Novel Repositioning Therapy for Drug-Resistant Glioblastoma: In Vivo Validation Study of Clindamycin Treatment Targeting the mTOR Pathway and Combination Therapy with Temozolomide.

Takeyoshi Eda,Jun Watanabe,Makoto Oishi,Manabu Natsumeda,Nobuyuki Takei,Hiroshi Aoki,Masayasu Okada,Yu Kanemaru,Jotaro On,Yoshihiro Tsukamoto,Yukihiko Fujii,Ryosuke Ogura

doi:10.3390/cancers14030770

Takeyoshi Eda, Jun Watanabe + Show 10 more

Open Access

https://doi.org/10.3390/cancers14030770

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Abstract

Simple SummaryGiven the significant costs and lengthy timelines of drug development and clinical trials, drug repositioning is a promising alternative to find effective treatments for brain tumors quickly and inexpensively. In the present study, using a simple drug screen of macrolides, we found that clindamycin (CLD) had cytotoxic effects on glioblastoma (GBM) cells. Further studies showed the inhibition of the mammalian target of rapamycin (mTOR) pathway as the key mechanism of action. Interestingly, we found that co-treatment with temozolomide (TMZ), the alkylating agent considered as standard therapy in GBM, enhanced these effects and proposed the inhibition of O6-methylguanine-DNA methyltransferase (MGMT) protein by CLD as a potential mechanism for this combination effect.Multimodal therapy including surgery, radiation treatment, and temozolomide (TMZ) is performed on glioblastoma (GBM). However, the prognosis is still poor and there is an urgent need to develop effective treatments to improve survival. Molecular biological analysis was conducted to examine the signal activation patterns in GBM specimens and remains an open problem. Advanced macrolides, such as azithromycin, reduce the phosphorylation of p70 ribosomal protein S6 kinase (p70S6K), a downstream mammalian target of rapamycin (mTOR) effector, and suppress the proliferation of T-cells. We focused on its unique profile and screened for the antitumor activity of approved macrolide antibiotics. Clindamycin (CLD) reduced the viability of GBM cells in vitro. We assessed the effects of the candidate macrolide on the mTOR pathway through Western blotting. CLD attenuated p70S6K phosphorylation in a dose-dependent manner. These effects on GBM cells were enhanced by co-treatment with TMZ. Furthermore, CLD inhibited the expression of the O6-methylguanine-DNA methyltransferase (MGMT) protein in cultured cells. In the mouse xenograft model, CLD and TMZ co-administration significantly suppressed the tumor growth and markedly decreased the number of Ki-67 (clone MIB-1)-positive cells within the tumor. These results suggest that CLD suppressed GBM cell growth by inhibiting mTOR signaling. Moreover, CLD and TMZ showed promising synergistic antitumor activity.

Highlights

Glioblastoma (GBM) accounts for the majority of primary brain tumors and is considered as a grade IV glioma based on the WHO classification system [1]
We investigated the effects of approved macrolides on cell growth using human GBM cell lines
We investi5-of 15 gated the effects of approved macrolides on cell growth using human GBM cell lines

Summary

Introduction

Glioblastoma (GBM) accounts for the majority of primary brain tumors and is considered as a grade IV glioma based on the WHO classification system [1]. Despite the development of multimodal therapy with surgical resection, radiation, and temozolomide (TMZ)-based chemotherapy, GBM prognosis remains poor. EGFR amplification, PTEN mutations, CDKN2A deficiency, and TP53 gene mutations were investigated to establish the association between genetic alterations and GBM prognosis [8]. Comprehensive genomic analysis revealed aberrant signal transduction through various pathways, including the receptor tyrosine kinase (RTK)–Rasphosphoinositide 3-kinase (PI3K) pathway, Rb pathway, and p53 pathway [9,10]. These studies suggest that genetic alterations or RTK–Ras–PI3K, Rb, and p53 pathways act cooperatively and contribute to the proliferation and maintenance of GBM cells [11]. Further studies are required to better understand the GBM etiology and to develop novel molecular targeted strategies

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