Sequence-Dependent Antiproliferative Effects of Gefitinib and Docetaxel on Non-Small Cell Lung Cancer (NSCLC) Cells and the Possible Mechanism

Purpose

Recent clinical trials showed that the sequential combination of epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) and chemotherapy could prolong the PFS and/or OS of advanced non-small cell lung cancer (NSCLC) patients with EGFR mutation. The aim of present study was to assess the optimal combination sequence and to explore its possible mechanism.

Methods

PC-9 cells and A549 cells, the lung adenocarcinoma cells with mutant and wide-type EGFR respectively, were treated with docetaxel/gefitinib alone or in different combination schedules. The EGFR and K-ras gene status was determined by qPCR-HRM technique. Cell proliferation was detected by MTT assay. The expression and phosphorylation of EGFR, ERK, Akt and IGF-1R were detected by western blot. Cell cycle distribution was observed by flow cytometry.

Results

Only sequential administration of docetaxel followed by gefitinib (D→G) induced significant synergistic effect in both cell lines (Combination Index<0.9). The reverse sequence (G→D) resulted in an antagonistic interaction in both cell lines (CI>1.1), whereas the concurrent administration (D+G) showed additive (0.9<CI<1.1)-synergistic effect in PC-9 cells and antagonistic-additive effect in A549 cells. Mechanism studies showed that docetaxel-induced phosphorylation of EGFR and ERK was repressed by subsequently used gefitinib, but not by concurrent exposure of gefitinib. The gefitinib-repressed phosphorylation of EGFR and ERK was reversed neither by concurrent nor by subsequent administration of docetaxel. D+G reinforced their inhibition on the phosphorylation of IGF-1R in PC-9 cells.

Conclusions

The cytotoxic drugs followed by EGFR-TKIs may be the optimal combination for antiproliferative effects in EGFR-mutant NSCLC cells, and the phosphorylation of EGFR and ERK might contribute to this effect.     

Psoralen reverses docetaxel-induced multidrug resistance in A549/D16 human lung cancer cells lines

Chemotherapy is the recommended treatment for advanced-stage cancers. However, the emergence of multidrug resistance (MDR), the ability of cancer cells to become simultaneously resistant to different drugs, limits the efficacy of chemotherapy. Previous studies have shown that herbal medicine or natural food may be feasible for various cancers as potent chemopreventive drug. This study aims to explore the capablility of reversing the multidrug resistance of docetaxel (DOC)-resistant A549 cells (A549/D16) of psoralen and the underlying mechanisms. In this study, results showed that the cell viability of A549/D16 subline is decreased when treated with psoralen plus DOC, while psoralen has no effect on the cell proliferation on A549 and A549/D16 cells. Furthermore, mRNA and proteins levels of ABCB1 were decreased in the presence of psoralen, while decreased ABCB1 activity was also revealed by flow cytometry. Based on these results, we believe that psoralen may be feasible for reversing the multidrug resistance by inhibiting ABCB1 gene and protein expression. Such inhibition will lead to a decrease in ABCB1 activity and anti-cancer drug efflux, which eventually result in drug resistance reversal and therefore, sensitizing drug-resistant cells to death in combination with chemotherapeutic drugs.     

索拉菲尼联合阿霉素对人肝癌细胞株HepG2的抑制作用

目的：探讨索拉非尼（Sorafenib）和阿霉素（adriamycin）联合用药对肝癌细胞株nepG2的作用及可能的机制。方法：以不同浓度索拉非尼和不同浓度阿霉素分别组成单药组和索拉非尼＋阿霉素联合用药组作用于HepG2细胞,MTT法检测增殖抑制率、流式细胞仪分析细胞周期和凋亡率。结果：索拉非尼、阿霉素单药与联用均能抑制HepG2细胞增殖,呈剂量依赖效应,两药联用有协同效应（P〈0.01）。索拉非尼、阿霉素单药与联用均能诱导HepG2细胞凋亡,并以联合组更为明显,与对照组比较有显著的统计学意义（P〈0.01）。索拉非尼及阿霉素单药作用均可使细胞周期阻滞于G0-G1期,联合用药组G0/Gl期细胞比率低于索拉非尼及阿霉素单药组,S期细胞比率高于单药组;阿霉素能抑制HepG2细胞Survivin mRNA表达诱导细胞的凋亡。结论：索拉非尼与阿霉素联合作用于人肝癌HepG2细胞具有协同作用,其机制可能是通过多途径共同抑制HepG2细胞增殖及诱导细胞凋亡。     

