Fluorinated 2-Nitroimidazoles: Non-Invasive Probes for Detecting Therapeutically Relevant Tumour Hypoxia by Magnetic Resonance Spectroscopy

Tumour hypoxia is a well described phenomenon which is primarily created by an inadequate and non-uniform vascular network. Importantly, hypoxia within certain solid tumours has been linked to the failure of conventional therapy, including radiotherapy and chemotherapy. For this reason, many attempts have been made to identify, characterise, and quantify hypoxic cells within these tumours as a prelude to the design of rational therapies aimed to kill all the cancer cells present within tumours. The use of 2-nitroimidazoles containing appropriate labels as markers for the detection of hypoxic cells, is based on the ability of these compounds to undergo selective nitroreduction and adduct formation within hypoxic cells. The fluorinated 2-nitroimidazole, SR-4554, was rationally designed as a non-invasive hypoxia probe with low toxicity and high sensitivity for detection by magnetic resonance spectroscopy (MRS) and imaging (MRI). SR-4554 was demonstrated to be enzymatically reduced by mouse liver microsomes, SCCVII tumour homogenates and purified rat and human NADPH; cytochrome P450 reductase under hypoxia. In this regard, NADPH: cytochrome P450 reductase was found to be the major enzyme involved in this bioreduction of SR-4554. In a panel of murine and human tumour xenografts, only a 3 fold variation in NADPH: cytochrome P450 reductase activities was observed. These differences in NADPH: cytochrome P450 activities are unlikely to significantly influence SR-4554 adduct formation in vivo. Importantly, the reduction of SR-4554 by mouse liver microsomes showed a characteristic oxygen dependence with a half- maximal inhibition of 0.48%. Using a high resolution nuclear magnetic resonance (NMR) technique, soluble hypoxia-dependent metabolites of various fluorinated 2-nitroimidazoles, including SR-4554, were identified. The chemical shifts of these metabolites were found to be less than those required to give resolved peaks in in vivo MRS studies. Determination of the possible regions of SR-4554 adduct formation within A2780 human ovarian multicellular spheroids was achieved by electron energy loss spectroscopic imaging. Using this technique, an 8 fold differential between the fluorinated probe levels retained in the inner hypoxic regions of the spheroid vs the outer more aerobic regions was observed. SR-4554 was localised mainly to the nuclear periphery, nucleus and cytoplasm within cells from the hypoxic region of the spheroids. The toxicity and pharmacokinetics of SR-4554 was studied in mice as a prelude to non-invasive MRS/MRI studies. SR-4554 was found to be non-toxic in mice up to a dose of 1300 mg/kg. Pharmacokinetics of SR-4554 fitted either a one compartment or two compartment open model depending on the route of administration. The probe was characterised by a relatively short half-life, linear kinetics, high urinary excretion, high oral bioavailability and low plasma protein binding. Importantly, the brain to plasma ratio of SR-4554 was lower than previously reported trends in the literature, thus confirming its potentially low toxicity. As a consequence of the low toxicity and favourable pharmacokinetic properties of SR-4554, a non-invasive multi-tuned 19F MRS technique was implemented to detect this compound in tissues. Using this MRS technique, SR-4554 was found to be selectively retained in both murine and human tumour xenografts. Importantly the 19F retention index was found to correlate with the reported radiobiological hypoxic fraction of the tumours used. This 19F retention index was also found to be higher in larger tumours but, interestingly, did not correlate with the bioenergetic status of the tumours, as determined by 31P MRS. Manipulation of tumour microenvironment to affect the degree of hypoxia within these tumours was studied in vivo. In mouse tumours for instance, the 19F retention index increased 2 fold compared to control values, following hydralazine pre-treatment, and decreased by 6 fold compared to control values, following carbogen breathing. Important to the clinical development of SR-4554, 19F MRI techniques showed localisation of SR-4554 in the bladder, tumour and liver of mice. This technique was, however, limited by low sensitivity due to the extremely short transverse relaxation, time of the probe in tissues. Finally this thesis has demonstrated that SR-4554 has suitable metabolic, pharmacological and MRS properties for its use in the quantification of critical levels of hypoxia within human tumours. As a consequence, this compound has been approved by CRC phase I/II committee for clinical development

Microfinance and Small Loans Centre (MASLOC) as a Model for Promoting Micro and Small Enterprises (MSEs) in the Ashaiman Municipality of Ghana

