Multimodal chelation platform for near-infrared fluorescence/nuclear imaging

Dual-Labelling Strategies for Nuclear and Fluorescence Molecular Imaging: Current Status and Future Perspectives

Molecular imaging offers the possibility to investigate biological and biochemical processes non-invasively and to obtain information on both anatomy and dysfunctions. Based on the data obtained, a fundamental understanding of various disease processes can be derived and treatment strategies can be planned. In this context, methods that combine several modalities in one probe are increasingly being used. Due to the comparably high sensitivity and provided complementary information, the combination of nuclear and optical probes has taken on a special significance. In this review article, dual-labelled systems for bimodal nuclear and optical imaging based on both modular ligands and nanomaterials are discussed. Particular attention is paid to radiometal-labelled molecules for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) and metal complexes combined with fluorescent dyes for optical imaging. The clinical potential of such probes, especially for fluorescence-guided surgery, is assessed.

PET/Fluorescence Imaging: An Overview of the Chemical Strategies to Build Dual Imaging Tools

Molecular imaging is a biomedical research discipline that has quickly emerged to afford the observation, characterization, monitoring, and quantification of biomarkers and biological processes in living organism. It covers a large array of imaging techniques, each of which provides anatomical, functional, or metabolic information. Multimodality, as the combination of two or more of these techniques, has proven to be one of the best options to boost their individual properties, hence offering unprecedented tools for human health. In this review, we will focus on the combination of positron emission tomography and fluorescence imaging from the specific perspective of the chemical synthesis of dual imaging agents. Based on a detailed analysis of the literature, this review aims at giving a comprehensive overview of the chemical strategies implemented to build adequate imaging tools considering radiohalogens and radiometals as positron emitters, fluorescent dyes mostly emitting in the NIR window and all types of targeting vectors.

PESIN Conjugates for Multimodal Imaging: Can Multimerization Compensate Charge Influences on Cell Binding Properties? A Case Study

Recently, anionic charges were found to negatively influence the in vitro gastrin-releasing peptide receptor (GRPR) binding parameters of dually radioisotope and fluorescent dye labeled GRPR-specific peptide dimers. From this, the question arose if this adverse impact on in vitro GRP receptor affinities could be mitigated by a higher valency of peptide multimerization. For this purpose, we designed two different hybrid multimodal imaging units (MIUs), comprising either one or two click chemistry-compatible functional groups and reacted them with PESIN (PEG₃-BBN_7-14, PEG = polyethylene glycol) dimers to obtain a dually labeled peptide homodimer or homotetramer. Using this approach, other dually labeled peptide monomers, dimers, and tetramers can also be obtained, and the chelator and fluorescent dye can be adapted to specific requirements. The MIUs, as well as their peptidic conjugates, were evaluated in terms of their photophysical properties, radiolabeling efficiency with ⁶⁸Ga and ⁶⁴Cu, hydrophilicity, and achievable GRP receptor affinities. Here, the hydrophilicity and the GRP receptor binding affinities were found to be especially strongly influenced by the number of negative charges and peptide copies, showing log_D (1-octanol-water-distribution coefficient) and IC₅₀ (half maximal inhibitory concentration) values of -2.2 ± 0.1 and 59.1 ± 1.5 nM for the homodimer, and -1.9 ± 0.1 and 99.8 ± 3.2 nM for the homotetramer, respectively. From the obtained data, it can be concluded that the adverse influence of negatively charged building blocks on the in vitro GRP receptor binding properties of dually labeled PESIN multimers can, at least partly, be compensated for by the number of introduced peptide binding motives and the used molecular design.

Comparison of HER2-Targeted Antibodies for Fluorescence-Guided Surgery in Breast Cancer

Background

Although therapeutic advances have led to enhanced survival in patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, detection of residual disease remains challenging. Here, we examine two approved anti-HER2 monoclonal antibodies (mAbs), trastuzumab and pertuzumab, as potential candidates for the development of immunoconjugates for fluorescence-guided surgery (FGS).

Methods

mAbs were conjugated to the near-infrared fluorescent (NIRF) dye, IRDye800, and for quantitative in vitro assessment, to the radiometal chelator, desferrioxamine, to enable dual labeling with ⁸⁹Zr. In vitro binding was evaluated in HER2-overexpressing (BT474, SKBR3) and HER2-negative (MCF7) cell lines. BT474 and MCF7 xenografts were used for in vivo and ex vivo fluorescence imaging.

