Tumor-associated mast cells (TAMCs) have been recently revealed to play a multifaceted role in the tumor microenvironment. Noninvasive optical imaging of TAMCs is thus highly desired to gain insights into their functions in cancer immunotherapy. However, due to the lack of a single enzyme that is specific to mast cells, a common probe design approach based on single-enzyme activation is not applicable. Herein, we reported a bienzyme-locked molecular probe (THC_MC) based on a photoinduced electron transfer-intramolecular charge-transfer hybrid strategy for in vivo imaging of TAMCs. The bienzyme-locked activation mechanism ensures that THC_MC exclusively turns on near-infrared (NIR) fluorescence only in the presence of both tryptase and chymase specifically coexpressed by mast cells. Thus, THC_MC effectively distinguishes mast cells from other leukocytes, including T cells, neutrophils, and macrophages, a capability lacking in single-locked probes. Such a high specificity of THC_MC allows noninvasive tracking of the fluctuation of TAMCs in the tumor of living mice during cancer immunotherapy. The results reveal that the decreased intratumoral signal of THC_MC after combination immunotherapy correlates well with the reduced population of TAMCs, accurately predicting the inhibition of tumor growth. Thus, this study not only presents the first NIR fluorescent probe specific for TAMCs but also proposes a generic bienzyme-locked probe design approach for in vivo cell imaging.

中文翻译：

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用于肿瘤相关肥大细胞特异性成像的双酶锁定可激活荧光探针

最近发现肿瘤相关肥大细胞（TAMC）在肿瘤微环境中发挥多方面的作用。因此，非常需要 TAMC 的无创光学成像来深入了解它们在癌症免疫治疗中的功能。然而，由于缺乏肥大细胞特异的单一酶，基于单酶激活的常见探针设计方法并不适用。在此，我们报道了一种基于光诱导电子转移-分子内电荷转移混合策略的双酶锁定分子探针（THC _MC），用于TAMC的体内成像。双酶锁定激活机制确保 THC _MC仅在肥大细胞特异性共表达的类胰蛋白酶和食糜酶同时存在的情况下才专门开启近红外 (NIR) 荧光。因此，THC _MC有效地将肥大细胞与其他白细胞（包括 T 细胞、中性粒细胞和巨噬细胞）区分开来，这是单锁探针所缺乏的能力。 THC _MC如此高的特异性使得能够在癌症免疫治疗期间无创地追踪活体小鼠肿瘤中 TAMC 的波动。结果表明，联合免疫治疗后 THC _MC瘤内信号的减少与 TAMC 数量的减少密切相关，从而准确预测了肿瘤生长的抑制。因此，这项研究不仅提出了第一个针对 TAMC 的近红外荧光探针，而且还提出了一种用于体内细胞成像的通用双酶锁定探针设计方法。