彭荷玲 綜述,李 衛(wèi),劉宏涌 審校
(廣西醫(yī)科大學(xué)第一附屬醫(yī)院兒科,南寧530021)
多藥耐藥(multidrug resistance,MDR)基因是一個(gè)相對(duì)保守的基因家族,人的 MDR基因主要由 MDR1、MDR2和MDR3組成。其中MDR2為動(dòng)物基因型,MDR3主要在物質(zhì)轉(zhuǎn)運(yùn)方面發(fā)揮作用,目前在藥物耐藥方面的研究非常有限。多個(gè)不同類型腫瘤的體外實(shí)驗(yàn)表明,細(xì)胞耐藥性主要由MDR1決定,并且MDR1超表達(dá)是限制化療藥物療效的主要因素。人MDR1位于染色體7q21-1,編碼相對(duì)分子質(zhì)量為170kb的膜糖蛋白(P-gp)。P-gp在抑制細(xì)胞凋亡、促進(jìn)毒素和代謝產(chǎn)物排出等方面起著重要作用,而且在細(xì)胞的藥物分布和排泄、對(duì)多種結(jié)構(gòu)及作用機(jī)制不同抗癌藥的耐受中扮演重要的角色[1]。
MDR1基因作為一種生物學(xué)標(biāo)記,其潛在價(jià)值正引起人們的注意。大量研究表明,MDR1基因與腫瘤的多種生物學(xué)行為密切相關(guān)。
MDR1不僅在腫瘤耐藥時(shí)呈高水平表達(dá),還廣泛存在于人體正常組織和未耐藥的腫瘤組織中。He等[2]指出 MDR1基因可在肝臟、腎臟、腸道、大腦等多種組織中表達(dá)。Fojo等[3]研究表明,MDR1基因在腎上腺極高表達(dá),在腎臟呈高表達(dá)。除腎上腺、腎臟外的大多數(shù)正常組織,MDR1表達(dá)的上調(diào)提示這些正常組織有向腫瘤組織轉(zhuǎn)化的傾向。例如,Lu等[4]發(fā)現(xiàn)P-gp在卵巢癌中的表達(dá)高于良性卵巢癌和正常卵巢組織。Shi等[5]研究顯示,P-gp在惡性組織中的表達(dá)率高于正常組織。另外,P-gp在發(fā)生明顯轉(zhuǎn)移的腫瘤組織中的表達(dá)明顯升高,且P-gp的表達(dá)與臨床病理分期密切相關(guān)。Mizoguchi等[6]研究表明,在癌變的結(jié)直腸組織中,分化程度高的部分較分化中等部分的MDR1表達(dá)高,在癌變的胃組織中,分化中等的部分較分化低的部分 MDR1表達(dá)高。Tokunaga等[7]通過(guò)對(duì)病例的分析和歸納得出,P-gp的表達(dá)與結(jié)直腸癌的組織分化程度相關(guān)。以上研究提示,腫瘤組織MDR1/P-gp的表達(dá)水平與組織分化程度及臨床病理分期密切相關(guān)。此外,Zajchowski等[8]對(duì)復(fù)發(fā)性晚期卵巢漿液性癌的研究顯示,復(fù)發(fā)病灶的P-gp表達(dá)顯著上調(diào)。Kurata等[9]發(fā)現(xiàn)多發(fā)性骨髓瘤(MDS)轉(zhuǎn)化為急性髓細(xì)胞性白血病(AML)過(guò)程中,MDR1基因的mRNA表達(dá)水平較初診患者明顯增高,而在MDS轉(zhuǎn)化為AML后表達(dá)減少,表明MDR1基因表達(dá)水平的變化與病情的進(jìn)展密切相關(guān)。
