Sally L. Pimlott

Targeting mTOR dependency in pancreatic cancer

Objective Pancreatic cancer is a leading cause of cancer-related death in the Western world. Current chemotherapy regimens have modest survival benefit. Thus, novel, effective therapies are required for treatment of this disease. Design Activating KRAS mutation almost always drives pancreatic tumour initiation, however, deregulation of other potentially druggable pathways promotes tumour progression. PTEN loss leads to acceleration of KrasG12D-driven pancreatic ductal adenocarcinoma (PDAC) in mice and these tumours have high levels of mammalian target of rapamycin (mTOR) signalling. To test whether these KRAS PTEN pancreatic tumours show mTOR dependence, we compared response to mTOR inhibition in this model, to the response in another established model of pancreatic cancer, KRAS P53. We also assessed whether there was a subset of pancreatic cancer patients who may respond to mTOR inhibition. Results We found that tumours in KRAS PTEN mice exhibit a remarkable dependence on mTOR signalling. In these tumours, mTOR inhibition leads to proliferative arrest and even tumour regression. Further, we could measure response using clinically applicable positron emission tomography imaging. Importantly, pancreatic tumours driven by activated KRAS and mutant p53 did not respond to treatment. In human tumours, approximately 20% of cases demonstrated low PTEN expression and a gene expression signature that overlaps with murine KRAS PTEN tumours. Conclusions KRAS PTEN tumours are uniquely responsive to mTOR inhibition. Targeted anti-mTOR therapies may offer clinical benefit in subsets of human PDAC selected based on genotype, that are dependent on mTOR signalling. Thus, the genetic signatures of human tumours could be used to direct pancreatic cancer treatment in the future.

Nicotinic α4β2 receptor binding in dementia with Lewy bodies using 123I-5IA-85380 SPECT demonstrates a link between occipital changes and visual hallucinations

INTRODUCTION To investigate in vivo differences in the distribution of alpha4beta2 subtypes of nAChR using the ligand (123)I-5-Iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (5IA-85380) and single photon emission computed tomography (SPECT) in DLB and similarly aged controls. METHODS Thirty-one subjects (15 DLB and 16 controls) underwent (123)I-5IA-85380 and perfusion ((99m)Tc-exametazime) SPECT scanning. Patient scans were compared to scans of control subjects on a voxel-by-voxel basis using SPM2. RESULTS Compared to controls, significant reductions in relative (123)I-5IA-85380 uptake were identified in frontal, striatal, temporal and cingulate regions in DLB. Elevation of scaled (123)I-5IA-85380 uptake in occipital cortex was observed in DLB relative to controls, as well as being associated with DLB subjects with a recent history of visual hallucinations. Changes in (123)I-5IA-85380 SPECT in DLB were different from perfusion. CONCLUSION Reductions in normalised (123)I-5IA-85380 uptake in DLB were distinct from their perfusion deficits. Significant increase in occipital lobe uptake was present in DLB, a change most pronounced in subjects with a recent history of visual hallucinations. The findings directly link cholinergic changes in occipital lobe to visual hallucinations in DLB.

Nickel-catalysed aromatic Finkelstein reaction of aryl and heteroaryl bromides

A fast and efficient nickel-catalysed iodination reaction of aryl and heteroaryl bromides has been developed. The transformation was found to be general for a wide range of substrates and was used for the synthesis of iodo-PK11195, an imaging agent of Alzheimers disease and iniparib, a compound used in the treatment of breast cancer.

Tumour necrosis factor blockade mediates altered serotonin transporter availability in rheumatoid arthritis: a clinical, proof-of-concept study

Depression in those who are ill is 5–10 times more common than in the general population. Increasing evidence implicates bidirectional biological mechanisms linking mood disorders and medical conditions.1 Depressive symptoms are significantly more common in rheumatoid arthritis (RA) than in the general population. Conservative estimates suggest major depressive disorder in between 13% and 17% of patients with RA. However, prevalence exceeding 40% has been reported in a recent study, with up to 11% of patients experiencing suicidal ideation.1 Major depressive disorder is an independent risk factor for both work disability and mortality in patients with RA.2 Cytokine dysregulation is central to the pathogenesis of RA with functional implications for breach of tolerance and autoimmunity, subsequent inflammation and articular dysfunction.3 Tumour necrosis factor (TNF), in particular, appears to be of pivotal importance in pathogenesis, based …

Stereoselective synthesis of (2S,3R)- and (2R,3S)-iodoreboxetine; potential SPECT imaging agents for the noradrenaline transporter

With the aim of developing a new SPECT imaging agent for the noradrenaline transporter, a twelve-step stereoselective synthesis of iodinated analogues of (2S,3R)- and (2R,3S)-reboxetine has been achieved from 4-bromobenzaldehyde. The key steps involve a Sharpless asymmetric epoxidation to establish the stereogenic centres and a copper catalysed aromatic halogen exchange reaction to introduce the key iodine atom. In vitro testing of these compounds using a [(3)H]nisoxetine displacement assay with homogenised rat brain shows both compounds to have significant affinity, with K(i) values of 320.8 nM and 58.2 nM for (2S,3R)- and (2R,3S)-iodoreboxetine respectively.

