Pump Prime Awards
Workshop on drug delivery to the brain – 27th February 2020
On Thursday 27th February 2020, we held our second workshop on drug delivery to the brain. As part of this day in Edinburgh, we awarded three pump prime awards, to Julia Benzel, Nicola Farrer and Peter Harvey. Read more about their projects below.
Julia Benzel, KiTZ / DKFZ, Germany
Monitoring drug-induced tumour responses in real-time
Setting the scene
Treatment responses and the direct effects of drugs at their site of action in brain tumours are difficult to estimate. Usually, in (pre)clinical studies, researchers use tissue biopsies to estimate these responses. An alternative approach is cerebral microdialysis for measuring drug concentrations in tumour or healthy tissue in real-time. This enables monitoring of drug penetration over the blood-brain barrier (BBB), and potentially drug-induced early tumour-responses, without being dependent on repeated biopsies.
We set out to evaluate the potential suitability of actinomycin D (a potent cytotoxic drug against paediatric brain tumour cells) for the therapy of paediatric patients with brain tumours. The aim was to monitor drug-induced tumour-responses in real-time.
Previous studies have shown possible therapeutic benefit for this drug in mouse models of glioblastoma, medulloblastoma and embryonal tumours, although blood-brain barrier penetration of actinomycin D has not been sufficiently investigated.
In this project, we established a cerebral microdialysis model in a mouse model of supratentorial ependymomas harbouring ZFTA/C11orf95 fusions. These aggressive brain tumours occur in children. Recently, p53 reactivation has been identified as promising therapeutic approaches. We know that low-dose actinomycin D can successfully re-establish p53 function in tumour cells in vitro, so, in this study, using cerebral microdialysis, we set out to analyse the actual penetration of the drug across the BBB.
We investigated the disposition of actinomycin D in the brain by quantifying the drug in cerebral microdialysis perfusate, brain tissue homogenate and plasma, using an ultraperformance liquid chromatography-tandem mass spectrometry assay.
After intravenous administration of actinomycin D, we found that unbound drug fractions could not be detected by cerebral microdialysis, but that we could measure actinomycin D in tissue homogenates two hours after drug administration. These brain tissue concentrations exceeded the amount of actinomycin D that has been shown to be effective in in vitro experiments. Furthermore, elimination of the drug from brain tissue was substantially slower than from plasma.
We conclude that actinomycin D should be further investigated as a therapeutic agent in central nervous system tumours such as ependymoma. However, it is likely that methods of either reducing peripheral (systemic) actinomycin D toxicity or increasing BBB penetration will be required for effective treatment.
Publications and presentations
Benzel J, Bajraktari-Sylejmani G, Uhl P, Davis A, Nair S, Pfister SM, Haefeli WE, Weiss J, Burhenne J, Pajtler KW, Sauter M; Investigating the Central Nervous System Disposition of Actinomycin D: Implementation and Evaluation of Cerebral Microdialysis and Brain Tissue Measurements Supported by UPLC-MS/MS Quantification (Pharmaceutics. 2021 Sept. 17;13(9):1498.)
In preparation: A recommendation manuscript about microdialysis; running title: 'Experimental recommendations to successfully perform cerebral microdialysis with hydrophobic drug candidates'.
Presentations at Microdialysis student`s day, 23rd November, 2021
Nicola Farrer, University of Oxford, UK
Acetylene cross-linking for improved platinum(IV) prodrug retention in liposomes
Setting the scene
The childhood cancer Diffuse Intrinsic Pontine Glioma (DIPG) is the leading cause of death from brain cancer in children and is currently fatal. New approaches and new treatments are urgently needed.
Platinum complexes are currently in use for treating DIPG. We are interested in packaging up into liposomes both new and existing platinum prodrugs, which show better solubility and are less reactive than established platinum drugs, so that they are significantly less toxic at the point of injection, and can be released selectively at the site of the tumour.
Liposomes are widely used in medicine. The packaging up of prodrugs in this way is anticipated to be compatible with targeting strategies, which would deliver more prodrug to the tumour and less to the rest of the body, with the aim of reducing the short-term side-effects of treatment for children with brain tumours. This project will seek to improve how the platinum complexes are packaged.
