Molecular imaging and chemistry: defining the future

09:45-10:15

Professor Franklin Aigbirhio, University of Cambridge

Abstract

• Listen to audio (mp3)

10:15-10:30 Discussion

10:30-11:00 PET in India

Professor Ajit Shinto, Kovai Medical Center and Hospital

Abstract

There are around 200 Nuclear Medicine Centers in India. PET based product mainly 18F-FDG is localized around big metropolitan cities where there is a centralized cyclotron facility for producing 18F and which can be transported quickly. At present around 18 cyclotrons are operational in India, which fulfill the need of 18F-FDG to greater part of the country. The first Medical cyclotron (16 MeV) was commissioned in the year 2002 at Radiation Medicine Centre, Mumbai. Since then a number of private set ups have installed cyclotron all over the country. The market for 18F-FDG is far superior to any other diagnostic product in India. Other than 18F-FDG, several other 18F based radiopharmaceuticals such as 18F-sodium fluoride for bone cancer detection (used since 2007), 18F-MISO for tumor hypoxia imaging and 18F-FLT for cancer detection (used since 2010) at the cellular level are now being used at limited nuclear medicine centers in India.

FDG is the only PET or SPECT radiopharmaceutical being supplied commercially to many centers. Today in our country we have 98 Running  PET/CT Centers and 70 centers are going be added in the next couple of years. Every center if doing average 5 cases a day and running 20 days then total FDG doses are 9800/month and 117600/year.

Another promising PET radionuclide i.e. 68Ga which is available through a generator is gaining wide acceptance among the clinics. 68Ga labelled peptide such as DOTA-NOC, DOTA-TATE for neuroendocrine tumor imaging is used in number of Nuclear medicine centers in India. There is a small percentage of use of 11C-CO2, 13N-NH3, 15O-H2O and 82Rb which are in use for myocardial perfusion imaging.

11:00-11:15 Discussion

11:45-12:15 PET for neuroimaging

Professor Jacob Hooker, Martinos Center for Biomedical Imaging

Abstract

Positron emission tomography has deep roots in neuroscience stemming from its first application in brain tumour and brain metabolism imaging. PET neuroimaging has evolved considerably since its birth and continues to play a prominent role in the study of neurochemistry in the living human brain-addressing research questions related to, among many others, protein density, drug occupancy, and endogenous neurochemical release.  New radiotracers combined with new imaging protocol and equipment (e.g. simultaneous MR-PET) position PET neuroimaging for major breakthroughs in our understanding of human brain function and disease.  Using recent studies of neuroinflammation and neuroepigenetics, I will attempt to highlight emerging opportunities with PET and the future needs of the field.  Additionally, I will highlight the use of simultaneous MR-PET and dissecting temporal information from neuroimaging in an attempt to understand and validate models of neurochemical transmission.

• Listen to the audio (mp3)

12:15-12:30 Discussion

13:30-14:00 PARACEST agents

Professor Dean Sherry, UT Southwestern Medical Center

Abstract

Like other MRI contrast agents, CEST contrast from an endogenous species or an exogenous agent depends upon agent concentration, water or proton exchange rates, the relaxation rate of water protons, and other factors.  CEST is governed by the exchange condition, k_ex <Dw, so if Dw is large, then faster exchanging systems can be used to initiate CEST contrast.  It is relatively easy to modify Dw with paramagnetic complexes but manipulating k_ex is generally more difficult.  Many types of paraCEST complexes have been reported over the past few years including those that can be CEST activated by irradiation at the frequency of a bound water molecule and others that are activated at the frequency of an exchanging ligand –NH or –OH proton.     Even though water exchange rates in paramagnetic lanthanide complexes can be modified quite dramatically, water exchange in most paraCEST complexes remains too fast to achieve optimal CEST contrast.  Conversely, many diaCEST agents that use an –OH or –NH resonance for CEST activation have proton exchange rates that are too slow for optimal CEST contrast.  Proton exchange rates can of course be modified by temperature but simple chemical principles can also be used.  For example, when a ligand –OH group coordinates directly to a metal ion, proton exchange from that bound –OH group is considerably faster. Using this principle, we have been exploring the possibility of using lanthanide shift reagents (LSR) to alter the frequency of slowing exchanging protons in endogenous metabolites such as glucose and lactate. The exchanging lactate –OH proton can potentially be used for CEST detection but the chemical shift of the lactate –OH proton is very close to water itself.  Hence, it is quite difficult to activate the exchanging lactate –OH proton without substantially altering the water signal.  Lactate is overproduced by most tumors even in the presence of abundant oxygen (the Warburg effect) so a method for direct imaging of lactate production by tumors could become a useful tool for monitoring tumor aggressiveness.  To test this idea, we have used EuDO3A and other derivatives as aqueous shift reagents (SR) to shift the –OH resonance of lactate far away from water protons and used CEST to quantify the amount of lactate produced by tumor cells growing in tissue culture and, more recently, in vivo. Interestingly, the intensity of the lactate CEST signal is more intense in a slightly acidic environment and is more intense at 37°C than at 25°C.  This new SR approach provides a framework for enabling metabolite-selective imaging of endogenous molecules by MRI.

