胰腺癌纳米递药系统靶向性设计研究进展

() ()

(1复旦大学附属中山医院介入科,上海 200032; 2上海市影像医学研究所 上海 200032)

胰腺导管腺癌(pancreatic ductal adenocarcinoma,以下简称胰腺癌)是一种常见的恶性肿瘤,具有极高的致死性,患者的5年生存率仅为6%,且近40年来胰腺癌的治疗无明显进展[1-2]。胰腺癌早期无典型症状,缺乏早期诊断的标记物及成像检测方法,手术根治性切除的患者不足20%。胰腺癌放射治疗效果不确切,最新的研究证实中晚期胰腺癌化疗4个月后再行同步放化疗,与单行化疗生存时间无明显差异[3]。因此,化疗是提高胰腺癌患者生存质量与延长生存时间的主要治疗方法[4-5]。

化疗是基于化疗药物的细胞毒性而抑制代谢旺盛的细胞生长[6]。由于大多数癌细胞比正常细胞代谢旺盛,因此会摄取更多的化疗药物,从而发挥药物的治疗作用;但化疗药物本身不具有选择性,代谢旺盛的正常细胞也会受到药物的影响,如毛囊细胞、骨髓造血细胞及胃肠黏膜上皮细胞等,故化疗药物又会产生不良反应[7]。然而胰腺癌不同于大多数癌症,其血供相对匮乏,癌细胞代谢活度较低,化疗药物不能在胰腺癌组织内高浓度富集并到达其有效治疗浓度,因此腺癌化疗药物使用强度高,不良反应明显,预后不理想[8]。

20世纪90年代末期,基于对癌细胞分化与增殖相关信号通路网络及机制的深入研究,通过靶向特定的生物分子以阻断癌细胞信号网络而控制肿瘤生长的治疗方式,癌症治疗进入靶向治疗的新时代[9]。2005年,美国FDA批准了中晚期胰腺癌治疗的首个也是目前唯一的靶向药物厄尔替尼(erlotinib),其与吉西他滨联合用药较吉西他滨单药可以显著延长受试者的中位生存时间(实验组与对照组分别为6.4与6.0个月,校正风险比HR=0.81,P=0.028)[10]。但是,传统细胞毒性药物在胰腺癌的药物治疗中仍然占据重要地位,其无选择地抑制癌细胞与正常细胞,在体内的快速降解失效,从而具有较高的毒性作用和不良反应[11]。

面对胰腺癌化疗的困境,靶向性纳米载体递送化疗药物治疗胰腺癌成为近年来的研究热点。纳米载体具有纳米级的尺寸(粒径为1 ～ 1 000 nm),可以靶向递送抗肿瘤药物达到靶组织,响应肿瘤微环境并实现智能控释的功能,提高药物在靶细胞的利用率,减少不良反应[12]。因此,靶向胰腺癌的纳米递药有望改变传统化疗的递药方式,提高药物治疗胰腺癌疗效,成为近年来的研究热点。

被动靶向性设计癌组织内通常含有大量不成熟的新生肿瘤血管,使肿瘤具有高灌注高渗透性,且瘤体内淋巴系统引流功能不完善 ,即通过EPR效应(enhanced permeability and retention effect)使药物更多富集于癌组织内。纳米载体经长循环修饰后在体内的半衰期更长,且不易从组织中廓清,因而可以被动靶向聚集在癌组织内[16]。EPR效应在众多癌症纳米递药中发挥了重要作用,但部分肿瘤并不具有明显的EPR效应,其中包括胰腺癌[17]。

胰腺癌具有独特的肿瘤微环境,包括丰富的肿瘤基质、匮乏的血供以及较高的瘤内组织液压强,限制了纳米递药系统通过EPR效应被动靶向提升肿瘤组织的药物浓度(图1)[17-18]。因此,克服胰腺癌肿瘤微环境对药物EPR效应的限制,是设计被动靶向纳米递药系统的重要策略。这包括:

重塑肿瘤血供 受肿瘤微环境的影响,胰腺癌的毛细血管纤细扭曲,是造成胰腺癌血供匮乏的重要因素之一,限制了药物的递送效率[12]。已经有研究报道,利用血管紧张素Ⅱ受体抑制剂氯沙坦(losartan),可以重塑肿瘤血管,提升血管内灌注,从而提升药物递送效能[19];同时,通过siRNA抑制胰腺癌组织内血管紧张素II受体表达也观察到上述现象[20]。

降解肿瘤基质 透明质酸酶(hyaluronidase)是一种可以降解透明质酸的生物蛋白酶,其PEG化的纳米尺度复合物全身性给药后可以降解胰腺癌肿瘤基质,提高药物在瘤体内的分布[21-22]。但基础研究发现,打破胰腺癌肿瘤基质在提高药物(如吉西他滨)渗透浓度的同时,使癌细胞趋向分化为更高的恶性程度及更强的转移倾向,荷瘤小鼠生存时间更糟糕[23-24]。临床研究也发现,在基础研究获得良好结果的纳米药物,在临床研究中并未得到令人乐观的数据,进一步说明了胰腺癌的复杂性及改变肿瘤微环境所产生的潜在风险[17]。

提升穿透肿瘤基质能力 通过优化纳米粒的直径、表面电荷及修饰特定配体,可以提高纳米粒在肿瘤基质内的穿透性。肿瘤基质内的胶原蛋白呈正电性而硫酸黏多糖呈负电性[25],两者与表面互补电荷的纳米粒结合而使纳米递药呈现分布异质性,降低递药效能,通过靶向的配体修饰(详见主动靶向部分)可以克服上述限制,提高递药效能[26]。我们在前期研究中利用细胞穿膜肽修饰纳米载体后局部瘤内注射纳米粒,提高了其在瘤体内的扩散范围和药物在癌细胞内的分布[13]。

主动靶向性设计不同于被动靶向,纳米载药系统经恰当的配体修饰后,可以与目标细胞的受体特异性结合,从而具有主动靶向的功能,这构成了纳米递药与小分子化疗药物的根本区别[27]。由于胰腺癌较弱的EPR效应,主动靶向性设计对提高纳米系统胰腺癌递药性能具有重要意义。选择适当的配体-受体(或抗体-抗原)对构建主动靶向的纳米递药系统至关重要。一般而言,为实现纳米粒的高度选择性,靶细胞表面受体具有高度特异性,以区别正常细胞;因一方面,为保证纳米粒具有较高识别效率,靶细胞表面的受体表达量一般高于105级别[28]。同时,部分受体与配体结合后可以启动受体介导的吞噬过程,这适用于需要入胞后释放药物的纳米粒,如基于CD20的靶向递药[29];而有的受体本身并不介入内吞过程,这对于实体肿瘤的靶向递药可能有帮助,可以实现靶向间质细胞和细胞外释药,作用于周围的癌细胞[30](此时,癌细胞本身可能没有合适的靶向标记物)。目前,在基础研究中,除了已经广泛报道的整合素-多肽[31-32]及叶酸-叶酸受体系统[33-34],近5年用于靶向胰腺癌的受体见表1。

A:The pathobiological barriers including:a dense desmoplastic stroma,excessive extracellular matrix deposition,increased interstitial fluid pressure,and compression of blood vessels.B:Vascular normalization;C:Normalizing the solid stress by reducing the desmoplastic stroma;D:Reduction of extracellular matrix.Figure was reprinted by permission from Macmillan Publishers Ltd:NatRevCliOncol[17],copyright 2016.