Durvalumab and taxane family combination therapy enhances the antitumoral effects for NSCLC: An in vitro study

Immunotherapy has lately become the most preferred cancer treatment method, and for non-small cell lung cancer (NSCLC) first-line treatment, there are many immunotherapy options. This study aimed to assess the effectiveness and toxicity of paclitaxel (PTX), docetaxel (DTX) chemotherapy, immune checkpoint inhibitor treatment (durvalumab; DVL), and their combination in NSCLC. A-549 cells were treated with DVL in combination with PTX and DTX (a quarter of the IC₅₀) to investigate their anticancer effects on these cells. The MTT assay, wound healing tests, and double-staining with Annexin V/PI were used to assess the cell viability, apoptosis, and migration. The results showed that a combination of 0.35 mg/mL DVL with 6.5 μg/mL PTX and 1.75 μg/mL DTX produced a synergistic effect with CI values of 0.88, 0.37, and 0.81, respectively. Moreover, the PTX + DTX + DVL combination led to a significantly increased apoptotic rate up to 88.70 ± 3.39% in the A549 cell line compared to monotherapy (p < .001). In addition, we found that the combination therapy with these agents increased the expression level of Bax, Cas-3, p53, and Bax/Bcl-2 ratio in all experimental groups. In conclusion, the results suggest that combining anti-PD-L1 antibody therapy with chemotherapy may provide a promising approach to enhance treatment outcomes and be a potentially efficacious strategy for treating NSCLC patients. Further research and clinical investigations are needed to elucidate the underlying molecular mechanisms and validate the therapeutic potential of these compounds in vivo.     

Lentinan exerts synergistic apoptotic effects with paclitaxel in A549 cells via activating ROS‐TXNIP‐NLRP3 inflammasome

Paclitaxel is generally used to treat cancers in clinic as an inhibitor of cell division. However, the acquired resistance in tumours limits its clinical efficacy. Therefore, the aim of this study was to detect whether co‐treatment with lentinan enhanced the anti‐cancer effects of paclitaxel in A549 cells. We found that the combination of paclitaxel and lentinan resulted in a significantly stronger inhibition on A549 cell proliferation than paclitaxel treatment alone. Co‐treatment with paclitaxel and lentinan enhanced cell apoptosis rate by inducing caspase‐3 activation. Furthermore, co‐treatment with paclitaxel and lentinan significantly triggered reactive oxygen species (ROS) production, and increased thioredoxin‐interacting protein (TXNIP) expression. Moreover, co‐treatment with paclitaxel and lentinan enhanced TXNIP‐NLRP3 interaction, and activated NLRP3 inflammasome whereat interleukin‐1β levels were increased and cell apoptosis was induced. In addition, combination of paclitaxel and lentinan could activate apoptosis signal regulating kinase‐1 (ASK1)/p38 mitogen‐activated protein kinase (MAPK) signal which also contributed to cell apoptosis. Taken together, co‐treatment with paclitaxel and lentinan exerts synergistic apoptotic effects in A549 cells through inducing ROS production, and activating NLRP3 inflammasome and ASK1/p38 MAPK signal pathway.     

Docetaxel/zoledronic acid combination triggers apoptosis synergistically through downregulating antiapoptotic Bcl-2 protein level in hormone-refractory prostate cancer cells

Docetaxel, a semi-synthetic taxane analogue, is used effectively in the treatment of metastatic prostate cancer. Zoledronic acid, the most potent member of bisphosphonates, has shown pleiotropic anti-tumoral effects on prostate cancer cells. We have explored the possible additive/synergistic effects and the apoptotic pathways induced by combination treatment of docetaxel and zoledronic acid in hormone and drug refractory, PC-3 and DU-145 prostate cancer cells. Combination of docetaxel and zoledronic acid synergistically inhibits cell growth in PC-3 and DU-145 cells. Moreover, this effect was due to downregulation of antiapoptotic protein Bcl-2 in PC-3 and DU-145 cells. In conclusion, docetaxel/zoledronic acid combination is potentially a novel and effective approach for the treatment of prostate cancer.     

