Dissecting the phenomenon of multidrug resistance transporter overexpression in a murine model of head and neck squamous cell carcinoma.

三磷酸腺苷结合盒(ABC-)转运体如P-糖蛋白(Pgp)的过表达在体外可导致多药耐药(MDR)，并与临床对化疗无反应有关。到目前为止，头颈部鳞状细胞癌(HNSCC)通过ABC转运蛋白的过表达而产生获得性化疗耐药的原因尚不清楚，是肿瘤的进展还是细胞抑素的治疗所致。这种医源性化疗耐药性可以通过转录诱导多药耐药基因或达尔文式选择先前存在的耐药亚克隆来引起。申请者将使用最先进的鼠标模型来解决这些基本问题。在组织特异性角蛋白启动子(mdr1a.flx/K5.Cre*PR1小鼠)的作用下，利用RU486可诱导的Cre重组酶进行同源重组，将两个mdr1基因中的一个替换为荧光素酶基因。因此，口腔中的发光是mdr1转录本表达的替代。口腔上皮细胞暴露在4-硝基-1-环氧喹啉(4-NQE)中会导致口腔癌变。在癌变和使用多西紫杉醇、紫杉醇或安慰剂治疗期间，将记录观察期末的发光、小鼠Pgp表达、肿瘤体积和Ki-67染色指数。为了比较这种4-NQE模型与突变的K-ras蛋白介导的致癌作用，mdr1a.flx/K5Cre*PR1小鼠还将与由RU486激活CRE后导致口腔特异恶性病变的LSL-K-RasG12D小鼠交配，结果将阐明HNSCC病因(K-ras突变与致癌毒素)或药物(多西紫杉醇与紫杉醇)之间是否存在差异，并仔细研究医源性ABC转运蛋白过表达的机制(转录诱导与选择)。

Overexpression of ATP-binding cassette (ABC-) transporters such as P-glycoprotein (Pgp) causes multidrug resistance (MDR) in vitro and has been associated with clinical unresponsiveness to chemotherapy in several cancer entities. So far, it is unclear whether acquired chemotherapy resistance of head and neck squamous cell carcinoma (HNSCC) through overexpression of ABC-transporters is caused by progression of the tumor disease or by treatment with cytostatics. Such iatrogenic chemotherapy resistance can in turn be caused by transcriptional induction of MDR genes or by Darwinian selection of pre-existing drug resistant sub-clones. Using state-of-the-art mouse models, these fundamental questions will be addressed by the applicant. One of the two murine MDR1 genes will be substituted with luciferase gene by homologous recombination using RU486-inducible Cre recombinase under tissue specific keratin promoter (mdr1a.flox/K5.Cre*PR1 mice). In consequence, luminescence in the oral cavity is a surrogate for MDR1 transcript expression. Carcinogenesis in the oral cavity will subsequently be caused by exposure of the epithelia to 4-nitroquinoline 1-epoxide (4-NQE). Luminescence, murine Pgp expression, tumor volume, and Ki-67 staining index at end of observation period will be recorded during carcinogenesis and treatments with docetaxel, paclitaxel, or placebo. To compare this 4-NQE model to carcinogenesis mediated by mutant K-ras protein, mdr1a.flox/K5.Cre*PR1 mice will also be mated with LSL-K-rasG12D mice leading to progeny with oral cavity specific malign lesions after Cre activation by RU486.Taken together, the results will clarify whether there are differences between HNSCC etiologies (K-ras mutation vs carcinogenic toxins) or drugs (docetaxel vs paclitaxel) and scrutinize the mechanism of iatrogenic overexpression of ABC-transporters (transcriptional induction vs selection).