Composition-Tunable Ultrasmall Manganese Ferrite Nanoparticles: Insights into their In Vivo T1 Contrast Efficacy.

The development of a highly efficient, low-toxicity, ultrasmall ferrite nanoparticle-based T1 contrast agent for high-resolution magnetic resonance imaging (MRI) is highly desirable. However, the correlations between the chemical compositions, in vitro T1 relaxivities, in vivo nano-bio interactions and toxicities remain unclear, which has been a challenge in optimizing the in vivo T1 contrast efficacy. Methods: Ultrasmall (3 nm) manganese ferrite nanoparticles (MnxFe3-xO4) with different doping concentrations of the manganese ions (x = 0.32, 0.37, 0.75, 1, 1.23 and 1.57) were used as a model system to investigate the composition-dependence of the in vivo T1 contrast efficacy. The efficacy of liver-specific contrast-enhanced MRI was assessed through systematic multiple factor analysis, which included the in vitro T1 relaxivity, in vivo MRI contrast enhancement, pharmacokinetic profiles (blood half-life time, biodistribution) and biosafety evaluations (in vitro cytotoxicity testing, in vivo blood routine examination, in vivo blood biochemistry testing and H&E staining to examine the liver). Results: With increasing Mn doping, the T1 relaxivities initially increased to their highest value of 10.35 mM-1s-1, which was obtained for Mn0.75Fe2.25O4, and then the values decreased to 7.64 m M-1s-1, which was obtained for the Mn1.57Fe1.43O4 nanoparticles. Nearly linear increases in the in vivo MRI signals (ΔSNR) and biodistributions (accumulation in the liver) of the MnxFe3-xO4 nanoparticles were observed for increasing levels of Mn doping. However, both the in vitro and in vivo biosafety evaluations suggested that MnxFe3-xO4 nanoparticles with high Mn-doping levels (x > 1) can induce significant toxicity. Conclusion: The systematic multiple factor assessment indicated that the MnxFe3-xO4 (x = 0.75-1) nanoparticles were the optimal T1 contrast agents with higher in vivo efficacies for liver-specific MRI than those of the other compositions of the MnxFe3-xO4 nanoparticles. Our work provides insight into the optimization of ultrasmall ferrite nanoparticle-based T1 contrast agents by tuning their compositions and promotes the translation of these ultrasmall ferrite nanoparticles for clinical use of high-performance contrast-enhanced MRI.

Dishevelled 1, a pivotal positive regulator of the Wnt signalling pathway, mediates 5-fluorouracil resistance in HepG2 cells.

Acquired resistance to 5-fluorouracil (5-FU) frequently occurs in patients with hepatocellular carcinoma (HCC), the underlying molecular mechanisms of which are poorly understood. The aim of this study was to identify candidate genes and associated signalling pathways that may play a role in developing drug resistance following repeated 5-FU treatments. In this work, we established 5-FU-resistant cells (HepG2/5-FU) using stepwise increasing concentrations of 5-FU in parental HepG2 cells. Using transcriptome sequencing, we found that the expressions of the Wnt signalling genes, including negative regulators (DKK1, DKK3, ZNRF3, RNF43 and APC2) and positive regulators (FZD10 and DVL1), were significantly downregulated and upregulated in HepG2/5-FU cells, respectively, resulting in increased Wnt signalling. Dishevelled-1 (DVL1) is an essential Wnt signalling pathway component that stabilizes ß-catenin and mediates the Wnt pathway. Silencing DVL1 using siDVL1 or other small molecular inhibitors in HepG2/5-FU cells could restore 5-FU responsiveness via reduced cell proliferation and migration, and increased apoptosis. Moreover, DVL1 was found to be upregulated in BEL-7402/5-FU cells when compared to the parental BEL-7402 cells. Collectively, our results provide the first clue towards understanding the contribution of DVL1-mediated acquired resistance to 5-FU in HepG2/5-FU cells, suggesting a promising therapeutic strategy for liver cancer resistant to 5-FU.