Dihydroartemisinin Sensitizes Human Lung Adenocarcinoma A549 Cells to Arsenic Trioxide via Apoptosis

Recent studies have shown that arsenic trioxide (ATO) is an effective anti-cancer drug for treatment of acute promyelocytic leukemia and other types of human cancer. However, we have found that lung cancer cells constantly develop a high level of resistance to ATO. In this study, we have explored a possibility of combination of dihydroartemisinin (DHA) and ATO treatments to reduce ATO resistance of lung cancer cells. We determined the combinatory effects of DHA and ATO on cytotoxicity of human lung adenocarcinoma (A549) cells. We showed that co-exposure to DHA and ATO of A549 cells synergistically increased the cytotoxicity and apoptotic cell death in the cells. We found that the synergistic effect of DHA and ATO in promoting apoptosis mainly resulted from increased cellular level of reactive oxygen species (ROS) and DNA damage. ATO alone only exerted moderate growth inhibitory effects on A549 cells. The results indicate that DHA can significantly sensitize ATO-induced cytotoxicity of A549 lung cancer cells through apoptosis mediated by ROS-induced DNA damage. Interestingly, we found that the combinatory treatment of DHA and ATO did not result in significant adverse effects in normal human bronchial epithelial (HBE) cells. Our results further provide evidence for the potential application of combinatory effects of DHA and ATO as a safe therapy for human lung cancer.     

Inhibition of doxorubicin-induced autophagy in hepatocellular carcinoma Hep3B cells by sorafenib--the role of extracellular signal-regulated kinase counteraction

A multikinase inhibitor of the Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, sorafenib, is increasingly being used in the management of hepatocellular carcinoma, and its combination with conventional chemotherapeutics has stimulated particular interest. Although the combination of sorafenib with doxorubicin (DOX) is presently being investigated in a phase III randomized trial, little is known about the molecular mechanisms of their interaction. Because DOX causes cell death through upregulation of the MEK/ERK pathway, and sorafenib has an opposite influence on the same cascade, we hypothesized that co-treatment with these drugs may lead to an antagonistic effect. DOX treatment arrested proliferation and induced autophagic cell death in Hep3B cells, whereas apoptotic changes were not conspicuous. Sorafenib alone affected viability and caused massive mitochondrial degradation. However, when added together with DOX, sorafenib facilitated cell cycle progression, increased survival, and reduced autophagy. To evaluate the molecular mechanisms of this phenomenon, we examined the expression of ERK1/2, protein kinase B (Akt), and cyclin D1, as well as the members of Bcl-2 family. ERK1/2 activation induced by DOX was suppressed by sorafenib. Similarly, ERK targeting with the selective inhibitor U0126 impaired DOX-induced toxicity. Treatment with sorafenib, either alone or in combination with DOX, resulted in Akt activation. The role of sorafenib-induced degradation of cyclin D1 in the suppression of DOX efficiency is discussed. In conclusion, MEK/ERK counteraction, stimulation of survival via Akt and dysregulation of cyclin D1 could contribute to the escape from DOX-induced autophagy and thus promote cancer cell survival. The use of MEK/ERK inhibitors in combination with chemotherapeutics, intended to enhance anticancer efficacy, requires the consideration of possible antagonistic effects.     

Combination treatment of Src inhibitor Saracatinib with GMI,a Ganoderma microsporum immunomodulatory protein,induce synthetic lethality via autophagy and apoptosis in lung cancer cells

Saracatinib is an oral Src‐kinase inhibitor and has been studied in preclinical models and clinical trials of cancer therapy. GMI, a fungal immunomodulatory protein from Ganoderma microsporum, possesses antitumor capacity. The aim of this study is to evaluate the cytotoxic effect of combination treatment with saracatinib and GMI on parental and pemetrexed‐resistant lung cancer cells. Cotreatment with saracatinib and GMI induced synergistic and additive cytotoxic effect in A549 and A400 cells by annexin V/propidium iodide assay and combination index. Using western blot assay, saracatinib, and GMI combined treatment synergistically induced caspase‐7 activation in A549 cells. Different from A549 cells, saracatinib and GMI cotreatment markedly increased LC3B‐II in A400 cells. ATG5 silencing abolished the caspase‐7 activation and reduced cell death in A549 cells after cotreatment. This is the first study to provide a novel strategy of treating lung cancer with or without drug resistance via combination treatment with GMI and saracatinib.     