• Listen to the audio (mp3)

14:00-14:15 Discussion

14:15-14:45 MRI in neuroscience

Professor Eva Toth, Center for Moelcular Biophysics

Abstract

Among imaging techniques, MRI has great potential to enable mapping of neural events with excellent specificity, spatiotemporal resolution and unlimited tissue penetration depth. Molecular imaging approaches using neurotransmitter-sensitive MRI agents have appeared recently to study neuronal activity, along with the first successful in vivo MRI studies. 

The design of bioresponsive MRI agents for molecular targets such as neurotransmitters is highly challenging. So far, two approaches have been explored to tackle this problem, one involving host molecules developed by nature (i.e. proteins), and the second one involving supramolecular chemistry and artificial host molecules. In this second approach, our objective was to create a synthetic molecular platform, smaller than the robust proteins, with appropriate recognition moieties for neurotransmitters that generate an MR signal change upon neurotransmitter binding. We targeted zwitterionic amino acid neurotransmitters without necessarily seeking for selectivity to individual neurotransmitters. Our chemical design offers ditopic binding via interactions between a positively charged metal complex and the carboxylate and between the crown ether moiety and the amine of amino acids. The probes show selectivity towards zwitterionic over non-zwitterionic neurotransmitters. Neurotransmitter binding leads to a remarkable relaxivity decrease, due to a decrease in the hydration number. One of the probes was successfully used to monitor neural activity in acute mouse brain slices by MRI.

• Listen to the audio (mp3)

14:45-15:00 Discussion

15:30-16:00 Functional MRI

Professor Steve Williams, University of Manchester

Abstract

Since functional magnetic resonance imaging (fMRI) was first demonstrated in 1991, the potential of the technique in cognitive neuroscience, neurology and psychiatry was apparent. Technical improvements in magnet and gradient hardware, combined with the work of many researchers to develop robust methods for experimental design, data acquisition and analysis have led to the method now being the pre-eminent technique in cognitive neuroscience research, with applications also in clinical neurology and in the understanding of psychiatric disease. The use of the technique has moved beyond the stage of relating simple functional tasks to anatomy, to investigating brain networks, neural connectivity and the anatomical substrates of complex neural processing. This work is nearly all based on exploiting the endogenous MRI contrast associated with deoxyhaemoglobin and the effect that local changes in neural activity have on blood oxygenation and consequently the local concentration of deoxyhaemoglobin (BOLD effect – blood oxygenation level dependent contrast).  In addition to investigating cognitive and sensory challenges, fMRI can also be used to explore the brain’s reaction to neuro-active drugs by recording the BOLD response to pharmacological challenge (phMRI).  The principles and application of phMRI will be discussed in this presentation, with examples of both human and animal implementations and the use of double challenges to elucidate neurotransmitter pathways and neurovascular coupling. There will be a focus on the serotonergic and glutamatergic neurotransmitter systems in the context of depression and schizophrenia.

