番荔素（Annonaceous acetogenins, ACGs）是从番荔枝科植物中提取出来的一类长链脂肪酸内酯化合物，为继紫杉醇之后又一个有前途的天然来源抗癌中药有效成分，相比其他常见的抗肿瘤药物具有更强的活性，且药理学机理独特，能逆转多药耐药，但毒副作用大、治疗窗口窄限制了其应用。为了克服这一问题，本研究构建了一种协同化疗与光热治疗的局部给药系统，其原理是通过肿瘤内局部注射给药减少ACGs在非靶部位的分布，在肿瘤局部激光照射下，光热转换材料升高肿瘤局部温度使肿瘤消融，也能促进ACGs纳米粒（ACGs NPs）的释放与渗透，同时在光热治疗对化疗的协同作用下可进一步减小ACGs 的给药剂量，最终达到减轻ACGs 的毒副作用，增强其疗效的目的，实现药物有效递送。而聚多巴胺（PDA）因具有良好的光热转换性能与生物相容性、易制备性、易修饰性被作为光热材料广泛应用。因此，我们以PDA 纳米粒（PDA NPs）为光热转换材料用于光热治疗。研究内容具体如下：

首先，利用PCL₂₀₀₀-mPEG₂₀₀₀作为稳定剂制备了ACGs NPs，利用盐酸多巴胺的氧化自聚合制备了PDA NPs。为了提高生理介质稳定性，将PDA NPs用聚乙二醇（PEG）进行修饰得到PEG化的PDA NPs（PDA-PEG NPs）。随后，通过测量纳米粒的粒径、电位以及傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、光热转换性能等对相应纳米粒进行表征。ACGs NPs的粒径为103.70±0.87 nm，PDA NPs与PDA-PEG NPs粒径较小（64.42±0.32，70.96±2.55 nm），PDA NPs经PEG修饰后在多种生理介质中可以稳定存在，并且1.5 mg/mL的PDA-PEG NPs在功率为5 W/cm²的808 nm NIR激光照射下照射330 s可升温至42 ℃以上，从而能够对肿瘤细胞产生杀伤作用。FTIR及XPS确证了PDA NPs上PEG的成功修饰。

体外细胞毒性实验证明：（1）4T1细胞对ACGs NPs的敏感性比B16细胞更高，因此后续采用了4T1细胞模型。（2）PDA-PEG NPs具有良好的生物相容性，可用作光热转换材料。（3）PDA-PEG NPs在指定浓度下经NIR激光照射可杀伤过半的4T1肿瘤细胞。（4）ACGs NPs与PDA-PEG NPs在激光照射下表现出优良的协同效应，使4T1细胞的存活率仅为1%。

体内研究表明：（1）PDA-PEG NPs在小鼠体内生物相容性良好。（2）光热治疗组，即注射PDA-PEG NPs经过激光照射后的抑瘤率为63.49%。（3）ACGs NPs经瘤内注射（0.2 mg/kg）与静脉注射（0.4 mg/kg）的抗肿瘤药效相似（69.87% vs 72.81%），但相比于静脉注射ACGs NPs导致了2只小鼠死亡，瘤内注射的ACGs NPs安全性明显更高，在肿瘤中的药物分布也更多。（4）更有趣的是，经瘤内注射的ACGs NPs在联合光热治疗后在肿瘤部位的药物分布会进一步提高。（5）ACGs NPs 与PDA-PEG NPs在激光照射下联合应用的局部给药系统抗肿瘤效果优良，抑瘤率可达82.65%，虽然对脾脏有一定的损伤，但对体重的影响不明显，且其在ACGs低剂量下与更低的给药频率能实现比高剂量静脉注射更强的抗肿瘤效果与更高的安全性，说明该给药系统起到了增效减毒的作用。

综上，基于ACGs和PDA的协同化疗与光热治疗的肿瘤局部给药药物递送系统具有优异的抗肿瘤效果，增强了ACGs的药效，也减轻了ACGs的毒性，是一种良好的递送系统，有望为乳腺癌探索新的治疗手段。