肿瘤靶向腺相关病毒携带干扰素β和TRAIL对A549肺癌移植瘤的增强治疗效应(英文)

干扰素β(IFN-β)和肿瘤坏死因子相关凋亡诱导配体(TRAIL)是有效抗癌药物。腺相关病毒(AAV)为目前最有应用前景的基因转移载体之一。利用AAV携带IFN-β和TRAIL基因并置于hTERT启动子控制下分别构建成肿瘤靶向病毒AAV-hTERT-IFN-β和AAV-hTERT-TRAIL,且单个IFN-β或TRAIL基因治疗发挥了一定的抗癌效果。将AAV-hTERT-IFN-β和AAV-hTERT-TRAIL进行联合,旨在研究其对A549肺癌细胞体内外的生长抑制效应。ELISA法检测了AAV-hTERT-IFN-β感染A549细胞后分泌型IFN-β的表达;MTT法检测AAV-hTERT-IFN-β联合AAV-hTERT-TRAIL对肿瘤细胞的生长抑制作用;凋亡细胞染色和流式细胞仪分别检测了AAV-hTERT-IFN-β、AAV-hTERT-TRAIL及其联合对A549细胞的凋亡效应;进一步评价了联合AAV-hTERT-IFN-β和AAV-hTERT-TRAIL对A549裸鼠移植瘤的抑癌效果。结果显示,联合治疗优于任一单独治疗并且导致了增强的肿瘤细胞毒性和凋亡诱导效应。更进一步显示,联合AAV-hTERT-IFN-β和AAV-hTERT-TRAIL治疗发挥了重要的抑制裸鼠移植瘤效果甚至消除全部移植瘤,为探究IFN-β和TRAIL联合抗癌的分子机制奠定了基础。     

The proliferative inhibition and apoptotic mechanism of Saikosaponin D in human non-small cell lung cancer A549 cells

Saikosaponin D is a saponin extract derived from several species of Bupleurum (Umbelliferae), which is used for the treatment of various liver diseases in traditional Chinese medicine. In this study, we report that Saikosaponin D inhibits the cell growth of human lung cancer cell line A549 and provide a molecular understanding of this effect. The results showed that Saikosaponin D inhibited the proliferation of A549 by inducing apoptosis and blocking cell cycle progression in the G1 phase. ELISA assay showed that Saikosaponin D significantly increased the expression of p53 and p21/WAF1 protein, contributing to cell cycle arrest. An enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), as well as Bax protein, was responsible for the apoptotic effect induced by Saikosaponin D. Taken together, our study suggests that the induction of p53 and activity of the Fas/FasL apoptotic system may participate in the antiproliferative activity of Saikosaponin D in A549 cells.     

A mutation in β‐tubulin and a sustained dependence on androgen receptor signalling in a newly established docetaxel‐resistant prostate cancer cell line

The mechanisms of docetaxel resistance in PC (prostate cancer) are unclear because of the lack of suitable experimental models, and no effective treatment exists for docetaxel‐resistant PC. We established a docetaxel‐resistant cell line, LNDCr, from an androgen‐refractory PC cell line, LNCaP‐hr, by intermittent exposure to docetaxel in vitro. The LNDCr cells harboured an F270I mutation in class I β‐tubulin, and demonstrated impaired tubulin polymerization by docetaxel. AR signalling was sustained in LNDCr cells, and AR knockdown suppressed the growth of LNDCr cells. These results suggest that an acquired mutation in β‐tubulin is associated with docetaxel resistance in PC and that a novel AR‐targeted therapy is effective for docetaxel‐resistant PC.     