Results

In vitro findings demonstrated HER2-mediated binding for both fluorescent immunoconjugates and were in agreement with radioligand assays using dual-labeled immunoconjugates. In vivo and ex vivo studies showed preferential accumulation of the fluorescently-labeled mAbs in tumors and similar tumor-to-background ratios. In vivo HER2 specificity was confirmed by immunohistochemical staining of resected tumors and normal tissues.

Conclusions

We showed for the first time that fluorescent trastuzumab and pertuzumab immunoconjugates have similar NIRF imaging performance and demonstrated the possibility of performing HER2-targeted FGS with agents that possess distinct epitope specificity.

Development of a tumor-targetable heteropolymetallic lanthanide-complex-based magnetoluminescent probe for dual-modal time-gated luminescence/magnetic resonance imaging of cancer cells in vitro and in vivo

Multifunctional heteropolymetallic lanthanide-complex-based magnetoluminescent probe for tumor-targeting TGL/MR imaging in vitro and in vivo.

Imidazole fused phenanthroline (PIP) ligands for the preparation of multimodal Re(I) and 99mTc(I) probes

A small library of [2 + 1] 99mTc(i) complexes based on phenyl-imidazole-fused phenanthroline (PIP) ligands were synthesized and evaluated as multimodal molecular imaging probes. Using either a two-step or a one-pot synthesis method, 99mTc-PIP complexes containing N-methylimidazole as the monodentate ligand were prepared and isolated in good (54 to 89%) radiochemical yield, with the exception of one derivative bearing a strongly electron-withdrawing substituent. The stability of the [2 + 1] complexes was assessed in saline and in cysteine and histidine challenge studies, showing 6 hours stability, making them suitable for in vivo studies. In parallel, the Re(i) analogues were prepared as reference standards to verify the structure of the 99mTc complexes. The optical properties were consistent with other previously reported [2 + 1] type Re(i) complexes that have been used as cellular dyes and sensors. To facilitate the development of targeted derivatives, a tetrazine-PIP ligand was also synthesized. The 99mTc complex of the tetrazine PIP ligand effectively coupled to compounds containing a trans-cyclooctene (TCO) group including a TCO-albumin derivative, which was prepared as a model targeting molecule. An added benefit of the Re-PIP-Tz construct is that the emission from the metal complex was quenched by the presence of the tetrazine. Following the addition of TCO, there was a 70-fold increase in fluorescence emission, which can in future be leveraged during in vitro studies to reduce background signal.

Recent developments in multimodality fluorescence imaging probes

Multimodality optical imaging probes have emerged as powerful tools that improve detection sensitivity and accuracy, important in disease diagnosis and treatment. In this review, we focus on recent developments of optical fluorescence imaging (OFI) probe integration with other imaging modalities such as X-ray computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT), and photoacoustic imaging (PAI). The imaging technologies are briefly described in order to introduce the strengths and limitations of each techniques and the need for further multimodality optical imaging probe development. The emphasis of this account is placed on how design strategies are currently implemented to afford physicochemically and biologically compatible multimodality optical fluorescence imaging probes. We also present studies that overcame intrinsic disadvantages of each imaging technique by multimodality approach with improved detection sensitivity and accuracy.

Optical and nuclear imaging of glioblastoma with phosphatidylserine-targeted nanovesicles

Multimodal tumor imaging with targeted nanoparticles potentially offers both enhanced specificity and sensitivity, leading to more precise cancer diagnosis and monitoring. We describe the synthesis and characterization of phenol-substituted, lipophilic orange and far-red fluorescent dyes and a simple radioiodination procedure to generate a dual (optical and nuclear) imaging probe. MALDI-ToF analyses revealed high iodination efficiency of the lipophilic reporters, achieved by electrophilic aromatic substitution using the chloramide 1,3,4,6-tetrachloro-3α,6α-diphenyl glycoluril (Iodogen) as the oxidizing agent in an organic/aqueous co-solvent mixture. Upon conjugation of iodine-127 or iodine-124-labeled reporters to tumor-targeting SapC-DOPS nanovesicles, optical (fluorescent) and PET imaging was performed in mice bearing intracranial glioblastomas. In addition, tumor vs non-tumor (normal brain) uptake was compared using iodine-125. These data provide proof-of-principle for the potential value of SapC-DOPS for multimodal imaging of glioblastoma, the most aggressive primary brain tumor.

