Professors Huabing Chen and Tao Yang report the new concept of holographic activation for illuminating tumors in Advanced Materials

Applying contrast agents (CAs) to increase signalsintumors specifically is considered an extensively applied approach among clinically relevant diagnostic modalities such as magnetic resonance imaging (MRI). Smartly improving tumor contrast has been widely explored to visualize tumors from surrounding healthy tissues through stimuli-responsive probes, enabling enhanced sensitivity and accuracy in response to subtle physiopathologic alterations such as tumor acidity, hypoxia, glutathione (GSH), and enzymes.However, many intracellular physiopathologic alterations (e.g.1-10 mM GSH or lysosomal pH) only occur within subcellular organelles, whereasit is difficult to activate probe retained in GSH- or acidity-deficient tumor stroma, andundesired distribution of probes in normal tissues might compromise their tumor contrasts.A major challenge remains in robustly activating CAs for holographic imaging in the whole tumor, together with suppressed background noise.

In recent years, Prof. Huabing Chen and Tao Yang’s group at the College of Pharmaceutical Science focused on the construction of multi-modal imaging probes for cancer diagnosis(Adv Mater, 2015, 27, 3874-3882;Adv Mater, 2015, 27, 5049-5056;Adv Mater, 2016, 28, 5923-5930;ACS Nano, 2017, 11, 1848-1857;Theranostics,2017, 7, 764-774;Biomaterials,2018, 154, 248-260;Small,2018, 14, 1802905;J Control Release,2021, 329, 997-1022;J Control Release,2022, 350, 761-776).Based on the previous research, this team further cooperates with Dr. Zhen Jiang’s group in the Second Affiliated Hospital of Soochow University to developa holographically activatable nanoprobe caging manganese tetraoxide for tumor-selective contrast enhancement in magnetic resonance imaging (MRI) through cooperative GSH/albumin-mediated cascade signal amplification in tumor and rapid elimination in normal tissues, thus achieving precise tumor malignancy detection, surveillance and surgical guidance (Figure 1).

Figure 1.Schematic illustration of holographic MR imaging using intelligent tProbe.

Firstly, single-moleculetransferrin was applied as the nanoreactor to synthesizethe tumor-targeted transferrin nanoprobe (tProbe) throughbiomineralization-mediated growth of Mn₃O₄-NCswithin the nanocage (Figure 2A and 2B). tProbe at pH 5.0 was found to have a six-order decrease oft_1/2(~ 0.002 h) under 5.0 mM GSH treatment as compared to that at pH 7.4 in the absence of GSH (t_1/2, 140 h) (Figure 3B) (Figure 2C), which was fundamentally due to the pH-accelerated and GSH-dominant decomposition behavior. The relaxivity (~ 0.6 mM^-1s^-1) of 12.2 nm tProbe was increased to ~ 1.6 mM^-1s^-1at pH 6.5, and was further promoted to ~ 3.5 mM^-1s^-1at pH 5.0 and underwent aninstantaneousincrease of relaxivity to ~ 7.8 mM^-1s^-1upon incubation with GSH (Figure 2D) with threshold GSH concentration of 0.04 mM, suggesting the GSH/pH-mediated cascade signal amplification (Figure 2E).

Figure 2.In vitrodecompositionand longitudinal relaxivities(r₁) amplification of of 12.2 nm tProbe through GSH-dominant and acidity-accelerated decomposition kinetics.

After intravenous injection, tProbe was found in both intracellular and extracellular space(Figure 3A).Owing to GSH/pH-mediated cascade signal amplification, MRI signals in the 12.2 nm tProbe group were considerably increased to theT/Nratio of 242% while the signals from Gd-DTPA group remained relatively unchanged, and tMn₃O₄-NPs also showed a slight change of signals (Figure 3B and 3C). GSH/pH-mediated cascade signal amplification was further verified by the decrease ofT/Nratio upon introduction of inhibitors to block acidity and GSH synthesis (Figure 3D-F).

Figure 3.Non-invasive report ofin vivodecompositionkinetics by tProbe.

There are still tProbe arrested outside tumor cells remaining non-decomposed due to weak acidity and GSH levels (pH_e6.5-6.8, and GSH_e< 10 µM). We established an up-regulated TME strategy to potentiate the GSH-dominant decomposition of extracellular tProbe for achieving enhanced MRI contrast, followed by the generation of Mn²⁺-albumin complex with much higher relaxivities (35.5 mM^-1s^-1) for improving theT/Nratio to 300% via holographic activation. More importantly, intravenous GSH injection not only boosts the decomposition of extracellular tProbe to synergize with intracellular activation for achieving cascade MR signal amplification but also allows the decomposition of tProbe into Mn²⁺in normal tissues for quick renal clearance, together with no impact on tumor retention, thus illuminating the undetectable tumor micrometastasis. In summary,the cascade activation and suppressed background of tProbe in the whole tumor enables tremendous breakthroughs of contrast enhancement for holographically diagnosing tumors from surrounding normal tissues, representing a new avenue for MR imaging of malignant tumors.

Figure 4.In vivodecompositionof tProbe after pharmacologically up-regulated GSH_efor improving MRI contrast.

References:Ting Li^#,Shuangxiu Tan^#,Mengjuan Li,Jie Luo,Yueyue Zhang,Zhen Jiang^*,Yibin Deng,Liang Han,Hengte Ke,Junkang Shen,Yong’an Tang, Fan Liu,Huabing Chen^*, andTao Yang^*Adv Mater, 2022, 202209603.

The original link:https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202209603