The purpose of the research was to assess the possibility of using the Microfinance and Small Loans Centre (MASLOC) in Ghana as a model for the development of micro and small scale enterprises (MSEs). The study did this by assessing the contributions MASLOC has made to the development of MSEs. Data gathered from 96 beneficiary MSEs and three institutions revealed that loans from MASLOC have contributed to increasing the beneficiary MSEs’ working capital by 120.6%. The business advisory services offered by MASLOC to beneficiaries were identified to have improved the enterprises’ customer relations and attractions. All these have culminated into increases in earnings averaging 46.9%. The sustainability of MASLOC is however constrained by the high rate of default. The default rates for individual loans and group loans were 20% and 25% respectively. Overdue payments were estimated at 20% and 30% for individual loans and groups loans respectively. The study concludes that MASLOC should intensively monitor the MSEs in order to address the misapplications of the loans they take which will in turn reduce the rate of loan default. Keywords: Micro and Small Enterprises, Microfinance, MASLOC, employment, poverty reduction.

The Informal Apprenticeship System in Ghana: Post Graduation Job Integration and Its Implications for the Management of Urban Space

In spite of the enormous contributions the informal apprenticeship system has made to empowering many creative intelligent young Ghanaians, it has over the years come under a barrage of criticism and forceful evictions in many urban areas in Ghana. The justification by  urban administrators and planners for forcefully removing these graduate apprentices who set up their businesses  have been on grounds of encroachment of public spaces and illegal occupation of precarious locations. Informal graduate apprentices have defended their locational choice on ground of unfairness on the part of the state and the market to cater for their space needs. In the awake of a growing informal apprenticeship system in Ghana, this paper sought to establish the inherent relationship that exist between the growth in apprentices, their locational preferences, and their implications for urban planning and management. Using a case study approach the study built upon earlier exploratory research works done in the area. Information was gathered from 162 graduate apprentices-now entrepreneurs in four broad trades namely wood worker; auto mechanics; textile and apparel; and beauticians and hairdressers in Accra using questionnaires. The responses were validated through a focus group discussion. The findings revealed the number of graduate apprentices who set up their businesses is on the rise.  Although they preferred highly accessible areas that guaranteed high patronage of their services the absence of such spaces due to inefficiencies in the urban land market or a lack of a clear regulation that addresses their specific needs have caused them to settle in areas that are available to them.  It was also evident that the more concentrated the location of their activities are the higher the number of trips it generates across the urban space. Having gained insight into the phenomenon, proposals have been made as to how best the unmet space needs of the graduate apprentices can be met so as to mitigate the negative effects that results from unplanned, uncoordinated and unmet space needs. Keywords Informal, graduate apprentices, space needs, urban managemen

Correction to: The relationship between endogenous thymidine concentrations and [18F]FLT uptake in a range of preclinical tumour models.

Unfortunately, the original version of Figs. 4, 5 and 6b in the article [1] contained errors in the n numbers as indicated on the columns. Please note that column heights and error bars in the original figures and data in the ESM tables are correct and statistical tests are valid. These corrections do not affect any results or conclusions in this article

Positron emission tomography imaging of tumor cell metabolism and application to therapy response monitoring

Cancer cells do reprogramme their energy metabolism to enable several functions such as generation of biomass including membrane biosynthesis, and overcoming bioenergetic and redox stress. In this article we review both established and evolving radioprobes developed in association with positron emission tomography (PET) to detect tumor cell metabolism and effect of treatment. Measurement of enhanced tumor cell glycolysis using 2-deoxy-2-[18F]-fluoro-D-glucose is well established in the clinic. Analogues of choline including [11C]-choline and various fluorinated derivatives are being tested in several cancer types clinically with PET. In addition to these, there is an evolving array of metabolic tracers for measuring intracellular transport of glutamine and other amino acids or for measuring glycogenesis, as well as probes used as surrogates for fatty acid synthesis or precursors for fatty acid oxidation. In addition to providing us with opportunities for examining the complex regulation of reprogrammed energy metabolism in living subjects, the PET methods open up opportunities for monitoring pharmacological activity of new therapies that directly or indirectly inhibit tumor cell metabolism

Selective Inhibition of Histone Deacetylation in Melanoma Increases Targeted Gene Delivery by a Bacteriophage Viral Vector