Synthesis of a Fluorescently Labeled 68Ga-DOTA-TOC Analog for Somatostatin Receptor Targeting

Fluorescently labeled imaging agents can identify surgical margins in real-time to help achieve complete resections and minimize the likelihood of local recurrence. However, photon attenuation limits fluorescence-based imaging to superficial lesions or lesions that are a few millimeters beneath the tissue surface. Contrast agents that are dual-labeled with a radionuclide and fluorescent dye can overcome this limitation and combine quantitative, whole-body nuclear imaging with intraoperative fluorescence imaging. Using a multimodality chelation (MMC) scaffold, IRDye 800CW was conjugated to the clinically used somatostatin analog, ⁶⁸Ga-DOTA-TOC, to produce the dual-labeled analog, ⁶⁸Ga-MMC(IRDye 800CW)-TOC, with high yield and specific activity. In vitro pharmacological assays demonstrated retention of receptor-targeting properties for the dual-labeled compound with robust internalization that was somatostatin receptor (SSTR) 2-mediated. Biodistribution studies in mice identified the kidneys as the primary excretion route for ⁶⁸Ga-MMC(IRDye 800CW)-TOC, along with clearance via the reticuloendothelial system. Higher uptake was observed in most tissues compared to ⁶⁸Ga-DOTA-TOC but decreased as a function of time. The combination of excellent specificity for SSTR2-expressing cells and suitable biodistribution indicate potential application of ⁶⁸Ga-MMC(IRDye 800CW)-TOC for intraoperative detection of SSTR2-expressing tumors.

Hybrid intraoperative imaging techniques in radioguided surgery: present clinical applications and future outlook

PURPOSE

This review aims to summarise the hybrid modality radioguidance techniques currently in clinical use and development, and to discuss possible future avenues of research. Due to the novelty of these approaches, evidence of their clinical relevance does not yet exist. The purpose of this review is to inform nuclear medicine practitioners of current cutting edge research in radioguided surgery which may enter standard clinical practice within the next 5-10 years. Hybrid imaging is of growing importance to nuclear medicine diagnostics, but it is only with recent advances in technology that hybrid modalities are being investigated for use during radioguided surgery. These modalities aim to overcome some of the difficulties of surgical imaging while maintaining many benefits, or providing entirely new information unavailable to surgeons with traditional radioguidance.

METHODS

A literature review was carried out using online reference databases (Scopus, PubMed). Review articles obtained using this technique were citation mined to obtain further references.

RESULTS

In total, 2367 papers were returned, with 425 suitable for further assessment. 60 papers directly related to hybrid intraoperative imaging in radioguided surgery are reported on. Of these papers, 25 described the clinical use of hybrid imaging, 22 described the development of new hybrid probes and tracers, and 13 described the development of hybrid technologies for future clinical use. Hybrid gamma-NIR fluorescence was found to be the most common clinical technique, with 35 papers associated with these modalities. Other hybrid combinations include gamma-bright field imaging, gamma-ultrasound imaging, gamma-β imaging and β-OCT imaging. The combination of preoperative and intraoperative images is also discussed.

CONCLUSION

Hybrid imaging offers new possibilities for assisting clinicians and surgeons in localising the site of uptake in procedures such as in sentinel node detection.

A Modular Dual-Labeling Scaffold That Retains Agonistic Properties for Somatostatin Receptor Targeting