图1胰腺癌肿瘤微环境与被动靶向递药设计策略
Fig1StrategiestoovercomethepathophysiologicalbarriersimpedingthepassivetargeteddeliveryforPDAC

智能响应纳米递药系统的设计通过被动靶向及主动靶向设计,显著提高了纳米诊疗系统在目标组织内的分布。但是网状内皮系统及分布在肝脾的巨噬细胞仍然是影响纳米药物分布的关键因素,目前已经进入临床实验的纳米药物也证实肝脾肾肺等组织内的分布多于肿瘤组织[42]。为进一步提高纳米递送药物效率,研究者设计了多种局部智能响应的纳米载体,它基于体内或体外特定的刺激源触发并完成药物的智能可控释放[43]。

肿瘤内环境响应的纳米递药系统 与大多数恶性肿瘤一样,由于胰腺癌细胞的失控性生长,其内环境相对正常组织常表现出一些独特的生理特征,如肿瘤微环境内及癌细胞溶酶体的弱酸性[43]、肿瘤细胞内的高还原性物质(如谷胱甘肽GSH)[45]等。

外环境触发的纳米递药系统 通过影像引导下,以热、磁及机械波(含超声波)为媒介触发纳米递药系统释放负载药物,可以实现更高的递药效率。Wang等[46]学者组合了肿瘤内外环境,设计的新型纳米递药载体实现了三维响应触发递药(超声波、酸敏感及还原性物质谷胱甘肽)。

表1 用于胰腺癌主动靶向的受体药物递药系统Tab 1 Receptors for active targeted drug delivery in pancreatic cancer

未来研究的启示靶向性递药是胰腺癌纳米递药系统必备要素,一个理想的胰腺癌靶向性纳米递药系统可以有效克服胰腺癌微环境对药物递送的限制,提高纳米药物在目标细胞内的富积,并通过局部的智能控释提高药物的输送能力。但胰腺癌的纳米递药依然面临巨大挑战,突破胰腺癌独特的肿瘤微环境对纳米递药的限制,筛选胰腺癌高灵敏的靶向分子,设计构建智能响应的载药释药系统,适应胰腺癌复杂的分子生物学特征,是未来提高纳米靶向递药治疗胰腺癌效果的关键。

[1] SIEGEL RL,MILLER KD,JEMAL A.Cancer statistics,2016 [J].CACancerJClin,2016,66(1):7-30.

[2] ZHENG R,ZENG H,ZHANG S,etal.National estimates of cancer prevalence in China,2011 [J].CancerLett,2016,370(1):33-38.

[3] HAMMEL P,HUGUET F,VAN LAETHEM JL,etal.Effect of chemoradiotherapy vs chemotherapy on survival in patients with locally advanced pancreatic cancer controlled after 4 months of gemcitabine with or without erlotinib:The LAP07 randomized clinical trial [J].JAMA,2016,315(17):1844-1853.

[4] RYAN DP,HONG TS,BARDEESY N.Pancreatic adenocarcinoma[J].NEnglJMed,2014,371(11):1039-1049.

[5] VERMA V,LI J,LIN C.Neoadjuvant therapy for pancreatic cancer:systematic review of postoperative morbidity,mortality,and complications [J].AmJClinOncol,2016,39(3):302-313.

[6] GRESHAM GK,WELLS GA,GILL S,etal.Chemotherapy regimens for advanced pancreatic cancer:a systematic review and network meta-analysis [J].BMCCancer,2014,14(1):1-13.

[7] PEREZ-HERRERO E,FERNANDEZ-MEDARDE A.Advanced targeted therapies in cancer:Drug nanocarriers,the future of chemotherapy[J].EurJPharmBiopharm,2015,93:52-79.

[8] BUKKI J.Pancreatic adenocarcinoma[J].NEnglJMed,2014,371(22):2139-2140.

[9] BRANNON-PEPPAS L,BLANCHETTE JO.Nanoparticle and targeted systems for cancer therapy [J].AdvDrugDelivRev,2004,56(11):1649-1659.

[10] MOORE MJ,GOLDSTEIN D,HAMM J,etal.Erlotinib plus gemcitabine compared with gemcitabine alone in patients with advanced pancreatic cancer:a phase III trial of the National Cancer Institute of Canada Clinical Trials Group [J].JClinOncol,2007,25(15):1960-1966.

[11] PAULSON AS,TRAN CAO HS,TEMPERO MA,etal.Therapeutic advances in pancreatic cancer [J].Gastroenterology,2013,144(6):1316-1326.

