Inhibition of HSP90 by AUY922 Preferentially Kills Mutant KRAS Colon Cancer Cells by Activating Bim through ER Stress

Abstract

Oncogenic mutations of KRAS pose a great challenge in the treatment of colorectal cancer. Here we report that mutant KRAS colon cancer cells are nevertheless more susceptible to apoptosis induced by the HSP90 inhibitor AUY922 than those carrying wild-type KRAS. Although AUY922 inhibited HSP90 activity with comparable potency in colon cancer cells irrespective of their KRAS mutational statuses, those with mutant KRAS were markedly more sensitive to AUY922-induced apoptosis. This was associated with upregulation of the BH3-only proteins Bim, Bik, and PUMA. However, only Bim appeared essential, in that knockdown of Bim abolished, whereas knockdown of Bik or PUMA only moderately attenuated apoptosis induced by AUY922. Mechanistic investigations revealed that endoplasmic reticulum (ER) stress was responsible for AUY922-induced upregulation of Bim, which was inhibited by a chemical chaperone or overexpression of GRP78. Conversely, siRNA knockdown of GRP78 or XBP-1 enhanced AUY922-induced apoptosis. Remarkably, AUY922 inhibited the growth of mutant KRAS colon cancer xenografts through activation of Bim that was similarly associated with ER stress. Taken together, these results suggest that AUY922 is a promising drug in the treatment of mutant KRAS colon cancers, and the agents that enhance the apoptosis-inducing potential of Bim may be useful to improve the therapeutic efficacy.

Reactivation of ERK and Akt confers resistance of mutant BRAF colon cancer cells to the HSP90 inhibitor AUY922

“…We have previously shown that the HSP90 inhibitor AUY922 kills colon cancer cells through apoptosis and that wild-type KRAS colon cancer cells are more resistant to apoptosis induced by AUY922 compared with those carrying active mutations in KRAS [29]. In subsequent studies, we found that among wild-type KRAS colon cancer cells, those harbouring active mutations in BRAF were even more resistant to AUY922-induced apoptosis than cells with wild-type BRAF (Figure 1A and 1B).…”

“…However, to our surprise, treatment with AUY922 only moderately reduced the expression of mutant BRAF while it abolished the expression of other HSP90 client proteins such as CRAF and SKP2 in mutant BRAF colon cancer cells [29]. This suggests that mutant BRAF is less dependent on HSP90 for its stabilization than other HSP90 client proteins in colon cancer cells.…”

“…Cell viability was quantitated using the CellTiter-Glo Luminescent Cell Viability Assay Kit (Promega, San Luis Obispo, CA) as described previously [29]. Luminescence was recorded by Synergy 2 multi-detection microplate reader (BioTek, VT).…”

“…We have previously shown that the HSP90 inhibitor AUY922 preferentially induces apoptosis in colon cancer cells carrying mutant KRAS [29]. In this study, we have examined the impact of mutations in BRAF on the response of colon cancer cells to AUY922.…”

Therapeutic potency of heat-shock protein-90 pharmacological inhibitors in the treatment of gastrointestinal cancer, current status and perspectives

“…Further studies showed that KRAS mutant colon cancer cells are more susceptible to apoptosis induced by AUY922 compared with wild-type, supporting the role of KRAS signalling in pro-apoptotic signalling functions of the HSP90 inhibitor in colon cancer cells. [25] Consistent with the pro-apoptotic effect of HSP-90 pharmacological inhibitors on colorectal cancer, Lu et al showed that LD053, an HSP90 inhibitor, upon binding to the N-terminus of HSP90, enhances dissociation of cdc37 from HSP90, leading to inhibition of pro-survival signalling pathways including c-Raf/Mek/Erk as well as PI3K/Akt in gastric cancer cells. Consistent with cellular studies, administration of LD053 inhibits growth of gastric cancer cell xenografts in nude mice.…”