Fluorescence-guided surgery is an emerging imaging technique that can enhance the ability of surgeons to detect tumors when compared with visual observation. To facilitate characterization, fluorescently labeled probes have been dual-labeled with a radionuclide to enable cross-validation with nuclear imaging. In this study, we selected the somatostatin receptor imaging agent DOTATOC as the foundation for developing a dual-labeled analog. We hypothesized that a customized dual-labeling approach with a multimodality chelation (MMC) scaffold would minimize steric effects of dye conjugation and retain agonist properties. Methods: An MMC conjugate (MMC-TOC) was synthesized on solid-phase and compared with an analog prepared using conventional methods (DA-TOC). Both analogs were conjugated to IRDye 800 using copper-free click chemistry. The resulting compounds, MMC(IR800)-TOC and DA(IR800)-TOC, were labeled with Cu and ⁶⁴Cu and tested in vitro in somatostatin receptor subtype 2-overexpressing HEK-293 cells to assess agonist properties, and in AR42J rat pancreatic cancer cells to determine receptor binding characteristics. Multimodality imaging was performed in AR42J xenografts. Results: Cu-MMC(IR800)-TOC demonstrated higher potency for cyclic adenosine monophosphate inhibition (half maximal effective concentration [EC₅₀]: 0.21 ± 0.18 vs. 1.38 ± 0.54 nM) and receptor internalization (EC₅₀: 41.9 ± 29.8 vs. 455 ± 299 nM) than Cu-DA(IR800)-TOC. Radioactive uptake studies showed that blocking with octreotide caused a dose-dependent reduction in ⁶⁴Cu-MMC(IR800)-TOC uptake whereas ⁶⁴Cu-DA(IR800)-TOC was not affected. In vivo studies revealed higher tumor uptake for ⁶⁴Cu-MMC(IR800)-TOC than ⁶⁴Cu-DA(IR800)-TOC (5.2 ± 0.2 vs. 3.6 ± 0.4 percentage injected dose per gram). In vivo blocking studies with octreotide reduced tumor uptake of ⁶⁴Cu-MMC(IR800)-TOC by 66%. Excretion of ⁶⁴Cu-MMC(IR800)-TOC was primarily through the liver and spleen whereas ⁶⁴Cu-DA(IR800)-TOC was cleared through the kidneys. Ex vivo analysis at 24 h confirmed PET/CT data by showing near-infrared fluorescence signal in tumors and a tumor-to-muscle ratio of 5.3 ± 0.8 as determined by γ-counting. Conclusion: The findings demonstrate that drug design affected receptor pharmacology and suggest that the MMC scaffold is a useful tool for the development of dual-labeled imaging agents.

Technetium(I) Complexes of Bathophenanthrolinedisulfonic Acid

Bathophenanthrolinedisulfonate (BPS) complexes of technetium(I) of the type [Tc(CO)₃(BPS)(L)]ⁿ (L = imidazole derivatives) were synthesized and evaluated both in vitro and in vivo. [^99mTc(CO)₃(BPS)(MeIm)]^- (MeIm = 1-methyl-1H-imidazole) was prepared in near-quantitative yield using a convenient two-step, one-pot labeling procedure. A targeted analogue capable of binding regions of calcium turnover associated with bone metabolism was also prepared. Here, a bisphosphonate was linked to the metal through an imidazole ligand to give [^99mTc(CO)₃(BPS)(ImAln)]^2- (ImAln = an imidazole-alendronate ligand) in high yield. The technetium(I) complexes were stable in vitro, and in biodistribution studies, [^99mTc(CO)₃(BPS)(ImAln)]^2- exhibited rapid clearance from nontarget tissues and significant accumulation in the shoulder (7.9 ± 0.2% ID/g) and knees (15.1 ± 0.9% ID/g) by 6 h, with the residence time in the skeleton reaching 24 h. A rhenium analogue, which is luminescent and has the same structure, was also prepared and used for fluorescence labeling of cells in vitro. The data reported demonstrate the potential of this class of compounds for use in creating isostructural optical and nuclear probes.

EpCAM as multi-tumour target for near-infrared fluorescence guided surgery

Background

Evaluation of resection margins during cancer surgery can be challenging, often resulting in incomplete tumour removal. Fluorescence-guided surgery (FGS) aims to aid the surgeon to visualize tumours and resection margins during surgery. FGS relies on a clinically applicable imaging system in combination with a specific tumour-targeting contrast agent. In this study EpCAM (epithelial cell adhesion molecule) is evaluated as target for FGS in combination with the novel Artemis imaging system.

Methods

The NIR fluorophore IRDye800CW was conjugated to the well-established EpCAM specific monoclonal antibody 323/A3 and an isotype IgG1 as control. The anti-EpCAM/800CW conjugate was stable in serum and showed preserved binding capacity as evaluated on EpCAM positive and negative cell lines, using flow cytometry and cell-based plate assays. Four clinically relevant orthotopic tumour models, i.e. colorectal cancer, breast cancer, head and neck cancer, and peritonitis carcinomatosa, were used to evaluate the performance of the anti-EpCAM agent with the clinically validated Artemis imaging system. The Pearl Impulse small animal imaging system was used as reference. The specificity of the NIRF signal was confirmed using bioluminescence imaging and green-fluorescent protein.

