免疫抑制/分子靶向自组装纳米药物体系的构建及其在肝癌肝移植中作用机制研究

Systemic administration of immunosuppressant drugs could elicit tumor recurrence and metastasis in the patients with hepatocellular carcinoma (HCC) after liver transplantation (LT). Thus, we hypothesized that a rational paradigm simultaneously combining immunosuppressants and anti-tumor agents could provide the favorable clinical outcome in HCC patients. We previously demonstrated that a potent anti-tumor agent, SN38, could be esterified by polyunsaturated fatty acids to provide the generated prodrugs that were capable to form colloidal ultra-stable nanodrugs. On the basis of these findings, in this project, we aimed to construct novel single nanoparticulate platforms wherein both of immunosuppressant drugs and molecularly targeted agents are included. To this end, we will site-specifically attach a series of polyunsaturated fatty acids to the clinically approved immunosuppressant drugs, including mycophenolate mofetil (MMF) and tacrolimus (FK506) to construct the prodrugs. These synthetic prodrugs are conferred by the ability of self-assembling into nanoparticles in aqueous media relying on the strong intermolecular forces. Importantly, a library of molecularly targeted agents for HCC chemotherapies will be exploited to validate the ability to co-assemble with MMF or FK506 prodrugs, which further allows the construction of intravenously injectable nanodrug systems. These novel nanoplatforms are expected to locally deliver to the liver and tumor lesions, followed by the hydrolysis to release both drugs. Consequently, several unique synergistic effects will be obtained for those HCC patients after LT, including the suppression of the immunologic function and the inhibition of HCC recurrence with lesser side effect. In addition, we will carefully evaluate the in vivo pharmacokinetics and metabolism, as well as the therapeutic potential using rat models. These studies will open a new exciting perspective for the treatment of tumor recurrence after LT where immunosuppression is involved.

肝癌肝移植受者在全身免疫抑制状态下易发生肝癌的复发转移，如何进行有效防治是提高远期疗效的关键。我们前期基于化疗药SN-38酯化反应偶联具有强疏水性的长链不饱和烷烃分子，构建了自组装的纳米载药体系，大大提高了生物利用度和疗效。本课题以此为基础，对肝癌肝移植常规免疫抑制剂MMF和FK506进行结构改性，将其易于水解酶解的酯键与前期应用的不饱和长链脂肪酸等化合物共价偶联，使其生成水相中具有自组装成纳米粒的能力；并利用现有的肝癌分子靶向药物文库，筛选可自组装进入MMF或FK506前药纳米粒的分子靶向药物，构建两者联用的自组装纳米药物体系。通过与不饱和脂肪酸偶联后的代谢特征，来提高免疫抑制剂及分子靶向药物的肝脏区域浓度，以提升抗免疫排斥和肝癌复发转移的疗效，并减少药物毒副作用。通过免疫抑制剂/分子靶向药物自组装制备、体内转运规律及其作用机制的研究，为临床肝癌肝移植术后肝癌复发转移的防治提供新的方向。

肝移植是治疗肝癌的有效手段，而移植术后系统性长期免疫抑制剂的使用不仅导致各类严重的并发症也会增加肿瘤复发的风险，成为影响其疗效的关键临床问题。如何提高免疫抑制剂在移植肝脏及免疫器官区域内分布从而减轻全身用药的毒副作用并降低肿瘤复发风险是改善肝癌肝移植患者长短期移植获益的核心。本研究以肝癌肝移植常规免疫抑制剂MMF、FK506作为先导化合物，选用多种脂肪酸对MMF进行化学修饰并构建得到可静脉注射的生物利用度高的自组装纳米药物递送体系，筛选可与MMF前药、FK506共组装形成纳米递送系统的分子靶向药物、化疗药物，构建免疫抑制剂与抗肿瘤药物联用的纳米药物新剂型。研究发现不饱和脂肪酸修饰的免疫抑制剂自组装载药体系具有显著的肝脏及免疫器官靶向性，尤其是经亚油酸 (LA) 修饰的自组装纳米制剂短期低剂量即可有效抑制大鼠肝移植排斥反应，稳定性及药代动力学测定发现LA修饰的自组装纳米制剂具有更好的对抗酯酶降解、延长体内循环时间及提高Cmax和AUC的作用，揭示了其体内代谢规律。同时发现MMF-LA@DSPE-PEG纳米制剂在体内具有抗纤维化抗肝癌细胞增殖作用。我们进一步筛选可进行共递送的分子靶向药物或化疗药物，应用PCL-SN38纳米药物递送系统共载免疫抑制剂，证实其在移植/荷瘤模型中兼具显著的抗排斥和抗肿瘤效应。本项目通过前药策略对免疫抑制剂/抗肿瘤药物进行分子改性，构建共载药递送体系，提高免疫抑制剂或抗肿瘤药物的肝脏区域浓度，显著减少药物毒副作用，为临床肝癌肝移植术后肝癌复发转移和改善免疫抑制剂治疗指数的防治提供新的解决方案。