The project is a new collaboration between a medicinal chemistry research group at the University of Oxford, and a biophysics research group at the University of Leeds (headed by Professor Stephen Evans).
We investigated how to improve the packaging of the platinum prodrugs in liposomes. We found that optimal packaging depends on the exact structure of the particular prodrug, specifically, how easily the prodrug gains or loses protons, which can be exploited as a strategy to trap the prodrugs inside liposomes. We have looked at how quickly the prodrugs are released from the liposomes, which gives us an idea of what might happen in the human body, and we started to develop ways to further improve the nature of the liposome packaging.
We have conducted liposomal loading and leakage experiments, and cross-linking optimising experiments. We have also developed a good understanding of how the progress of these reactions can be monitored by Raman spectroscopy and UV-vis spectroscopy. We have determined optimal irradiation times for cross-linking blank liposomes and achieved relatively efficient encapsulation with plans for further improvement in conventional liposomes. We have also quantified the rate of leakage from non-cross linked liposomes by HPLC and ICP-MS. Interestingly, we observed that cross-linking appears to take longer to progress to completion than the irradiation times used by previous groups, so further work is needed to determine the reasons for this.
Although the pump-prime project has officially finished, we anticipate that the Oxford/Leeds collaboration will continue, with particular focus on combining optimised cross-linking with optimised prodrug loaded liposomes.
R. Browning, N. Thomas, L. K. Marsh, L. R. Tear, J. Owen, E. Stride, N. J. Farrer*."Ultrasound-triggered delivery of iproplatin from microbubble-conjugated liposomes", ChemistryOpen, 2021, https://doi.org/10.1002/open.202100222.
A. Delaney, L. K. Marsh, S. Evans, N. J. Farrer, “Acetylene cross-linking for improved platinum(IV) prodrug retention in liposomes“
Peter Harvey, University of Nottingham, UK
Monitoring Lipophilic Drug Delivery with Lipophilic MRI Contrast Agents
Setting the scene
Delivery of drugs to particular regions of the body is key to treating disease. This delivery is particularly difficult in the brain, due to the blood-brain barrier. A key issue in delivering drugs to the brain is not only the difficulty of transporting drugs into the brain, but also in determining whether the delivery has occurred and where the drug may subsequently have spread. MRI contrast agents are often used as model compounds for drugs to image these properties, but the chemistry of these contrast agents is wildly different to a typical chemotherapeutic, particularly in terms of lipophilicity.
In this project, we set out to use lipophilic MRI contrast agents to provide a more detailed outlook on the delivery of lipophilic drugs to the brain, and cage them inside nanoparticles in order for the imaging readout to be directly linked to the drug positioning.
We tackled this problem in a number of different ways. Firstly, we created and measured nanoparticle composites of existing fluorinated chemotherapeutics, with a view to using self-contained MR signals as the imaging marker. These markers aren’t contained within every drug, but could provide an imaging method for a subset of known cancer drugs. The second approach involved synthesising new lipophilic MRI contrast agents so that they are more drug-like. The third approach involved carrying out ex vivo MRI studies following in vivo spinal delivery of nanoparticle contrast agents to the brain.
These studies have allowed us to refine our approach to improve how we image the delivery of MRI-active drugs in the brain. We are now expanding on this project to combine different imaging techniques to give us a full picture of how drug delivery to the brain works in even more detail. We are hopeful that our research will lead to improved methods of delivering drugs to brain cancer patients and improved response to chemotherapeutics.
Since starting this project, I (in collaboration with CBTDDC Chair Ruman Rahman) have been part of a successful EPSRC New Horizons grant that will build upon the aims of this project and greatly expand our approach using MRI-tagged chemotherapeutics and advanced multi-modal imaging. I have also received an Academy of Medical Sciences Springboard Award, which, whilst not built upon the pump-prime research directly, was supported by collaborations built through involvement with CBTDDC and the pump prime award.