The Regenerating Spinal Cord of Gecko Maintains Unaltered Expression of β-Catenin Following Tail Amputation

Synergistic Effects of Resveratrol and Temozolomide Against Glioblastoma Cells: Underlying Mechanism and Therapeutic Implications

Purpose

Temozolomide (TMZ) is a commonly used anti-glioblastoma (GBM) drug. However, glioblastoma cells frequently show primary and acquired resistance to TMZ. As a promising anti-GBM candidate, resveratrol (Res) faces the similar problem as TMZ. Although resveratrol combined with TMZ (Res/TMZ) has been reported to be used to treat GBMs, it remains unclear whether this combination is broad-spectrum for all glioma cells until now, especially for GBM cells/cases with dual drug resistance. The study aimed to evaluate the synergistic effects of resveratrol and TMZ against GBMs and identify the underlying mechanisms.

Materials and Methods

Drug sensitivities of rat RG-2, human LN-18 and LN-428 cell lines and effectiveness of Res/TMZ combinations were investigated via multiple experimental methods. O⁶-methylguanine-DNA methyltransferase (MGMT) was observed by Western blotting and immunocytochemistry (ICC). Transducer and activator of transcription 3 (STAT3) signaling pathway and expression changes of STAT3-related gene were detected to explore the possible synergistic mechanism.

Results

One hundred micromolar resveratrol and 500 μM TMZ inhibited the growth of RG-2 cells and the low-dose combination (25 μM/250 μM) showed similar suppressive effects. LN-18 and, especially, LN-428 cells were neither sensitive to 100 μM resveratrol nor to 500 μM TMZ, while their growth was suppressed by combination of 75 μM Res/750 μM TMZ with the suppressive rates of 62.5% and 28.6% and apoptosis rates of 11.9% and 7.4%, respectively. Resveratrol had regulatory effect on the expression of MGMT and it could significantly down-regulate MGMT overexpression caused by TMZ. In addition, STAT3/Bcl-2/survivin signaling pathway was also remarkably inhibited in Res/TMZ-treated GBM cells.

Conclusion

Our results demonstrated synergistic effects of Res/TMZ on RG-2 cells and their bilaterally sensitizing effects to LN-18 and LN-428 cells. Frequent upregulation of MGMT and activation of STAT3 are the unfavorable factors for the treatment of GBMs and they may be the potential targets of Res/TMZ therapy.

Resveratrol restores sensitivity of glioma cells to temozolamide through inhibiting the activation of Wnt signaling pathway

Malignant gliomas are aggressive primary neoplasms that originate in the glial cells of the brain or the spine with notable resistance to standard treatment options. We carried out the study with the aim to shed light on the sensitization of resveratrol to temozolomide (TMZ) against glioma through the Wnt signaling pathway. Initially, glioma cell lines with strong resistance to TMZ were selected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Then, the glioma cells were subjected to resveratrol, TMZ, Wnt signaling pathway inhibitors, and activators. Cell survival rate and inhibitory concentration at half maximum value were detected by MTT, apoptosis by flow cytometry, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining, in vitro proliferation by hanging drop method and β-catenin translocation into nuclei by TOP/FOP-FLASH assay. The expressions of the Wnt signaling pathway-related and apoptosis-related factors were determined by western blot analysis. Nude mice with glioma xenograft were established to detect tumorigenic ability. Glioma cell lines T98G and U138 which were highly resistant to TMZ were selected for subsequent experiments. Resveratrol increased the efficacy of TMZ by restraining cell proliferation, tumor growth, and promoting cell apoptosis in glioma cells. Resveratrol inhibited Wnt2 and β-catenin expressions yet elevated GSK-3β expression. Moreover, the Wnt signaling pathway participates in the sensitivity enhancing of resveratrol to TMZ via regulating O ⁶ -methylguanine-DNA methyltransferase (MGMT) expression. Resveratrol sensitized TMZ-induced glioma cell apoptosis by repressing the activation of the Wnt signaling pathway and downregulating MGMT expression, which may confer new thoughts to the chemotherapy of glioma.

Neurotrophic factor-α1 modulates NGF-induced neurite outgrowth through interaction with Wnt-3a and Wnt-5a in PC12 cells and cortical neurons

Wnt-3a and Wnt-5a signaling activities inhibit and promote neurite outgrowth, respectively, to regulate dendritic and axonal genesis during neurodevelopment. NF-α1, a neurotrophic factor, has been shown to modulate dendritic remodeling and negatively regulate the canonical Wnt-3a pathway. Here, we investigated whether NF-α1 could modify nerve growth factor (NGF)-induced neurite outgrowth through interaction with Wnt-3a and Wnt-5a in PC12 cells and mouse primary cortical neurons. We showed that NGF-induced neurite outgrowth was inhibited by Wnt-3a, and this inhibition was prevented by NF-α1. Western blot analysis revealed that NF-α1 reduced the expression of both β-catenin in the canonical Wnt-3a pathway and Rho, a downstream effector of Wnt-3a's non-canonical signaling pathway. Treatment of PC12 cells with a ROCK inhibitor prevented the inhibition of NGF-induced neurite outgrowth by Wnt-3a, suggesting that NF-α1 promotes neurite outgrowth in the presence of Wnt-3a by down-regulating its canonical and non-canonical activities. Interestingly, treatment of PC12 cells with Wnt-5a, which formed a complex with NF-α1, induced neurite outgrowth that was enhanced by treatment with the combination of Wnt-5a, NGF, and NF-α1. These effects of NF-α1 on Wnt 3a's and Wnt 5a's regulation of neurite outgrowth in PC12 cells were also demonstrated in primary cultures of mouse cortical neurons. In addition, we showed in PC12 cells that NF-α1 acts by upregulating adenomatous polyposis coli (APC) accumulation at neurite tips, thereby providing positive and negative Wnt-3a/Wnt-5a mediated cues to modulate neurite outgrowth, a process important during neurodevelopment.