Endogenous biomaterials in organisms, with native biocompatibility and biodegradability, appear more advantageous in the development of nanoscale diagnostic and therapeutic systems for future clinical translation. Herein, a novel tumor-targeting Magnetic Resonance Imaging (MRI) contrast agent was developed based on Mn²⁺-chelating ultrasmall water-soluble melanin nanoparticles (MNP-PEG-Mn). The nanoparticles, with a size of about 5.6 nm, presented high chelation stability and showed negligible cytotoxicity as estimated by MTT assay. Moreover, the r₁ longitudinal relaxivity (20.56 mM⁻¹ s⁻¹) of MNP-PEG-Mn was much higher than that of Gadodiamide (6.00 mM⁻¹ s⁻¹), which is a clinically approved MRI contrast agent. In vivo MRI experiments revealed excellent tumor-targeting specificity after tumor-bearing mice were intravenously injected with MNP-PEG-Mn. Additionally, MNP-PEG-Mn could be excreted via renal and hepatobiliary pathways with negligible toxicity to body tissues. These preliminary results indicated the clinically translatable potential of MNP-PEG-Mn as a T₁ MRI contrast agent for tumor-targeted imaging.

中文翻译：

---

黑色素锰纳米粒子在体内具有超高效清除率，可用于靶向肿瘤的T ₁磁共振成像造影剂†

具有天然生物相容性和生物可降解性的生物体内的内源性生物材料在开发纳米级诊断和治疗系统以用于未来的临床翻译中似乎更具优势。本文中，基于Mn ²⁺螯合的超小型水溶性黑色素纳米颗粒（MNP-PEG-Mn），开发了一种新型的肿瘤靶向磁共振成像（MRI）造影剂。通过MTT测定估计，具有约5.6nm的尺寸的纳米颗粒表现出高的螯合稳定性并且显示出可忽略的细胞毒性。此外，MNP-PEG-Mn的r ₁纵向弛豫性（20.56 mM ^-1 s ^-1）远高于Gadodiamide（6.00 mM ^-1 s ^-1）），这是临床认可的MRI造影剂。体内MRI实验显示，荷瘤小鼠静脉注射MNP-PEG-Mn后具有出色的肿瘤靶向特异性。此外，MNP-PEG-Mn可以通过肾脏和肝胆途径排出，对人体组织的毒性可以忽略不计。这些初步结果表明，MNP-PEG-Mn作为T ₁ MRI造影剂在肿瘤靶向成像中具有临床可翻译的潜力。