Abstract
Glioblastoma multiforme (GBM) is one of the most aggressive human tumors with poor survival rates. The current standard treatment includes chemotherapy with temozolomide (TMZ), but acquisition of resistance is a persistent clinical problem limiting the successful treatment of GBM. The purpose of our study was to investigate therapeutic effects of nitroxoline (NTX) against TMZ-resistant GBM in vitro and in vivo in TMZ-resistant GBM-bearing mouse model, which was correlated with diffusion-weighted imaging (DWI). For in vitro study, we used TMZ-resistant GBM cell lines and evaluated therapeutic effects of NTX by clonogenic and migration assays. Quantitative RT-PCR was used to investigate the expression level of TMZ-resistant genes after NTX treatment. For in vivo study, we performed 9.4 T MR imaging to obtain T2WI for tumor volume measurement and DWI for assessment of apparent diffusion coefficient (ADC) changes by NTX in TMZ-resistant GBM mice (n = 8). Moreover, we performed regression analysis for the relationship between ADC and histological findings, which reflects the changes in cellularity and apurinic/apyrimidinic endonuclease-1 (APE-1) expression. We observed the recovery of TMZ-induced morphological changes, a reduced number of colonies and a decreased rate of migration capacity in TMZ-resistant cells after NTX treatment. The expression of APE-1 was significantly decreased in TMZ-resistant cells after NTX treatment compared with those without treatment. In an in vivo study, NTX reduced tumor growth in TMZ-resistant GBM mice (P = 0.0122). Moreover, ADC was increased in the NTX-treated TMZ-resistant GBM mice compared to the control group (P = 0.0079), which was prior to a tumor volume decrease. The cellularity and APE-1 expression by histology were negatively correlated with the ADC value, which in turn resulted in longer survival in NTX group. The decreased expression of APE-1 by NTX leads to therapeutic effects and is inversely correlated with ADC in TMZ-resistant GBM. Therefore, NTX is suggested as potential therapeutic candidate against TMZ-resistant GBM.
Highlights
Our study demonstrates that NTX can act as an anticancer compound against TMZ-resistant Glioblastoma multiforme (GBM) through the in vitro and in vivo studies
NTX could reduce the expression of apyrimidinic endonuclease-1 (APE-1), an essential protein for DNA base excision repair and redox regulation, in TMZ-resistant GBM cells
We observed an increase in the apparent diffusion coefficient (ADC) value before a significant tumor volume change soon after NTX treatment in the TMZ-resistant GBM mouse model, which indicates a prior decrease in GBM cellularity before the shrinkage of tumor burden, as well as a long-term survival gain of NTX treatment in the TMZ-resistant GBM mouse model
Summary
One study showed that the DNA base excision repair enzyme, APNG confers resistance to TMZ and the downregulation of APNG using siRNA increased the TMZ sensitivity in several established as well as primary GBM cell lines. Sugahara et al reported that the ADC is negatively correlated with the tumor cellularity, with a high cell density and extracellular tortuosity resulting in an increased restriction of the diffusion of water molecules[15]. Considering all these findings, our purpose was to investigate the therapeutic effects of NTX against TMZ-resistant GBM in vitro and in vivo in a TMZ-resistant GBM bearing mouse model, which was correlated with DWI
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