Near-Infrared Bioluminescence Imaging of Macrophage Sensors for Cancer Detection In Vivo

Optimized in vivo multispectral bioluminescent imaging of tumor biology using engineered BRET reporters

The ability to visualize and track multiple biological processes in vivo in real time is highly desirable. Bioluminescence imaging (BLI) has emerged as an attractive modality for non-invasive cell tracking, with various luciferase reporters enabling parallel monitoring of several processes. However, simultaneous multiplexed imaging in vivo is challenging due to suboptimal reporter intensities and the need to image one luciferase at a time. We report a multiplexed BLI approach using a single substrate that leverages bioluminescence resonance energy transfer (BRET)-based reporters with distinct spectral profiles for triple-color BLI. These luciferase-fluorophore fusion reporters address light transmission challenges and use optimized coelenterazine substrates. Comparing BRET reporters across two substrate analogs identified a green-yellow-orange combination that allows simultaneous imaging of three distinct cell populations in vitro and in vivo. These tools provide a template for imaging other biological processes in vivo during a single BLI session using a single reporter substrate.

In vivo bioluminescence imaging of the intracerebral fibroin-controlled AAV-α-synuclein diffusion for monitoring the central nervous system and peripheral expression

Among the several animal models of α-synucleinopathies, the well-known viral vector-mediated delivery of wild-type or mutated (A53T) α-synuclein requires new tools to increase the lesion in mice and follow up in vivo expression. To this end, we developed a bioluminescent expression reporter of the human A53T-α-synuclein gene using the NanoLuc system into an AAV2/9, embedded or not in a fibroin solution to stabilise its expression in space and time. We first verified the expression of the fused protein in vitro on transfected cells by bioluminescence and Western blotting. Next, two groups of C57Bl6Jr mice were unilaterally injected with the AAV-NanoLuc-human-A53T-α-synuclein above the substantia nigra combined (or not) with fibroin. We first show that the in vivo cerebral bioluminescence signal was more intense in the presence of fibroin. Using immunohistochemistry, we find that the human-A53T-α-synuclein protein is more restricted to the ipsilateral side with an overall greater magnitude of the lesion when fibroin was added. However, we also detected a bioluminescence signal in peripheral organs in both conditions, confirmed by the presence of viral DNA corresponding to the injected AAV in the liver using qPCR.

Biosensors for melanoma skin cancer diagnostics

Skin cancer is a critical global public health concern, with melanoma being the deadliest variant, correlated to 80% of skin cancer-related deaths and a remarkable propensity to metastasize. Despite notable progress in skin cancer prevention and diagnosis, the limitations of existing methods accentuate the demand for precise diagnostic tools. Biosensors have emerged as valuable clinical tools, enabling rapid and reliable point-of-care (POC) testing of skin cancer. This review offers insights into skin cancer development, highlights essential cutaneous melanoma biomarkers, and assesses the current landscape of biosensing technologies for diagnosis. The comprehensive analysis in this review underscores the transformative potential of biosensors in revolutionizing melanoma skin cancer diagnosis, emphasizing their critical role in advancing patient outcomes and healthcare efficiency. The increasing availability of these approaches supports direct diagnosis and aims to reduce the reliance on biopsies, enhancing POC diagnosis. Recent advancements in biosensors for skin cancer diagnosis hold great promise, with their integration into healthcare expected to enhance early detection accuracy and reliability, thereby mitigating socioeconomic disparities.

Caged luciferins enable rapid multicomponent bioluminescence imaging

Bioluminescence is a sensitive technique for imaging biological features over time. Historically, though, the modality has been challenging to employ for multiplexed tracking due to a lack of resolvable luciferase-luciferin pairs. Recent years have seen the development of numerous orthogonal probes for multi-parameter imaging. While successful, generating such tools often requires complex syntheses and lengthy enzyme evolution campaigns. This work showcases an alternative strategy for multiplexed bioluminescence that takes advantage of already-orthogonal caged luciferins and established uncaging enzymes. These probes generate unique bioluminescent signals that can be distinguished via a linear unmixing algorithm. Caged luciferins enabled two- and three-component imaging on the minutes time scale. We further showed that the tools can be used in conjunction with endogenous enzymes for multiplexed studies. Collectively, this approach lowers the barrier to multicomponent bioluminescence imaging and can be readily adopted by the broader community.

Bioluminescence imaging on-chip platforms for non-invasive high-content bioimaging

Incorporating non-invasive biosensing features in organ-on-chip models is of paramount importance for a wider implementation of these advanced in vitro microfluidic platforms. Optical biosensors, based on Bioluminescence Imaging (BLI), enable continuous, non-invasive, and in-situ imaging of cells, tissues or miniaturized organs without the drawbacks of conventional fluorescence imaging. Here, we report the first-of-its-kind integration and optimization of BLI in microfluidic chips, for non-invasive imaging of multiple biological readouts. The cell line HEK293T-GFP was engineered to express NanoLuc® luciferase under the control of a constitutive promoter and were cultured on-chip in 3D, in standard ECM-like hydrogels, to assess optimal cell detection conditions. Using real-time in-vitro dual-color microscopy, Bioluminescence (BL) and fluorescence (FL) were detectable using distinct imaging setups. Detection of the bioluminescent signals were observed at single cell resolution on-chip 20 min post-addition of Furimazine substrate and under perfusion. All hydrogels enabled BLI with higher signal-to-noise ratios as compared to fluorescence. For instance, agarose gels showed a ∼5-fold greater BL signal over background after injection of the substrate as compared to the FL signal. The use of BLI with microfluidic chip technologies opens up the potential for simultaneous in situ detection with continuous monitoring of multicolor cell reporters. Moreover, this can be achieved in a non-invasive manner. BL has great promise as a highly desirable biosensor for studying organ-on-chip platforms.

Advances in luminescence-based technologies for drug discovery

INTRODUCTION

Luminescence-based technologies, specifically bioluminescence and chemiluminescence, are powerful tools with extensive use in drug discovery. Production of light during chemiluminescence and bioluminescence, unlike fluorescence, doesn't require an excitation light source, resulting in high signal-to-noise ratio, less background interference, and no issues from phototoxicity and photobleaching. These characteristics of luminescence technologies offer unique advantages for experimental designs, allowing for greater flexibility to target a wide range of proteins and biological processes for drug discovery at different stages.

AREAS COVERED

This review provides a basic overview of luciferase-based technologies and details recent advances and use cases of luciferase and luciferin variations and their applicability in the drug discovery toolset. The authors expand upon specific applications of luciferase technologies, including chemiluminescent and bioluminescent-based microscopy. Finally, the authors lay out forward-looking statements on the field of luminescence and how it may shape the translational scientists' work moving forward.

EXPERT OPINION

The demand for improved luciferase and luciferin pairs correlates strongly with efforts to improve the sensitivity and robustness of high-throughput assays. As luminescent reporter systems improve, so will the expansion of use cases for luminescence-based technologies in early-stage drug discovery. With the synthesis of novel, non-enzymatic chemiluminescence-based probes, which previously were restrained to only basic research applications, they may now be readily implemented in drug discovery campaigns.