HSP90 Inhibition Overcomes Resistance to Molecular Targeted Therapy in BRAFV600E-mutant High-grade Glioma

Abstract

Purpose: Molecular targeted therapy using BRAF and/or MEK inhibitors has been applied to BRAFV600E mutant high-grade gliomas (HGGs); however, the therapeutic effect is limited by the emergence of drug resistance. Experimental Design: We established multiple paired BRAFV600E mutant HGG patient-derived xenograft (PDX) models based on tissues collected prior to and at relapse after molecular targeted therapy. Using these models, we dissected treatment resistant mechanisms for molecular targeted therapy and explored therapeutic targets to overcome resistance in BRAFV600E HGG models in vitro and in vivo. Results: We found that, despite causing no major genetic and epigenetic changes, BRAF and/or MEK inhibitor treatment deregulated multiple negative feedback mechanisms, which led to the re-activation of the MAPK pathway through c-Raf and AKT signaling. This altered oncogenic signaling primarily mediated resistance to molecular targeted therapy in BRAFV600E mutant HGG. To overcome this resistance mechanism, we performed a high-throughput drug screening to identify therapeutic agents that potently induce additive cytotoxicity with BRAF and MEK inhibitors. We discovered that HSP90 inhibition combined with BRAF/MEK inhibition coordinately deactivated the MAPK and AKT/mTOR pathways, and subsequently induced apoptosis via dephosphorylation of GSK3β (Ser9) and inhibition of Bcl-2 family proteins. This mediated potent cytotoxicity in vitro and in vivo in refractory models with acquired resistance to molecular-targeted therapy. Conclusions: The combination of an HSP90 inhibitor with BRAF or MEK inhibitors can overcome the limitations of the current therapeutic strategies for BRAFV600E mutant HGG.

Resistance mechanisms in BRAFV600E paediatric high-grade glioma and current therapeutic approaches

“…Baseline upregulation of several RTKs, RAS, p-CRAF and p-p90rsk were also seen in three BRAF V600E HGG tumours (including one paediatric and one adolescent sample) collected following relapse after BRAF inhibitor treatment (40). Interestingly, in contrast to Schreck et al (13), no known mutations of RAS, MAPK or PI3K/AKT were identified in the resistant tumour samples and no novel driver mutations were able to be identifi ed (40). Additionally, DNA methylation status was also largely unaffected in these patients following BRAF inhibition treatment, overall indicating that nongenomic and nonepigenomic events may also be involved in driving resistance mechanisms (40).…”

“…Single-nucleotide variants conferring functional alterations in ERRFI1 S251* and TET2 V1199E were observed in each of the respective resistant cell lines, suggestive of possible mechanisms of BRAF inhibitor resistance in vitro ( 13 ). Baseline upregulation of several RTKs, RAS, p-CRAF and p-p90rsk were also seen in three BRAF V600E HGG tumours (including one paediatric and one adolescent sample) collected following relapse after BRAF inhibitor treatment ( 40 ). Interestingly, in contrast to Schreck et al.…”

“…These identified mutations in genes that modulate RTK activity, such as CBL , alterations in RAS/RAF signalling through NF1 missense mutations, secondary point mutations of BRAF , activating mutations of MAP2K1 and mutations in PTEN . Alterations in the PI3K/AKT/mTOR pathway have also been identified as a mechanism of resistance in pHGG, with mutations in PIK3C2G and upregulation of p-AKT identified ( 13 , 40 ). Furthermore, mutations in BAP and ANKHD1 in post-BRAF inhibitor treated tissues have also implicated cell cycle drivers as contributors towards BRAF inhibitor resistance ( 13 ).…”

Targeting Heat-Shock Protein 90 in Cancer: An Update on Combination Therapy

“…HSP90 inhibitors can deactivate the MAPK and AKT/mTOR pathways, which are reactivated by BRAF and/or MEK inhibitors. Therefore, HSP90 inhibitors combined with BRAF and/or MEK inhibitors induced apoptosis of HGG cells [ 101 ].…”

HSP90 mediates the connection of multiple programmed cell death in diseases

“…For example, multiple myeloma is a type of cancer with high recurrence and resistance, which is alleviated by blocking the interaction of HSP90 and CDC37 [ 59 ]. Due to the compatibility of unstable kinases with HSP90, inhibitors are beneficial to eliminate resistance after kinase inhibition in the treatment of cancer [ 60 , 61 ]. 17-AAG affects radiosensitivity which is a pivotal point of clinical treatment by increasing the F-box protein 6 mediated polyubiquitination of CD147 [ 59 ].…”