細(xì)胞增殖與凋亡由多基因嚴(yán)格調(diào)控,如Bcl-2家族、caspase家族、癌基因C-myc及抑癌基因P53等。正常情況下,細(xì)胞的增殖與凋亡處于動(dòng)態(tài)平衡,該平衡狀態(tài)對(duì)維持細(xì)胞的數(shù)目及個(gè)體的生存非常重要。但當(dāng)該平衡狀態(tài)出現(xiàn)失調(diào)時(shí),易引發(fā)疾病,其中腫瘤的發(fā)生與其密切相關(guān)。MDR1基因能與細(xì)胞增殖凋亡相關(guān)的多基因相互作用,引起細(xì)胞增殖與凋亡之間的平衡失調(diào)。Han等[10]對(duì)胃腸道癌變組織化療敏感性的研究發(fā)現(xiàn),P-gp與Bcl-2的表達(dá)明顯相關(guān)。Chauhan等[11]的研究結(jié)果顯示,MDR1、MDR相關(guān)蛋白1和Bcl-2的表達(dá)與成人急性白血病患者對(duì)誘導(dǎo)化學(xué)治療的反應(yīng)有關(guān)。Rocco等[12]揭示,在幽門(mén)螺旋桿菌相關(guān)胃癌中,P-gp和胚胎蛋白一樣,通過(guò)與Bcl-x(L)相互作用,起著抗凋亡的作用。Chen等[13]研究表明,CacyBP/SIP可通過(guò)提高P-gp和Bcl-2水平,增加胰腺癌細(xì)胞MDR1表達(dá),從而抑制胰腺癌細(xì)胞的凋亡。Wang等[14]證實(shí),對(duì)尼洛替尼耐藥的人白血病細(xì)胞株K562-RN的 MDR1表達(dá)與caspase-3的表達(dá)水平呈負(fù)相關(guān)。Thévenod等[15]對(duì)腎癌致病因素的研究顯示,c-myc、細(xì)胞周期蛋白D1及 MDR1/ABCB1表達(dá)的增高可導(dǎo)致細(xì)胞增殖增加,凋亡減少,從而引發(fā)腎癌。Wang等[16]通過(guò)對(duì)硼替佐米逆轉(zhuǎn)白血病耐藥的研究發(fā)現(xiàn),通過(guò)阻止核轉(zhuǎn)錄因子(NF-κB)進(jìn)入細(xì)胞核可下調(diào)MDR1和P-gp的表達(dá),細(xì)胞內(nèi)藥物蓄積誘導(dǎo)腫瘤細(xì)胞凋亡。
正常條件下,原癌基因和抑癌基因處于動(dòng)態(tài)平衡狀態(tài),共同控制著細(xì)胞的增殖活動(dòng)。p53作為最常見(jiàn)的抑癌基因,在腫瘤的進(jìn)展、侵襲、轉(zhuǎn)移和腫瘤耐藥中起著非常重要的作用。Chuang等[17]的研究闡明,人肺癌細(xì)胞p53基因可被低劑量多西紫杉醇誘導(dǎo)激活,抑制 MDR1基因表達(dá)。Cheng等[18]的研究表明,在野生型PTEN基因轉(zhuǎn)染的K562/ADM白血病細(xì)胞中,NF-κB、MDR1及Bcl-2的表達(dá)下調(diào),而p53及Bax的表達(dá)增強(qiáng),細(xì)胞對(duì)藥物的敏感性增加甚至耐藥性得到逆轉(zhuǎn)。Yan等[19]研究表明p53突變后獲得的功能與C-myc、MDR1及NF-κB基因的表達(dá)增加有關(guān),印證了Cheng等[18]的觀點(diǎn)。Qi等[20]的研究表明,腺病毒聯(lián)合p53能逆轉(zhuǎn)阿霉素耐藥的人乳腺癌細(xì)胞MCF-7/MDR,其逆轉(zhuǎn)機(jī)制為抑制P-gp的表達(dá),誘導(dǎo)細(xì)胞凋亡。
MDR1基因獲取簡(jiǎn)便,可動(dòng)態(tài)觀測(cè),及逆轉(zhuǎn)錄PCR(RTPCR)、免疫組織化學(xué)等各種具有高靈敏度檢測(cè)方法的應(yīng)用,結(jié)合對(duì)不同組織MDR1基因表達(dá)水平的認(rèn)識(shí),MDR1基因檢測(cè)在腫瘤早期診斷治療以及評(píng)估患者預(yù)后中發(fā)揮重要作用。如Lü等[21]的研究結(jié)果表明,MDR1基因多態(tài)性是急性淋巴細(xì)胞性白血?。ˋLL)患者的遺傳易感性因素,其中單體型 MDR1可以為臨床診斷提供重要參考。Kourti等[22]通過(guò)對(duì)49例ALL患兒分析得出,ALL患兒MDR1基因表達(dá)水平顯著高于健康者,且表達(dá)水平越高患者預(yù)后越差。Amiri-Kordestani等[23]回顧性分析發(fā)現(xiàn),腫瘤中 MDR1高表達(dá)提示腫瘤具有更高侵襲性,且患者預(yù)后不良。
