability assessment. A combination of
siRNA/17-AAG treatment significantly induced Hsp90α gene and
protein knockdown by 95% and 98%, respectively, concomitant to 84% Akt
kinase activity attenuation, induced cell cycle arrest and
tumor-specific cytotoxicity by 88%. Efficient complex formation between
CPP and
siRNA exhibited improved serum stability of the
siRNA with minimal intrinsic toxicity in vitro. The preliminary in vivo results showed that combination
therapy induced hsp90α knockdown and attenuated Akt
kinase activity in intracranial
glioblastoma mouse models. The results imply that RNAi-mediated hsp90α knockdown increases
17-AAG treatment efficacy in GBM. In addition, the cytotoxic response observed was the consequence of downregulation of hsp90α gene expression, reduced Akt
kinase activity and S-G2/M cell cycle arrest. These results are novel and highlight the ability of Tat to efficiently deliver
siRNA in GBM and suggest that the dual inhibition of Hsp90 has therapeutic potentials.