Results

All tumour types could clearly be delineated and resected 72 h after injection of the imaging agent. Using NIRF imaging millimetre sized tumour nodules were detected that were invisible for the naked eye. Fluorescence microscopy demonstrated the distribution and tumour specificity of the anti-EpCAM agent.

Conclusions

This study shows the potential of an EpCAM specific NIR-fluorescent agent in combination with a clinically validated intraoperative imaging system to visualize various tumours during surgery.

Near-Infrared-Emitting BODIPY-trisDOTA(111) In as a Monomolecular Multifunctional Imaging Probe: From Synthesis to In Vivo Investigations

A new generation of monomolecular imaging probes (MOMIP) based on a distyryl-BODIPY (BODIPY=boron-dipyrromethene) coupled with three DOTA macrocycles has been prepared (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The MOMIP presents good fluorescence properties and is very stable in serum. The bimodal probe was conjugated to trastuzumab, and an optical in vivo study showed high accumulation of the imaging agent at the tumor site. (111) In radiometallation of the bioconjugate was performed in high radiochemical yield, highlighting the potential of this new BODIPY-chelators derivative as a bimodal imaging probe.

Response to di-functionalized hyaluronic acid with orthogonal chemistry grafting at independent modification sites in rodent models of neural differentiation and spinal cord injury

Hyaluronic acid functionalized with two orthogonal chemistries at different targets expedites neural maturation in vitro, while reducing inflammation in vivo.

Stable confinement of positron emission tomography and magnetic resonance agents within carbon nanotubes for bimodal imaging

AIMS

Simultaneous positron emission tomography/MRI has recently been introduced to the clinic and dual positron emission tomography/MRI probes are rare and of growing interest. We have developed a strategy for producing multimodal probes based on a carbon nanotube platform without the use of chelating ligands.

MATERIALS & METHODS

Gd(3+) and (64)Cu(2+) ions were loaded into ultra-short single-walled carbon nanotubes by sonication. Normal, tumor-free athymic nude mice were injected intravenously with the probe and imaged over 48 h.

RESULTS & CONCLUSION

The probe was stable for up to 24 h when challenged with phosphate-buffered saline and mouse serum. Positron emission tomography imaging also confirmed the stability of the probe in vivo for up to 48 h. The probe was quickly cleared from circulation, with enhanced accumulation in the lungs. Stable encapsulation of contrast agents within ultra-short single-walled carbon nanotubes represents a new strategy for the design of advanced imaging probes with variable multimodal imaging capabilities.

Targeted multimodal imaging modalities

Molecular imaging non-invasively visualizes and characterizes the biologic functions and mechanisms in living organisms at a molecular level. In recent years, advances in imaging instruments, imaging probes, assay methods, and quantification techniques have enabled more refined and reliable images for more accurate diagnoses. Multimodal imaging combines two or more imaging modalities into one system to produce details in clinical diagnostic imaging that are more precise than conventional imaging. Multimodal imaging offers complementary advantages: high spatial resolution, soft tissue contrast, and biological information on the molecular level with high sensitivity. However, combining all modalities into a single imaging probe involves problems yet to be solved due to the requirement of high dose contrast agents for a component of imaging modality with low sensitivity. The introduction of targeting moieties into the probes enhances the specific binding of targeted multimodal imaging modalities and selective accumulation of the imaging agents at a disease site to provide more accurate diagnoses. An extensive list of prior reports on the targeted multimodal imaging probes categorized by each modality is presented and discussed. In addition to accurate diagnosis, targeted multimodal imaging agents carrying therapeutic medications make it possible to visualize the theranostic effect and the progress of disease. This will facilitate the development of an imaging-guided therapy, which will widen the application of the targeted multimodal imaging field to experiments in vivo.

A peptide probe for targeted brown adipose tissue imaging

The presence of brown adipose tissue responsible for thermogenic energy dissipation has been revealed in adult humans and has high clinical importance. Owing to limitations of current methods for brown adipose tissue detection, analysing the abundance and localization of brown adipose tissue in the body has remained challenging. Here we screen a combinatorial peptide library in mice and characterize a peptide (with the sequence CPATAERPC) that selectively binds to the vascular endothelium of brown adipose tissue, but not of intraperitoneal white adipose tissue. We show that in addition to brown adipose tissue, this peptide probe also recognizes the vasculature of brown adipose tissue-like depots of subcutaneous white adipose tissue. Our results indicate that the CPATAERPC peptide localizes to brown adipose tissue even in the absence of sympathetic nervous system stimulation. Finally, we demonstrate that this probe can be used to identify brown adipose tissue depots in mice by whole-body near-infrared fluorescence imaging.

