纳米生物催化与肿瘤代谢疗法研究

Metabolic reprogramming is one of the distinguishing features between normal cells and highly proliferating cells like cancer cell. This reprogramming is purported to facilitate the survival and growth of cancer cells by enhancing macromolecular synthesis and antioxidant defense, besides the energy production. Exploiting cancer metabolism offers a unique biochemical foundation for selective eradication of malignant cells with minimal side effects. Thus, the development of metabolism-based precision nanomedicine has the potential to overcome the challenges and limitations associated with traditional cancer therapeutics. It is a nearly universal trait that all cancer cells acquire more nutrients (glucose, glycine, glutamine, etc.) and convert these nutrients into biosynthetic building blocks for constructing a new cell. In view of such metabolic dysregulations, here we introduce a simple and efficient concept of sequential and amplified catalytic nanomedicine into efficient tumor therapy by designing biocompatible nanocatalysts and delivering them into tumor sites. Two different natural enzymes are both integrated into the large pore-sized and biodegradable Fe3O4 nanoclusters coated by perfluorocarbon polymer. Through actively generating O2 from hybrid nanocatalysts, natural enzymes could effectively deplete glucose and glycine, and meanwhile produce substantial amount of H2O2 and acids for subsequent Fenton-like reactions catalyzed by Fe3O4 clusters in response to mild acidic tumor microenvironment. Highly toxic hydroxyl radical will be formed through the sequential and amplified catalytic reactions to trigger the apoptosis and death of tumor cells. This strategy, if applicable, can only give rise to the therapeutic effects within tumor tissues rather than other normal ones. It hopefully provides a promising strategy to solve the barriers such as tumor heterogeneity and metabolic replenishment, which may get breakthroughs in tumor precision therapy.

代谢重编程是肿瘤细胞区别于正常细胞的重要特征。这种普遍存在且又高度异常的代谢依赖性提供了用于选择性杀死肿瘤细胞的生化基础，基于此发展精准肿瘤干预策略将是突破现有治疗瓶颈的关键。无论肿瘤细胞从基因型到表型上如何改变，为了实现快速生长和增殖，肿瘤细胞都需要大量摄取糖和氨基酸等营养物质。申请人拟从癌变发生的代谢源头出发，以肿瘤细胞中异常丰富的葡萄糖和甘氨酸为靶点，秉承“简以致用”的材料设计理念，全部使用FDA认证的医用材料来构建纳米生物催化体系。基于两步串联放大的酶催化和Fenton催化机制，借助主动携氧和原位产酸策略，安全无毒的杂化磁簇在瘤内生成局域浓度高且毒性强的活性氧物种，同时实现（1）从代谢源头剥夺肿瘤细胞营养物质供应、（2）全面阻断肿瘤能量和合成代谢通路，突破肿瘤异质性和代谢补偿机制的限制。通过本项目实施，极有可能开发出更简单有效的肿瘤治疗新手段，推动肿瘤精准诊疗研究的步伐。

本项目的目标是发展面向肿瘤的精准医学，主要研究内容涉及到两个方面：高分辨肿瘤活体成像（精准诊断）和肿瘤催化代谢疗法（精准治疗）。在肿瘤的精准诊断方面，我们发展了一种全新的肿瘤成像技术：近红外二区磷光成像技术。借助于肿瘤微环境的特定扰动（例如pH改变），实现了从微弱的荧光到高强度近红外二区磷光的快速转变。具体表现为pH在约0.4区间内发生变化时，与初始相比，所设计的CISe探针的近红外二区光学强度增加了约5800倍。更为重要的是，伴随着受限自组装过程的发生，CISe探针迅速实现从73 ns短寿命荧光到336 μs长寿命、近红外二区（最大发射峰在1130 nm左右）磷光光学性质的转变。这类可激活的近红外二区磷光成像，能够获得较高的信噪比，进一步提高对早期疾病检测的特异性和灵敏度。同时能够在分子水平上完成实时敏感的成像病理因素分析，实现在分子水平上理解潜在的病理机制与进程，为优化疾病的治疗和干预提供保障。例如，基于CISe纳米探针的荧光-磷光转变机理，将其应用于活体小动物的体内实时强度和寿命成像。结果显示，来源于正常器官和组织的生物背景信号干扰得到了明显抑制，仅显示出针对肿瘤的特异性成像能力，尾静脉注射纳米探针24 h后的信噪比高达190，血管分辨率低至7.6 μm，显示出在动物活体内高分辨、高质量的实时成像。在第二个层次肿瘤的精准治疗方面，针对活性氧在维持生命活动中扮演着举足轻重的角色，我们证实生物分子稳定的少原子金属铜团簇具有优异的类酶活性和活性氧清除能力，该结论有助于进一步了解细胞内抗氧化酶防御系统的反应机理，并为开发新型的纳米酶协同系统提供重要的实验参考。在进一步的工作中，我们发现以肿瘤细胞中旺盛的葡萄糖为靶点，借助两步串联放大的酶和Fenton反应，Fe3O4@MnO2纳米催化剂能够原位形成局域浓度高毒性强的羟基自由基，达到特异性杀死肿瘤细胞的同时而不会对正常细胞和组织造成明显的毒副作用。