Annonaceous acetogenins (ACGs) are a kind of long-chain fatty acid lactone compounds extracted from the Annonaceous plants. They are promising natural anticancer active ingredients after paclitaxel. Compared with other common anticancer drugs, ACGs have stronger activities and unique pharmacological mechanism, and they can reverse multidrug resistance. However, their side effects and narrow treatment window have limited their application. To overcome this problem, a local drug delivery system that combines chemotherapy and photothermal therapy (PTT) has been constructed in this study. The principle is that local administration can reduce the distribution of ACGs in non-target sites. And under laser irradiation, the photothermal conversion material can increase the temperature of tumor to ablate the tumor and promote the release and penetration of ACGs nanoparticles (ACGs NPs). At the same time, the dosage of ACGs can be further reduced due to the synergistic effect of PTT and chemotherapy. Finally, it is expected to enhance efficiency and reduce toxicity of ACGs to achieve effective drug delivery. Polydopamine (PDA) is widely used as a photothermal material due to its good photothermal conversion performance, biocompatibility, easy preparation and modification. Therefore, we use PDA nanoparticles (PDA NPs) as photothermal conversion materials for PTT. The research contents are as follows:

First, ACGs NPs were prepared using PCL₂₀₀₀-mPEG₂₀₀₀ as a stabilizer, and PDA NPs were prepared by oxidative self-polymerization method using dopamine hydrochloride. In order to improve the stability in physiological media, PDA NPs were modified with polyethylene glycol (PEG) to obtain PEGylated PDA NPs (PDA-PEG NPs). Subsequently, the nanoparticles (NPs) were characterized by measuring the particle size, zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and photothermal conversion performance of the corresponding NPs. ACGs NPs have a particle size of 103.70±0.87 nm. PDA NPs and PDA-PEG NPs have small particle sizes (64.42±0.32, 70.96±2.55 nm). PDA-PEG NPs can stably exist in a variety of physiological media, and when 1.5 mg/mL PDA-PEG NPs were irradiated under an 808 nm NIR laser at a power density of 5 W/cm² for 330 s, the temperature could be raised to above 42 ℃, which can kill tumor cells. FTIR and XPS confirmed the successful modification of PEG on PDA NPs.

In vitro cytotoxicity assays have proved that: (1) 4T1 cells were more sensitive to ACGs NPs than B16 cells, so we adopted the 4T1 cell model later. (2) PDA-PEG NPs had good biocompatibility and could be used as photothermal conversion materials. (3) PDA-PEG NPs at a given concentration could kill more than half of 4T1 cells under NIR laser irradiation. (4) ACGs NPs and PDA-PEG NPs showed excellent synergistic effects under laser irradiation, making the survival rate of 4T1 cells only 1%.

In vivo studies showed that: (1) PDA-PEG NPs had good biocompatibility in mice. (2) The tumor inhibition rate of the photothermal therapy group treated with PDA-PEG NPs plus NIR laser irradiation was 63.49%. (3) The antitumor effects of ACGs NPs injected intratumorally (0.2 mg/kg) and intravenously (0.4 mg/kg) were similar (69.87% vs 72.81%). However, compared with ACGs NPs injected intravenously which caused the death of 4 mice, ACGs NPs injected intratumorally had significantly higher safety and more drug distribution in tumor site. (4) More interestingly, the drug distribution in tumor site of ACGs NPs injected intratumorally would be further improved after combining with PTT. (5) The local drug delivery system that combined ACGs NPs with PDA-PEG NPs had excellent antitumor effects under laser irradiation, and the tumor inhibition rate can reach 82.65%. Although it may damage the spleen to a certain extent, it had no obvious effects on body weight, and it can achieve stronger antitumor effects and higher safety than a high dose of ACGs NPs injected intravenously when the dosage and administration frequency of ACGs were reduced, indicating that the drug delivery system plays a role in enhancing efficiency and reducing toxicity of ACGs.

In summary, the local drug delivery system that combined PTT (based on PDA) and chemotherapy (based on ACGs) has excellent antitumor effects, enhances the efficiency and reduces the toxicity of ACGs. And this good drug delivery system is expected to explore new methods for the therapy of breast cancer.