一种可促成肿瘤微环境“正常”化而利于胰腺癌纳米药物递送的智能白蛋白纳米载体的研究

The existing strategies, by modulating the tumor microenvironment to break the barriers of drug delivery in the pancreatic cancer, risk enhancing the tumor invasiveness. Calcipotriol (Ca) can normalize the tumor microenvironment to break the barriers of drug delivery by acting on activated pancreatic stellate cells (PSCs). And Ca modulation does not enhance tumor invasiveness. However, Ca only works in certain tumor areas because it could not be effectively delivered to those activated PSCs located in the deep region of the tumor, thus greatly compromising its modulating effect. Therefore, we design a smart HSA nanocarrier PFC-gHSA/Ca. First, glutaraldehyde cross-linking can avoid the disintegration of PFC-gHSA/Ca in blood, thereby improving tumor distribution of Ca. Second, the particle size of ~30 nm and superficial PEGylation make it possible for PFC-gHSA/Ca to pass through the barriers of fibrotic matrix and penetrate deeply into the tumor tissue. Finally, PFC-gHSA/Ca will intelligently take off its PEG corona and expose the cell penetrating peptide under the cleavage of FAP on the surface of activated PSCs, thus achieving high cellular uptake within PSCs. Moreover, HSA can promote the modulating effect of Ca. Through rational design, PFC-gHSA/Ca can effectively deliver Ca into activated PSCs located in the deep region of the tumor, thus normalizing the tumor microenvironment and greatly enhancing the delivery and therapeutic effect of nanomedicines in the pancreatic cancer. Therefore, it has important scientific significance and application value.

现有改善胰腺癌递药屏障的肿瘤微环境调控方式，具有增强肿瘤侵袭性的风险。卡泊三醇（Ca）通过作用于活化成纤维细胞（PSCs）实现肿瘤微环境正常化，改善递药屏障，不会增强肿瘤侵袭性。但由于无法有效递送至肿瘤深部的活化PSCs，Ca调控具有区域选择性，从而严重制约其调控效果。因此，我们设计了一种智能白蛋白纳米载体PFC-gHSA/Ca：通过戊二醛交联避免该载体血中崩散，增强Ca肿瘤分布；粒径~30nm及PEG化使该纳米载体可穿透纤维基质屏障，到达肿瘤深部；在活化PSCs表面FAP酶作用下，该纳米载体可智能脱卸PEG冠，暴露细胞穿膜肽，实现在PSCs的高效摄取。此外白蛋白可辅助巩固Ca调控功能。该纳米载体通过合理化设计，可将Ca有效递送至肿瘤深部的活化PSCs，实现肿瘤微环境正常化，显著增强胰腺癌纳米药物的递送及疗效，且不会增强肿瘤侵袭性。因此，具有重要的科学意义和应用价值。

胰腺癌号称癌中之王， 80%以上患者依赖化疗，然而，病人5年生存率不足10%。一方面，胰腺癌病人肿瘤组织血供贫乏，制约化疗药物递送；另一方面，胰腺癌组织存在具有肿瘤促生作用的活化胰腺星型细胞（pancreatic stellate cells，PSCs），这些因素是其化疗疗效不佳的重要原因。因此，如果能突破胰腺癌递送屏障，改善化疗药和PSCs调控剂在靶细胞的暴露，将有助于改善化疗效果。为此，我们设计合成了两种酶可活化前药—膜型基质金属蛋白酶1（membrane type 1-matrix metalloproteinase, MT1-MMP）可活化的cRGDfK肽（MT1-MMP-activated cRGDfK, MR）前药及磷酸化卡泊三醇（phosphorylated calcipotriol, PCAL）前药；并将MR、PCAL前药及DOX分别装载于热敏脂质体（thermosensitive liposomes，TSLs）表面或内核，制得智能脂质体MR-T-PD。静脉注射后，MR-T-PD表面MR可被肿瘤内皮细胞MT1-MMP活化，释放cRGDfK肽，促进内皮迁移及血管生成，改善脂质体瘤内递送。在肿瘤局部热作用下，MR-T-PD可迅速释放包载的DOX和PCAL；DOX可迅速被肿瘤细胞摄取，而PCAL可被活化PSCs表面碱性磷酸酶活化，释放原型，从而可被PSCs摄取，将其调控至静息态，促进DOX抗肿瘤效果。最终，MR-T-PD显著改善了胰腺癌化疗效果，且未引起明显副作用。因此，MR-T-PD代表一种安全、有效的化疗方式，可为解决胰腺癌药物递送难、疗效差的难题提供新思路。