[12] HOFFMAN RM,BOUVET M.Nanoparticle albumin-bound-paclitaxel:a limited improvement under the current therapeutic paradigm of pancreatic cancer [J].ExpertOpinPharmacother,2015,16(7):943-947.

[13] WANG Q,LI J,AN S,etal.Magnetic resonance-guided regional gene delivery strategy using a tumor stroma-permeable nanocarrier for pancreatic cancer [J].IntJNanomedicine,2015,10(1):4479-4490.

[14] COUVREUR P.Nanoparticles in drug delivery:Past,present and future[J].AdvDrugDelivRev,2013,65(1):21-23.

[15] CHAUHAN VP,JAIN RK.Strategies for advancing cancer nanomedicine [J].NatMater,2013,12(11):958-962.

[16] ANG CY,TAN SY,ZHAO Y.Recent advances in biocompatible nanocarriers for delivery of chemotherapeutic cargoes towards cancer therapy[J].OrgBiomolChem,2014,12(27):4776-4806.

[17] ADISESHAIAH PP,CRIST RM,HOOK SS,etal.Nanomedicine strategies to overcome the pathophysiological barriers of pancreatic cancer[J].NatRevClinOncol,2016,13(12):750-765.

[18] LUNARDI S,MUSCHEL RJ,BRUNNER TB.The stromal compartments in pancreatic cancer:are there any therapeutic targets? [J].CancerLett,2014,343(2):147-155.

[19] DIOP-FRIMPONG B,CHAUHAN VP,KRANE S,etal.Losartan inhibits collagen I synthesis and improves the distribution and efficacy of nanotherapeutics in tumors [J].ProcNatlAcadSciUSA,2011,108(7):2909-2914.

[20] GUO R,GU J,ZHANG Z,etal.MicroRNA-410 functions as a tumor suppressor by targeting angiotensin II type 1 receptor in pancreatic cancer [J].IUBMBLife,2015,67(1):42-53.

[21] WHATCOTT CJ,HAN H,VON HOFF DD.Orchestrating the tumor microenvironment to improve survival for patients with pancreatic cancer:normalization,not destruction [J].CancerJ,2015,21(4):299-306.

[22] MANUEL ER,CHEN J,D′APUZZO M,etal.Salmonella-based therapy targeting indoleamine 2,3-dioxygenase coupled with enzymatic depletion of tumor hyaluronan induces complete regression of aggressive pancreatic tumors [J].CancerImmunolRes,2015,3(9):1096-1107.

[23] CHENG XB,KOHI S,KOGA A,etal.Hyaluronan stimulates pancreatic cancer cell motility [J].Oncotarget,2015,7(4):4829-4840.

[24] SHERMAN MH,YU RT,ENGLE DD,etal.Vitamin D receptor-mediated stromal reprogramming suppresses pancreatitis and enhances pancreatic cancer therapy [J].Cell,2014,159(1):80-93.

[25] LIELEG O,BAUMGARTEL RM,BAUSCH AR.Selective filtering of particles by the extracellular matrix:an electrostatic bandpass[J].BiophysJ,2009,97(6):1569-1577.

[26] STYLIANOPOULOS T,JAIN RK.Design considerations for nanotherapeutics in oncology[J].Nanomedicine,2015,11(8):1893-1907.

[27] PEER D,KARP JM,HONG S,etal.Nanocarriers as an emerging platform for cancer therapy[J].NatNanotechnol,2007,2(12):751-760.

[28] PARK JW,HONG K,KIRPOTIN DB,etal.Anti-HER2 immunoliposomes:enhanced efficacy attributable to targeted delivery[J].ClinCancerRes,2002,8(4):1172-1181.

[29] SAPRA P,ALLEN TM.Internalizing antibodies are necessary for improved therapeutic efficacy of antibody-targeted liposomal drugs [J].CancerRes,2002,62(24):7190-7194.

