Experimental studies on potentiation of antitumor agent by the second generation MDR1 inhibitors in malignant brain tumors : Monitoring multidrug resistance using ^<99m>Tc-MIBI

本研究旨在探讨^<99m>Tc-MIBI是否适用于阐明恶性肿瘤中MDR1抑制剂的多药耐药和预测抗肿瘤药物的增强作用。体外实验：用低剂量长春新碱（VCR）培养恶性肿瘤细胞（RG2和C6胶质瘤，Walker 256癌：W256），诱导多药耐药。MTT分析显示，与未接触药物的细胞系（RG2, C6, W256）相比，所有vcr耐药亚系（RG2R, C6R, W256R）的存活部分显著增加。在所有vcr耐药亚系中，RT-PCR显示MDR1 mRNA的表达高于药物初始细胞系。表达高水平MDR1 mRNA的vcr耐药亚系的Vds ^<99m>Tc-MIBI显著低于表达低水平MDR1 mRNA的药物初始细胞系。Vd ^<99m>Tc-MIBI与MDR1 mRNA在药物初始细胞系和vcr耐药亚系中的表达呈负相关。用第二代MDR - 1抑制剂（PSC833, MS209）治疗后，MTT试验显示其对VCR细胞毒性有增强作用。在所有vcr耐药亚组中，MDR 1抑制剂治疗后，Tc-MIBI的Vd <99m>显著增加。体内实验：分别在Sprague-Dawley大鼠右侧基底节区和左侧基底节区接种C6和C6R细胞。肿瘤植入后10天采用^<99m>Tc-MIBI放射自显影。在使用或不使用MDR 1抑制剂（PSC833, MS209）的大鼠中测量了^<99m>Tc-MIBI摄取。Tc-MIBI在两种肿瘤中的积累都比非肿瘤区域强烈。C6的^<99m>Tc-MIBI吸收量显著高于C6R。在MDR - 1抑制剂治疗后，两种肿瘤的^<99m>Tc-MIBI摄取显著增加。采用^<14> c -甲基- l-蛋氨酸（Met）和mb -5指数，通过放射自显影评估有或没有MDR - 1抑制剂的VCR的治疗效果。在MDR 1抑制剂治疗后，VCR治疗的两种肿瘤的Met摄取和mb -5指数明显低于单独使用VCR治疗的肿瘤。Tc-MIBI SPECT可用于检测MDR1介导的耐药性和监测MDR1抑制剂对恶性脑肿瘤患者的治疗效果。少

The aim of this study is to explore whether ^<99m>Tc-MIBI is suitable to elucidate multidrug resistance and prediction of potentiation of antitumor agents by MDR1 inhibitors in malignant tumors.In vitro experiments : Malignant tumor cells (RG2 and C6 gliomas, Walker 256 carcinoma : W256) were incubated with low dose vincristine (VCR) to induce multidrug resistance. MTT assay demonstrated significant increase of surviving fractions in all VCR-resistant sublines (RG2R, C6R, W256R) compared with those of drug-naive cell lines (RG2, C6, W256). In all VCR-resistant sublines, RT-PCR revealed higher expression of MDR1 mRNA compared with drug-naive cell lines. Vds of ^<99m>Tc-MIBI in VCR-resistant sublines expressing higher level of MDR1 mRNA was significantly lower than those of drug-naive cell lines expressing lower levels of MDR1 mRNA. Vd of ^<99m>Tc-MIBI is negatively correlated with MDR1 mRNA expression among drug-naive cell lines and VCR-resistant sublines. After treatment with second ge … More neration MDR 1 inhibitors (PSC833, MS209), MTT assay revealed enhancing effects on VCR cytotoxity. Vd of ^<99m>Tc-MIBI significantly increased after treatment with MDR 1 inhibitors in all VCR-resistant sublines.In vivo experiments : C6 and C6R cells were inoculated in the right and left basal ganglia of Sprague-Dawley rats, respectively. Autoradiography using ^<99m>Tc-MIBI was performed 10 days after tumor implantation. The ^<99m>Tc-MIBI uptake was measured in rats treated with or without the MDR 1 inhibitors (PSC833, MS209). ^<99m>Tc-MIBI accumulated more intensely in both tumors than the nontumor regions. The ^<99m>Tc-MIBI uptake of C6 was significantly higher than that of C6R. The ^<99m>Tc-MIBI uptake of both tumors significantly increased after the MDR 1 inhibitor treatment. The therapeutic effects of VCR with or without the MDR 1 inhibitors were also evaluated by autoradiography using ^<14>C-methyl-L-methionine (Met) and MIB-5 index. Met uptake and MIB-5 index of both tumors treated with VCR following the MDR 1 inhibitor treatment significantly decreased than those of tumors treated with VCR alone.^<99m>Tc-MIBI SPECT could be suitable imaging for detecting MDR1-mediated drug resistance and for monitoring therapeutic effects of MDR1 inhibitors in patients with malignant brain tumors. Less