此外,凋亡抑制蛋白Survivin的過(guò)表達(dá)和NF-κB活性的失控與人類腫瘤的發(fā)生、浸潤(rùn)轉(zhuǎn)移、耐藥和預(yù)后密切相關(guān)。因而Survivin與NF-κB可作為腫瘤耐藥的間接診斷指標(biāo),為腫瘤的診斷提供新思路。Liu等[24]表示P-gp與Survivin等的過(guò)表達(dá)與腫瘤的進(jìn)程密切相關(guān)。Survivin的轉(zhuǎn)錄與P-gp/MDR1的過(guò)表達(dá)相關(guān),在人乳腺癌耐藥細(xì)胞系mcf-7中,PI3K/Akt/NF-κB通路參與了 P-gp/MDR1相關(guān)的 Survivin轉(zhuǎn)錄活動(dòng)。Souza等[25]發(fā)現(xiàn)高劑量長(zhǎng)春新堿可誘導(dǎo)P-gp和Survivin超表達(dá)。P-gp和Survivin在細(xì)胞質(zhì)的共定位表明,這兩個(gè)蛋白通過(guò)一個(gè)共性機(jī)理控制凋亡。P-gp和Survivin對(duì)慢性粒細(xì)胞白血病MDR有重大影響。Tran等[26]的研究結(jié)果表明,在阿霉素耐藥的人乳腺癌細(xì)胞 MCF-7/adr的治療中,大葉茜草素可通過(guò)抑制cox-2表達(dá)和阻斷NF-κB信號(hào)傳導(dǎo)途徑以抑制P-gp的表達(dá)。Xia等[27]研究證實(shí),在人白血病細(xì)胞中,NF-κB/p6表達(dá)下調(diào)與二烯丙基三硫化物誘導(dǎo)的耐藥機(jī)制顯著相關(guān)。
另外,研究人員陸續(xù)發(fā)現(xiàn)一些新的能快速、準(zhǔn)確、靈敏檢測(cè)MDR1基因的方法。如Barnadas等[28]發(fā)現(xiàn)新的高通量方法多路嵌套PCR聯(lián)合連接酶檢測(cè)反應(yīng)-熒光微球測(cè)定,可同時(shí)檢測(cè)MDR1耐藥相關(guān)基因及其突變。Starkey等[29]應(yīng)用飛秒雙波長(zhǎng)近紅外線雙光子成像技術(shù),可高靈敏度及高特異度地區(qū)別出被正常細(xì)胞包圍的癌細(xì)胞,結(jié)果與細(xì)胞MDR1基因表達(dá)的蛋白水平相關(guān),當(dāng)癌細(xì)胞中MDR1基因表達(dá)增高時(shí),正常細(xì)胞中僅存少量的癌細(xì)胞也可以被檢測(cè)到。
腫瘤MDR是導(dǎo)致腫瘤低緩解率、高復(fù)發(fā)率、化療療效差、生存期短的主要原因。對(duì)MDR1基因與腫瘤治療關(guān)系的研究成為了當(dāng)前的熱點(diǎn)。大量研究證實(shí),對(duì)腫瘤MDR1基因進(jìn)行動(dòng)態(tài)檢測(cè),可指導(dǎo)更好地選擇及調(diào)整治療方案。Lu等[4]研究表明,P-gp的表達(dá)可影響腫瘤患者術(shù)后生存時(shí)間,對(duì)P-gp表達(dá)的檢測(cè)可為卵巢癌患者提供更準(zhǔn)確的診斷和更好的化療方案。Mignogna等[30]研究發(fā)現(xiàn),在腎細(xì)胞癌患者中,MDR1基因過(guò)表達(dá)者,腫瘤侵襲性更強(qiáng),提示預(yù)后不良。Li等[31]研究表明,MDR1基因多態(tài)性與胃癌患者接受術(shù)后輔助化療療效有關(guān)。Litviakov等[32]對(duì)84例接受新輔助化療的(術(shù)前2~4周期的多柔比星+CAX/紫杉醇治療)ⅡA~ⅢC期乳腺癌患者的研究發(fā)現(xiàn),MDR1基因的表達(dá)與患者對(duì)化療的反應(yīng)相關(guān),MDR1基因表達(dá)上調(diào)的患者對(duì)化療反應(yīng)減弱。
