Potent effect of the MDM2 inhibitor AMG232 on suppression of glioblastoma stem cells

Abstract

Testing new ways to identify untapped opportunities for glioblastoma therapies remains highly significant. Amplification and overexpression of MDM2 gene is frequent in glioblastoma and disrupting the MDM2−p53 interaction is a promising strategy to treat the cancer. RG7112 is the first-in class inhibitor and recently discovered AMG232 is the most potent MDM2 inhibitor known to date. Here, we compared the effects of these two clinical MDM2 inhibitors in six glioblastoma cell lines and ten patient-derived glioblastoma stem cells. Targeted sequencing of the TP53, MDM2 genes and whole transcriptome analysis were conducted to verify genetic status associated with sensitivity and resistance to the drugs. Although TP53 wild-type glioblastoma cell lines are similarly sensitive to AMG232 and RG7112, we found that four TP53 wild-type out of ten patient-derived glioblastoma cells are much more sensitive to AMG232 than RG7112 (average IC50 of 76 nM vs. 720 nM). Among these, 464T stem cells containing MDM2 gene amplification were most sensitive to AMG232 with IC50 of 5.3 nM. Moreover, AMG232 exhibited higher selectivity against p53 wild-type cells over p53 mutant stem cells compared to RG7112 (average selectivity of 512-fold vs. 16.5-fold). Importantly, we also found that AMG232 is highly efficacious in three-dimensional (3D) tumor spheroids growth and effectively inhibits the stemness-related factors, Nestin and ZEB1. Our data provide new evidence that glioblastoma stem cells have high susceptibility to AMG232 suggesting the potential clinical implications of MDM2 inhibition for glioblastoma treatment. These will facilitate additional preclinical and clinical studies evaluating MDM2 inhibitors in glioblastoma and direct further efforts towards developing better MDM2-targeted therapeutics.

ZEB1: A Critical Regulator of Cell Plasticity, DNA Damage Response, and Therapy Resistance

“…Thus, an intact p53-ZEB1 feedback loop represents an important regulatory mechanism for epithelial phenotype maintenance, suppression of metastasis, and protection against enhanced chemoresistance. Importantly, two independent studies with MDM2 inhibitors, which both reactivated p53 and downregulated ZEB1, also documented decreased stemness features and glioblastoma aggressiveness (Giacomelli et al, 2017;Her et al, 2018). Such effects of p53 reactivation on ZEB1 may be mediated via activation of microRNAs that p53 can activate such as miR-34, miR-145, and miR-200 (Chang et al, 2011;Siemens et al, 2011;Ren D. et al, 2013).…”

The p53 Pathway in Glioblastoma

“…AMG232 effects were tested in the therapy resistant and putative tumor initiating GBM stem cells. AMG232 exhibited relative selectivity to wt-p53 stem cells was very efficacious in inhibiting three-dimensional tumor spheroids growth and stemness-related factors [ 116 ]. Another study found that nutlin3a-mediated inhibition of MDM2/p53 interaction and led to an impairment in DNA repair that correlated with potentiation of temozolomide-mediated cell death both in vitro and in vivo in GBM [ 45 ].…”

Targeting the Ubiquitin System in Glioblastoma

“…However, they suffer from the caveat that canonical ubiquitination of p53 mutants is MDM2independent (355). An interesting example is AMG-232 (KRT-232) which averaged IC 50 s in the low nanomolar range in GBM cell lines and patient-derived GBM stem cells (356). More importantly, AMG-232's suppressive effects seemed to extend selectively to GBM stem cells as the compound displayed efficacious inhibition of stemness-related factors Nestin and ZEB1 in a spheroid culture model.…”