• Listen to the audio (mp3)

16:00-16:15 Discussion

16:15-16:45 Challenges in molecular imaging from an industry perspective

Dr Philip Murphy, GSK

Abstract

Most imaging applied within clinical drug development relies upon downstream markers of disease response (e.g. CT measurement of tumour size). Whilst such techniques remain important there is no doubt that molecular imaging has the potential to fill critical knowledge gaps in the early development of a drug. Important questions include- has the drug reached and engaged with the intended target and has there been some pharmacological response? Too often large, costly clinical trials proceed without these questions being adequately addressed. Whilst there are good examples of molecular imaging in pharmaceutical product development what are the impediments to a broader and more impactful use? In some cases molecular imaging may not be tractable based on current chemistry, it may be perceived as too costly or there may be insufficient time to develop a method. To ensure drug research benefits from molecular imaging tools, drug R&D organisations must develop strong multi-disciplinary partnerships with academic and commercial imaging groups. Through close collaboration we must share challenges and promote early scientific engagement with a focus on translation to the clinical experiment. If successful we will kill off poor drug candidates early, accelerate promising medicines towards clinical use and reduce the cost of drug development. All of these will improve industry productivity and deliver much needed medicines to patients. This talk will highlight the opportunities for molecular imaging and begin to identify the impediments towards broader use.

• Listen to the audio (mp3)

16:45-17:00 Discussion

09:00-09:30 Mulitmodual imaging: new probes for positron emission tomography combined with magnetic resonance or optical imaging

Professor Steve Archibald, University of Hull

Abstract

The design of multimodal imaging constructs requires consideration of the optimal method to combine components. Targeting to specific tissues or physiological processes introduces a further aspect to the system. 

In general two approaches have been taken: 

(1)    Molecular constructs where components are combined in a stepwise manner allows more exquisite control of the imaging probe formed but can be laborious. This approach is most effective when components are multifunctional (i.e. a combined dye and targeting component). The development of molecular probes that combine positron emission tomography/optical imaging potential will be discussed. The use of molecular properties such as lipophilicity and charge to influence tissue/ cellular uptake and localisation will be exemplified in the determination of mitochondrial function and cell surface receptor targeting in vitro and in vivo.

(2)    Nanoparticles and polymers offer opportunity for conjugation of multiple types of imaging or targeting groups on the surface and the core can also have imaging or contrast agent properties. Examples will be presented of the construction of nanoparticles for multimodal imaging in tissue engineering applications.

The design of probes from synthesis and characterisation through to in vivo imaging will be used to validate these approaches and demonstrate the potential for translational studies. 

• Listen to the audio (mp3)

09:30-09:45 Discussion

09:45-10:15 Multi-modal nanparticles

Professor Willem Mulder, Mount Sinai School of Medicine

Abstract

Nanodrugs are self-assembled assembled structures for which drug loading stability is strongly influenced by the in vivo environment. Interactions between nanodrugs and blood components have been reported to cause drug leakage. Therefore, thoroughly understanding in vivo drug-carrier association stability and dissociation kinetics should improve delivery efficiency and, as a result, therapeutic efficacy. We have recently shown that optical imaging techniques, including Förster resonance energy transfer (FRET) imaging, can monitor the drug-carrier association and help identify key parameters that determine drug-carrier compatibility. These findings can serve as drug delivery efficiency guidelines that can be applied to improve nanodrug design.

Despite nanomedicine’s promise and the field’s research activity, its potential is not being fully met and implementation in clinical care is falling behind. In part this is due to the technology’s immaturity, but – more importantly – ways to stratify patients that may benefit from nanodrug-based therapy are nonexistent. The ability to non-invasively evaluate targeting would greatly improve patient care by allowing swift adjustments in dosage and/or treatment regimen. Strategies in which nanodrugs are labeled for imaging-facilitated delivery are extensively studied. Unfortunately, such theranostic approaches have little clinical relevance. 

As has been shown for antibody therapy, an easy-to-prepare companion diagnostic for quantitative imaging of nanodrugs can overcome these issues. Practically, the companion diagnostic can be applied to screen for patient amenability, but can also be used as an agent that is co-injected with the actual nanodrug to aid in treatment continuation decision. 

In this presentation, imaging-facilitated optimization of nanodrugs and the “companion diagnostic’ concept, the latest advances in these fields, as well as translational considerations will be discussed.