受到MDR1基因耐藥機(jī)制的啟示,目前更多研究集中在P-gp逆轉(zhuǎn)劑的研發(fā)和細(xì)胞增殖凋亡與耐藥關(guān)系等方面的探索。Chen等[33]研究證實(shí)K562/A02細(xì)胞的 MDR可以部分被伊馬替尼或5-溴粉防己堿逆轉(zhuǎn),逆轉(zhuǎn)機(jī)制與MDR1mRNA和P-gp表達(dá)下調(diào)有關(guān)。Lv等[34]發(fā)現(xiàn),作用于肺癌細(xì)胞系A(chǔ)549/DDP的酪氨酸激酶活性抑制劑能有效逆轉(zhuǎn)細(xì)胞的MDR,并增加細(xì)胞對(duì)藥物的敏感性,其機(jī)制與MDR1和人肺耐藥蛋白(LRP)表達(dá)下調(diào)有關(guān)。Ascione等[35]發(fā)現(xiàn),具有細(xì)胞毒性的強(qiáng)谷胱甘肽轉(zhuǎn)移酶(GST)抑制劑參與殺死 MDR1/Pg-p過(guò)表達(dá)的AML細(xì)胞。Tang等[36]通過(guò)對(duì)氟尿嘧啶耐藥肝癌細(xì)胞的研究發(fā)現(xiàn),RNA干擾參與誘導(dǎo)損耗基因增強(qiáng)子人類同源物2,通過(guò)下調(diào)MDR1的表達(dá),使細(xì)胞凋亡增加,同時(shí)使細(xì)胞停滯在G1/S期。Zhang等[37]證實(shí),腫瘤壞死因子相關(guān)凋亡誘導(dǎo)配體通過(guò)下調(diào)耐藥相關(guān)基因 MDR1、LRP和GST-Tt的表達(dá),促進(jìn)化療后的腫瘤細(xì)胞凋亡,抑制腫瘤細(xì)胞生長(zhǎng),發(fā)揮逆轉(zhuǎn)胃癌細(xì)胞MDR的作用。Sun等[38]發(fā)現(xiàn),克力托辛通過(guò)下調(diào)凋亡抑制基因NF-κB來(lái)逆轉(zhuǎn)P-gp相關(guān)的 MDR。Cai等[39]研究發(fā)現(xiàn),粉防己堿聯(lián)合柔紅霉素可有效逆轉(zhuǎn)K562/A02耐藥,促進(jìn)腫瘤細(xì)胞凋亡,機(jī)制與下調(diào)Survivin表達(dá)有關(guān),Survivin是逆轉(zhuǎn)造血系統(tǒng)惡性腫瘤 MDR的治療靶標(biāo)。Ling等[40]研究指出,抗腫瘤藥物聯(lián)合耐藥蛋白Survivin負(fù)調(diào)節(jié)劑可增強(qiáng)藥物對(duì)MDR腫瘤的療效,調(diào)節(jié)Survivin表達(dá)是增強(qiáng)藥物靈敏度及控制腫瘤耐藥的重要機(jī)制,這種抗腫瘤藥聯(lián)合藥物靈敏度調(diào)節(jié)劑的方法有望為未來(lái)臨床聯(lián)合用藥提供新的思路。
隨著對(duì)MDR1和腫瘤相關(guān)關(guān)系研究的深入,人們認(rèn)識(shí)到腫瘤MDR機(jī)制由多種因素共同參與構(gòu)成。MDR1與細(xì)胞增殖凋亡相關(guān)關(guān)系及各種MDR相關(guān)蛋白間的相互作用使MDR1在腫瘤診斷治療的應(yīng)用范圍得到延伸。但是,研究出更多具有選擇性抑制MDR1基因表達(dá)、毒性更小、能克服腫瘤化療后耐藥的MDR1逆轉(zhuǎn)劑仍是未來(lái)的巨大挑戰(zhàn)。
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