Optical imaging for the new grammar of drug discovery

Harnessing the Power of Optical Microscopic and Macroscopic Imaging for Natural Products as Cancer Therapeutics

Natural products (NPs) are an important source for new drug discovery over the past decades, which have been demonstrated to be effectively used in cancer prevention, treatment, and adjuvant therapy. Many methods, such as the genomic and metabolomic approaches, immunochemistry, mass spectrometry, and chromatography, have been used to study the effects of NPs on cancer as well as themselves. Because of the advantages in specificity, sensitivity, high throughput, and cost-effectiveness, optical imaging (OI) approaches, including optical microscopic imaging and macroscopic imaging techniques have also been applied in the studies of NPs. Optical microscopic imaging can observe NPs as cancer therapeutics at the cellular level and analyze its cytotoxicity and mechanism of action. Optical macroscopic imaging observes the distribution, metabolic pathway, and target lesions of NPs in vivo, and evaluates NPs as cancer therapeutics at the whole-body level in small living animals. This review focuses on the recent advances in NPs as cancer therapeutics, with particular emphasis on the powerful use of optical microscopic and macroscopic imaging techniques, including the studies of observation of ingestion by cells, anticancer mechanism, and in vivo delivery. Finally, we prospect the wider application and future potential of OI approaches in NPs as cancer therapeutics.

Development of Activity-Based Reporter Gene Technology for Imaging of Protease Activity with an Exquisite Specificity in a Single Live Cell

Imaging of an active protease with an exquisite specificity in the presence of highly homologous proteins within a living cell is a very challenging task. Herein, we disclose a new method called "Activity-based Reporter Gene Technology" (AbRGT). This method provides an opportunity to study the function of "active protease" with an unprecedented specificity. As a proof-of-concept, we have applied this method to study the function of individual caspase protease in both intrinsic and extrinsic apoptosis signaling pathways. The versatility of this method is demonstrated by studying the function of both the initiator and effector caspases, independently. The modular fashion of this technology provides the opportunity to noninvasively image the function of cathepsin-B in a caspase-dependent cell death pathway. As a potential application, this method is used as a tool to screen compounds that are potent inhibitors of caspases and cathepsin-B proteases. The fact that this method can be readily applied to any protease of interest opens up huge opportunities for this technology in the area of target validation, high-throughput screening, in vivo imaging, diagnostics, and therapeutic intervention.

Investigations of the Biological Effects of Airborne and Inhalable Substances by Cell-Based In Vitro Methods: Fundamental Improvements to the ALI Concept

The state of the art for cell-based in vitro investigations of airborne and inhalable material is “air-liquid interface” (ALI) technology. Cell lines, primary cells, complex 3D models, or precision-cut lung slices (PCLS) are used to represent the lung or skin by way of an in vitro barrier model. These models have been applied in toxicity or pharmacological testing. However, contrasting with a clear demand for alternative methods, there is still no widely accepted procedure for cell-based in vitro testing of inhalable substances. In the light of this, an analysis was undertaken of common drawbacks of current approaches. Hence, the pivotal improvements aimed at were the cellular exposure environment, overall performance and applicability, operability of online investigations during exposure and routine setup. It resulted in an improved device (P.R.I.T. ExpoCube) based on an “all-in-one-plate” concept including all phases of the experiment (cell culture, exposure, and read-out) and all experimental groups (two test gas groups, controls) in one single commercial multiwell plate. Verification of the concept was demonstrated in a first experimental series using reference substances (formaldehyde, ozone, and clean air). The resulting ALI procedure enables the application of inhalable substances and mixtures under highly effective exposure conditions in routine utilization.

Bioluminescence imaging correlates with tumor serum marker, organ weights, histology, and human DNA levels during treatment of orthotopic tumor xenografts with antibodies

PURPOSE

In this study, we correlate results of bioluminescence measurements with established readouts for assessing therapeutic efficacy of antibodies in orthotopic cancer xenografts.

PROCEDURES

An orthotopic tumor model of pancreatic cancer (AsPC-1-luc) and experimental lung metastasis (A549-luc) were established. Whole-body bioluminescence imaging (BLI) was performed to observe tumor progression under therapy with antibodies targeting different receptor kinases (primary readout). For purpose of verification, anti-tumoral efficacy was cross-validated with results obtained by measurement of organ weights, histology, tumor serum marker analysis (CYFRA 21-1), and quantification of human DNA concentration in the organ of interest (secondary readouts).