Bimodal imaging probes for combined PET and OI: recent developments and future directions for hybrid agent development

Molecular imaging—and especially positron emission tomography (PET)—has gained increasing importance for diagnosis of various diseases and thus experiences an increasing dissemination. Therefore, there is also a growing demand for highly affine PET tracers specifically accumulating and visualizing target structures in the human body. Beyond the development of agents suitable for PET alone, recent tendencies aim at the synthesis of bimodal imaging probes applicable in PET as well as optical imaging (OI), as this combination of modalities can provide clinical advantages. PET, due to the high tissue penetration of the γ-radiation emitted by PET nuclides, allows a quantitative imaging able to identify and visualize tumors and metastases in the whole body. OI on the contrary visualizes photons exhibiting only a limited tissue penetration but enables the identification of tumor margins and infected lymph nodes during surgery without bearing a radiation burden for the surgeon. Thus, there is an emerging interest in bimodal agents for PET and OI in order to exploit the potential of both imaging techniques for the imaging and treatment of tumor diseases. This short review summarizes the available hybrid probes developed for dual PET and OI and discusses future directions for hybrid agent development.

How brown is brown fat that we can see?

There are many unanswered questions related to the heterogeneity of adipose tissue depots and the paucity of their function, development, and organization at the cellular level. Much effort has been directed at studying white adipose tissue (WAT), the driver of obesity and the associated metabolic disease. In recent years, the importance of brown adipose tissue (BAT) has also been appreciated. While BAT depots are prominent in many small mammal species, their detection in adult humans has been technically challenging and the identity of brown human adipocytes found within depots of WAT has remained controversial. We recently reported a peptide probe that binds to BAT vasculature and, when coupled with a near-infrared fluorophore, can be used to detect BAT in whole body imaging. This probe reliably discriminates between endothelium associated with brown or brown-like (beige/brite) adipocytes and endothelium of visceral WAT. Improved probes based on this approach could aid in assessing human adipose tissue body distribution and remodeling, which is a process underlying various pathologies. This commentary aims at discussing open questions that need to be addressed before full clinical advantage can be taken from adipose tissue imaging, as well as its metabolic activation strategies.

Targeting pili in enterococcal pathogenesis

Passive protection, the administration of antibodies to prevent infection, has garnered significant interest in recent years as a potential prophylactic countermeasure to decrease the prevalence of hospital-acquired infections. Pili, polymerized protein structures covalently anchored to the peptidoglycan wall of many Gram-positive pathogens, are ideal targets for antibody intervention, given their importance in establishing infection and their accessibility to antibody interactions. In this work, we demonstrated that a monoclonal antibody to the major component of Enterococcus faecalis pili, EbpC, labels polymerized pilus structures, diminishes biofilm formation, and significantly prevents the establishment of a rat endocarditis infection. The effectiveness of this anti-EbpC monoclonal provides strong evidence in support of its potential as a preventative. In addition, after radiolabeling, this monoclonal identified the site of enterococcal infection, providing a rare example of molecularly specific imaging of an established bacterial infection and demonstrating the versatility of this agent for use in future diagnostic and therapeutic applications.

Photons across medicine: relating optical and nuclear imaging

The Optics in the Life Sciences conference sponsored by the Optical Society of America was held in Waikoloa Beach, HI on April 14 - 18, 2013. Papers were presented in the areas of Bio-Optics: Design & Application, Novel Techniques in Microscopy, Optical Molecular Probes, Imaging & Drug Delivery, and Optical Trapping Applications. A focal point of the meeting was a special symposium entitled "Photons Across Medicine", organized by Adam Wax, Duke University, highlighting activities of joint interest between the Optical Society of America (OSA) and the Society for Nuclear Medicine and Molecular Imaging (SNMMI). This paper is a synopsis of the presentations made at this joint symposium. Central to the special symposium presentations was the fact that the optical and nuclear imaging communities share common interests and challenges. These are highlighted in this article. Also discussed was the fact that the nuclear technologies in imaging have found their way into general clinical utility, a feat that has yet to be achieved by optical methods. Because of the common ground shared by the two technologies, coordination between the two societies should be planned.