Molecular interactions of tumor cells with the microenvironment are regarded as onset of chemotherapy resistance, referred to as cell adhesion mediated drug resistance (CAM-DR). Here we elucidate a mechanism of CAM-DR in breast cancer cells in vitro. We show that human MCF-7 and MDA-MB-231 breast cancer cells decrease their sensitivity towards cisplatin, doxorubicin, and mitoxantrone cytotoxicity upon binding to collagen type 1 (COL1) or fibronectin (FN). The intracellular concentrations of doxorubicin and mitoxantrone were decreased upon cell cultivation on COL1, while cellular cisplatin levels remained unaffected. Since doxorubicin and mitoxantrone are transporter substrates, this refers to ATP binding cassette (ABC) efflux transporter activities. The activation of the transporters BCRP, P-gp and MRP1 was shown by fluorescence assays to distinguish the individual input of these transporters to resistance in presence of COL1 and related to their expression levels by western blot. An ABC transporter inhibitor was able to re-sensitize COL1-treated cells for doxorubicin and mitoxantrone toxicity. Antibody-blocking of β1-integrin (ITGB1) induced sensitization towards the indicated cytostatic drugs by attenuating the increased ABC efflux activity. This refers to a key role of ITGB1 for matrix binding and subsequent transporter activation. A downregulation of α2β1 integrin following COL1 binding appears as clear indication for the relationship between ITGB1 and ABC transporters in regulating resistance formation, while knockdown of ITGB1 leads to a significant upregulation of all three transporters. Our data provide evidence for a role of CAM-DR in breast cancer via an ITGB1 - transporter axis and offer promising therapeutic targets for cancer sensitization.

中文翻译：

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β1-整联蛋白与1型胶原蛋白的结合通过激活ABC外排转运蛋白将乳腺癌细胞传递给化学抗性。

肿瘤细胞与微环境的分子相互作用被认为是化学疗法抗性的开始，被称为细胞粘附介导的药物抗性（CAM-DR）。在这里，我们阐明了CAM-DR在体外乳腺癌细胞中的机制。我们显示，人MCF-7和MDA-MB-231乳腺癌细胞在结合1型胶原（COL1）或纤连蛋白（FN）后，会降低其对顺铂，阿霉素和米托蒽醌细胞毒性的敏感性。细胞在COL1上培养后，阿霉素和米托蒽醌的细胞内浓度降低，而细胞顺铂水平保持不受影响。由于阿霉素和米托蒽醌是转运蛋白的底物，因此这是指ATP结合盒（ABC）外排转运蛋白的活性。转运蛋白BCRP的激活，通过荧光测定法显示P-gp和MRP1可以区分这些转运蛋白在COL1存在下的抗性输入，并通过蛋白质印迹法与其表达水平相关。ABC转运蛋白抑制剂能够使经COL1处理的细胞对阿霉素和米托蒽醌的毒性重新敏感。β1-整合素（ITGB1）的抗体阻断通过减弱增加的ABC外排活性来诱导对所示细胞抑制药物的致敏。这是指ITGB1在基质结合和随后的转运蛋白激活中的关键作用。COL1结合后α2β1整联蛋白的下调似乎是ITGB1和ABC转运蛋白之间在调节抗性形成中的关系的明确指示，而敲低ITGB1则导致所有三个转运蛋白的显着上调。