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

ATP结合盒（ABC-）转运蛋白，如P-糖蛋白（Pgp）的过表达导致体外多药耐药（MDR），并与几种癌症实体对化疗的临床无反应性有关。到目前为止，还不清楚是否通过ABC转运蛋白过表达头颈部鳞状细胞癌（HNSCC）的获得性化疗耐药是由肿瘤疾病的进展或细胞抑制剂治疗引起的。这种医源性化疗耐药性又可以由MDR基因的转录诱导或由预先存在的耐药亚克隆的达尔文选择引起。 申请人将使用最先进的鼠标模型来解决这些基本问题。两个鼠MDR 1基因之一将通过在组织特异性角蛋白启动子下使用RU 486诱导型Cre重组酶的同源重组被荧光素酶基因取代（mdr1a.flox/K5.Cre* PR 1小鼠）。因此，口腔中的发光是MDR 1转录物表达的替代物。口腔中的致癌作用随后将由上皮细胞暴露于4-硝基喹啉1-环氧化物（4-NQE）引起。 将在癌变和多西他赛、紫杉醇或安慰剂治疗期间记录观察期结束时的发光、鼠Pgp表达、肿瘤体积和Ki-67染色指数。为了将该4-NQE模型与由突变K-ras蛋白介导的致癌作用进行比较，mdr1a.flox/K5.Cre* PR 1小鼠还将与LSL-K-rasG 12 D小鼠交配，导致在通过RU 486激活Cre后具有口腔特异性恶性病变的后代。结果将阐明HNSCC病因之间是否存在差异（K-ras突变与致癌毒素）或药物（多西他赛与紫杉醇），并仔细检查ABC转运蛋白的医源性过表达机制（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).