Role of Bcl-xL/Beclin-1 in synergistic apoptotic effects of secretory TRAIL-armed adenovirus in combination with mitomycin C and hyperthermia on colon cancer cells

In this study, we attempted to develop a multimodality approach using chemotherapeutic agent mitomycin C, biologic agent tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L), and mild hyperthermia to treat colon cancer. For this study, human colon cancer LS174T, LS180, HCT116 and CX-1 cells were infected with secretory TRAIL-armed adenovirus (Ad.TRAIL) and treated with chemotherapeutic agent mitomycin C and hyperthermia. The combinatorial treatment caused a synergistic induction of apoptosis which was mediated through an increase in caspase activation. The combinational treatment promoted the JNK-Bcl-xL-Bak pathway which transmitted the synergistic effect through the mitochondria-dependent apoptotic pathway. JNK signaling led to Bcl-xL phosphorylation at serine 62, dissociation of Bak from Bcl-xL, oligomerization of Bak, alteration of mitochondrial membrane potential, and subsequent cytochrome c release. Overexpression of dominant-negative mutant of Bcl-xL (S62A), but not dominant-positive mutant of Bcl-xL (S62D), suppressed the synergistic death effect. Interestingly, Beclin-1 was dissociated from Bcl-xL and overexpression of dominant-negative mutant of Bcl-xL (S62A), but not dominant-positive mutant of Bcl-xL (S62D), suppressed dissociation of Beclin-1 from Bcl-xL. A combinatorial treatment of mitomycin C, Ad.TRAIL and hyperthermia induced Beclin-1 cleavage, but the Beclin-1 cleavage was abolished in Beclin-1 double mutant (D133A/D146A) knock-in HCT116 cells, suppressing the apoptosis induced by the combination therapy. We believe that this study supports the application of the multimodality approach to colon cancer therapy.     

The regulation of ERK and p-ERK expression by cisplatin and sorafenib in gastric cancer cells

Previous studies have reported strong antitumor effects of cisplatin and sorafenib. Our results indicated that cisplatin and sorafenib exhibited anti-tumor effects on gastric cancer cells. They significantly inhibited gastric cell growth and induced apoptosis. They effectively inhibited gastric cancer cell proliferation and induced G0/G1 phase arrest. Western blotting analysis indicated that it also promoted the phosphorylation extracellular signal regulated kinase (p-ERK). Moreover, cisplatin and sorafenib played a synergistic antitumor effect. These results suggested that the antitumor mechanism of cisplatin and sorafenib involved altering the cell cycle and stimulating ERK phosphorylation in the ERK signaling pathway.     

原子力显微镜研究多西他赛对人肺腺癌A549细胞的作用机制

利用原子力显微镜(AFM)研究了化疗药物多西他赛对肺腺癌细胞A549的作用机制。选取了不同浓度多西他赛作用下的A549细胞,观察和分析了多西他赛对A549细胞形貌信息和生物力学特性的影响。结果表明细胞的峰谷差和超微结构的平均粗糙度随着药物浓度增加而减小,表面粘附力随着药物浓度增加而增大。该结果对AFM可作为一种利用纳米量级分辨率进行药物药效评估的工具进行了佐证。     

MEK blockade overcomes the limited activity of palbociclib in head and neck cancer

Head and neck cancer (HNC) is characterized with multiple aberrations in cell cycle pathways, including amplification of cyclin D1. Palbociclib (PAL), a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, has been reported to regulate cell cycle progression in HNC. However, recent studies have revealed the acquired resistance of certain cells to PAL through activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway. Therefore, we investigated whether the inhibition of MEK/ERK pathway by trametinib (TRA) may overcome the limited efficacy of PAL in HNC. We evaluated the effect of PAL alone and in combination with TRA on the viability of HNC cells, and found that the combination treatment synergistically inhibited the proliferation of HNC cells. The combination treatment induced G0/G1 cell cycle arrest and apoptotic cell death. In particular, apoptosis mediated by the combination treatment was accompanied with an increase in caspase-3 activity and the number of TUNEL-positive apoptotic cells. These results were consistent with the decrease in cell cycle progression and mitogen-activated protein kinase (MAPK) pathway activation. In a xenograft mouse model of HNC, PAL and TRA synergistically inhibited tumor growth and enhanced tumor cell apoptosis, consistent with the increase in the number of TUNEL-positive cells. The anti-proliferative effects were evident in tumor tissues subjected to the combination treatment as compared with those treated with single drug. Taken together, our study demonstrates that the combination of PAL and TRA exerts synergistic anticancer effects and inhibits cell cycle check points and MEK/ERK pathway in HNC, suggestive of their potential application for HNC treatment.     

