Description

    The brain is one of the most essential tissues in humans. Regardless of whether the brain tumor is benign or malignant, its compression of any brain region will adversely impact human health.

    The prevalence of cerebral malignancies has recently increased. Statistics indicate that brain tumors represent roughly 5% of all body tumors and approximately 70% of cancers in children. Furthermore, 20% to 30% of various malignant tumors will eventually metastasis to the cerebral region [1]. If intracranial tumors occupy a specific space, regardless of whether they are benign or malignant, they will inevitably elevate intracranial pressure, resulting in central nervous system harm and a threat to the patient's life, as a result of their expansive and invasive growth.

    Surgical removal of the tumor is the most effective therapy for brain tumors. Nevertheless, the majority of malignant brain tumors are not entirely surgically removed and will recur. Consequently, it is vital to employ a tracer to monitor the tumor during the treatment of patients [2].

    Bioluminescence imaging (BLI), as a reliable, sensitive, convenient, and non-invasive in vivo imaging modality [3,4], has been extensively applied to the identification of physiological and pathological processes within biomedical research, including pathogen detection, tumor proliferation[5], therapeutic responses, gene regulation patterns[6], protein-protein interaction examinations[7], and ADMET (absorption, distribution, metabolism, excretion, and toxicity) evaluations[8, 9]. The firefly luciferase-luciferin system is a very successful and widely recognized bioluminescence system for noninvasive visualization of molecular and cellular properties in living mice[10, 11]. However, specific limitations of natural substrates such as D-luciferin and aminoluciferin hinder the use of bioluminescent imaging with firefly luciferase, such as short red-light (tissue-penetrating) emission[12, 13], insufficient in vivo bioluminescence duration, and inadequate blood-brain barrier permeability[14, 15].

    The objective of this research is to develop cyclic N-aminoluciferins (cyL) as viable firefly luciferase substrates with improved bioluminescence properties after rational design as depicted in Scheme 1. In the synthesis part, using various cycloaminobenzothiazol-2-nitriles as starting materials, four novel cyL compounds were generated following a cyclization with D-cysteine in the presence of potassium carbonate.

    Scheme 1. The flowchart of this project

    We then conducted bioluminescence emission spectra assessment, in vitro bioluminescence assay, cell bioluminescence imaging, nude xenograft tumor mice imaging, FVB-Tg transgenic mice imaging, and brain tumor bioluminescence imaging in the biological evaluation to ascertain whether cyL compounds can address challenges such as short red-light (tissue-penetrating) emission, short in vivo bioluminescence duration, and low blood-brain barrier permeability.

    In a nutshell, herein we developed four novel sensitive firefly luciferase substrates: 5-cyL, 6-cyL, 7-cyL, and 8-cyL, by modifying the chemical structures of aminoluciferin. The increased permeability of the blood-brain barrier renders 7-cyL a suitable substrate for brain tumor bioluminescence imaging. Our approach integrates a distinctive combination of red-shifted bioluminescent emission, prolonged bioluminescence duration, the ability to penetrate the blood-brain barrier, and enhanced cell permeability, thereby enabling direct examination of cancer progression and addressing a significant gap in live animal imaging capabilities that current tools cannot achieve. We assert that these innovative firefly luciferase substrates will enhance the array of current bioluminescence imaging techniques and may fundamentally alter prevailing perspectives on cancer progression as well as therapeutic approaches[16].

    References

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