Development of Brain MRI Contrast Agents

National Institute Of Neurological Disorders And Stroke

Investigators

Linked publications, trials & patents

Abstract

We have made substantial progress towards Aims 1-5, 7&8. Specifically: a) We have reproducibly fabricated 3 nm iron oxide nanoparticles independently in our own lab. These serve as good T1 MRI contrast agents and have strong T2 contrast properties as well. b) We have developed several camelid VHH antibody fragment targeting domains for pathological targets relevant to neurological disease, and made specific modifications to enhance the affinity of the targeting domains. Several additional targeting domains are under development, including nanobodies for pathological relevant forms of the tau protein. We are also exploring the use of single chain antibodies derived from IgGs, which are larger than nanobodies but still substantially smaller than full sized IgGs. c) We have validated the efficacy of several blood-brain barrier transcytosis functionalization domains for mouse and human work. We have demonstrated blood brain barrier transcytosis in vivo by coupling these domains to the neurotensin peptide. When neurotensin crosses the blood brain barrier, it causes a rapid and transient reduction in body temperature, whereas neurotensin that remains in the blood does not have this effect. We have found robust and dose-dependent reduction in body temperature in mice injected intravenously with transferrin receptor binding nanobodies coupled to neurotensin, but no effect of the same concentrations of mutant nanobodies in which transferrin receptor binding is eliminated coupled to neurotensin. d) We have produced a novel transgenic mouse that expresses the extracellular domain of the human transferrin receptor in place of the homologous mouse domain to test the human specific nanobody that will be used for human studies. The mice are healthy as heterozygotes and appear to have normal blood brain barrier function at baseline. A nanobody that binds specifically to human transferrin receptor extracellular domain but does not bind mouse transferrin receptor appears to cross the blood brain barrier in these transgenic mice. e) We have determined that MP2RAGE MRI sequences have excellent properties for detecting T1 MRI contrast agents in both mice (at 4.7T and 9.4T) and humans (at 3T). Specifically, the test-retest reliability for MP2RAGE MRI was found to be superior to other T1 methods given similar scan times. One manuscript has been published (Sensitive detection of extremely small iron oxide nanoparticles in living mice using MP2RAGE with advanced image co-registration Scientific Reports (nature.com) and another manuscript has been submitted for publication. We are able to reliably detect as little as 0.04 mM iron oxide nanoparticle contrast agents f) We have optimized method for R2 and R2* MRI mapping with very high test retest reliability at 3T and 9.4T. We have tested these methods in healthy volunteers and in mice and found that they provide acceptable contrast, but that R1 mapping using MP2RAGE is superior with regard to sensitivity. A manuscript detailing these results has been submitted. g) We have performed extensive in vivo experiments in mice to assess molecular contrast agent kinetics using infrared tracking. We have constructed detailed mathematical models of the pharmacokinetics in living mice for contrast agents of various sizes. A manuscript has been published. IJMS Free Full-Text Pharmacokinetics of Single Domain Antibodies and Conjugated Nanoparticles Using a Hybrid near Infrared Method (mdpi.com) i) We developed a series of SARS-CoV-2 nanobodies that have potential for use as therapeutics, diagnostics, and laboratory reagents. A manuscript has been published. High affinity nanobodies block SARS-CoV-2 spike receptor binding domain interaction with human angiotensin converting enzyme Scientific Reports (nature.com). We have initiated three important collaborations: 1) With Dr. Richard Bowen at Colorado State University. Dr. Bowens lab demonstrated that nebulized treatment of hamsters with our lead nanobody protected them from SARS-CoV-2 infection and reduced lung pathology at 3 and 7 days after injection. An additional manuscript is in preparation. 2) With Dr. Terry Rabbitts at Quadrucepts Inc. Dr. Rabbitts group has engineered a tetravalent version of the nanobody with 10 fold higher affinity for SARS-CoV-2. We are currently testing this engineered nanobody. 3) With Dr. John Cirrito at Washington University in St Louis. Dr. Cirrito is using the nanobody to develop ultrasensitive electrochemical sensors for environmental detection of SARS-CoV-2. We are searching for additional partners for additional development and potential commercialization.