RESULTS

Anti-tumoral efficacy is demonstrated for the antibodies tested. In the pancreas xenograft, a tumor growth inhibition of 95% (p < 0.01) was achieved as compared to control. Therapeutic efficacy could be identified as soon as 1 week after initiation of treatment. In the model of experimental lung metastasis, antibody treatment significantly suppressed tumor growth up to 75% (p < 0.05). All imaging results were confirmed by correlation analysis showing excellent agreement with the secondary readouts.

CONCLUSIONS

BLI was demonstrated to be a reliable tool for monitoring early drug responses in orthotopic small animal cancer models. BLI allows rapid and non-invasive assessment of tumor load in the animal over time and, thus, provides a suitable method for routine use in preclinical cancer research.

A versatile, bar-coded nuclear marker/reporter for live cell fluorescent and multiplexed high content imaging

The screening of large numbers of compounds or siRNAs is a mainstay of both academic and pharmaceutical research. Most screens test those interventions against a single biochemical or cellular output whereas recording multiple complementary outputs may be more biologically relevant. High throughput, multi-channel fluorescence microscopy permits multiple outputs to be quantified in specific cellular subcompartments. However, the number of distinct fluorescent outputs available remains limited. Here, we describe a cellular bar-code technology in which multiple cell-based assays are combined in one well after which each assay is distinguished by fluorescence microscopy. The technology uses the unique fluorescent properties of assay-specific markers comprised of distinct combinations of different 'red' fluorescent proteins sandwiched around a nuclear localization signal. The bar-code markers are excited by a common wavelength of light but distinguished ratiometrically by their differing relative fluorescence in two emission channels. Targeting the bar-code to cell nuclei enables individual cells expressing distinguishable markers to be readily separated by standard image analysis programs. We validated the method by showing that the unique responses of different cell-based assays to specific drugs are retained when three assays are co-plated and separated by the bar-code. Based upon those studies, we discuss a roadmap in which even more assays may be combined in a well. The ability to analyze multiple assays simultaneously will enable screens that better identify, characterize and distinguish hits according to multiple biologically or clinically relevant criteria. These capabilities also enable the re-creation of complex mixtures of cell types that is emerging as a central area of interest in many fields.

In vivo Cerenkov luminescence imaging: a new tool for molecular imaging

Cerenkov radiation is a phenomenon where optical photons are emitted when a charged particle moves faster than the speed of light for the medium in which it travels. Recently, we and others have discovered that measurable visible light due to the Cerenkov effect is produced in vivo following the administration of β-emitting radionuclides to small animals. Furthermore, the amounts of injected activity required to produce a detectable signal are consistent with small-animal molecular imaging applications. This surprising observation has led to the development of a new hybrid molecular imaging modality known as Cerenkov luminescence imaging (CLI), which allows the spatial distribution of biomolecules labelled with β-emitting radionuclides to be imaged in vivo using sensitive charge-coupled device cameras. We review the physics of Cerenkov radiation as it relates to molecular imaging, present simulation results for light intensity and spatial distribution, and show an example of CLI in a mouse cancer model. CLI allows many common radiotracers to be imaged in widely available in vivo optical imaging systems, and, more importantly, provides a pathway for directly imaging β(-)-emitting radionuclides that are being developed for therapeutic applications in cancer and that are not readily imaged by existing methods.

Making light work: illuminating the future of biomedical optics

In 1996, the Royal Society held a Discussion Meeting entitled 'Near-infrared spectroscopy and imaging of living systems'. In 2010, this topic was revisited in a Theo Murphy Royal Society Scientific Discussion Meeting entitled 'Making light work: illuminating the future of biomedical optics'. The second meeting provided the opportunity for leading researchers to reflect on how the technology, methods and applications have evolved over the past 14 years and assess where they have made a major impact. Particular emphasis was placed on discussions of future prospects and associated challenges. This Introduction provides an overview of the state of the art of near-infrared spectroscopy (NIRS) and biomedical optics, with specific reference to the contributed papers from the invited speakers included in this issue. Importantly, we also reflect on the contributions from all of the attendees by highlighting the issues raised during oral presentations, facilitated panel sessions and discussions, and use these to summarize the current opinion on the development and application of optical systems for use in the clinical and life sciences. A notable outcome from the meeting was a plan to establish a biennial international conference for developers and users of NIRS technologies.