The previously developed adeno-associated virus/phage (AAVP) vector, a hybrid between M13 bacteriophage (phage) viruses that infect bacteria only and human Adeno-Associated Virus (AAV), is a promising tool in targeted gene therapy against cancer. AAVP can be administered systemically and made tissue specific through the use of ligand-directed targeting. Cancer cells and tumor-associated blood vessels overexpress the αν integrin receptors, which are involved in tumor angiogenesis and tumor invasion. AAVP is targeted to these integrins via a double cyclic RGD4C ligand displayed on the phage capsid. Nevertheless, there remain significant host-defense hurdles to the use of AAVP in targeted gene delivery and subsequently in gene therapy. We previously reported that histone deacetylation in cancer constitutes a barrier to AAVP. Herein, to improve AAVP-mediated gene delivery to cancer cells, we combined the vector with selective adjuvant chemicals that inhibit specific histone deacetylases (HDAC). We examined the effects of the HDAC inhibitor C1A that mainly targets HDAC6 and compared this to sodium butyrate, a pan-HDAC inhibitor with broad spectrum HDAC inhibition. We tested the effects on melanoma, known for HDAC6 up-regulation, and compared this side by side with a normal human kidney HEK293 cell line. Varying concentrations were tested to determine cytotoxic levels as well as effects on AAVP gene delivery. We report that the HDAC inhibitor C1A increased AAVP-mediated transgene expression by up to ~9-fold. These findings indicate that selective HDAC inhibition is a promising adjuvant treatment for increasing the therapeutic value of AAVP

Positron Emission Tomographic Imaging of CXCR4 in Cancer: Challenges and Promises

Molecular imaging is an attractive platform for noninvasive detection and assessment of cancer. In recent years, the targeted imaging of the C–X–C chemokine receptor 4 (CXCR4), a chemokine receptor that has been associated with tumor metastasis, has become an area of intensive research. This review article focuses on positron emission tomography (PET) and aims to provide useful and critical insights into the application of PET to characterize CXCR4 expression, including the chemical, radiosynthetic, and biological requirements for PET radiotracers. This discussion is informed by a summary of the different approaches taken so far and a comparison of their clinical translation. Finally, our expert opinions as to potential future advances in the field are expressed

Clinical Translation of Quantitative Magnetic Resonance Imaging Biomarkers – an Overview and Gap Analysis of Current Practice

PURPOSE: This overview of the current landscape of quantitative magnetic resonance imaging biomarkers (qMR IBs) aims to support the standardisation of academic IBs to assist their translation to clinical practice. METHODS: We used three complementary approaches to investigate qMR IB use and quality management practices within the UK: 1) a literature search of qMR and quality management terms during 2011-2015 and 2016-2020; 2) a database search for clinical research studies using qMR IBs during 2016-2020; and 3) a survey to ascertain the current availability and quality management practices for clinical MRI scanners and associated equipment at research institutions across the UK. RESULTS: The analysis showed increased use of all qMR methods between the periods 2011-2015 and 2016-2020 and diffusion-tensor MRI and volumetry to be popular methods. However, the "translation ratio" of journal articles to clinical research studies was higher for qMR methods that have evidence of clinical translation via a commercial route, such as fat fraction and T2 mapping. The number of journal articles citing quality management terms doubled between the periods 2011-2015 and 2016-2020; although, its proportion relative to all journal articles only increased by 3.0%. The survey suggested that quality assurance (QA) and quality control (QC) of data acquisition procedures are under-reported in the literature and that QA/QC of acquired data/data analysis are under-developed and lack consistency between institutions. CONCLUSIONS: We summarise current attempts to standardise and translate qMR IBs, and conclude by outlining the ideal quality management practices and providing a gap analysis between current practice and a metrological standard

Positron Emission Tomographic Imaging of CXCR4 in Cancer: Challenges and Promises

Molecular imaging is an attractive platform for noninvasive detection and assessment of cancer. In recent years, the targeted imaging of the C–X–C chemokine receptor 4 (CXCR4), a chemokine receptor that has been associated with tumor metastasis, has become an area of intensive research. This review article focuses on positron emission tomography (PET) and aims to provide useful and critical insights into the application of PET to characterize CXCR4 expression, including the chemical, radiosynthetic, and biological requirements for PET radiotracers. This discussion is informed by a summary of the different approaches taken so far and a comparison of their clinical translation. Finally, our expert opinions as to potential future advances in the field are expressed