[30] ALLEN TM.Long-circulating (sterically stabilized) liposomes for targeted drug delivery [J].TrendsPharmacolSci,1994,15(7):215-220.

[31] JI S,XU J,ZHANG B,etal.RGD-conjugated albumin nanoparticles as a novel delivery vehicle in pancreatic cancer therapy [J].CancerBiolTher,2012,13(4):206-215.

[32] MURATA M,NARAHARA S,KAWANO T,etal.Design and function of engineered protein nanocages as a drug delivery system for targeting pancreatic vancer vells via neuropilin-1 [J].MolPharm,2015,12(5):1422-1430.

[33] XU S,XU Q,ZHOU J,etal.Preparation and characterization of folate-chitosan-gemcitabine core-shell nanoparticles for potential tumor-targeted drug delivery [J].JNanosciNanotechnol,2013,13(1):129-138.

[34] LU J,LI Z,ZINK JI,etal.Invivotumor suppression efficacy of mesoporous silica nanoparticles-based drug-delivery system:enhanced efficacy by folate modification [J].Nanomedicine,2012,8(2):212-220.

[35] ZHOU H,QIAN W,UCKUN FM,etal.IGF1 teceptor targeted theranostic nanoparticles for targeted and image-guided therapy of pancreatic cancer [J].ACSNano,2015,9(8):7976-7991.

[36] XU J,GATTACCECA F,AMIJI M.Biodistribution and pharmacokinetics of EGFR-targeted thiolated gelatin nanoparticles following systemic administration in pancreatic tumor-bearing mice [J].MolPharm,2013,10(5):2031-2044.

[37] CAMP ER,WANG C,LITTLE EC,etal.Transferrin receptor targeting nanomedicine delivering wild-type p53 gene sensitizes pancreatic cancer to gemcitabine therapy [J].CancerGeneTher,2013,20(4):222-228.

[38] WU SC,CHEN YJ,LIN YJ,etal.Development of a mucin4-targeting SPIO contrast agent for effective detection of pancreatic tumor cellsinvitroandinvivo[J].JMedChem,2013,56(22):9100-9109.

[39] QIAN C,WANG Y,CHEN Y,etal.Suppression of pancreatic tumor growth by targeted arsenic delivery with anti-CD44v6 single chain antibody conjugated nanoparticles [J].Biomaterials,2013,34(26):6175-6184.

[40] LEE GY,QIAN WP,WANG L,etal.Theranostic nanoparticles with controlled release of gemcitabine for targeted therapy and MRI of pancreatic cancer [J].ACSNano,2013,7(3):2078-2089.

[41] TER WEELE EJ,TERWISSCHA VAN SCHELTINGA AG,KOSTERINK JG,etal.Imaging the distribution of an antibody-drug conjugate constituent targeting mesothelin with 89Zr and IRDye 800CW in mice bearing human pancreatic tumor xenografts[J].Oncotarget,2015,6(39):42081-90.

[42] ALEXIS F,PRIDGEN E,MOLNAR LK,etal.Factors affecting the clearance and biodistribution of polymeric nanoparticles[J].MolPharm,2008,5(4):505-515.

[43] VAN ELK M,MURPHY BP,EUFRASIO-DA-SILVA T,etal.Nanomedicines for advanced cancer treatments:Transitioning towards responsive systems[J].IntJPharm,2016,515(1-2):132-164.

[44] LEI Y,HAMADA Y,LI J,etal.Targeted tumor delivery and controlled release of neuronal drugs with ferritin nanoparticles to regulate pancreatic cancer progression [J].JControlRelease,2016,232:131-142.

[45] ANAJAFI T,SCOTT MD,YOU S,etal.Acridine orange conjugated polymersomes for simultaneous nuclear delivery of gemcitabine and doxorubicin to pancreatic cancer cells[J].BioconjugChem,2016,27(3):762-771.

[46] YANG P,LI D,JIN S,etal.Stimuli-responsive biodegradable poly(methacrylic acid) based nanocapsules for ultrasound traced and triggered drug delivery system [J].Biomaterials,2014,35(6):2079-2088.