Circulating tumour necrosis factor is highly correlated with brainstem serotonin transporter availability in humans

Preclinical studies demonstrate that pro-inflammatory cytokines increase serotonin transporter availability and function, leading to depressive symptoms in rodent models. Herein we investigate associations between circulating inflammatory markers and brainstem serotonin transporter (5-HTT) availability in humans. We hypothesised that higher circulating inflammatory cytokine concentrations, particularly of tumour necrosis factor (TNF-α), would be associated with greater 5-HTT availability, and that TNF-α inhibition with etanercept (sTNFR:Fc) would in turn reduce 5-HTT availability. In 13 neurologically healthy adult women, plasma TNF-α correlated significantly with 5-HTT availability (rho=0.6; p=0.03) determined by [(123)I]-beta-CIT SPECT scanning. This association was replicated in an independent sample of 12 patients with psoriasis/psoriatic arthritis (rho=0.76; p=0.003). Indirect effects analysis, showed that there was a significant overlap in the variance explained by 5-HTT availability and TNF-α concentrations on BDI scores. Treatment with etanercept for 6-8weeks was associated with a significant reduction in 5-HTT availability (Z=2.09; p=0.03; r=0.6) consistent with a functional link. Our findings confirm an association between TNF-α and 5-HTT in both the basal physiological and pathological condition. Modulation of both TNF-α and 5-HTT by etanercept indicate the presence of a mechanistic pathway whereby circulating inflammatory cytokines are related to central nervous system substrates underlying major depression.

5-123I-A-85380 binding to the α4β2-nicotinic receptor in mild cognitive impairment

Treatments currently licensed for Alzheimers dementia target cholinergic brain systems. In vivo nicotinic receptor binding may provide an early marker of illness and treatment suitability. In this pilot, we examined nine patients with amnestic mild cognitive impairment (MCI) and 10 age and education matched healthy volunteers with high resolution SPECT and the nicotinic receptor ligand 5-(123)I-A-85380. Uptake data were analysed using voxel-based techniques for group comparisons and regression analyses with cognitive impairment as covariates. MCI patients had discrete reductions in uptake in medial temporal cortex. Correlations with cognitive impairment were found in left temporo-parietal areas (Addenbrookes Cognitive Examination) and bilateral temporo-limbic areas (Rey Auditory Verbal Learning Test), and right parahippocampal gyrus (Rey Complex Figure Test) within the patient group. In vivo nicotinic receptor binding appears to be sensitive to brain changes in MCI. Larger scale explorations of patients undergoing treatment will be necessary to evaluate its use in predicting or monitoring treatment response.

Nicotinic 123I-5IA-85380 Single Photon Emission Computed Tomography as a Predictor of Cognitive Progression in Alzheimer's Disease and Dementia With Lewy Bodies

OBJECTIVE To investigate normalized I-5-Iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (5IA-85380) single photon emission computed tomography (SPECT) imaging, a marker for the alpha4beta2 nicotinic receptor, as a predictor of cognitive progression in Alzheimers disease (AD) and dementia with Lewy bodies (DLB). METHODS Thirty-one patients with dementia (16 patients with AD and 15 patients with DLB) underwent I-5IA-85380 SPECT scanning. Image analysis was performed using statistical parametric mapping (SPM2), which involved spatial preprocessing of scans to standard Montreal Neurological Institute space and intensity normalization of each image to its mean global brain activity. RESULTS Regression analysis revealed that reduced normalized I-5IA-85380 uptake in left superior, middle, and inferior frontal gyri and prepost central and anterior cingulate regions significantly correlated with decline in executive function in a pooled group comprising AD and DLB. CONCLUSION The findings, although preliminary, suggest that the cholinergic system may be more involved in neurodegenerative processes affecting some cognitive processes more than others, as such, this procedure may be useful for increased understanding of the pathophysiological mechanisms responsible for neurodegeneration.

Highly Regioselective Iodination of Arenes via Iron(III)-Catalyzed Activation of N-Iodosuccinimide

An iron(III)-catalyzed method for the rapid and highly regioselective iodination of arenes has been developed. Use of the powerful Lewis acid, iron(III) triflimide, generated in situ from iron(III) chloride and a readily available triflimide-based ionic liquid allowed activation of N-iodosuccinimide (NIS) and efficient iodination under mild conditions of a wide range of substrates including biologically active compounds and molecular imaging agents.

Radiotracer properties determined by high performance liquid chromatography: a potential tool for brain radiotracer discovery

INTRODUCTION Previously, development of novel brain radiotracers has largely relied on simple screening tools. Improved selection methods at the early stages of radiotracer discovery and an increased understanding of the relationships between in vitro physicochemical and in vivo radiotracer properties are needed. We investigated if high performance liquid chromatography (HPLC) methodologies could provide criteria for lead candidate selection by comparing HPLC measurements with radiotracer properties in humans. METHODS Ten molecules, previously used as radiotracers in humans, were analysed to obtain the following measures: partition coefficient (Log P); permeability (P(m)); percentage of plasma protein binding (%PPB); and membrane partition coefficient (K(m)). Relationships between brain entry measurements (Log P, P(m) and %PPB) and in vivo brain percentage injected dose (%ID); and K(m) and specific binding in vivo (BP(ND)) were investigated. Log P values obtained using in silico packages and flask methods were compared with Log P values obtained using HPLC. RESULTS The modelled associations with %ID were stronger for %PPB (r(2)=0.65) and P(m) (r(2)=0.77) than for Log P (r(2)=0.47) while 86% of BP(ND) variance was explained by K(m). Log P values were variable dependant on the methodology used. CONCLUSIONS Log P should not be relied upon as a predictor of blood-brain barrier penetration during brain radiotracer discovery. HPLC measurements of permeability, %PPB and membrane interactions may be potentially useful in predicting in vivo performance and hence allow evaluation and ranking of compound libraries for the selection of lead radiotracer candidates at early stages of radiotracer discovery.