• Listen to the audio (mp3)

10:15-10:30 Discussion

11:00-11:30 Upconverting nanoarticles

Professor Chunhua Yan, Peking University

11:30-11:45 Discussion

11:45-12:15 Lanthanide probes

Professor Gary Wong, Hong Kong Baptist University

Abstract

One of the major limitations of the existing anticancer agents is their differentiation of cancer cells and normal cells. Recently, some studies in the literature have suggested that some overexpressed cancer cell cycle regulating proteins (e.g. Cyclin(s), Plk1 and EBNA1) can be the particular cancer targets. Several small molecules as their inhibitors have been reported; however, those reported inhibitors are not emissive and cannot directly evaluate their effectiveness, such as real time imaging, biodistribution and pharmacokinetic studies. Over the recent two decades, luminescent lanthanide materials have shown extensive applications in the detection of various bioactive molecules and for in vitro/in vivo imaging, addressing the problem of autofluorescence. For this reason, one of our driving forces for synthesizing new lanthanide materials for imaging these cell cycle regulated protein relates to their unique photophysical properties, such as long emission lifetimes (effective elimination of biological auto-fluorescence in time-resolved spectroscopy) and characteristic hypersensitive emissions, (providing real-time information about the effect on coordination environment by surrounding entities, especially with europium) which are attractive substitutes to the more commonly used organic fluorophores.

In this seminar, I would like to share our development recently on emissive lanthanide materials as dual bioprobes for in vitro/in vivo imaging and inhibition of overexpressed tumor regulator proteins, such as Cyclin(s), Plk1 and EBNA1. It is hoped that the success in research could also lead to the success in practice, thereby providing more powerful tools to get more complete pictures of the roles of Cyclin(s)/Plk1/EBNA1. 

• Listen to the audio (mp3)

12:15-12:30 Discussion

13:30-14:00 Near IR probes

Professor Vasilis Ntziachristos, Technische Universität München and Helmholtz Zentrum München, National Research Centre for Environment and Health, Germany

Abstract

Optical imaging is unequivocally the most versatile and widely used visualization modality in the life sciences. Yet it is significantly limited by photon scattering, which complicates imaging beyond a few hundred microns. For the past few years however there has been an emergence of powerful new optical imaging methods that can offer high resolution imaging beyond the penetration limits of microscopic methods. These methods can prove essential in cancer research. Of particular importance is the development of multi-spectral opto-acoustic tomography (MSOT) that brings unprecedented optical imaging performance in visualizing anatomical, physiological and molecular imaging biomarkers. Some of the attractive features of the method are the ability to offer 10-100 microns resolution through several millimetres to centimetres of tissue and real-time imaging. In parallel we have now achieved the clinical translation of targeted fluorescent probes, which opens new ways in the interventional detection of cancer in surgical and endoscopy optical molecular imaging. This talk describes current progress with methods and applications for in-vivo optical and opto-acoustic imaging in cancer and outline how new opto-acoustic and fluorescence imaging concepts are necessary for accurate and quantitative molecular investigations in tissues.

14:00-14:15 Discussion

14:15-14:45 Future chemistry challenges in molecular imaging with radionuclides

Professor Phil Blower, King's College London

Abstract

Cooperation of clinicians, physicists, engineers, biologists and chemists identifies capabilities, conceives challenges, discovers solutions and applies them in the clinic. Each discipline produces innovations that drive innovations in the others, leading to progressions in the last half-century from gamma imaging towards PET, from “simple” easily-prepared but uncharacterised 99mTc complexes for imaging physiology and function towards well-characterised biomolecular radiopharmaceuticals for molecular imaging, and from single-modality towards combined modality imaging and contrast agents (PET/CT, PET/MRI and combination with optical imaging). The next decade may see this recapitulated: a new generation of gamma/SPECT scanners with resolution to rival or exceed that of PET will renew development of ^99mTc tracers. The recent global fragility of ^99mTc supply, far from foreshadowing the demise of ^99mTc and SPECT, has stimulated international planning of new production facilities, and perhaps in turn, a reversal in the recent decline of ^99mTc chemistry research. New initiatives to develop a whole body PET scanner will stimulate use of short half-life radionuclides in combination (e.g. 82Rb, 62Cu, 13N, 18O) in a research setting, for metabolic characterisation of tissues in unprecedented detail by imaging multiple molecular processes in a single subject, again potentially in combination with MRI and MR spectroscopy. The arrival of cell-based therapies requires improved tracers for cell tracking. Conversely, the arrival of new, simple chemistry for generator-produced 68Ga may drive the installation of more PET scanners. The adverse regulatory climate in the new millennium has held back clinical and commercial translation of new radiotracers shows signs of becoming more amenable.

• Listen to the audio (mp3)

14:45-15:15 Overview: future directions