Synergistic effect and mechanism of vitamin A and vitamin D on inducing apoptosis of prostate cancer cells

To explore the mechanism and synergistic effect of vitamin A and vitamin D in inducing apoptosis of prostate cancer cells. The cell proliferation activity was determined by MTT assay. The proportion of apoptotic cells was analyzed by FACS and fluorescence intensity. TUNEL was used to evaluate vitamin A and vitamin D’s induction of apoptosis in prostate cancer cells. The protein and mRNA expression level of Cyclin D1 and Bax were determined by real time-PCR and western blot. The results of MTT showed vitamin A and vitamin D’s inhibition on proliferation ratio in prostate cancer cells is time and concentration dependent. FACS and fluorescence intensity analysis proved that the proportion of apoptotic cells increased after vitamin A and vitamin D treatment. TUNEL showed vitamin A and vitamin D induced prostate cancer cells apoptosis. The combination of vitamin A and vitamin D markedly enhanced the expression of Bax and reduced the expression of Cyclin D1 by real time-PCR and western blot assay. In conclusion, vitamin A and vitamin D could synergistically induce apoptosis in prostate cancer cells.     

KIF26B在非小细胞肺癌发生发展过程中的表达与功能研究

驱动蛋白与肿瘤的发生有密切联系，但对 KIF26B驱动蛋白在非小细胞肺癌的表达和相关功能作用的研究甚少。为了探索KIF26B在非小细胞肺癌中的表达水平及潜在机制，通过干扰KIF26B后探索对非小细胞肺癌增殖、侵袭、迁移、细胞周期、凋亡以及相关蛋白表达量的影响。对mRNA TCGA 数据库信息分析得出，KIF26B基因在非小细胞肺癌中高表达。qRT-PCR 检测 KIF26B在几株常见非小细胞肺癌细胞系中的表达水平，筛选出 KIF26B在A549 和 NCI-H292细胞系中高表达。利用 RNA干扰技术(RNA interference, RNAi)敲低 A549 和 NCI-H292细胞的 KIF26B基因，通过CCK8、采用实时细胞分析仪、平板克隆及 Transwell 实验检测敲低 KIF26B基因后的生物学功能，免疫印迹法检测蛋白表达水平。结果显示，敲低KIF26B后A549 和 NCI-H292细胞增殖明显降低，侵袭及迁移能力明显减弱。敲低KIF26B后阻碍了A549 和 NCI-H292细胞从G1期向S期的转变，同时凋亡细胞明显增多，与之相关的细胞周期蛋白 D1、Bcl-2、E-cadherin和Vimentin的表达水平显著下调，同时活化的半胱天冬酶-3（active Caspase-3）和其剪切底物 PARP1 的剪切体（cleaved PARP1）表达水平显著上调。结果表明KIF26B可能作为非小细胞肺癌发生的促癌基因，参与了非小细胞肺癌的发生及发展过程。KIF26B有望成为非小细胞肺癌治疗的潜在靶点。     

Targeted delivery of vitamin D3-loaded nanoparticles to C6 glioma cell line increased resistance to doxorubicin,epirubicin, and docetaxel in vitro

In recent years, targeted delivery systems have been used along with combinatorial therapy to decrease drug resistance and increase cancer therapy efficacy. The anti-proliferative effects of vitamin D3 (VD3) on cancerous cells, such as C6 glioma, with active hedgehog pathways raised the question as to whether pre-targeting C6 glioma cells with VD3-loaded nanoparticles (VD3NPs) can enhance the anti-tumor effects of doxorubicin, epirobicin, and docetaxel on this drug-resistant cell line. Here, studying at cellular, nuclear, protein, and gene levels we demonstrated that VD3NP-doxorubicin and VD3NP-epirobicin combinations increased the probability of chemotherapy/radiotherapy resistance and cancer stem cell (CSC) properties in C6 glioma significantly (P < 0.05), compared to doxorubicin and epirobicin alone. However, VD3NP-docetaxel combination may have the potential in sensitizing C6 cells to ionizing irradiation, but this combination also increased the CSC properties and the probability of drug resistance significantly (P < 0.05), compared to docetaxel alone. Although our previous study showed that targeted delivery of VD3 reduced the rate of proliferation significantly (P < 0.05) in C6 glioma cells (a drug-resistant cell line), here we concluded that combinatorial therapy of exogenous VD3 with doxorubicin, epirobicin, and docetaxel not only did not lead to the enhancement of cytotoxic effects of the aforementioned drugs but also increased the cancerous characteristics in C6 glioma, in vitro.